Pass Citation 12 - Page 3 - diyAudio
Go Back   Home > Forums > Amplifiers > Pass Labs

Pass Labs This forum is dedicated to Pass Labs discussion.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 10th April 2013, 09:33 PM   #21
diyAudio Member
 
Join Date: Jan 2008
Location: Montreal, Quebec
I'm getting +/-45 VDC out of the original transfos with 4 Philips 8200uF 100 volts caps.

I'm using exactly (hope so...) the enclosed schematics at the exception of the IRF130/9230 which are replaced by 2SK135/J50.

...And it sounds damned good!!!! In Tracer 100 speakers...

And I did not forget to swap drain and source pins.
Attached Files
File Type: pdf Comp_CT12_FET.pdf (292.3 KB, 110 views)

Last edited by electrochap; 10th April 2013 at 09:39 PM.
  Reply With Quote
Old 10th April 2013, 10:24 PM   #22
juma is offline juma  Germany
diyAudio Member
 
juma's Avatar
 
Join Date: Nov 2005
Location: Berlin
Quote:
Originally Posted by electrochap View Post
...
I'm using exactly (hope so...) the enclosed schematics at the exception of the IRF130/9230 which are replaced by 2SK135/J50.
...
To lower the bias current, you'll have to lower the value of R14 to 4k7 (or to 5k by adding another 10k in parallel to R14).
If you want to take out the Vbe multiplier circuit (Q4, R14, R17) and use a single resistor to bias the output stage just put a 1k or 2k multi-turn pot in parallel with C5 instead. Don't forget to set that pot to 0 Ohm before turning the amp on.
Also, check the current through Q3 (should be about 5 mA) by measuring the voltage across R13. If that's so, you'll have the output stage bias at 150-200 mA with pot set at 400-500 Ohms.
  Reply With Quote
Old 11th April 2013, 04:05 PM   #23
diyAudio Member
 
Join Date: Jan 2008
Location: Montreal, Quebec
I put a 10k in parallel of R14. Worked fine of 1 side; lowering the value of the pot in parallel of R15 got me a bias of 150ma measured at the + rail output of the diode bridge. And I had more range if needed.

On the other side, a strange thing happened; at first, the current lowered to 250ma but when lowering the value of R15 & the pot, current increased instead of getting lower...??? I guess I have something wrong somewhere in this channel... I'll dig in it.

Didn't have time to look at the sinewave, neither the clipping.
  Reply With Quote
Old 12th April 2013, 03:00 PM   #24
diyAudio Member
 
Join Date: Jan 2008
Location: Montreal, Quebec
Default Problem!!!

Oups problem. I've decided to look a bit deeper in this biasing problem and end up with a channel non working anymore... I get the + rail at output.

Didn't change nada... Just disconnected the + rail between bridge and + feed of the board to measure current but no current on the channel; verified and found +45 at +output...?

Start verifying the FETs and don't know if this is supposedly normal but even without gate voltage there is current going through the FET between drain & source. Checked the other J50 I have and same thing. Checked a IRF130 and same again so it may be normal.

Do I have to "ground" the gate to close the junction? I've verified with ohm meter in diode check and get .330 on the good side and open in backward. So no short there.

I'm used to check Mosfet with a 1K pot, tap on the gate and both sides on the drain & source. + at drain for N channel and gnd on drain for P channel. Is this OK? I've measured the K135 to close junction with .5VDC but the J50 is always closed...

The other channel is fine and now running at 190 ma with the addition of 10K in parallel of R14. I'm kind of afraid to remove anything from there... I could also just swing the board reverve as it's miror but if I've shorted something I don't want to do the same on the other channel...

I've verified all the B139/B140 and they are all good none shorted.

What's wrong?


HAHA .... just noticed the test setup I'm using for FETs comes from: https://www.passdiy.com/pdf/mos.pdf

Last edited by electrochap; 12th April 2013 at 03:21 PM.
  Reply With Quote
Old 12th April 2013, 03:51 PM   #25
diyAudio Member
 
Join Date: Jan 2008
Location: Montreal, Quebec
Default Forget last post

Can't edit it my last post anymore, too late.

I was stupidly measuring the FET backward... Don't do too many things at the same time... Both are fine. The K135 starts conducting around.5V and the J50 around .2V.

I'll continue measuring voltages across... Will see where I'll get. I know I have the +45 all over on this channel, up to the N FET gate.
  Reply With Quote
Old 12th April 2013, 04:12 PM   #26
juma is offline juma  Germany
diyAudio Member
 
juma's Avatar
 
Join Date: Nov 2005
Location: Berlin
Quote:
Originally Posted by electrochap View Post
...
HAHA .... just noticed the test setup I'm using for FETs comes from: https://www.passdiy.com/pdf/mos.pdf
That's a fine article and you should read it carefully in order to understand how these devices operate.

For a quick check use the attached schematic. If MOSFETs are OK you'll have about 9V across the 100R resistors which means that they conduct current as they should. Be careful with pinouts and polarities.

Quote:
Originally Posted by electrochap View Post
..... I have the +45 all over on this channel, up to the N FET gate.
Be careful not to burn the MOSFETs. They can't take more than 15V between Source and Gate.
Attached Images
File Type: gif Mosfet-test.gif (2.8 KB, 235 views)
  Reply With Quote
Old 12th April 2013, 06:01 PM   #27
diyAudio Member
 
Join Date: Jan 2008
Location: Montreal, Quebec
GOT IT!

No Idea why, I've verified everything, I replaced the 10K parallel of R14 (I removed for troubleshooting this 45 V O/P) and everything is on spot...

I then replaced both R14 by a single 2.2K and I am now running at 150ma bias both sides and have room to increase or lower bias value. Is 2.2K OK ? Should I also replace R15 & 17 to have more equal values?

Problem probably was another of these "lunatic" goof...

Have a bit high voltage at output: 37ma on one side and 80 on the other. I'll try the other FETs I have to see if I can lower this value a bit more decent; under 50ma...

Thanks all for your help, specially Juma!! I understand a bit more this VBE thing.

I need to get back to my semi books. Left school some years ago and did a lot of electronics: troubleshooting systems & replacing modules & equipment. Never worked on discrete components. Never had to.
  Reply With Quote
Old 12th April 2013, 06:37 PM   #28
diyAudio Member
 
Join Date: Jan 2008
Location: Montreal, Quebec
Well... couldn't be that fast...

Clipping is not too good... I get lower side to clip quite earlier then top side. I've tested in 8 ohms dummy loads. I can get to 20 volts RMS even but higher only gets me clipping the low side.

Does that mean 150 ma of bias current not enough? I remember having one amp with the lower K133/J48 and it was running pretty hot too after a while...

Should I replace R18 & R19 instead of R14? Or go with the single pot parallel of C5 ?
  Reply With Quote
Old 16th August 2013, 04:52 PM   #29
diyAudio Member
 
marc brown's Avatar
 
Join Date: Sep 2007
Location: Henderson, NV
Electrochap, did you ever get your Citation 12 finished?
  Reply With Quote
Old 16th August 2013, 09:02 PM   #30
diyAudio Member
 
Join Date: Jan 2008
Location: Montreal, Quebec
Dooooo Yes I did...

Problem is I like it so much I put it in my cabinet with the other stuff and cant get it out of there.. I like it too much !!! Warm like tubes and punch and details like a Bryston with a hughe 3D image. Can't ask for better....

I've bought some cct cards from a swedish guy here on DIY and am planning on building another one without any H-K stuff. I have 2 toroidal transfos from a burned SIMA amp, a bunch of PS audio gold 3300 uf 70 V caps ( 3 on each side on each channel ) some new 240 & 9240 FETs with some 1% metal film (I think?) resistors. Can it be better then this one? I'll see. I'm more then really satisfied with this one. Plenty of power, clean and detailed, image and warmth. What more?

I'll post some pictures I promise when I'll have some free time in the next month... It is a Deluxe oone with the big wood box (repolished as well...). One thing, you'll see with the picture, there seems to be a missing "trim" between front panel and the wood box but all the pictures of a "deluxe" CT12 I've seen seems to be te same...?

Anything else you'ld like to know?

Don't know if it is because the Hitachi lateral FETs but this amp is the best I`ve heard so far home... And I've tried a few...
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Simulation - Pass MF-12 MOSFET Quasi Comp (Original) Modification for HK Citation 12 PB2 Pass Labs 30 14th March 2013 05:31 PM
Simulation - Pass MF-12 MOSFET Fully Comp Modification for HK Citation 12 PB2 Pass Labs 0 10th May 2011 03:11 AM
Pass mosfet citation 12 clone Tekko Pass Labs 34 27th September 2010 11:48 AM
Citation 12 nickgreek Solid State 6 22nd September 2003 03:20 AM
Pass version of Citation 12 (Mosfet) G Solid State 13 10th November 2002 03:18 AM


New To Site? Need Help?

All times are GMT. The time now is 11:15 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2