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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