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Old 27th May 2012, 05:55 PM   #51
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Quote:
Originally Posted by Elvee View Post
About the low pass capacitor, I advise against actually using 8.2nF: it was meant as an illustration with a test signal, but for actual use, such a high value could cause excessive roll-off if the source impedance is much larger than 470 ohm.

Anyway, normal audio signals do not contain 10ns maximum amplitude edges.
It is good to you point out this issue Elvee. I was a bit curious about that high filter capacitor value. You mean we can stick with 330pF until an official version provided by yourself? I think that CFP edition rises attention due to its unique features.

Also, you didn't mention about stability margin variance after latest compensation value changes. I hope that any counter productive effects didn't occur.
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Old 28th May 2012, 04:46 AM   #52
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Originally Posted by danielwritesbac View Post
Did you use a gray Philips BD139 (COB=6pF) for Q5 Q6?
Nope, I don't have it at hand, 2N3019 is currently out of stock, I might as well check on the BD139 they are complement to BD140.

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Are you testing with output devices connected?
Yes, I actually did a quick test without the outputs, BD140 gets hot real fast.
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Old 28th May 2012, 05:08 AM   #53
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Originally Posted by terranigma View Post
Good to see measure healthy offset values. That heatsink looks very fit and nice!
Thanks, I got them from a discarded PC PSU I was surprised to see that it was exactly the same width with the board.

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Originally Posted by terranigma View Post
I see you are using wires for easy testing power transistors.
I always do this when testing my build, for convenience saves time and when something when wrong with the output it won't damage other parts and the PCB as well..

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Originally Posted by terranigma View Post
Are you sure that BD140's won't survive
Well, I am not exactly so sure about the maximum heat dissipation of the device but I think but for longer hours of use, they cannot hold on.

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Originally Posted by terranigma View Post
As I mentioned earlier, I suggest you to use slower device for output. I tested Bourns brand of BD249C (they were made in Philippines) and their sonic behaviour was outstanding.
I will see if I can find those BD249C here, I do know however that semiconductors manufactured here is hard to obtain. They are being exported to other countries
.
Originally my plan was to use TO-220 devices for Q9, Q11 but the CFP board cannot accomodate it, the footprints were rather small for TO-220 (I hope piersma is working on his design...)
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Old 28th May 2012, 05:12 AM   #54
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Originally Posted by Elvee View Post
That is perfectly normal for discrete devices: it is equivalent to less than 1C difference between transistors, and random variations caused by draughts for example reach easily that level.
The quiescent dissipation in the drivers is ~1W, and increase with signal, so nothing abnormal.
If you have doubts about the 2SC5200, try a slower device, TIP3055 or BD249.

About the low pass capacitor, I advise against actually using 8.2nF: it was meant as an illustration with a test signal, but for actual use, such a high value could cause excessive roll-off if the source impedance is much larger than 470 ohm.

Anyway, normal audio signals do not contain 10ns maximum amplitude edges.
Thanks for the feedback Sir Elvee.
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Old 28th May 2012, 07:03 AM   #55
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Originally Posted by abeteer View Post
Nope, I don't have it at hand, 2N3019 is currently out of stock, I might as well check on the [Philips] BD139. . .
See also post #7 for a larger listing. Oh yes, it would be good to put some useful devices at Q5, Q6 before proceeding further.


P.S.
I'm working on a clear CFP Circlophone schematic.
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Last edited by danielwritesbac; 28th May 2012 at 07:05 AM.
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Old 28th May 2012, 11:55 PM   #56
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Originally Posted by danielwritesbac View Post
P.S.
I'm working on a clear CFP Circlophone schematic.
Good to hear that, this is going to be a lot of help!

While at work I've been contemplating on my build, figuring what could be the error..If my hint was correct, it is probable that VAS D669 is pushing the BD140 drivers hard. I think It should work the other way, where drivers should be the stronger ones than the VAS. Probable solution is to either replace VAS D669 with (say) BD139 or replace drivers BD140 with the stronger B649. Using fakes is a possibility too for they could be insufficient to handle the job.

Anyway I may have to confirm this, in the coming weekend (DIY time!) just a thought though....
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Old 29th May 2012, 09:31 AM   #57
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The new schematic is awaiting proofreading by people smarter than me.
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Old 2nd June 2012, 11:12 AM   #58
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It looks like I'm in big trouble right now, I just worked on my amp again and following the latest mod according with Daniels CFP Schematic here's what the amp say's..

Idle current, measured across R8/R11= 0.12ma
DC offset = 30.0mv when measured at AC = 15.0v
I've lost two 5.6 ohms resistor at Zobel network, they instantly went up in smoke right at power on. I am now using D1047C for the output and they heat-up fast.

I used 2N5053 for VAS 'found them at one local supplier and the specs was very close to 2N2219 but I don't think the amps having problems at VAS. Drivers and VAS are less warmer, better than my previous set-up using D669A. I have tried to dissect the whole thing but after finding a few parts with no signs of fault I gave up.

All help will be appreciated!
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Old 2nd June 2012, 11:33 AM   #59
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That amp is oscillating with that 15v of noise. Question: Was it THIS schematic: CFP Circlophone I really need to know.

If so, then may I suggest using a Standard Circlophone schematic yet also getting almost all of the advantages of the CFP by simply using BC560C input pair at Q3, Q4 instead of all that hullabaloo?
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Old 2nd June 2012, 11:51 AM   #60
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The link yes, I double-check that with Sir Elvees' correction,.. looks OK to me.
Actually I'm saving my spare parts for the official circlophone (to date, according to Elvee) I plan to use AlexMMs lay-out. I just can't give-up on the CFP....anyway..


Here's the revised amp..
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File Type: jpg CFP_June02.jpg (373.5 KB, 354 views)
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