Impedance Matching/Mismatch

[Simon_LDT]

Yep, just tried with both amps switched on and the problem goes away completely. Looks like it's not a fault with the outputs but just the way they're implemented. I don't know the technical reasons why or what is going on but I assume because the outputs are not individually buffered that is what is causing the poor distorted sound when both connected amps are not on.

Obviously I don't really want to leave my amps on when not in use so I guess my options are to either go through the active tape out or passive loop out on the pre amps or maybe try a buffer between DAC and amp/s.

[RothwellAudio]

Yep, just tried with both amps switched on and the problem goes away completely. Looks like it's not a fault with the outputs but just the way they're implemented. I don't know the technical reasons why or what is going on...

What are the amps that the DAC is connected to? (Sorry if you've already mentioned this.)
I don't understand why powering-up the amps cures the problem unless an un-powered amp has a much lower input impedance than a powered amp. That would be unusual but not impossible and would provide an explanation - the DAC trying to drive a low impedance (or even short circuit) would produce severe distortion.

[Simon_LDT]

What are the amps that the DAC is connected to? (Sorry if you've already mentioned this.)
I don't understand why powering-up the amps cures the problem unless an un-powered amp has a much lower input impedance than a powered amp. That would be unusual but not impossible and would provide an explanation - the DAC trying to drive a low impedance (or even short circuit) would produce severe distortion.

Arcam P1 Monos (22k input impedance)
Schiit Asgard (100k input impedance)

[RothwellAudio]

Arcam have a very comprehensive service manual for the P1 on their website and I took a look. It appears (though I haven't studied all 26 pages of the manual) that the phono inputs are shorted unless the amp's logic control circuits un-mute them, ie it has to be powered-up or else the input impedance is a short circuit. That would explain why the DAC was distorting.

[Simon_LDT]

Arcam have a very comprehensive service manual for the P1 on their website and I took a look. It appears (though I haven't studied all 26 pages of the manual) that the phono inputs are shorted unless the amp's logic control circuits un-mute them, ie it has to be powered-up or else the input impedance is a short circuit. That would explain why the DAC was distorting.

Thanks for taking the time to look at this, really appreciate it. Does that also happen with the XLR input too? Reason I ask is because when I had the active Arcam C31 connected I was using balanced and the same problem occured, now with the passive Tisbury I'm using phono input.

[RothwellAudio]

To be honest I'm pretty confused about what you have and what is connected to what. The P1 power amps seem to have a mute circuit at their RCA inputs but not their XLR inputs. I don't about the active pre-amp.

[Simon_LDT]

To be honest I'm pretty confused about what you have and what is connected to what. The P1 power amps seem to have a mute circuit at their RCA inputs but not their XLR inputs. I don't about the active pre-amp.

Apologies, I will try explain better. For the last 2 years I've used the Arcam C31 pre and Arcam P1 amps, always connected via XLR. I then added the Arcam D33 DAC, connected via it's phono outputs into the pre-amp. When I then added the Asgard h/phone amplifier and using the 2nd set of outputs on the DAC for connecting it, that is when the distortion occured so I resorted to using the tape out on the pre-amp instead.

Fast forward about a year and I'm thinking of adding a passive (never tried one before) which is the main reason I started the thread and thought I'd try get to the root of the problem with the h/phone amp and DAC also.

I then acquired the tisbury passive so now that has replaced the C31 pre in the chain. The only difference in connection now is that the tisbury > P1 amps are now via phono rather than XLR. All other connections are the same, and using the same cables.

[Spectral Morn]

Yep, just tried with both amps switched on and the problem goes away completely. Looks like it's not a fault with the outputs but just the way they're implemented. I don't know the technical reasons why or what is going on but I assume because the outputs are not individually buffered that is what is causing the poor distorted sound when both connected amps are not on.

Obviously I don't really want to leave my amps on when not in use so I guess my options are to either go through the active tape out or passive loop out on the pre amps or maybe try a buffer between DAC and amp/s.

Just dawns on me that I had that problem with a Chapter Audio pre amp. If I connected my Anthony Gallo cross over bass amp using the RCA outs and had the main amp connected to the XLRs there was a loud hum Only just remembered that reading your post above.

[struth]

Dare say the 2 amps coul be on when using it. shouldnt cause any problems if the other amp isnt class A.

[RothwellAudio]

For the last 2 years I've used the Arcam C31 pre and Arcam P1 amps, always connected via XLR. I then added the Arcam D33 DAC, connected via it's phono outputs into the pre-amp. When I then added the Asgard h/phone amplifier and using the 2nd set of outputs on the DAC for connecting it, that is when the distortion occured so I resorted to using the tape out on the pre-amp instead.

Er...I'm still confused
So the DAC was never connected directly to the power amps anyway? It always went via the C31? Did the distortion only occur with the C31 switched off? In that case, presumably the C31 has a similar input muting arrangement as the P1, The muting on the P1 shouldn't make a scrap of difference to things that are connected to the C31. Are the C31 and P1s configured so that one switch powers them all?

Anyway, the solution is simple enough - have the C31/P1 powered up when using headphones.