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

Message [#101] posted on: 10-17-2008 02:56 AM CST (US).

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

For those who do not visit the other forum, we have just completed a group-build 4-channel balanced β22 with dual σ22 PSUs. Here are some pics for your enjoyment. I am listening to it right now and can't put the headphones down.

housing

Message [#102] posted on: 10-17-2008 04:05 AM CST (US).

Joined: Dec. 16, 2006
Locale: N/A
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Beautiful Work !!!!!

tenorsaxophone

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Locale: Ferrara, Italy
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Message [#103] posted on: 10-25-2008 10:18 AM CST (US).

Hello AMB!
I have found only MuRata, type 3102W Trim Pots, instead of Vishay and Bourns as suggested in β22 part list. Can I use them, or are they not good enough?
Many thanks. Best regards.
Davide.

amb

Message [#104] posted on: 10-25-2008 07:46 PM CST (US).

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

[Quoting tenorsaxophone]
I have found only MuRata, type 3102W Trim Pots, instead of Vishay and Bourns as suggested in β22 part list. Can I use them, or are they not good enough?

As long as they have similar specifications to the recommended ones, you can use them.

set300b

Message [#105] posted on: 10-26-2008 01:26 AM CST (US).

Joined: Aug. 1, 2001
Locale: San Francisco, CA, USA
Total Posts: 151

Hi Ti, just finished building a fully balanced B22. Run into some trouble: One channel is only audible at full volume. Almost inaudible at lower volume. Each channel is controlled by a stereo Goldpoint stepped attenuator.

All measurements are OK.

Communication conducted offline.

[Edited by set300b on 10-26-2008 at 02:47 AM.]

amb

Message [#106] posted on: 10-26-2008 04:35 AM CST (US).

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

Seems like a solder joint problem somewhere.

GRUN

Message [#107] posted on: 10-26-2008 06:51 AM CST (US).

Joined: Oct. 26, 2008
Locale: Japan
Total Posts: 2

Hellow amb.

I finished building Beta22.
Beta22's sound is wonderful!
But, my Beta22 have a little problem.
My Beta22 oscillates only when I'm using "edition9".
There is no problem when I'm using other headphones.
It doesn't oscillate when my Edition9 is used with amplifiers other than my beta22.

I set Gain of my Beta22 in 2x.
R3-R4 is 2.49kohm and C2-C5 is 100pF.
Should I raise gain or capacity of C2-C5?

amb

Message [#108] posted on: 10-26-2008 01:17 PM CST (US).

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

GRUN, if you don't already have it, try adding the zobel network to the output as described at the β22 website.

Smeggy

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Joined: May 27, 2008
Locale: seattle
Total Posts: 3

Message [#109] posted on: 10-28-2008 03:42 PM CST (US).

Very nice build indeed amb, beautiful work.

Do any of you know what would make a good four-way speaker output selector switch? I ask because I'm looking at putting headphone adapter boxes in a beta. It'd be along the lines of:

1-Speaker out
2-Speaker out wired to a 1/4" headphone adapter (orthodynamics and K1000)
3-Stax electrostatic transformer
4-Sony electret transformer

all inside the case with sockets on the front except the original binding posts. I want a nice all-in-one compact solution to my burgeoning pile of boxes and headphone variety.

I may be adding a two or 3 way input selector switch as well if anyone has good recommendations.

dougigs

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Joined: Sep. 21, 2005
Locale: London England
Total Posts: 372

Message [#110] posted on: 10-28-2008 06:54 PM CST (US).

Personally, I like to use relays, which can be controlled by any sort of switch.

For inputs I like high-quality reed relays. Outputs at speaker level require something with more current capacity (though not tons for this application). A plain old rotary switch (with an attractive knob) is a good way to control these. You can then upgrade to a fancier digital control if you like, and keep the same relay board on the inputs and outputs.

amb

Message [#111] posted on: 10-28-2008 07:28 PM CST (US).

Joined: Apr. 1, 2004
Locale: Sunnyvale, CA. USA
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Yes, relays controlled by mechanical switch or (if you want to get fancy) some kind of logic circuit would by my choice.

Smeggy

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Joined: May 27, 2008
Locale: seattle
Total Posts: 3

Message [#112] posted on: 10-28-2008 08:05 PM CST (US).

thanks guys, do you have any make/type you favor? I'm new to all this and have no clue what I'm looking for. Sticking it all together is fine, I just need to know what to look for and what to avoid.

alfie

Message [#113] posted on: 10-29-2008 02:31 AM CST (US).

Joined: Jul. 12, 2006
Locale: Italy
Total Posts: 70

Hi amb,

after months of using my 3 channel beta22, all of a sudden I noticed a typical burning smell while I was playing some music. I opened the case to find out that R32 on the left channel and R33 on the ground channel were burning. Tomorrow I am going to change them, but the question is obvious: what the problem could be? What other components might be gone?

- alfonso

amb

Message [#114] posted on: 10-29-2008 04:10 AM CST (US).

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

Smeggy, for output switching for speaker and headphone use, I recommend a relay with contacts that are rated at least 10A. For strictly headphone use, 1A is enough. If you use one relay per channel and output option, you could get by with a bunch of simple SPST relays. There are many suitable relays, it all depends on what power supply voltage you'll use on the coil and the switching arrangement, as well as their mounting style. Choose a relay with a DC coil rather than AC. Go to the Mouser or Digikey websites and browse through their catalog for ideas.

alfie, these two resistors burning is indicative of failure of the Q23 and Q24 MOSFETs, They become short circuited internally, causing the resistors to fry. Other casualties might include the D9 and D10 zener diodes. You should also check R34, R35, Q21 and Q22.

As for why this might happen, an overcurrent condition at the output or overheating is most likely the cause. See this thread for a similar failure.

alfie

Message [#115] posted on: 10-29-2008 02:37 PM CST (US).

Joined: Jul. 12, 2006
Locale: Italy
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[Quoting amb]

alfie, these two resistors burning is indicative of failure of the Q23 and Q24 MOSFETs, They become short circuited internally, causing the resistors to fry. Other casualties might include the D9 and D10 zener diodes. You should also check R34, R35, Q21 and Q22.
As for why this might happen, an overcurrent condition at the output or overheating is most likely the cause. See this thread for a similar failure.

Thanks amb. I changed all the 8 mosfets, various resistors and D10 on one board. I tend to think it is some overheating fault. I need a top ventilated plate for sure.

GRUN

Message [#116] posted on: 10-30-2008 05:59 AM CST (US).

Joined: Oct. 26, 2008
Locale: Japan
Total Posts: 2

[Quoting amb]
GRUN, if you don't already have it, try adding the zobel network to the output as described at the β22 website.

Hello amb.
I added the zobel network to the output.
My beta22 does not oscillate!
My fixed up beta22 is working so good, and my favorite headphones and musics is making me so glad! <big grin>

amb, thank you for your advice!

amb

Message [#117] posted on: 10-30-2008 06:30 AM CST (US).

Joined: Apr. 1, 2004
Locale: Sunnyvale, CA. USA
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GRUN, that's great. Enjoy the amp!

set300b

Message [#118] posted on: 10-30-2008 07:11 PM CST (US).

Joined: Aug. 1, 2001
Locale: San Francisco, CA, USA
Total Posts: 151

Here are some picts of a fully balanced B22 w/ S22 I just finished for someone.

http://ybmaudio....2/beta22.16.jpg
http://ybmaudio....2/beta22.13.jpg
http://ybmaudio....2/beta22.14.jpg
http://ybmaudio....2/beta22.10.jpg
http://ybmaudio....22/beta22.9.jpg

mike b

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Joined: Sep. 3, 2008
Locale: Perth
Total Posts: 5

Message [#119] posted on: 10-30-2008 09:23 PM CST (US).

Very nice set300b.
Seems to me a tidy two box solution is The Standard for balanced B22's.

Where is that enclosure from? Is the top custom?

set300b