2. amps-preamps
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Preamp sending amp into protect

Hello everyone,
I recently took delivery of a Denafrips Athena preamp and their Apollo power amp, as well as a Lumin U1 Mini and an Ares 2 DAC. When the amp is connected via xlr outs to the preamp, it goes into protect within a few seconds. However, when connected directly to the Ares 2 DAC, everything is working as it should. Before I got the amp in I was using the xlr outs of the preamp to connect a set of powered monitors, which worked fine. I’m confused as to what would cause this issue with the preamp and amp combo. Any help would be appreciated.
jdown88
12 responses Add your response
erik_squires
16,058 posts
 
It's possible the pre has an ultrasonic oscillation happening. As the name implies, you can't hear it, or it could have a strong DC offset which the amp, if it is DC coupled, is responding to. You can test for the later with a DC meter on the preamp or amp outs. :)
fuzztone's avatar
fuzztone
5,600 posts
 
Same brand amp fails fed by their own pre?
Time for support from the manufacturer.
Hope you understand Mandarin.



jackd
1,068 posts
 
Did you try reaching out to Alvin as he is a better source than this forum of non owners.
bigkidz
3,381 posts
 
Sounds like a kind of DC offset.
jdown88 OP
3 posts
 
Went through some troubleshooting steps with Alvin and the NA repair rep and it seems this only happens when the left channel on the amp is connected to the preamp. Connecting just the right has no problems
tweak1
3,660 posts
 
Check your speaker cable connections. They can come loose, or, be too close to the opposite binding post.
rodman99999
6,131 posts
 
Some preamps have (coupling) capacitors in series with their outputs, to block DC from the power amp.    You may have a bad one, in that channel.       Try swapping the outputs of the pre and see if the problem follows (L to R).     If so: at least you'll be certain, it's an issue in the pre.
jdown88 OP
3 posts
 
After going over some tests with Alvin, I have noticed that no matter what combination of outputs I use from the preamp(both sets of XLR outputs, both L/R channels) as long as the left channel of the amp is involved in the mix, it goes into protect when using the preamp. Does not do this coming straight in from the DAC.
rodman99999
6,131 posts
 
Then again: some amps have coupling caps, at their inputs.   ie: The early Haflers had a, "C1", for blocking DC, on the driver board's input.     Perhaps a bad one, on the left (if applicable)?
atmasphere's avatar
atmasphere
11,803 posts
 
After going over some tests with Alvin, I have noticed that no matter what combination of outputs I use from the preamp(both sets of XLR outputs, both L/R channels) as long as the left channel of the amp is involved in the mix, it goes into protect when using the preamp. Does not do this coming straight in from the DAC.
Clearly the preamp is making a bit of DC at its output. It may well be that your powered speakers have coupling caps at their inputs. At any rate, the preamp needs service. It likely has 4 output coupling caps as its running balanced and likely also does not support the balanced standard or else it would have output transformers.


Any competent service technician should be easily able to sort this out.
jdown88 OP
3 posts
 
Would that also cause the right channel of the amp to have a problem as well though? When I use any of the preamp outputs on the right channel input of the amp there is no problem. 
atmasphere's avatar
atmasphere
11,803 posts
 
If the amp is stereo, yes, since the protection relay is common to both channels.
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