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CA-F1 on the bench

Hyperion

Hyperion

Roobarb & Custard
Subscriber
As per the title, I currently have a JDM (100V mains) CA-F1 on the bench - according to its original (Japanese) owner it has a channel dropped. :( But I think I've already found the problem during checks I like to perform before I power up anything with a fault on it. Namely a couple of badly drifted 330Ω fuse resistors in the OP stage of the MM Phono amp. :thumbsup:

Its new owner - an AK member, already has a BA-F1, (which I reconditioned) and wants me to give this 'the treatment' as well. :banana:
 
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Hyperion said:
Yep, :thumbsup: the owner of the BA-F1 really likes it, and spent quite a while looking for a CA-F1 to partner it. ;)

Here is a picture of the underside (bottom cover removed).
View attachment 1664231

The square-ish metal screen on the top left of the picture conceals the MC Phono amp. ;)
Click to expand...
I did one of those earlier in the year John, came up nicely, great pre-amp, but I wasn't particularly fussed about the sound of the BA-F1 I did not so long ago... I was expecting better to be honest...but that is slightly nit picking, they all sound great, but I prefer the X1 and the G22/33000..
 
I just spent a fun couple of hours finding out why I couldn't zero the DC offset on one channel of the Flat Amp, when I found out what was causing it I could scarcely believe it!

I could only get the offset on one channel down to -47mV on one channel (target 0mV), the other channel was fine. So I began measuring voltages, and checking resistors were the correct value, and I couldn't find much wrong apart from the voltage differences caused by the problem itself. So I finally got as far back as the Dual FET, checking voltages - something funny here, I have roughly -0.5V on the 'slider' of the bad channel offset trimmer, and ~0V on the good channel. :idea:

So I am wondering if the offset trimmer is faulty or perhaps the wrong value? - I check the resistance of the trimmer in the good channel and from the slider to each 'track end' is around 50Ω, and the full track is just over 100Ω - very good, just what we want. So I check the trimmer for the faulty channel, and it is quite different - measuring 100Ω from what I thought was the slider to a 'track end' even after I had centered it. :confused: - so I measure other pins on the trimmer and discover that it is soldered in incorrectly!!! - making correct DC offset adjustment impossible with it installed like that. So I remove the trimmer and put it back in the right way round - and Bingo! - DC offset adjusted fine. :thumbsup:

Just after I began working on the problem I noticed that very many of the solder joints (for this channel of the MM Phono amp), have been re-run and there is evidence that the µPA68H in that channel has been changed at some point. I just wonder if all that re-work and component change had been caused by this wrongly mounted trimmer - and that was the problem all along - the solder joints on the trimmer looked factory original and untouched. :whip:

:)
 
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Well done, John.

I can easily relate to putting the replacement incorrectly myself... and spending hours, why its become complex, (not just audio electronics) you name it I've been there..
 
Hyperion said:
I just spent a fun couple of hours finding out why I couldn't zero the DC offset on one channel of the Flat Amp, when I found out what was causing it I could scarcely believe it!

I could only get the offset on one channel down to -47mV on one channel (target 0mV), the other channel was fine. So I began measuring voltages, and checking resistors were the correct value, and I couldn't find much wrong apart from the voltage differences caused by the problem itself. So I finally got as far back as the Dual FET, checking voltages - something funny here I have roughly -0.5V on the 'slider' of the bad channel offset trimmer, and ~0V on the good channel. :idea:

So I am wondering if the offset trimmer is faulty or perhaps the wrong value? - I check the resistance of the trimmer in the good channel and from the slider to each 'track end' is around 50Ω, and the full track is just over 100Ω - very good, just what we want. So I check the trimmer for the faulty channel, and it is quite different - measuring 100Ω from what I thought was the slider to a 'track end' even after I had centered it. :confused: - so I measure other pins on the trimmer and discover that it is soldered in incorrectly!!! - making correct DC offset adjustment impossible with it installed like that. So I remove the trimmer and put it back in the right way round - and Bingo! - DC offset adjusted fine. :thumbsup:

Just after I began working on the problem I noticed that very many of the solder joints have been re-run and there is evidence that the µPA68H in that channel has been changed at some point. I just wonder if all that re-work and component change had been caused by this wrongly mounted trimmer - and that was the problem all along - the solder joints on the trimmer looked factory original and untouched. :whip:

:)
Click to expand...

Well found.

This is a sign to check-over everything on this unit very carefully...

Did I ever tell you about the time I bought a CA-F1 with a "phono section in need of repair"? Well I opened her up and quickly located the issue; the phono section was entirely missing. It was one of the rare occasions I dropped a 1star on ebay (the seller clearly had restoration/tech experience with all their other items being modified or serviced/recapped...). I do have another CA-F1, but I'm left with a choice.... keep this phono-less CA-F1 as just a line level unit, or insert in a phono section of my own. At this stage I'm thinking I will not mess around turning this into Frankenstein's creation. Such a shame as the phono section on the CA-F1 is more than moderately nice.
 
John, The Ca F1 preamp should be interesting to compare with your AU-919 restoration.
I’m using one of these to drive a BA 2000, both original. There’s very little out there on these preamps. I’ve got replacements for the black flags at this point.
 
markkb said:
John, The Ca F1 preamp should be interesting to compare with your AU-919 restoration.
Click to expand...
Hi Mark, Funny you should say that as it happens, I was listening to it via the 'amp-in' inputs on the AU-919, and it did sound like it had hidden depths, you know, just that feeling you get that it has more to give, a little bit constrained and lacking in sparkle. I'll be working on the power supply first, I'll get that sorted out, then I'll probably do pretty much all of the rest before I give it another listen, - it should be interesting. :thumbsup:

The power supply only has a dozen or so components that I'll definitely be replacing, maybe a few more before I'm satisfied. However I feel that it is so important to get right, I'll be taking my time with it. After all, its bigger partner the BA-F1 sounded so good, I really have to pull out all the stops on this too. ;)
 
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Hyperion said:
it did sound like it had hidden depths, you know, just that feeling you get that it has more to give, a little bit constrained and lacking in sparkle.
Click to expand...
. Yep, that’s how I feel about the unrestored sound I’m hearing. Ahhh though it has that Sansui vibe...
 
Here is the PSU after component changes.

IMG_3006a.jpg

The two large black filter capacitors are now Nichicon KW's 3300µF, 63V (85°C) - Initially I was a bit concerned about using them as the PSU before restoration got VERY hot due to the heat from the series pass transistors. These transistors have now been replaced and I was pleased to note that the PSU now runs an order of magnitude cooler - hence the KW's were deemed suitable. I have left all the MOX resistors alone, they are all well within spec' and do their job well. Other items changed are seven electrolytic capacitors, one zener - replaced with a precision 2% type and, two trimmers. One of the trimmers was 680Ω (as marked) ! - I replaced this with a 500Ω without any issues. (the track resistance in use with the 680Ω trimmer was around 270Ω).

I note on the schematic for the main filter capacitors it says 'Note C601 & C602 = 1000µF, 63V, (Japan Model 2200µF, 63V)'. As you will note above they are now 3300µF, 63V as this is my rebuild spec' :king: other capacitors (with careful consideration) have received similar treatment, a restore methodology copied shamelessly from Ben, @Leestereo :thumbsup:

The remainder of the restore is progressing well, although quite slowly, as I am taking measures (within reason), to maximise stability, and hopefully to get noise output reduced to a minimum, and fidelity improved. ;)
 
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