Author Topic: DIY Precision fidelity C7A  (Read 1443 times)

Offline Ingvar Ahlberg

Re: DIY Precision fidelity C7A
« Reply #15 on: September 12, 2021, 11:24:23 AM »
Very good choise for a DIY RIAA/Preamp, I canīt think of any better route to walk when it comes to building a copy/replica of a classic design and in this case it looks extremely well executed too.

The C7 A I had for some Years is the next best phono preamp I ever owned, as mentioned the build quality was horrible all the
way down to poor solderings and the really lousy RCA connectors and an extremely stupid chassis design but despise this
records sounded better through this than any other preamp i had used.

(the reason that I donīt have/use it still is so stupid that I will never tell You. As it was only a RIAA with volume control and input selector and the Pioneer CD player I had sounded ridiculous through this due to a very poor output stage so I got a CJ preamp as that had a line stage too and was very highly regarded, problem solved? No after just a week or two I realised that the CJ was pure junk for LP replay compared to the C7 that I had given away,ven more stupid in the rearview mirror as I havenīt playd CD records the last 8 years, the only cd player leftt is in my workshop and not used there either)

Ingvar
A senile Swedish loudspeakermanufacturer, ponytail and all, why is he here?

Responsible for H.A.D Halland Audio Design and The vacuumed cat Company.

Offline Crankshaft

Re: DIY Precision fidelity C7A
« Reply #16 on: September 12, 2021, 02:38:00 PM »

Me too, please.
This is EXACTLY what I'm looking for.

Making some boards, Ari? I'm in

Offline reeman

  • Trade Count: (+6)
  • AVForums Veteran
  • ***
  • Posts: 660
  • Total likes: 72
  • Yellow cones are for.......
Re: DIY Precision fidelity C7A
« Reply #17 on: September 12, 2021, 06:22:37 PM »
Although both Reeman and I have mentioned the name, a louder shout is maybe necessary.

As I said before I knew the Bruce Moore (MFA, Audible Illusions etc) designed, Precision Fidelity C7 very well.  Audio memory is never very accurate but I remember the unit as sweet and maybe not the last word in detail. Its bugbear was a somewhat subdued dynamic performance, it was polite, maybe too polite.

What Garth had to work on was the circuit as printed in the back of the manual, a power transformer and a much "modified " case. Layout and circuit board design (always crucial in such low signal devices) was entirely Garth's own. My further brief was little as possible money to be spent. So parts all came from what Garth had. Many were pulls from Telecoms devices so probably better than we Adiophools can spend on. The only concession was right at the end when he called me to tell me I may want to get some "fancy" output capacitors.

When I first heard the unit with the mono EMT OFD 25 mono cartridge I was simply blown away. The EMT is a dinosaur. A true mono cartridge that tracks at 5 grammes, it only has horizontal displacement. Anyone who has heard such a cart in a modern system is always astounded by the sheer heft and guts of the sound. Enormously powerful bass with thundering dynamics. The mono C7 perfectly reproduced that.

It is for that reason that I rushed back to Garth to build a second board, do some changes to the PSU and a devilishly clever way to allow the use of the mono EMT at the flick of a switch. It would appear that the wonderful mono sound was as much due to the C7 as the EMT cart. Freed from the shackles of the output pots and selectors the phono section became a true reference product.

Garth spent a lifetime in Telecommunication and is an avid Radio Amateur. He once told me he started his career assembling telephone switchboards and that is there where his knowledge of proper wiring and earth techniques came from. He is an avid builder of valve amps for his own use and often builds or repair gigantic tube radios and transmitters.

Over the last 20 years, Garth has fixed or modified every single piece of equipment  I own. Heavily modifying or repairing complex Studer, Ampex and MCI tape machines, fixed the massively complex Thorens Reference turntable, all power amps and if there is an issue with a Valve Audio product, Garth fixes it. Even Schalk won't be able to see where he has worked.

My most embarrassing moment with the man was years ago when we had just met. Someone recommended I take my sick Cary 805 to him. The Cary use 211 output valves. In his lounge, I said to his friend that she should watch out when he works on this as there are some extremely high voltages in there, around 850V. She smiled and Garth said nothing. When I went to collect the amp it was in his workshop. There was some serious radio stuff around including a radio he had designed and was building. I stared in awe at the valves, some the size of a watermelon. " Have to be careful around those" said Garth " That one has 5000V on the top  and rather large current too"

I have no doubt that my music enjoyment would not have been 10% of what it is if not for the quiet man with an extremely organised brain and golden hands. I am sure the same goes for Reeman and a bunch of others too. Thanks, Garth Moore!



I could not agree more. The man is a genius. He keeps quietly to himself and helps the select few with their projects and broken gear. I'm just glad I'm one of the few. Ontop of it all he is an absolute gentleman.

Offline reeman

  • Trade Count: (+6)
  • AVForums Veteran
  • ***
  • Posts: 660
  • Total likes: 72
  • Yellow cones are for.......
Re: DIY Precision fidelity C7A
« Reply #18 on: September 14, 2021, 07:40:24 AM »
Just a bit of added info.

If you have distortion then you will need to pd the output. This circuits gain is insane. If you look at the circuit you will see a 25k pot that everything goes to. I initially padded the output with 27k resistor. I still found the slightest bit of distortion in vocals. I then went back to the circuit and saw there was an additional 10k resistor that things goe through before getting to the pot. So I added 10k to the 27k and so far it looks like it's solved my issue.

I have to go to work now but will listen later and confirm if it's completely fixed the issue.

Offline fredeb

Re: DIY Precision fidelity C7A
« Reply #19 on: September 14, 2021, 04:34:25 PM »
Making some boards, Ari? I'm in


What about a point to point layout for the phonostage section ?  ;D

Or....

If someone offers to create gerbers for the phono section , I'll have the boards made up . Perhaps a more refined layout with double layer boards and large ground planes .

Perhaps Mark Johnson's Class A capacitance multiplier boards (I have a few those and can make more) , and a modern good adjustable filament supply regulation circuit .

Thank you @reeman and @Agaton Sax for making us aware of this great phonostage .

I downloaded the C7a schematics from hifi-manuals and tried to clean them up and make them more legible . Click to enlarge .



...evolution is the gradual development and stratification of progressive series of wholes, stretching from the inorganic beginnings to the highest level of spiritual creation.
Jan Smuts

Offline reeman

  • Trade Count: (+6)
  • AVForums Veteran
  • ***
  • Posts: 660
  • Total likes: 72
  • Yellow cones are for.......
Re: DIY Precision fidelity C7A
« Reply #20 on: September 14, 2021, 05:08:07 PM »

What about a point to point layout for the phonostage section ?  ;D

Or....

If someone offers to create gerbers for the phono section , I'll have the boards made up . Perhaps a more refined layout with double layer boards and large ground planes .

Perhaps Mark Johnson's Class A capacitance multiplier boards (I have a few those and can make more) , and a modern good adjustable filament supply regulation circuit .

Thank you @reeman and @Agaton Sax for making us aware of this great phonostage .

I downloaded the C7a schematics from hifi-manuals and tried to clean them up and make them more legible . Click to enlarge .





This is exactly what I did just by hand.

Double sided board with filaments on top and a massive screen which is grounded.

Let me know if anybody makes up boards from Gerber files

Offline Ajay-L

Re: DIY Precision fidelity C7A
« Reply #21 on: September 15, 2021, 10:54:25 AM »
Not the "A" model, but something for you guys to look at in terms of layout, etc.

https://www.monarchy-audio.com/Precision_Fidelity_Preamp.htm

Offline fredeb

Re: DIY Precision fidelity C7A
« Reply #22 on: September 15, 2021, 04:50:25 PM »
Nice @Ajay-L ! $650 is pretty reasonable too . Obviously only phonostage is amplified , other inputs are passive .

I found a dutch guy willing to do the gerbers for EU60 . I can then also get gerbers for regulated filament and regulated B+ , modern equivalents , not the Precision Fidelity ones .


« Last Edit: September 15, 2021, 04:54:53 PM by fredeb »
...evolution is the gradual development and stratification of progressive series of wholes, stretching from the inorganic beginnings to the highest level of spiritual creation.
Jan Smuts

Offline MusicMan_ZA

Re: DIY Precision fidelity C7A
« Reply #23 on: September 15, 2021, 06:52:06 PM »
I would be interested in building this too, Ari.
Please keep us updated, as/should you go ahead.  :thumbs:
I love music - analog and digital. Even listening to the Blues makes me happy. During the day I coach and counsel, after hours I indulge in my second passion - listening to vinyl and restoring turntables. Some I keep, some I sell...

Offline Agaton Sax

Re: DIY Precision fidelity C7A
« Reply #24 on: September 17, 2021, 07:13:02 AM »
This is one of my rambles. . One person seems to enjoy them so here is one. It probably doesn't belong in the "Where's the circuit" "Where can I get this transistor?" section but what the hell, it is my preamp. So just walk on by.

In the year 1 AC. That is 1 year before Covid, Achim lent me a DAC. I wrote it up here. At the time, before Covid, before this crippling drought my wife and I sat under a tree. I remarked that with this DAC, I could easily walk away from Analogue. With typical Dutch impassiveness, she looked at me and said "No". Well aware of my histrionic outbursts, Elizabeth knows; tomorrow I'll regret what I said today.

2(maybe 3)  years on I own that DAC and blow me down, after years of denialistic kicking and screaming, I  have now gone from 95% Analog to 90% Digital. So when Reeman wanted to try the PF C7R(ecreation) I didn't think twice. My Analog was (90%) Vd Hul Crimson XWYCPGX# on a Reed P3 arm and Schalk's magic Whisper. The C7 R was on 100% of every day but seldomly listened to.

It was the reading of the Reeman that made me curious again. How good is it really? So it came back and much as I remembered it is a little hissier than the Whisper and the ghostly Digital, Now remember my system sensitivity is above 110db/W and my room is super quiet. Noise heard here is mostly inaudible elsewhere.

Still, there was one noisy valve. 5 years 100% operation-not bad. I tried my ancient stash of ECC83s but finally, of to Garth. Now Garth never sells his own stuff, so with eyes popping, I saw him pull 4  red boxes from the shelf. Mullards, NOS, sealed! But in red boxes? Where is the blue with the red writing? Better still, he is actually going to sell them to me! Me, Me, Mine.



Turns out these are the industrial versions. Purists will scoff "The same thing" but hey, grant me my fantasy? Anyway, Garth fiddled little (I think he is secretly very proud of this thing but won't admit it out loud) so C7R came home. And it is super quiet!

So I play Jazz. big fat Ortofon SPU, Koetsu arm, C7R. Wow, juicy fat. Jimmy Smith bopping on the Hammond P3 to Lalo Schifrin arrangements. Music to a thousand 60s movies never seen and never made. Horace Silver, Ornette and of course, Myles, impossible, obnoxious, racistic, awful, brilliant, incredible Myles. And then: something I haven't listened to in 30 years. Dave Brubeck, Concord on a Saturday night:



30 Years after "Take5" Brubeck returns to his hometown of Concord, California. and on beautiful Saturday night plays those songs outdoors. This album used to be a staple of mine for the superb sound and atmosphere. But one gets tired of albums and those Concord albums get noisy fast, so it hasn't been played for a long time.

However now it was the turn of the Koetsu Onyx, FR64S. The last time around it would have been a Goldmund Studio and T3 arm with this Koetsu. However, the Koetsu has been back to Koetsu 4 times so all that is original is the terminal plate.  Nevertheless, marvellous night, crickets chirping and wham! Take 5 had Chris Wright on Acoustic Bass, now it's Dave's son, Chris, on electric. Grinding crunching bass exploding. My friend Mike always says Brubeck wearing boxing gloves could play better than most pianists and he was right. Contrast that other, tragic, great, Bill Evans. Evans was a drug addict and had supposedly damaged his left arm with IV Heroin so had a relatively weak left arm, compensated for by his brilliant bassist, Scot LaFaro. When LaFaro died, Evans was devastated. Not, Brubeck no, his left hand can build Meccano, while his right plays the piano. So, 30 years ago I listened to this album for hi-fi reasons, now I was nailed by the bass, crosseyed by Brubecks left and right hand. Living the music, not the night.

The Koetsu Onyx now retails for $10995, a good FR64S will cost you $6000. The Airtight ATH 2 step-up transformer is $3500, The 2 lengths of Cardas Neutral Reference Phono cables is about $ 1000 each. The CA7R you can build for whatever you can scrounge and it is not the bottleneck here, definitely not





Offline Ingvar Ahlberg

Re: DIY Precision fidelity C7A
« Reply #25 on: September 17, 2021, 09:40:28 AM »
This is a bit anoying Johan, You woke my memory of the C7 A and they way it plays music, ok Reeman started the problem, does this mean I have to start a search, or build one, to accompany the TD165 presently undergoing surgery?

Probably.

Ingvar
A senile Swedish loudspeakermanufacturer, ponytail and all, why is he here?

Responsible for H.A.D Halland Audio Design and The vacuumed cat Company.

Offline reeman

  • Trade Count: (+6)
  • AVForums Veteran
  • ***
  • Posts: 660
  • Total likes: 72
  • Yellow cones are for.......
Re: DIY Precision fidelity C7A
« Reply #26 on: September 17, 2021, 06:40:47 PM »
This is a bit anoying Johan, You woke my memory of the C7 A and they way it plays music, ok Reeman started the problem, does this mean I have to start a search, or build one, to accompany the TD165 presently undergoing surgery?

Probably.

Ingvar

Build one for sure. Agaton always said the original was never as good as the home brew due to the passive pre and pot. Also mentioned was the originals unreliability.

These are rock solid pure phono no pots and its a dream. I spoke to garth about the fault finding on Agaton unit when it went in.

Was a valve issue and that 12M resistor needed replacing. For mine I used 10M+2.2M

Offline fredeb

Re: DIY Precision fidelity C7A
« Reply #27 on: September 17, 2021, 09:26:25 PM »
Here are pics of Maida style reg that I got gerbers for from dutch diyaudio member , let me know what you think . I'm thinking of subbing 6P3S/6L6 for EL34 here , because they're cheap , and I have loads of them that I've been buying up - love the sound , use them in my Quadll's and custom ST70 and Byrith 4 30 .

Still wondering whether or not to pay the EU60 for phono gerbers , a bit of cash if only 4 of us will build it .
...evolution is the gradual development and stratification of progressive series of wholes, stretching from the inorganic beginnings to the highest level of spiritual creation.
Jan Smuts

Online naboo

Re: DIY Precision fidelity C7A
« Reply #28 on: September 17, 2021, 10:29:26 PM »
Is that price per unit, @fredeb?

Offline fredeb

Re: DIY Precision fidelity C7A
« Reply #29 on: September 18, 2021, 12:31:30 AM »
Is that price per unit, @fredeb?

No that;s paying someone to make up gerber files used for fabricating phono boards only , not PSU boards . With new layout .

Apologies here are Maida style regulator boards and shematic :






...evolution is the gradual development and stratification of progressive series of wholes, stretching from the inorganic beginnings to the highest level of spiritual creation.
Jan Smuts