Thursday, March 11, 2021

Turntable Basics and Buyers Guide


 Here is a short video I made about buying turntables; geared toward beginners or anyone looking to upgrade to a new record player.

Friday, February 26, 2021

Review: a Frankenstein Eico ST-70 tube amplifier

 I bought this strange modified amplifier on Ebay. It looks as if someone took a stock integrated and modified it to be a basic power amp. Gone is the normal set of controls on the front plate, replaced with a generic black panel and power indicator light.


[​IMG] 
A peek on top of the grille - what is inside?

[​IMG]

Of course you know - you read the title of this post! Someone took an Eico ST-70, removed the preamplifier portion and converted it to use 5881s instead of the stock 7591s.

[​IMG]

Since I didn't have any 5881s on hand, I modified this amplifier to use the military 6AR6. Since the 6AR6 has a completely different pinout (and bias points!) it took an entire rewire of the output stage, along with more negative bias than the stock circuit.

[​IMG]

I also changed the power supply with new electrolytic capacitors for the main bucket, 6SN7 phase-splitters, and 12AX7 input tube. I also added a little 1.5H Dynaco choke to reduce the B+ ripple. After a little troubleshooting, and bias modifications, I finally got this amp to work; with 40mA per output tube. 

So how does this pentode output Frankenstein weird output tube sound? Even with old Russian 6N8S tubes, surprisingly good. Bass extension - with the large output transformers - is really deep. And there is the old tube midrange and smooth treble thing happening. Maybe it's been too long with an SS (Aleph J clone) amplifier, but this little push-pull tube amp is quite magical.

Chet Baker Sings, for example, really is holographic - for a mono recording - with his voice and trumpet sounding natural and forward. Compared to the Aleph J solid-state amplifier, music is more relaxed but, at the same time, more dynamic. The tube amplifier sounds way more powerful than its approximate 30 or 35Ws per channel.

I'm surprised that the KEF R500s work so well with this vintage Frankenstein; you never really know what you are going to get with modern speakers.

Once I get over the excitement of having a new amplifier, I plug in some old Zenith 6SN7s that I have on hand. Maybe things will get even better-better.

 

 

Thursday, January 28, 2021

Short Review: a Hafler SE-120 amplifier

 


This is a Rockford Corp era amplifier good for 60WPC; made to be _not_ user friendly versus the kit amps of yore. This one looks to have been around the block though some face plate cleaning helped to remove a bit of yellowing.

The amp sounded a little tired so I went in and replace the main electrolytic capacitors, the input caps, and two of the smaller power supply rail caps. Needless to say getting to the underside was very frustrating with the number of screws, removing the output mosfets from the heatsink, and pinching the nylon standoffs to free the PCB. In the end I also checked the bias, cleaned the RCAs and speaker jacks.

After my work: Overall it is a nice sounding budget amp - to my ears a little warmer than something like an Adcom 535. Good bass, and more of a rock 'n' roll sound than say the Musical Fidelity. My Aleph J clone is a bit more refined with a touch more detail and "space" around the instruments. Though all three amps are "warm" none of them exactly sound like a tube amp. An old Frankenstein Eico ST70 - modified to be a power amp with 6AR6 output tubes - I have kicking around has a presence and sense of dynamics that I just don't hear with these (admittedly low powered) SS amps. Nonetheless I could live with the Hafler if I really needed a compact amplifier.

Thursday, January 21, 2021

Short Review: the Musical Fidelity A1 integrated amplifier

Musical Fidelity A1
This is one of those little amplifiers that I've always wanted to hear for years but didn't get a chance until today.  You probably know the history: designed by Tim de Paravicini, may he rest in peace, this integrated was very popular in the mid-80s and very hot running, but providing that Class A magic for a relative bargain.  It was apparently Musical Fidelity's biggest seller.  It wasn't without its well-documented issues with noisy volume controls and switching, but this particular unit seemed to have held up quite well over the years.

How does it sound?  Like my Aleph J clone, very Class A.  But also very British polite.  I would say the phono stage doesn't quite stack up to my (much more expensive) tubed Audio Research SP8, but the amplification portion was a real surprise.  In my small/medium sized listening room it had no problem driving the 88dB efficinet KEF R500 towers.  Lower bass, like on my UK pressing of the Bee Gees - Trafalgar - was deep and controlled.  The midrange is quite magical, but the sense of dynamics work better with Chet Baker jazz albums then say something like AC/DC.  There is a distinct lack of glare and edge in the treble, the overall sound hewing further to the warmer side than neutral.

So overall a nice little integrated - that runs so hot that after an hour of use I can only hold my hand on top for a half a second before I fear getting burned.  Not a good napping place for those with cats, or children with curious hands!  Nonetheless, back in the past I would have been very happy with this amplifier since it images quite well and does a very good job with vocals.  And it is the sort of sound that makes me search through my stack of records and pull out some old favorites.  Very much a music lover's amp than audiophile-extremis.
This is one of those little amplifiers that I've always wanted to hear for years but didn't get a chance until today.  You probably know the history: designed by Tim de Paravicini, may he rest in peace, this integrated was very popular in the mid-80s and very hot running, but providing that Class A magic for a relative bargain.  It was apparently Musical Fidelity's biggest seller.  It wasn't without its well-documented issues with noisy volume controls and switching, but this particular unit seemed to have held up quite well over the years.

How does it sound?  Like my Aleph J clone, very Class A.  But also very British polite.  I would say the phono stage doesn't quite stack up to my (much more expensive) tubed Audio Research SP8, but the amplification portion was a real surprise.  In my small/medium sized listening room it had no problem driving the 88dB efficinet KEF R500 towers.  Lower bass, like on my UK pressing of the Bee Gees - Trafalgar - was deep and controlled.  The midrange is quite magical, but the sense of dynamics work better with Chet Baker jazz albums then say something like AC/DC.  There is a distinct lack of glare and edge in the treble, the overall sound hewing further to the warmer side than neutral.

So overall a nice little integrated - that runs so hot that after an hour of use I can only hold my hand on top for a half a second before I fear getting burned.  Not a good napping place for those with cats, or children with curious hands!  Nonetheless, back in the past I would have been very happy with this amplifier since it images quite well and does a very good job with vocals.  And it is the sort of sound that makes me search through my stack of records and pull out some old favorites.  Very much a music lover's amp than audiophile-extremis.

 

This is one of those little amplifiers that I've always wanted to hear for years but didn't get a chance until today. You probably know the history: designed by Tim de Paravicini, may he rest in peace, this integrated was very popular in the mid-80s and very hot running, but providing that Class A magic for a relative bargain. It was apparently Musical Fidelity's biggest seller. It wasn't without its well-documented issues with noisy volume controls and switching, but this particular unit seemed to have held up quite well over the years.

How does it sound? Like my Aleph J clone, very Class A. But also very British polite. I would say the phono stage doesn't quite stack up to my (much more expensive) tubed Audio Research SP8, but the amplification portion was a real surprise. In my small/medium sized listening room it had no problem driving the 88dB efficient KEF R500 towers. Lower bass, like on my UK pressing of the Bee Gees - Trafalgar - was deep and controlled. The midrange is quite magical, but the sense of dynamics work better with Chet Baker jazz albums then say something like AC/DC. There is a distinct lack of glare and edge in the treble, the overall sound hewing further to the warmer side than neutral.

So overall a nice little integrated - that runs so hot that after an hour of use I can only hold my hand on top for a half a second before I fear getting burned. Not a good napping place for those with cats, or children with curious hands! Nonetheless, back in the past I would have been very happy with this amplifier since it images quite well and does a very good job with vocals. And it is the sort of sound that makes me search through my stack of records and pull out some old favorites. Very much a music lover's amp than audiophile-extremis.

Review System:
Thorens TD-309 turntable with Ortofon 2M Bronze
Cardas Iridium interconnects
KEF R500 speakers with Cardas Twinlink speaker cable

Tuesday, January 19, 2021

Review: The Audio Research SP-8 preamplifier

 

History: Audio Research has a long and, dare I say, storied past.  Back in the era when vacuum tubes where being consigned to the ash heap of history, they, and a just a handful of manufacturers were still making gear that used these ancient amplification devices.  Even in 1990 I remember being at a used electronics company in Colorado and receiving less-than-kind words when inquiring if they had any tubes or tube gear.  "Vacuum tubes?  Why would you want to use tubes?  Are you fixing an old piece of equipment?"

William Z. Johnson obviously didn't get the message,  Like so many afterwards, he started out modifying Dynaco gear, and branched out making his own equipment under the banner of Electronic Industries.  This latter became Audio Research which started with the SP-1 preamplifier and the Dual 50 amplifier.  They really didn't have a hit on their hands until the venerable SP-3A preamplifier, and D-70 plus D-115 amplifiers (and the various following iterations) came and made them serious contenders in the audiophile world.  They also dabbled - and still do! - with solid-state equipment but are, of course, really known for vacuum tubes.

The Audio Research SP-8, first introduced in 1981, went through several minor redesigns.  I tend to think of the circuitry as being the ultimate Dynaco PAS or Marantz 7. For example the phono amplification is done through a pair of 12AX7s with a 6DJ8+FET cathode follower, RIAA handled via the negative feedback loop.  The linestage is similar with a pair of 12AX7s and a 6DJ8+FET cathode follower with loop feedback.  Where Audio Research shines is the power supply.  In this case a solid-state regulator makes sure the phono state receives a dead quiet high voltage.  And, oddly enough, a combination of a 12BH7 and 12AT7 provide the regulated supply for the linestage.

Controls are fairly simple but with some older ideas that have gone out of fashion.  ie, of course there is a volume but there is also the increasingly rare balance control.  And something else - there is a stereo, mono, reverse, left, and right mode.  Add in the switchable AC outlets for that extra vintage feel.  There is, however, no tone controls or a loudness switch.  But one can mute, select the phono or four other line sources, and switch between tape out monitoring or input.

This particular SP-8 under review is a Mark II, Revision 5, and has only had three previous owners.  When my friend offered to sell me this well-known classic, I jumped at the chance even though it needed to be repaired.  It turned out, due to years of being in storage, the power supply section that handles the muting and 12AX7 filament voltage was no longer working.  Instead of troubleshooting it myself, I sent the unit out to the Audio Research service department, who still does repair work on this 30+ year old gear.  They not only repaired the power supply in question, but also cleaned the volume pot, replaced all of the electrolytic capacitors, put on new feet, and found an additional issue with the linestage that needed to be fixed.  Now this SP-8 is ready to provide service for many more years of service.

 

First Impressions: After unboxing the returned SP-8, I first had to figure out where to place the eight different tubes.  It isn't obvious since the circuit board is not marked.  Instead one has to look at the manual, figure out what version you have, and then double-check your work.  I'm glad I did because I had to swap the location of the 6DJ8 and 12AX7 in the phono preamplifier.  Luckily I did not power on the unit!  After switching the location of my two turntables, due to the interconnect lengths and phono input location, I was finally able to sit down and do some quick listening.

With new electrolytics and NOS tubes that needed to be broken in, I found the bass rather lightweight.  The top end was also bright and the midrange was a bit muddled.  Nonetheless I could tell there was an increase in detail over the replaced Classe Five.  I let the preamplifier cook for a few hours and things started to snap in place.  For example, Chet Baker's voice on the title song from the album She Was Too Good To Me, was very emotional; perhaps the closest one could get to the now deceased trumpet player.  Pink Floyd - The Wall had fantastic imaging without any blurring of the instrumental or voice outlines.  The Classe Five, in comparison, sounded a little darker and less forward.  The SP8, at least with the excitement that new gear brings, seemed to be a real step up in fidelity.


Listening Test: After a few days of background music duty, it was time to put the "new" Audio Research through its paces.  I could tell right from the get-go that the bass had become more extended and some of the forwardness had been reduced.  Note that tube selection will, of course, change the sound.  ie, a set of new production tubes may not be as satisfying as some original 1950s Mullard 12AX7s that I was lucky enough to have on hand.


I have an interest in electronic instrumental music, to the point where I have made my own albums.  For this review I didn't have the ego to listen to my own work but instead picked out the soundtrack Beyond the Black Rainbow by Sinoia Caves.  This has a heavy Tangerine Dream influenced album with one or two sequencers often going at once.  The SP8 did an extremely good job capturing the attack of the electronically produced notes, putting them into their shifting artificial space in the soundstage width.  Bass was also deep without any "classic tube" coloration or overhang.  This is no golden-hued Dynaco PAS experience but instead has a speed that, until now, I thought was impossible with the 12AX7 tube.

 

Neil Young's Tuscaloosa is a live album from his Ditch Trilogy days, starting with two acoustic numbers before the whole band takes the stage.  With the Audio Research his voice had a real presence, the body and the diapraghm can be heard projecting much like the "real thing".  I've done sound for a few live shows and this albums captures that experience quite well, also with the proper amount of hall/stage reverberation, along with the oddly recorded, cardboard sounding drums.  Likewise with the dynamic shifts, which were recorded in a honest way, capturing what it must have sounded like being there; provided you had access to the soundboard instead of being in the back row!


Imaging and soundstage depth was among the best I've heard in my system .  An example of this is the song Warm Ways on the self-titled Fleetwood Mac album.  This is a busy mix but the outlines of the instruments and voices weren't slightly blurred like lesser preamplifiers.  This led to more detail, or, as Audio Research would say, High Definition.  I've owned plenty of other preamps in my life but none have quite approached the sound of the SP8, which, given it's rather pedestrian signal circuitry, a real surprise.  It's neither dark nor bright (tube dependent, of course!) but seems to pass the sound from the Thorens TD309 turntable along in a refreshingly honest way.


Dead Can Dance albums, by some strange miracle, are usually very well-recorded.  My original 1994 UK pressing of Toward the Within is no exception, capturing the vibrancy and the crowd excitement of this live recording.  The song Sanvean, with Lisa Gerrard's voice taking center stage, is a beautiful tear-inducing song.  I was swept away by the emotion of her voice, proving that the Audio Research is no clinical piece of gear.  The depth and power of the music was, once again, presented very naturally without any undue added coloration that one would find in a vintage "warm" preamplifier, but neither did the overall sound swing the other way towards hyper-detailed iciness. 


Parting Thoughts:  Given the age of this preamplifier, it may be a surprise to many that I find it quite neutral.  However I look at this era, the late 1970s to the late 1980s, as a golden age of audio reproduction.  Yes there were fewer companies back then, but they were really pushing the envelope of technology.  There are many examples of this - Krell, Mark Levinson, Threshold, and, of course Audio Research.  The SP-8 is the sound of a classic 12AX7 feedback circuit taken to the extreme.  And it pays off - given the right tubes! - with a very neutral, high definition sound that is also transparent.  If you can find one, and have the patience to have it properly serviced, then the Audio Research SP8 is worth the trouble, especially if you are into vinyl reproduction.

I had to add the caveat about vinyl reproduction because of the high gain nature of the linestage.  The average CD player or DAC with a healthy 2V output will give one a very limited volume control range.  An example of this, with my second turntable, a Dual CS5000 and the Schiit Mani phono preamplifier.  I had to set the latter to its lowest gain setting - 42dB - otherwise the SP8 at the bottom of the detented pot mean I was only two click away before the music became too loud.  And this with an amplifier that is not particularly sensitive.


Review System:
Thorens TD-309 turntable with Ortofon 2M Bronze
First Watt Aleph J clone amplifier
Cardas Iridium interconnects
KEF R500 speakers with Cardas Twinlink speaker cable