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-   -   Pass Citation 12 (http://www.diyaudio.com/forums/pass-labs/228536-pass-citation-12-a.html)

iso 24th January 2013 10:46 AM

Pass Citation 12
 
Audio has been my hobby since early 70īs, but I have been tinkering last 5 years mostly with tube gear. Last weekend I bought HK Citation 12, as it was amplifier I could not afford in mid 70īs. I also remember Nelson Pass Citation 12 mods from 1981 AA.

However I have some questions about this topic. Maybe Nelson or other fellow members have useful information available?

It seems that here are two Pass Citation 12 versions available. I usually think that simpler is better, but now I have wondered if the original or later complementary version is way to go? Do complementary FETs have so much lower capacitance that driver stage will become unnecessary? Also modern day replacements would be appriciated for MPSL51, MPSL01, IFR100, IFR130, IFR9130.

Nelson specified usual passive components to be used. However when I did Quad 22/II combo rebuild few years ago, I replaced all carbon comp and two precision carbon film resistors from 22 line stage with better spec metal film resistors as suggested. This produced inferior sound quality. When I later reassembled 22 with original parts, pair by pair, I discovered that original carbon comp and carbon films produced better sound at anode and grid circuits. However MF:s were OK in low impedance cathode and feedback circuits.

I do not believe in snake oil, but it seems that also passive parts do have effect on sound quality. It would be nice to know which resistor types Nelson would use today in different Citation 12 locations. This would be interesting, as there is so much high spec close tolerance hype here. It was so refressing to read Nelsons remark about 10% wirewounds to be perfect for L300 crossovers.

Best Regards

Kimmo Salminen

Nelson Pass 24th January 2013 05:16 PM

I think the complementary version is better.

Your story about the Quad resistors may have more to do with the exact
values than composition. I recall that there is some delicate trimming needed
to create a distortion null.

:cool:

electrochap 24th January 2013 09:22 PM

Well hello everybody, I've been waiting for almost 2 years and today is the day I will do this Citation 12 MOSFET. I've bought all the stuff at leist a year ago and it was sitting in my shelf waiting for me.

Just to be a bit rude it is a "deluxe" edition with the wood case and faceplate...in very nice shape.

My plans were to use the first plan I've red from the "audio amateur" review. Reading some thread here, I've found R8 being unnecessary, should be direct to gnd. Are there other things from the original plan I should change? I have IRF130 as MOSFET, BD139/140 as pre-fet and 2N5551 and 2SA916 for differential. Should I use BD139/140 for diff too?

Thanks gentlemens!

electrochap 24th January 2013 09:29 PM

Oups, forgot to say I have a few sets of old Hitachi J50 K140 (or J140 K50? I'm getting old...) lying around. Could they be of use in that setup? Or are todays MOSFET well ahead of these old "cadillac" ones?

Tks

electrochap 24th January 2013 10:43 PM

1 Attachment(s)
second oups: K135 & J50...

Zen Mod 24th January 2013 10:47 PM

just compare bias voltage and xconductance in corespondent datasheets

Jay 25th January 2013 12:53 AM

Quote:

Originally Posted by iso (Post 3340003)
...but I have been tinkering last 5 years mostly with tube gear.

...I usually think that simpler is better, but now I have wondered if the original or later complementary version is way to go? Do complementary FETs have so much lower capacitance that driver stage will become unnecessary?

...I discovered that original carbon comp and carbon films produced better sound at anode and grid circuits. However MF:s were OK in low impedance cathode and feedback circuits.

...but it seems that also passive parts do have effect on sound quality

After tinkering with tubes you should jump to Pass' class-A instead of Citation. The Citation is the worst amp associated with NP that I know of. Well, high capacitance mosfet in class-B, that's even against NP philosophy I guess. And then there is that splitter because it is a quasi one (For quasi one I prefer that amp from Alex Nikitin, based on JLH, but with output cap). And then, say who simpler is better in class-B mosfet.

I haven't seen (I guess) a later complementary Citation. If there is so, it shouldn't be called Citation 12. I know only the original BJT Citation that is modified to use Mosfet with one driver stage removed.

If you look at oscilloscope, or simulation or whatever numbers, you may find that omitting the driver is fine. But soundwise? It's subjective but I think it is required in class-B mosfet, even with low capacitance lateral mosfets.

You have been tinkering with tube amps. Not surprising that you can "hear" the carbon resistor sound. And I agree with your finding regarding resistor positions. For carbon composition (Allen Bradley), I like to use it in input (series) but not in FB.

electrochap 25th January 2013 02:15 AM

Hey Jay !

at the end of this document is the NP MOSFET citation schematic with complementary IRFs.

http://passdiy.com/pdf/citation.pdf

iso 25th January 2013 10:36 AM

Pass Citation 12
 
I would like to thank everybody for your kind response.

Nelsonīs comment about nulling distortion in Quad 22 line stage is one possible answer. However, I measured all original parts and they actually were quite close to target values. Actually much better than original 20% tolerance would allow for carbon comps, carbon films were even closer to target. So, horror stories about 50 year old carbon comp being most often off spec, are not 100% true. Most likely there has always been good and bad quality parts.

Jays question about why bother to build Mosfet Citation is sound, if I only sound quality is issue. But I have collected and rebuilt some extremly rare audio gear like Conrad Johnson Premier 7b, Quad 240 and KEF P60 with Pro Kube. If only 220, 180 or 300 pairs in case of P60 in total, but propably less than 50 pairs with Prokube EQ, were made they should be preserved.

On the other hand I have collected, rebuilt and in some cases upgraded gear like Quad 22/II/FM1/MPX, EAR509, ARC Classic 60, Conrad Johnson Premier 11a, Garrard 301, Kef Cantata, JBL L36, Tannoy LRM which were made in ample quantities, but I have somehow felt that they had been pretty important products when they were introduced. I think that Pass Citation 12 fits in this category pretty nicely. Especially as the original HK Citation 12 was the amplifier that I could no afford, instead I had to buy HK930 receiver.

Anyway suggestions for IFR130 and IFR9130 replacements would be appriciated.

Best Regards

Kimmo Salminen

electrochap 30th January 2013 11:07 PM

Best amp I've ever heard with Tannoy red monitor 15" were Heathkit EA1 with a single 6BQ5 output and "Grand" trannies; uinbeatable. Probably worth $50 or less new?

Specs, flatness, THD, noise floor, etc. just don't sing.


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