HeadWize: DIY Workshop > β22: A discrete, cascoded, fully complementary, pure class A amplifier (part 3)

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DIY Workshop » β22: A discrete, cascoded, fully complementary, pure class A amplifier (part 3)
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jazzist

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Joined: May 9, 2008
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Total Posts: 30

Message [#180] posted on: 12-23-2008 09:19 PM CST (US).

Sure, will post info soon.

Is now 03:15AM... debugging the above pictured and my first B22 board made so far, the VAS stage was not behaving at all.. it does help if C3 is connected accross the pads designated by the II marking on the silkscreen <crying> ...big d'oh!, what a goof. Thanks AMB for your voltages PDF on your website, else i'd never have spotted it <smile>

Now is all good, 4.5-4.6 R9-R12 dialled in, 0.18mV DC offset (no adjustment!).

Very relieved now <smile>

[Edited by jazzist on 12-23-2008 at 09:40 PM.]

fc911c

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Joined: Jun. 6, 2008
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Total Posts: 49

Message [#181] posted on: 12-25-2008 08:31 AM CST (US).

I have a question, I am seeing 20mv on the output with my HD650 ballanced phones plugged in, this only happens when the volume in turned off. When phones are not plugged in I get well below .5mv with volume turned on or off.

I also seem to be getting some oscillation on my scope at idle. The trace is very fuzzy.

I had a problem with fast drifting mv readings on output before, now all is well when I changed the JFets.

Thanks
Frank

[Edited by fc911c on 12-25-2008 at 11:42 AM.]

amb

Headphone Council

Joined: Apr. 1, 2004
Locale: Sunnyvale, CA. USA
Total Posts: 4408

Message [#182] posted on: 12-25-2008 11:36 AM CST (US).

[Quoting fc911c]
I have a question, I am seeing 20mv on the output with my HD650 ballanced phones plugged in, this only happens when the volume in turned off. When phones are not plugged in I get well below .5mv with volume turned on or off.

AC or DC? All channels?

[Quote]
I also seem to getting some oscillation on my scope at idle. The trace is very fuzzy.

Cold joints on any of the compensation capacitors (C1-C5)? All channels?

fc911c

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Joined: Jun. 6, 2008
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Total Posts: 49

Message [#183] posted on: 12-25-2008 11:41 AM CST (US).

Hi
DC all channels

I am using sockets on C1-C5, is this not a good idea? I am also using sockets on some of the resistors for gain.

[Edited by fc911c on 12-25-2008 at 11:46 AM.]

amb

Headphone Council

Joined: Apr. 1, 2004
Locale: Sunnyvale, CA. USA
Total Posts: 4408

Message [#184] posted on: 12-25-2008 11:45 AM CST (US).

Do you have a zobel network at the output? If not, try adding one.

fc911c

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Joined: Jun. 6, 2008
Locale: N/A
Total Posts: 49

Message [#185] posted on: 12-25-2008 11:50 AM CST (US).

[Quoting amb]
Do you have a zobel network at the output? If not, try adding one.

Please read my post above I added to it. Yes I did, it helped a little but not much.

amb

Headphone Council

Joined: Apr. 1, 2004
Locale: Sunnyvale, CA. USA
Total Posts: 4408

Message [#186] posted on: 12-25-2008 11:59 AM CST (US).

Is this a 2-ch, 3-ch or 4-ch config? Single or dual chassis? How is the grounding done?

fc911c

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Joined: Jun. 6, 2008
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Total Posts: 49

Message [#187] posted on: 12-25-2008 12:02 PM CST (US).

[Quoting amb]
Do you have a zobel network at the output? If not, try adding one.

With Zobel installed I don't get the 20mv reading with volume off with phones plugged in now. I still get the fuzzy trace with zobel installed which is some what reduced now.

amb

Headphone Council

Joined: Apr. 1, 2004
Locale: Sunnyvale, CA. USA
Total Posts: 4408

Message [#188] posted on: 12-25-2008 12:06 PM CST (US).

[Quoting fc911c]
With Zobel installed I don't get the 20mv reading with volume off with phones plugged in now. I still get the fuzzy trace with zobel installed which is some what reduced now.

Do you actually hear anything through your headphones? What you see on the scope might just be the noise floor of the amp. What is the amplitude? Is there a definite shape to the waveform? If so what is its time period?

fc911c

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Joined: Jun. 6, 2008
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Total Posts: 49

Message [#189] posted on: 12-25-2008 12:07 PM CST (US).

This is a 4 channel config with PS and trans to be in a sperate box. Right now its on a test bench there is no ground going from PS to B22 boards.

amb

Headphone Council

Joined: Apr. 1, 2004
Locale: Sunnyvale, CA. USA
Total Posts: 4408

Message [#190] posted on: 12-25-2008 12:11 PM CST (US).

No ground? <confused>

There should be V+/G/V- connections from the σ22 to the β22 boards...

Also, checking the noise floor when the boards are not yet in a case is not really a useful exercise.

housing

HeadWizer

Joined: Dec. 16, 2006
Locale: N/A
Total Posts: 163

Message [#191] posted on: 12-25-2008 12:13 PM CST (US).

[Quoting fc911c]
Hi
DC all channels
I am using sockets on C1-C5, is this not a good idea? I am also using sockets on some of the resistors for gain.

This is definitely not a good idea. <big grin>

fc911c

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Joined: Jun. 6, 2008
Locale: N/A
Total Posts: 49

Message [#192] posted on: 12-25-2008 12:16 PM CST (US).

[Quoting amb]
[Quoting fc911c]
With Zobel installed I don't get the 20mv reading with volume off with phones plugged in now. I still get the fuzzy trace with zobel installed which is some what reduced now.

Do you actually hear anything through your headphones? What you see on the scope might just be the noise floor of the amp. What is the amplitude? Is there a definite shape to the waveform? If so what is its time period?

I don't hear any noise it sounds quiet. As for what I am seeing on the scope it's hard for me to say as I don't really now much about how to operate one. When I hook up probe to any of the outputs the flat thin trace line gets very fuzzy and widens to about 4 times its original size. I have not seen this happen with any of the other amps I built.

fc911c

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Joined: Jun. 6, 2008
Locale: N/A
Total Posts: 49

Message [#193] posted on: 12-25-2008 12:18 PM CST (US).

[Quoting housing]
[Quoting fc911c]
Hi
DC all channels
I am using sockets on C1-C5, is this not a good idea? I am also using sockets on some of the resistors for gain.
This is definitely not a good idea.

ok I will remove them. thanks

amb

Headphone Council

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Locale: Sunnyvale, CA. USA
Total Posts: 4408

Message [#194] posted on: 12-25-2008 12:19 PM CST (US).

Oh yeah, I missed the edit on your use of sockets for the compensation caps. Depending on the type of socket, the contact may introduce some extra impedance to reduce the effectiveness of the compensation caps and is thus not recommended.

MrMajestic2

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Joined: Jun. 5, 2007
Locale: N/A
Total Posts: 90

Message [#195] posted on: 12-25-2008 12:20 PM CST (US).

[Quoting housing]
[Quoting fc911c]
Hi
DC all channels
I am using sockets on C1-C5, is this not a good idea? I am also using sockets on some of the resistors for gain.
This is definitely not a good idea.

How come? I was under the impression that it was ok to do that.

[Edited by MrMajestic2 on 12-25-2008 at 12:20 PM.]

amb

Headphone Council

Joined: Apr. 1, 2004
Locale: Sunnyvale, CA. USA
Total Posts: 4408

Message [#196] posted on: 12-25-2008 12:22 PM CST (US).

[Quoting MrMajestic2]
How come? I was under the impression that it was ok to do that.

As above. You might get away with it, but I would still not recommend it.

MrMajestic2

Member

Joined: Jun. 5, 2007
Locale: N/A
Total Posts: 90

Message [#197] posted on: 12-25-2008 12:43 PM CST (US).

[Quoting amb]
[Quoting MrMajestic2]
How come? I was under the impression that it was ok to do that.

As above. You might get away with it, but I would still not recommend it.

Ah ok. I see you managed to sneak that post in while I was still writing it <smile> Thanks.

fc911c

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Joined: Jun. 6, 2008
Locale: N/A
Total Posts: 49

Message [#198] posted on: 12-25-2008 01:53 PM CST (US).

[Quoting amb]
Oh yeah, I missed the edit on your use of sockets for the compensation caps. Depending on the type of socket, the contact may introduce some extra impedance to reduce the effectiveness of the compensation caps and is thus not recommended.

Yes, I just changed one channel (2 boards) and noticed a much cleaner signal on the scope now with sockets removed. I will take the sockets of the Gain resistors also.

thanks

fc911c

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Joined: Jun. 6, 2008
Locale: N/A
Total Posts: 49

Message [#199] posted on: 12-25-2008 01:55 PM CST (US).

[Quoting amb]
No ground? There should be V+/G/V- connections from the σ22 to the β22 boards...
Also, checking the noise floor when the boards are not yet in a case is not really a useful exercise.

sorry Yes there are V+ V- and the gnd. I meant no grond other than that.

fc911c

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Joined: Jun. 6, 2008
Locale: N/A
Total Posts: 49

Message [#200] posted on: 12-25-2008 07:05 PM CST (US).

Good news and thanks for the help.

I have removed all the sockets and this cleared up the oscillation problem, and it also sounds much better.

The zobel network cleared up the problem with high mv reading when phones are plugged in and volume is turned off. What would cause that to happen?

Frank

[Edited by fc911c on 12-25-2008 at 07:28 PM.]

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