Review: Adcom GFA-535 amplifier

The Adcom GFA-535 is the little brother to the famed 545 and 555 amplifiers. It features true dual mono construction with each channel getting its own power transformer and power supply capacitors. With a simple design by the famed Nelson Pass, it features pretty much the same input/driver circuit as the big amplifiers and also has bi-polar output transistors. Rated at a conservative 60WPC, the original version has two sets of speaker output using twist connectors for bare wires. The small size makes it perfect for sitting on top or underneath a matching Adcom preamplifier.

For $125USD, I soon found an early version in my hands. It worked perfectly out of the box too. Adcom stuff seems to hold up fairly well and this has been a joy compared to some of my older pieces of gear.


Sonically, it drives my KEF Q60 speakers without any trouble at all. Bass is solid and only a faint touch of solid-state glare exists that smooths out with continued use. Oddly enough, the much more vintage Dynaco ST-80 sounds more colorful and tubey - perhaps it is the aged carbon composition resistors and electrolytic output coupling capacitors. The 535 having a much more leaner/modern sound. The Adcom also has more power in reserve and can handle more complex loads. So pick your poison and run with it. I can live with either amplifier for low powered solid-state, but the 535 wins out for its matching aesthetics with the GTP-400 preamplifier.


Second System:
Adcom GTP-400 tuner preamplifier
Dynaco ST-80 refurbished
Dual CS-5000 turntable with AT95E cartridge
Pioneer DVD-V7400 DVD player
KEF Q60 speakers
various budget cables


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Review: Adcom GTP-400 tuner preamplifier

Owning vintage gear from the hey-day of the 60s and 70s can be troublesome since switches, pots and electronic components can go bad. Replacing aged capacitors and resistors is an easy task, but finding the right fitting switch can be difficult. For that reason, basic amplifiers seem to age better than preamplifiers which can be noisy. With that in mind, I decided to replace my Dynaco PAT-4 preamplifier & AF-6 tuner combination with something a little more modern for family use.

Adcom has been around since the 1970s, starting as company that made phono cartridges. By the time the 80s rolled around, they were one of the go-to companies for budget solid-state gear. Several of their components made Stereophile's Recommended Component list and even to this day, my father runs the classic GFP-555 preamplifer and GFA-555 amplifier. During the early 90s, I owned the highly regarded GFP-565 which did not work out for me due to overall system imbalances - it just didn't sound right with my then Snell JIII speakers and a Harman-Kardon Citation V tube amplifier.

After much thought, I decided on purchasing an Adcom GTP-400 for a paltry $125. The GTP-400 is a basic preamplifier that also includes an AM/FM tuner and tone controls are included along with a MM phono preamplifier. The number of switches and knobs makes for a busy looking unit, but the simple black case and blue tuner LED lettering give it a conservative look. There is nothing flashy going on here, just stolid engineering.


Removing the Dynaco preamplifier and tuner was easy enough to do and I soon had the GTP-400 hooked up to sources and a Dynaco ST-80 amplifier. Now there is a strange pair! I have an Adcom GFA-535 coming soon and will report on that in due time.

At least on this low resolution system, sound differences between the Adcom and Dynaco are fairly minor. The strong character of the Dual CS-5000 & AT95E combination still shines through in all its analog glory, while the line section is smooth. I would never mistake the GTP-400 for a tube preamplifier since there isn't tons of depth or dimensionality to the sound. But dynamics and bass control are excellent, plus there is no hiss or hum to worry about. This is trouble free audio at a budget and is highly recommended for those looking to get into this crazy hobby.

A quick word on the tuner section - I'm no fan of digital tuners since they can skip over weaker signals. In comparison, an analog tuner can be fine-tuned with fine gradual turns of the knob. I would think of the GTP-400 as a preamplifier with the side-benefit of having a decent tuner - perfect for background music while cleaning or reading books.


Second System:
Dynaco PAT-4 modified
Dynaco AF-6 tuner
Dynaco ST-80 refurbished
Dual CS-5000 turntable with AT95E cartridge
Pioneer DVD-V7400 DVD player
KEF Q60 speakers
various budget cables


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Review: Dual CS5000 turntable

On my second system, I've been less than happy with my Panasonic linear tracking turntable. The sound, with a budget p-mount cartridge, has been tiny and prone to inner groove distortion. Since I spin tons of vinyl, I've decided to replace it with something better. Since this was going to be a turntable for family use, I wanted something that would lift the tonearm at the end of the record. Some searching online brought me to a used $395 Dual CS-5000 turntable.

The CS5000 was a popular 80s semi-automatic European turntable that came from the long line of 505 tables. It features a microprocesser controlled, quart referenced DC motor that drives the platter with the use of a belt. The tonearm is low mass and has a removable headshell and adjustable VTA. The CS5000 is also a suspended design, isolating the motor, arm and platter from the plinth. I found that construction quality is very good and the overall look with the oak plinth and smokey dustcover is very classy. The platter is a little on the lightweight side, but the mat is extremely thick and dense.


Upon receiving the Dual, I had to buy a cartridge. Since this is a budget rig, an Audio-Technica AT95E was selected for its reported smooth sound. Installation with the removable headshell was a snap and I soon had the turntable up and running. Using the CS5000 is easy - turn it on and push the arm until the needle rests over the record. The platter spins up to speed and 2-3 seconds later, the needle drops onto the records. When playing is done, the arm lifts but does not automatically return. Hence the term "semi-automatic".

Even through my vintage solid-state Dynaco gear, the overall sound is extremely rich and involving. Compared to my old Panasonic table, the CS5000 is more dynamic and boasts deeper bass too. Inner groove distortion is now so minimized that I have a hard time knowing that the end of the record is coming. The Dual also has a pure analog sound that is oh so enjoyable. Though lacking the detail of my VPI turntable, the Dual still has a rightness that digital seems to have a hard time matching. Vinyl noise is kept to a minimum and even normally hard to play records have an extremely clean presentation. There is a bit of a golden honey-tone to the sound that reminds me of good vacuum tube systems. Perhaps things could get a little thick with the wrong amplification chain, but it sounded just right with my current setup.

I don't know if it is the DC motor or faulty memory, but the Dual seems to have a less "washy" sound than my old Rega P2 (that I foolishly sold). The arm on the CS5000 is a little chintzy but works. I can't really comment on soundstaging, depth or the lowest/highest frequencies since this system really isn't about that.

The Dual CS-5000 is highly recommended for a budget or even a mid-priced system. This is an excellent way for someone just starting to get into vinyl.


Second System:
Dynaco PAT-4 modified
Dynaco AF-6 tuner
Dynaco ST-80 refurbished
Panasonic linear tracking turntable
Pioneer DVD-V7400 DVD player
KEF Q60 speakers
various budget cables

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A Visit with the VPI SDS turntable motor controller

Accurate analog production with a turntable is a tricky business. There is the cartridge, which produces millivolts that have to be amplified up to line level. Then there is the arm, which requires rigidity, vibration dampening, the ability to ride warped and off-center records all while adding nothing to the sound. The turntable body itself is another source of vibration, especially if the AC motor is clamped to the plinth. On top of this, we have speed inaccuracies and vibrations from the motor which can be transmitted to the rest of the turntable system. It's amazing that records can sound as good as they do.

VPI created the Synchronous Drive System (SDS) in order to help correct turntable motor issues. It is essentially a turntable motor controller and line isolator through the use of amplifier with a semi-adjustable quart crystal sinewave generator. This allows the user to dial in the exact frequency for their AC turntable motor, resulting in a locked 33 1/3 rpm. It also has a current sensor to adjust the amount of voltage to the motor, allowing 115VAC as the platter spins up to speed and then it tails down 20-30Vs for normal operation. This has the effect of reducing motor vibration.

I bought mine used via Audiogon and through the use of the KAB Speedtrobe, adjusted the AC frequency down to 59.69Hz to achieve an almost perfect 33 1/3 rpm on my VPI HW19 Mark III turntable.

Sound differences are hardly earth shattering, but more of a baby step towards that impossible goal of achieving audio perfection. Music has more of a "locked in" feel as images are rock steady. Bass sounds slightly deeper as does the soundstage depth. Pitch control is excellent, reminding me of the solidity of the compact disc. I'm very happy with the changes and can't wait to purchase the VPI SAMA outboard motor and a new tonearm.


System:
preamp: Threshold FET-10/HL
phono preamp: Audio Sector Phono Stage
amplifier: Threshold S/500
analog: VPI HW19 MkIII - Rega RB300 with Incognito wiring - Denon DL-103R
speakers: Magnepan 1.6/QR with Sound Anchor Stands
speaker cable: Kimber 4PR/8PR Bi-wire with banana jacks
Interconnects: Cardas Cross and Cardas Quadlink 5C


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Upgrading the Threshold FET-10/HL linestage

My beloved Threshold FET-10/HL linestage is getting a little long in the tooth. The few electrolytics need replacement and the couplers are due for an upgrade as I'm no fan of Mylar capacitors.

I first tackled the Power Supply, replacing the original four diodes with UF4007s. It's hard to find quality axial capacitors and the outboard power supply is too small for fitting in radial capacitors. With that in mind, I ended up replacing the 2200uF/25V electrolytics with 3300uF/35V Nichicon FGs.

Next up is the actual signal unit. 4.7uF power supply bypass capacitors were replaced with Elna Silmics. Inside, it's a tight fit height wise with the input and output coupler capacitors. So I used 1.0uF Rel-Cap PPMFs on the input and 10.0uF Wima Polycarbonates on the output section. This is a much improved upgrade over the original input film and output metallized Mylar capacitors.

How does it sound? Polycarbonate have always been some of my favorite 'sleeper' capacitors and once again they proved their mettle. They are much superior to the original Ero Mylar capacitors with a cleaner, less fuzzy soundstage. There seems to be more minute detail too. The combination of the new parts makes for a much better preamp and a brings this old girl back up to world class level again.


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Upgrading the B&K ST-140 amplifier

This was an easy upgrade - on both boards, replace the 100uF/100V and 47uF power supply electrolytics. The 47uF electrolytic input capacitor was replaced by a 10uF film unit. You can use anything from 10uF to 47uF here. Due to the size of the film capacitors, I bypassed the circuit board capacitors with wire and installed the new units inline on the leads from the RCA jacks.

The end result was an amplifier that sounded much more detailed and immediate. Gone was the treble roll off and plummy bass. The big 47uf electrolytic input definitely added some major coloration to the sound as now it sound much more neutral. Though not in league with my big Threshold S/500, the B&K is now one heck of an amp for the money.


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A Visit with the B&K ST-140 amplifier

My Threshold S/500 amplifier is in need of a rebuild. With that in mind, I decided to buy a interim amplifier to drive my Magnepan speakers. I wanted something cheap as this was also going to be an expendable unit to practice my solid state upgrade skills on. After examining several amplifiers on Audiogon, I selected the budget-priced B&K ST-140 since it is renowned for a smooth tube-like sound. It is also a simple design that would lend itself to potential modifications and allow an easy upgrade path.

As far as I can tell, there are three iterations of the B&K ST-140. The first one, from the early 80s, used a iron core transformer and each channel had a pair of Mosfets to make 70Ws. The second version has a toroidal transformer, bumped up power supply voltage to drive the pair of Mosfets to 105Ws of power. With the increased voltage and power came a decrease in handling lower impedance loads. After all, there is only so much you can ask from a pair of output devices. Both of these versions have gold front panel lettering and rear mounted heatsinks. The final version had blue and red lettering and can handle lower impedance loads with four output Mosfets per channel.



The ST-140 I purchased comes from the second generation. After delivery, I opened up the box and was greeted with a larger than expected amplifier. Though a lightweight compared to the Threshold S/500, it still has a substantial footprint. However, cracking open the case revealed mostly empty space! I suppose some of this is marketing as it is easier to sell an amplifier that looks big and burly compared to some lightweight case size.

First stop was my second system. Out came the Dynaco ST-80 amplifier and in went the B&K. The power difference between the two was immediately apparent as the bass on the KEF Q60s was deeper and more energetic. Spinning a few CDs and records revealed a warm amplifier with plenty of reserve. Treble seemed a touch rolled off, but was plenty smooth. This is obviously someone's idea of how a tube amplifier sounds and perhaps they are right on some level. But tube amps can run the gamut of "soft n' slow" to "rip your ears off" so I'll leave that comparison behind and move on to the main system.

With much back wrenching, I moved the Threshold S/500 off of the rack and installed the B&K ST-140 in its place. The ST-140 is a definite lightweight with a measly two output devices per channel. In comparison, the S/500 has twenty(!!) and can drive just about any insane load imaginable with plenty of reserve.

Spinning up some Blue Nile - "Hats" on vinyl gave the B&K a chance to show its stuff. The sound was very warm and inviting. This is an amplifier made for the music lover. Treble extension was lower than the S/500, but the overall effect was very pleasing. With the ST-140 bass was wooly and underdamped, but fun. Jackson Browne - "Running on Empty" revealed a midrange, that in comparison, was less detailed but was very pleasant. The overall sound was a little darker and more compressed than the Threshold, but it was so easy to sit back and spin records, allowing one's emotions to get carried away with the music. The experience was like listening to a great FM radio station!

The B&K ST-140 highlights the classic conundrum with high end audiophile gear - more resolution has the side-effect of revealing more flaws, lessening the appreciation of the music unless it is well recorded. It also challenges your front end more, shining a spotlight on cartridge, turntable and other flaws. An amplifier like the ST-140 diminishes flaws, having a darker, more "Yin" sound. It is pleasant, but in the end I felt like I was missing something.

Since this is an old amplifier, I still have some capacitor replacements in mind. It will be interesting to see how the character of the sound changes. Stay tuned!


System:
preamp: Threshold FET-10/HL
phono preamp: Audio Sector Phono Stage
amplifier: Threshold S/500
analog: VPI HW19 MkIII - Rega RB300 with Incognito wiring - Denon DL-103R
speakers: Magnepan 1.6/QR with Sound Anchor Stands
speaker cable: Kimber 4PR/8PR Bi-wire with banana jacks
Interconnects: Cardas Cross and Cardas Quadlink 5C


Second System:
Dynaco PAT-4 modified
Dynaco AF-6 tuner
Dynaco ST-80 amplifier
Panasonic linear tracking turntable
Pioneer DVD-V7400 cd player
various budget cables


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A Visit with the Denon DL-103R phono cartridge

With the success of my Audio Sector Phono Stage, I decided it was time to pair it up with a low output moving coil cartridge. Low output MCs can be expensive beasts, ranging from the low hundreds up to the price of a brand new car. The Denon DL-103 is known to be a giant slayer and has a number of users clamoring that it is one of the best sub-$1k carts around. However, looking at the specifications, the low output impedance made it's brother the DL-103R the better candidate. Why is that? The Audio Sector Phono Stage has a zero impedance, so gain is determine by voltage and output impedance. The DL-103R also features better coils and a little more compliance than it's less expensive sibling.

The arrival of the Denon DL-103R revealed a well packaged cartridge with a handwritten test note, a manual and a little cleaning brush. Installation on the Rega RB300 arm was a snap with a my protractor and digital stylus gauge. After everything was lined up, I dialed in the pressure at 2.5G and started spinning some records.

Right out of the box, the 103R is a nice sounding cartridge. Compared to the high output Dynavector 10X5, the sound is a little more laid back. Bass is also a touch reduced but perhaps this is just more control over the lower octaves. The midrange was amazingly clean, quick and utterly involving. The treble is a touch brash, but this could be the effect of a cartridge that needs some break-in or the revealing forward sound of my phono stage. Record noise is also a little more evident.

On Frank Sinatra's "Sinatra At The Sands", the left/right split of the instruments are laid out nicely with ol' Blue Eyes vocals taking center stage. Detail with the Denon was very good with nice hall reverberation and the picking out of individual instruments. When the band got going, the sound never got congested or uncontrolled.

Steely Dan - "Aja" is a complicated album with several time changes and tight drumming. Again the Denon kept everything in control, putting each instrument in the space given by the producer. Stunning, to say the least.

Dire Straits - "Love Over Gold" again showed a cartridge that could handle large dynamic swings and complicated instrument interactions. This was especially evident in the song 'Telegraph Road' where the volume levels crests and recedes with Mark Knopfler's guitar sweeping guitar keeping the musical thread sewn together.

In conclusion, the Denon 103-R is a choice budget low output moving coil cartridge. Any problems are sins of omission as my only complaints so far is the slightly etchy treble and perhaps the last bit of 'inner' detail is missing. But it still is an enjoyable cartridge that punches way above its price. As much as I would like to buy an expensive Dynavector or Shelter cartridge, I would prefer to spend my money on other pursuits - like buying more records!


System:
preamp: Threshold FET-10/HL
phono preamp: Audio Sector Phono Stage
amplifier: Threshold S/500
analog: VPI HW19 MkIII - Rega RB300 with Incognito wiring - Dynavector 10x5
speakers: Magnepan 1.6/QR
speaker cable: Kimber 4PR/8PR Bi-wire with banana jacks
Interconnects: Cardas Cross and Cardas Quadlink 5C


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Building the Audio Sector Phono Stage

(Picture by Audio Sector)

I've had some turntable upgrades in mind, starting with a low output moving coil cartridge and a new tonearm. With my current setup I was worried about having enough gain for a .3mv MC, so I decided to build the Audio Sector Phono Stage. This is based on the 47 Labs Phono Cube, but utilizes better parts and a shunt regulated power supply. Audio Sector just provides the PCB board, while you provide the sweat, enclosure and passive parts selection. The board quality is excellent and is designed so the power supply transformer can even be mounted within the same enclosure. For my build, I mostly stuck with the recommended parts, but opted for RelCap Teflon and Polysterene film caps over the specified (and expensive) V-Caps. Instead of Blackgates, I chose Nichicon for power supply capacitor duties. Building was done over the course of a few days as I have a hard time soldering such small parts onto the PCB board.

The signal path is unique as there is no cartridge loading per se - the input impedance is zero, which is pretty much a straight current-to-voltage converter. Gain and frequency response are determined by the cartridge voltage and output impedance. There are also no signal capacitors in the signal path as RIAA equalization is done in the feedback loop. Feedback? Oh no! Did I mention the OPA627 op-amps that are used? Now things are getting weird for a discrete parts builder like myself.

Don't let the integrated circuits and feedback put you off as the end results were beyond my expectations. This the most transparent phono preamplifier I have ever heard. Hyper detailed, it shows every flaw in your turntable setup and the recording quality. It's not a kind, mellow sound at all - but is revealing, quick but still grain free. Bass is also oh-so fluid, deep and bouncily rhythmic which started my feet a-tappin'. With my Magnepan speakers, vocals are eerily real and float wonderfully between the two panels. This is a very forward sounding preamplifier and pulls the listener right into the soundstaging. In comparison, my Threshold FET-10/PC sounds a touch muffled and dark.

I can't stress patience enough as the upper-midrange energy is extreme until some time has been burned into the circuit. I don't think I've ever heard any audio component break-in like this. It literally takes hours for everything to settle down and start sounding good.

As I'm using a high output Dynavector 10X5 phono cartridge, I'm expecting some better results with a low output moving coil. Stay tuned!


System:
preamp: Threshold FET-10/HL
phono preamp: Threshold FET-10/PC
amplifier: Threshold S/500
analog: VPI HW19 MkIII - Rega RB300 with Incognito wiring - Dynavector 10x5
speakers: Magnepan 1.6/QR
speaker cable: Kimber 4PR/8PR Bi-wire with banana jacks
Interconnects: Cardas Cross and Cardas Quadlink 5C


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Upgrading the Dynaco ST-80 power amplifier

After the success of my Dynaco SCA-80Q and PAT-4 treatment, I decided to tackle the ST-80. This would prove to be a fairly easy to do job as I used many of the upgraded parts from the SCA-80Q. I've always been a separates guy, so I had no problem cannibalizing the parts for the amplifier upgrade.

The Dynaco ST-80 was introduced in 1969 and is roughly a pared down version of the venerable ST-120. The '80 features a single rail power supply, quasi-complementary output, dc blocking output capacitors and the use of only 12 transistors. However, unlike the ST-120, the ST-80 does not feature a regulated power supply, which may have improved the sound since the amplifier would clip more gently when running hard.


I bought my Dynaco ST-80 on Ebay for a paltry $45. It was in working condition, but you can see by the auction picture, the parts are aged and in need of replacement. I decided against any serious modifications and just went for a straight parts replacement. The resistors tested within spec, so that left the capacitors to upgrade.

Note that modern values are a little different than the days of yore. For example, I used 47uF instead of 50uF. Radial capacitors fit in axial PCB locations without issue. However, modern capacitors are about 1/3 the size of the originals, so new clamps for the standalone capacitors also need to be purchased. Also note that the foil on the circuit boards is flimsy - use a low wattage iron and take care when pulling out parts! The stock 'wire-around-the-capacitor' inductors were replaced by modern toroid inductors I bought from an Ebay seller who specializes in Dynaco amplifiers. Do a search on "Dynaco inductor" if you want to buy a pair for yourself.



For the power supply, I merely replaced the old capacitors with larger values. The four 400 ohm resistors on the power supply PCB were replaced with 390 ohm / 10W units. Make sure to keep the resistors directly off of PCB-19 as the SCA-80 and ST-80 are known to start on fire here as the board takes a lot of heat.



For testing, I hooked the amplifier up to a pair of test Radio Shack Minimus 7 loudspeakers and fed a signal in from my Threshold preamplifier combination and VPI turntable. This is a pretty intensive front end for such a budget amplifier and speaker. I was very surprised how good this strange combination sounded, which just proves (at least to me) how important a good front end is to getting the best out of your system. Having passed the smoke test, I decided to bring the amplifier upstairs to replace my McIntosh MC-250 amplifier.


Initial results has an amplifier that sounds pretty classic solid-state. It thas great bass and is very fast sounding, but in comparison to the McIntosh 250, the upper mids and treble are a touch 'hard'. However, the ST-80 has very nice detail and it sounds a little less grainy than the McIntosh. The ol' Mac does win out on slam and warmth, sounding much like a poor man's tube amplifier. Hopefully some extra burn in time will smooth the Dynaco ST-80 sound out and make it a viable replacement.


Second System:
Dynaco PAT-4 modified
Dynaco AF-6 tuner
McIntosh MC250 amplifier
Panasonic linear tracking turntable
Pioneer DVD-V7400 cd player
various budget cables


Update on 06/09/10. Some break-in had smoothed out the more aggressive aspects of this amplifier and the end results are very pleasing. Though not warm like a tube amplifier or the McIntosh 250, the reborn Dynaco ST-80 is now a good budget amplifier with a cohesive dynamic sound. Good for efficient speakers and rock n' roll, it's not bad at all for a $45 amplifier with $50 worth of parts.

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Upgrading the Dynaco PAT-4 preamplifier

Ever since I've been into audio, the Dynaco PAT-4 has gotten a fairly deserved bad rap. I first owned one of these vintage solid-state preamplifiers back in 1990 and the sound, even with a tube amplifier, was certainly nothing to remember - harsh, flat and very unpleasant with any speaker with a working tweeter. Eventually the whole thing was gutted and used as an experimental op-amp platform!

Flash forward twenty years and I'm stuck with a large Ikea Expedit bookcase with 13 by 13 inch slots. Though perfect for holding hundreds of LPs, finding quality small gear that can fit inside has always been a challenge. The Dynaco line of preamplifers, tuners and integrateds slide right into the slots perfectly, which is one of the reasons I keep coming back to these venerable components. Of course another reason is the easy to get manuals and parts which makes modifications and repairs easy on the wallet.

The Dynaco PAT-4 was designed by the late Ed Laurent who had a hand in many of Dynaco's more famous products. An examination of the schematic reveals a simple single power supply, two transistors for each channel of the phono section and two transistors for each channel of the line section. Negative feedback is used to control overall gain and lower output impedance as there is no buffer stage to drive the output. This circuitry actually reminds me of the Dynaco PAS and probably came directly out of the transistor manufacturer's specification sheet.

I began to wonder if this old preamplifier could be made good with a few part upgrades, so I decided to tackle upgrading a Dynaco PAT-4 using the AVA Audio 1986 Audio Basics (starting on page 29) as my basic guideline. I soon found a nice looking PAT on Ebay for an absurdly low price and upon arrival was greeted by a fairly mint specimen. I hooked it up to my McIntosh 250 and was not impressed by the results. The PAT-4 was as harsh and grainy as I remembered it, plus one of the phono channels was weaker than the other. My old PAS certainly bettered it on all levels except the PAT-4 did have a slightly better rhythmic bass. Could I gain any sonic improvements by replacing the ancient capacitors and bypassing the touchy tone controls? Let's find out.


Cracking open the PAT-4 revealed a bevy of leaking electrolytic coupling capacitors and even two connections that were missed by the solder iron of the original kit builder. Using some cut up white address labels, I marked the wire connections to the PCB boards and soon had the whole PCB assembly removed. This is also a good time to replace the four small electrolytic capacitors located near the front input jack and back tape outs with wire.

With the tone control bypass, I also figured out a clever way of removing one of the large coupling capacitors from the signal path while keeping the emitter bias dc voltage out of the signal output. See image below for the tone control bypass instructions and the capacitor upgrade locations.


As far as parts quality, this is a budget rebuild so I shied away from the ultra-expensive tweak parts. Instead, standard Digikey parts were used except for the four 10uF Polyester signal and Nichicon Muse power supply capacitors I found cheaper on Ebay. Replacing the components on the PCB boards is easier if the metal brackets are gently bent to a 90 degree angle.


The power supply was next. I originally envisioned a LM317 regulator, but feared the original transformer could not handle the extra current demands. Dynaco built everything to a price point and I wasn't sure if the transformer would overheat. Since this is a budget build anyways, I decided on just improving the basic unregulated supply with the use of slightly more capacitance and better parts. Three 1000uF/63V Nichicon Muse capacitors mounted on a terminal strip replaced the old can cap. A more intrepid builder could remove the original transformer, use an outboard SMPS supply that feeds an onboard regulator using a LM317 (or whatever) .

After checking supply voltages and DC offset, I hooked the Dynaco PAT-4 as a phono only preamp into my main Threshold/Magnepan system. The sound wasn't half-bad. A little lacking in 'color' and drama, the signal was clean and certainly listenable. It vaguely reminded me of an old Adcom 555 preamplifier, but my memory of that unit is fairly sketchy, rendering any comparison fruitless. Compared to the more expensive Threshold FET-10/PC, the refurbished PAT-4 was definitely second tier material with a slight sterility to the sound.

On the upstairs second system, the Dynaco PAS-3X was taken out and the PAT-4 installed. Paired with the McIntosh MC-250, this could have been a fairly common solid-state system back in 1969! The sound was certainly different than the previous preamplifier as this classic all solid-state combination was faster and had deeper bass. Some fairly minor upper-midrange/treble glare still existed with the use of PAT-4, but has been greatly reduced by the film capacitors and newer electrolytics. The new sound is now quite modern and the phono stage is also extremely quiet without any channel imbalance.

The refurbished Dynaco PAT-4 is now a nice little budget preamplifier and would be an inexpensive project for anyone handy with a soldering iron. Your results may vary depending on the new parts used and the overall condition of the stock unit.


Second System:
Dynaco PAS-3X modified
Dynaco AF-6 tuner
McIntosh MC250 amplifier
Panasonic linear tracking turntable
Pioneer DVD-V7400 cd player
various budget cables


(05/23/10) Update: Component break in? I don't know, but a few more hours on this preamplifier and it has really smoothed out. Most of the glare is gone and I'm quite pleased with the end results. For a budget system, I can really live with the refurbished Dynaco PAT-4. With new parts and the tone control bypass, it is a screaming deal for the little time and money put into it. The phono stage is dead quiet and the linestage is very quick and dynamic. Music is tons of fun to listen to with good detail, deep bass and snappy transients. Not bad for something that's normally considered a vintage piece best forgotten.


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Upgrading the Dynaco SCA-80 integrated amplifier

Some things in life are always worth doing, while others require a furrowed brow. Upgrading a Dynaco SCA-80Q amplifier doesn't exactly define common sense as the design is antiquated at best. However my Ikea record/bookshelf has narrow 13" slots and I already had a matching Dynaco AF-6 tuner that fits nicely. A $25 Ebay win soon had a dusty and decrepit '80Q' in my hands.



Featuring the Dynaco PAT-4 preamplifier and ST-80 amplifier all in one chassis, the 'Q' version added a primitive 'quadraphonic' sound with the use of a single 10 ohm resistors. Looking at the schematic of the SCA-80Q reveals a single common power supply, no regulation, a simple (almost tube-like) topology, and a plethora of electrolytic coupling capacitors. Surely much of the associated harshness must come from the aged parts and poor power supply design.

An article from Van Alstine pointed the way to bypassing the tone controls and a few dollars at Digikey and Ebay soon had some parts speeding my way.

1) Bypass the tone controls by snipping out the tone control wires that lead to numbers 13-18 on the preamp PCBs. On the PCBs, tie leads 13-15 together. See page 29 of the 1986 Audio Basics newletter.

2) On the preamp PCBs, replace the six 50uF/25V Elna electrolytics with 10uF/100V film types. I used some low budget metallized units. I also replace every other low voltage electrolytic as these can be troublesome. Make sure to also replace the two grey electrolytics coming off the PCB boards, located behind the volume control, as these are from the phono stage output. This whole capacitor swapping process is easier if the PCBs are removed from the unit. Of course this requires marking the location of the old wires and some deft use of the soldering iron.

3) Replace 5000/80V power supply capacitor with a 6800uF unit. Replace the four 400 ohm / 7W units on the back power supply PCB with four 390 / 10W units. On the stock unit, this board is known to start on fire, so I kept the new resistors directly off of it.

4) Replace the two side mounted 5000F/80V speaker coupling capacitors. I used some nice modern 4700uF Panasonic units bypassed with some 4.7uF/250V caps from my junk box.

5) The white wire wrapped around the speaker coupling capacitors are actually small valued chokes. I bought a smaller packaged pair from an Ebay seller who specializes in Dynaco parts and mounted them on some terminal strips.

6) I decided to regulate the preamp section by using a simple 7824 regulator. Electronics 123 has a nice like PCB to accomplish this but the 7824 still needs to be bought from Digikey.  This required the changing of the original 4.7k dropper resistor to a 400 ohm / 10W unit. I also changed the phono section power supply to come from the regulated supply and I used a 1.2K / 2W dropping resistor.


Due to laziness and the number of wires to desolder from the board, I did not tackle the amplifier PCBs yet. There are still some electrolytics that need replacing and I have an idea of improving the negative feedback as the output caps and chokes are not included in the loop.

So how does the amplifier sound? Quite modern now. With my KEF Q60s, much of the harshness is gone and only some faint residual 'solid-state' upper midrange hardness can be heard. I was surprised how dynamic the amplifier sounds now as rhythm gels better than my trusty Dynaco PAS-3X preamplifier and McIntosh 250 amplifier. The tube / solid state combination does sound smoother and warmer, but lacks the impact and speed of the refurbished Dynaco SCA-80Q.

Note: for a more detailed upgrade, check out the latter posts on the Dynaco PAT-4 and ST-80 upgrades.

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Review: Cardas Cross and Quadlink 5C interconnects

At the urging of a friend, I decided to replace my old Belden and Cardas Crosslink interconnects. For the phono preamplifier to linestage connection, I bought a used one meter set of Cardas Cross cables, which are considered mid-priced. Between the linestage and the amplifier, a new one meter set of Cardas Quadlink 5C cables were selected. The quality of construction leaves nothing to be desired as the rhodium RCA jacks fit like a glove and the cables are extremely flexible.

Why Cardas? They've been in the business for a long time and have a theory to cable construction that actually makes some sense (at least to me). Further details can be found on their website here.

Differences, compared to the older set of wire, are minor and not the type to be necessarily detected using an ABX box. To some, this means that the differences don't exist. But, psychological expectations aside, I still heard some changes. Trailing notes and minor 'inner' detail was bumped up a bit. The new Cardas cable also has a warmer, more organic presentation that manages not to sound sluggish. In general, my system took on a slightly more relaxed sound.

The big question that still remains is upgrading interconnects worth it? Realistically for the price, no. I've heard bigger diferences between cartridges, phono stages and whatnot. But like any other 'extreme' hobbies, nearly insignificant changes to one person make all the difference to another. In the end, my adventure into wire upgrades has given me a more enjoyable stereo. I couldn't ask for anything more except for a lower price!

System:
preamp: Threshold FET-10/HL
phono preamp: Threshold FET-10/PC
amplifier: Threshold S/500
analog: VPI HW19 MkIII - Rega RB300 with Incognito wiring - Dynavector 10x5
speakers: Magnepan 1.6/QR
speaker cable: Kimber 4PR/8PR Bi-wire with banana jacks
Interconnects: Cardas Crosslink and Belden


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Review: Kimber 4PR/8PR Bi-Wire Speaker Cables

I never thought I would be writing a review on speaker cables as differences between wire is a contentious issue. I've never been one afraid of disagreement, but in all honesty I've never heard any change I could honestly attribute to interconnects or speaker cables. And really, in my heart of hearts, I didn't want to hear differences in cable. The thought put fear into my wallet, not to mention my engineer orientated brain.

As part of recent system finalization, I've decided to replace the old Canare Quadlink speaker wire. I did this for several reasons. I had a fear that the spades could short against each other in the tight confines of the Threshold amplifier and I also wanted a bit longer reach than the six foot length afforded. My Magnepan 1.6/QR speakers can also be bi-wired, removing the metal straps between the high and low inputs. With that in mind, I ordered an eight foot pair of Kimber Kable 4PR/8PR Bi-Wire speaker cables terminated with bananas.

Upon arrival, I removed them from the supplied packaging and was impressed by the construction quality. Though the 4PR / 8PR cables are Kimber's most budget cable, the termination and braiding job was well done. The 4PR consists of four brown and four black conductors braided together to make a 14awg cable. The 8PR is built the same way with eight cables per leg, producing a 10awg cable. I removed the Canare wire from the system and also removed the hi/lo straps from the Magnepan speakers. Installation of the Kimber cable was a breeze as I used the 4PR set for the tweeter and the 8PR set for the woofer panel. I then settled down to give my system a quick listen.

Initial impressions were certainly interesting and not at all what I expected. At this price point I expected no change at all, but was instead greeted with a brighter but edgier treble. Bass extension also seemed deeper, perhaps the 10awg cable helping with the high amount of current I use to drive the Magnepan speakers. Deciding some more break-in may be required, I let the system play in the background in the evenings while I worked out.

A few days later, I had time for some further listening, which revealed the Kimber 4PR/8PR to be one smooth cable. There is a warm coherency from top-to-bottom and the bright edginess of the treble disappeared. The speaker drivers, a slightly strange term to use with Magnepans, seemed to now play as-one. The lowest bass, never a strong point on the Magnepans, was better too. Though the differences were not staggering compared to the old Canare, the changes were still audible.

So there you go - my prejudices once again have been shattered. I never thought solid-state amplification could cut it and now I'm hearing differences in cables. I think part of the reason for this change comes from finally having a better front end, revealing speakers and a certain amount of stability. Before, I was always trying new amplification (often DIY), speakers and moving to different rooms. Such circumstances clouded my ability to discern subtle changes as the amount of given variables were too high. Now once I get the chance, I will be willing to spend the dough on some even more expensive cables. Somewhere I hear my wallet screaming.

System:
preamp: Threshold FET-10/HL
phono preamp: Threshold FET-10/PC
amplifier: Threshold S/500
analog: VPI HW19 MkIII - Rega RB300 with Incognito wiring - Dynavector 10x5
speakers: Magnepan 1.6/QR
speaker cable: Canare Quad
Interconnects: Cardas Crosslink and Belden


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