50K pot is good.

For mounting LEDs, you can use a special LED holder/mounting bezel, or just drill an appropriate sized hole and glue the LED in place.

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[Quoting amb]

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[Quoting kschong]

Q21 -27.3 (relative to ground)
Q22 8.95 (relative to ground)

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You probably had your red probe on ground and black probe on Q21 tab while measuring this, resulting in the negative reading. At any rate. looks like your Q23 is internally shorted from D to S. Also check R32 to make sure it's still 75 ohms. Replace Q23 (and R32 if the resistance is not correct). I suspect that R35 is probably partially burnt as a side effect of this failure.

The damage is probably caused by short circuited output while you plug/unplug your headphones. Be sure to set the volume to minimum while doing so.

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[Quote]

No signs of burning parts. R34 and R35 looks normal.

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A partially-burnt metal oxide resistor may not look obviously charred.

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[Quote]

Say if I change the metal oxide resistors, I should change to another with a higher rating right?

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No. Keep the same rating resistor. Under normal circumstances the wattage is more than enough. In failure conditions, these resistors burn up by increasing their resistance (to the point of becoming an open circuit in severe cases), which could save the amp and your headphones from much worse damage.

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Great. Q23 is indeed short circuited at the D and S. I ordered a pair from Farnell, but they ran out of the exact IRFZ24N and I had to get IRFZ24NPBF as a result. The same specs actually.

R32 is still at 75ohms.

Also, do I have to match Q23 and Q24 for this case? Is it essential? So long after I change Q23 the readings are reasonable, it is fine right?

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[Quoting amb]

alwayshungry, are you building a balanced β22 or unbalanced? If unbalanced, a gain of 5 or 8 are both good for HD650. For balanced, consider a gain of 2 or 5.

50K pot is good.

For mounting LEDs, you can use a special LED holder/mounting bezel, or just drill an appropriate sized hole and glue the LED in place.

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I'm going to be building a balanced setup that is switchable to single-ended (as shown earlier in this thread and on your site).
Thanks for confirmation on the gain and pot impedance.

Also, thanks MisterX for the fast response about the power switch.

[Edited by johnwmclean on 01-25-2009 at 07:03 AM.]

I am currently building (well, just waiting for the stuff from the AMB shop; should be here early next week) an M3.

I have added up the price of pretty much everything I would need, and estimate a final cost of the B22/o22 of a shade under 350 GBP.

Would it be worth building? Are we looking at 2-3 times better performance as the price would suggest or what? What is the level of commercial amplifier that the B22 contends with?

I will be using Alessandro MS-1s, and possibly Sennheiser HD600s, which I will be evaluating when the M3 is built.

In my previous set up I had two 50k pots, one for left one for right. All worked well.

I removed these pots after adding a digital volume control (so-called volumite, by twistedpear) to the DAC (a twistedpear buffalo), and connecting the beta22's directly to the I/V stage (Twisted pear IVY). The noise if not related to music being played or the (now digital) volume settings.

I realize there are an awful lot of non-beta22 parts in this equation, but I feel the problem is somewhere in the connections to the beta22. Perhaps this setup is not possible at all. I noticed that with the twisted pear DAC parts turned off, dc-offset is <1mV on all 4 beta22 boards. With the source parts on this changes to ~30mV on all beta22 boards. A grounding issue or short distance between amp and source parts (see pic), or perhaps something else?

Are there any adjustments I can try to the beta22?

Is there anyone with similar setup that can share his/her experience?

Thanks!

Can anyone explain this?

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[Quoting ZMN]

Just a short update the issue I described above. With the 50k pots back in place, I can create the "hum" when turning the pot completely open (100%) on either or both of the channels (left, right). turning the pot back to, say 99% completely removes the hum.

Can anyone explain this?

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Sounds like a grounding issue. Is the amp grounded properly?

Olli1324, there is no commercial "equivalent" to a β22, because even with a $5K+ USD price tag a company would have a hard time justifying building something like it. How much better is β22 than a M³ is mostly subjective, but β22 has almost 4 times the output voltage swing capability in unbalanced form.

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[Quoting johnwmclean]

Just waiting on reply to post 285. Thanks!

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[Quoting amb]

alwayshungry, that Bulgin power switch cannot handle the full current of the amp, so we used it only to switch an AC relay (Omron G4B-112T-US-AC120), which then in turn controls the power to the amp.

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Thanks amb. From the pictures of the internals I figured I would have some more homework to do to figure out the wiring but you've pointed me in the right direction.

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[Quote]

ZMN, maybe post a diagram of your connections? It's a bit difficult to figure out what the problem is based just on the descriptions.

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I attempted to draw a readible overview of the wiring of my setup. The parts are in two housings, connected by two 8-wire lines. All lines are drawn except from the signal lines between ivy--beta22 and beta22-- headphone.

here is the drawing

What do you think?

I agree on the "ground" spagetti. I will do as you suggest and report my findings.

I’m going to be building a balanced ß22 along with two σ22.

I have some areas of concern, the first is hook up from the two transformers to IEC socket. My transformer is 30V+30V 50VA toroidal Y236207.
from: http://www.avel...range_specs.htm
I am 240V (AUST), could you please let me know if the attached diagram is the correct configuration.

Audio input/output wiring, in regards to the best way to link up the ground cable. I’ve based this the diagram from the AMB site, is there a more efficient way of doing this?

One other thing is when wiring up the Audio input/output wiring, is it crucial to keep wires at the same length where possible. Geographically this won’t be possible with the distance of some of the boards.

Please see attachments.

Thanks
John

[Edited by johnwmclean on 01-29-2009 at 05:19 AM.]

[Edited by johnwmclean on 01-29-2009 at 05:15 AM.]

Also, the input ground should be tied to the chassis. Otherwise, this should be ok.

[Edited by amb on 01-29-2009 at 12:58 PM.]