Causing damage? [Archive] - The Art of Sound Forum

bbbiker800

23-02-2019, 19:34

Seeking some views... Here's what I'm thinking :
My passive preamp has 2 outputs. 1 will go to the power amp, the other to a headphone amp (MF X-CAN). I'd prefer these permanently connected at the pre. The headphone amp will be powered off when I'm using speakers and power amp powered off when using the headphone amplifier. Now given I'm an electrical numpty - could I cause any damage doing this?

... Be nice...

Cheers Richard

Barry

24-02-2019, 01:34

Lawrence001

24-02-2019, 09:12

Always wondered, if the second component is switched off, will there still be a reduction in impedance?

There might be a reduction in sound quality or frequency response at the highest and/or lowest frequencies as a result depending on the input impedance of the power amp. Others will know more than me, I just speak from experience with class D amps.

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bbbiker800

24-02-2019, 10:32

Thanks guys that's really useful to know that at least I won't affect the amps. Its a phono & dac on the inputs so they are low volts really. Actually before I got the Pre (dual mono khozmo) I did do lot of reading on passives and I now remember the point you are making but obviously didn't understand it. With my 60yrs old ears its likely I won't hear the effect you mention.

Would like to hear others experiences too - I might learn something!!
Cheers Richard

Simon_LDT

24-02-2019, 11:11

It's worth a try but I know that from my experience it can have a huge effect on the sound quality. I tried a similar thing and got distorted sound when running my headphone amp (although I couldn't hear the same thing via my speakers).

In my case I was running 2 outputs from my DAC, 1 straight into my headphone amp, the other into my pre-amp and then onto my power amp. Sound seemed fine when running my amp/speaker set up but there was a haze of mild distortion across the sound whenever using my headphone amp, very noticeable.

I don't know the proper electrical knowledge of why but I do remember being told about amps connected in parallel which are switched off and that it can cause this effect.

I got around this by removing the headphone amp from the DAC output and having to run it through the tape out on my pre amp. Obviously not ideal as now I was running through 2 volume control stages, but it did solve the distortion issue.

I did make a thread about it so will have a dig and will post the link

Simon_LDT

24-02-2019, 11:24

Here's my original problem thread. Around page 3 where it starts getting to the nitty gritty of the problem.
https://theartofsound.net/forum/showthread.php?50946-Impedance-Matching-Mismatch

Mand

24-02-2019, 19:39

In my case I was running 2 outputs from my DAC, 1 straight into my headphone amp, the other into my pre-amp and then onto my power amp. Sound seemed fine when running my amp/speaker set up but there was a haze of mild distortion across the sound whenever using my headphone amp, very noticeable.

I had a similar issue with my set up - dac xlr to pre, dac rca to headphone amp.
Everything was fine with first power amp. I could listen to headphones (with main pre and power amp off) or listen to the main system.

Then I changed power amp. After that the headphone amp would play really quiet and distorted unless i turned the pre amp on, then it worked fine, or disconnect the power amp then headphones worked.
The designer of the pre and both power amps told me the new power amp shorts it output to ground when powered off, and this affected the pre inputs and hence back to the dac and headphone amp.
I got lost trying to understand the explanation.

So I recently changed headphone amp to a dac/amp to make life easier and be sure no components are in risk of being damaged.

bbbiker800

24-02-2019, 22:29

Thank you Simon and guys for that. I read thru the old thread and my main take away is that I'm going to have experiment with the power amp on. So to listen to the headphones I'll start with the power amp powered on but I'll have to disconnect the speakers (the amp is a Cyrus x-power and it stays in standby until a signal is detected - I can't mute the speakers). The DAC (AudioLab MDAC) has its preamp configured off so I think I'll have to turn the passive attenuators to maximum. I'm thinking that amounts to 'pass-thru' with practically no attenuation. Then use the headphone amps volume control. So hopefully that's a good place to start as I shouldn't be blowing anything up!
Cheers Richard....

struth

24-02-2019, 23:07

My xs dac pre has 2 separate outputs. 1 valve one ss. I used to have one in main system and other onto my actives. I could have both on and playing together with no change in output.
Don't currently have it like that now but it worked fine

Blackdog

25-02-2019, 02:00

First off, you won't do any damage. However depending on the design of the two amps, you may experience signal loss, reduced frequency response, or distortion. Some amplifiers when switched off can exhibit a much lower non-linear input impedance which can affect the other components.
The only way to know is to try it.

bbbiker800

03-03-2019, 14:08

Hi to all those who contributed. Thought I should send you an update :

Setup is x-power powered on; speakers disconnected (at the speakers); x-can connected to a khozmo output with the attenuators at maximum volume; using the x-can control to manage the volume. I'm listening to cd atm not vinyl.

I'm finding the top end to be harsh (splashy cymbols) and there may be a touch of distortion there. Other parts of the frequency range sounded OK but need more listening. Some cds will definitely be be tiring....

By comparison the m-dac headphone output has a much softer top end but it's inferior with less detail and separation.

So next steps will be to disconnect the x-power and try it; then leave it connected (at the khozmo) but powered off at the mains and try that.

I could try different interconnects and a roll off filter on the mdac too.

Happy to post updates should anyone be interested.

Thanks Richard