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Channel malfunction

beta22

Channel malfunction

Postby OliverD » October 1st, 2019, 9:35 am

Hi everyone, I guess it's me again with a weird problem.

My current chain is
Code: Select all
 y3 -> balanced b22 with delta1/delta2 i/o and attenuation -> headphones
which is working excellent.
However, I also have single ended power amps and sometimes use them with speakers.

This is where the weird part happens. I assume it is a grounding issue of some sorts, but I have no ideas left:
When I use the y3 at full volume into the b22 via balanced interconnects, I get lots of unpleasant distortion in the right channel when using speakers but not with headphones.
The problem is resolved by either using single ended interconnects or by using something around -30db on the y3. As soon as I drop the output volume of the y3, the music is fine.
When using single ended interconnects, the cold side of the inputs is shorted to ground on the delta board.

Now to the grounding:
input ground is connected to chassis ground
output ground is connected to chassis ground
b22 power ground is connected via ferret to chassis ground
delta boards digital side ground is connected to chassis ground

I have tried isolating digital side of the delta boards and not connecting the b22 boards power ground to chassis ground via ferret to no avail.

The problem exists only in the right channel and by switching input and output cabling while monitoring whether it changes to a different speaker I have isolated the problem to only the right channel of the b22.
Both b22 boards on that side pass the initial setup procedure without any problems and work absolutely marvelous when used with my recabled headphones.

To any of you still reading this... do you have any idea what might be the cause of all this? Any kind of feedback is appreciated! Thanks in advance for your time!
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Re: Channel malfunction

Postby amb » October 1st, 2019, 2:17 pm

Usually for problems that occur only on one stereo channel, my instinct is to try to isolate the problem by swapping wires/cables or boards from side to side to see if the problem moves to the other channel. Once that happens you’ve found the item of interest.

But your description of the β22 chassis ground does reveal a problem, whether it’s the cause of the volume control issue or not. There should only be one thing connected to the chassis. You have input and output grounds, plus power ground all tied to the chassis. For the recommended grounding scheme please refer to the β22 website “wiring & ground” section.

Also, do you have a zobel network at the β22’s output? For driving speakers I highly recommend it.
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Re: Channel malfunction

Postby OliverD » October 1st, 2019, 3:12 pm

Okay, that actually makes a lot of sense. I kinda dug myself too deep into this topic I guess.
I kept getting ridiculously loud noise from the speakers before grounding the output to chassis, but I now suspect that maybe my power amps are not properly grounded.

The ferret for the power ground was taken from a discussion I read somewhere here about the alpha10 and its power ground being connected with a ferret to get rid of the noise.

I will check whether maybe the power amps have no proper grounding and it never became a problem because their input signal was always grounded to the output of the preamps I have been using.

All in all I started off with just the inputs being connected to chassis ground and that worked well for phones but then I want d to get the power amps to work and I probably leveled myself into too much grounding since it improved the situation.

Though the Zobel network is only needed when driving speakers directly right? Not when using the b22 as a preamp to drive power amps, or am I mistaken in that as well?
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Re: Channel malfunction

Postby amb » October 1st, 2019, 7:55 pm

The zobel network may be needed in different circumstances, depending on the nature of the load as seem by the amp. This includes the connecting cable!
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Re: Channel malfunction

Postby OliverD » October 2nd, 2019, 4:41 am

Okay, after your comment and me revisiting the sources for my ideas I now realize the mistake I made. I should have grounded output ground to power supply ground via ferrite and not both to chassis ground.

Can I assume that this grounding scheme is correct?:
input ground is connected to chassis ground
output ground is connected to b22 power ground is via ferrite
delta 1 attenuator ground is connected to chassis ground
delta boards digital ground is connected to chassis ground

This configuration resolves all problems with noise in the right channel (though I still don't know why it is limited to the right channel) and works perfectly for speakers and headphones. Although I have not tested single ended headphones yet.
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Channel malfunction

Postby amb » October 2nd, 2019, 4:53 am

OliverD wrote:input ground is connected to chassis ground

By "input ground", you mean at the input XLR jacks, pin 1 as well as the jack body, correct?

output ground is connected to b22 power ground is via ferrite

What do you refer to as "output ground"? There is no "ground" pad at the output of the β22 PCB, only the "G" pad as part of the V+/G/V- triplet. Those G pads should be wired to the σ22 PSU.

delta 1 attenuator ground is connected to chassis ground

You mean GL and GR (on the δ1 INPUTL and INPUTR connectors) right? If you don't have any δ2 boards, then these should just be wired directly to the input jack ground (which is then connected to the chassis there).

delta boards digital ground is connected to chassis ground

Yes, via the L1 ferrite bead on only one of the δ1 boards, through a PCB mounting hole and metal standoffs. No explicit wiring needed here.
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