Amplifiers destroyed by DAC?

V

Vaclav

New Member
Dear All,

I have a strange problem with my audio equipment.

I bought an amplifier (from 80's, old Denon PMA-860) for which the source (via AUX input) was DAC Dragonfly Black v.1.5 (connected by minijack-RCA cable). After several hours of playing occurred problems with the left channel - began to play more quietly. Switching the amplifier off, turning the power plug by 180 degrees and on again was solving the issue for a while. After few days the left channel began to hiss (even at the minimum volume) until it finally got stuck.

The amplifier has been repaired - power terminals were damaged.

I've connected repaired amplifier with DAC - after a few dozen same problems occurred. I've changed speakers for another pair - problem still persists. I changed the amplifier to another from the 80s. After several days left channel began to "click", hiss, etc.

Throughout the whole time, the DAC plays without a problem (headphones plugged in - everything is perfect).

What is causing the problems described above? What should I redesign in connections/devices to solve the described problem? I came across the opinion that old audio equipment is not adapted to the signal (high frequency or something like that?) broadcasted by the modern equipment. Is it true? Does change to another DAC (with dedicated RCA outputs) may solve the problem?
 
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Change the souce and test again. In other words use anything but that DAC as an input and report back. Your phone, TV, CD player.

It's likely the amp itself IMO.
 
IT's likely that the DAC vs. Amp has an impedance mismatch OR the output voltage of the DAC is too high for the input of the Amp and overloading the amplifier. Check the specs of the DAC and the amp. If the DAC has a gain or volume control, you need to reduce the gain or volume to a level that the amp can handle without problems.
 
larryderouin said:
IT's likely that the DAC vs. Amp has an impedance mismatch OR the output voltage of the DAC is too high for the input of the Amp and overloading the amplifier. Check the specs of the DAC and the amp. If the DAC has a gain or volume control, you need to reduce the gain or volume to a level that the amp can handle without problems.
Click to expand...

From the specs. - the DAC has a line level output (with volume set to 100%) of 1.8V, while the Denon PMA-860 has an AUX input sensitivity of 150mV, so amplifier overload indeed seems quite possible.

Maybe the OP can confirm how they've normally been running the DAC & Amp in terms of volume settings etc. ?
 
In volume mixer in W10 I was setting volume = 20% or lower. But even at level =5% (but the scale probably isn't linear) the problem occured. The same situation with other devices (notebook or TV).
Audioquest Dragonfly Black 1.5 by tech. spec. is max. 1.2V on output. Denon has sensitivity 150mV. Then I look at Wikipedia "Line level" and I see different values.
I don't know which one I should look at, but neither of them responds either to DragonFly (1.2V) or to Denon (0.150V) :/

I look at another DAC with RCA connectors - NuForce Icon μDAC-3. According to the specification the RCA output has 2 Vrms Wow. Next one - FX-Audio DAC-X7. RCA output: 1.9 Vrms. Both of them have higher voltage than DragonFly, Denon and Line Level.

Is not it standardized? Or maybe I look at different parameters...? What can I do in this situation?
 
Vaclav said:
Audioquest Dragonfly Black 1.5 by tech. spec. is max. 1.2V on output. Denon has sensitivity 150mV.
Click to expand...

You are comparing maximum output to minimum acceptable input--opposite ends of the spectrum. 1.2V is well within the normal range of output for a line-level source device. If the "issue" occurs in the same manner with different line-level sources (like a CD player, tuner or tape deck) the issue is with the amp.
 
Vaclav said:
In volume mixer in W10 I was setting volume = 20% or lower. But even at level =5% (but the scale probably isn't linear) the problem occured. The same situation with other devices (notebook or TV).
Audioquest Dragonfly Black 1.5 by tech. spec. is max. 1.2V on output. Denon has sensitivity 150mV. Then I look at Wikipedia "Line level" and I see different values.
I don't know which one I should look at, but neither of them responds either to DragonFly (1.2V) or to Denon (0.150V) :/

I look at another DAC with RCA connectors - NuForce Icon μDAC-3. According to the specification the RCA output has 2 Vrms Wow. Next one - FX-Audio DAC-X7. RCA output: 1.9 Vrms. Both of them have higher voltage than DragonFly, Denon and Line Level.

Is not it standardized? Or maybe I look at different parameters...? What can I do in this situation?
Click to expand...

Most CD players have an output of 2.0v as well, and they typically work fine with the preamp source inputs of 150 mv used in many receivers and integrated amps.

I think the 2.0v is the max obtained with a very low impedance. The input impedance of the preamp's source inputs is high enough to keep overloads in check. Much the same way a power amp that deliver 30v into an 8 ohm load would react when connected to a 32 ohm load, A big drop in voltage (and corresponding power).

I doubt very much modern equipment has anything to do with your problems. It is conceivable recently purchased vintage equipment was sold because it was malfunctioning. My 40 year old Realistic receiver, Which I bought new works fine with new equipment, as does most everyone's else's I suspect.

I suppose there is a remote possibility you have a problem with your AC power, Perhaps over voltage or a faulty ground. I've heard that can create problems. Also make sure the amp/receiver is clean and well ventilated and double check your connections, Especially the speaker connections.
 
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I agree - has to be the amp. There's nothing exceptional or worrisome about the output of that Dragonfly DAC (except for the fact that it's a truly mediocre DAC, but that's another story).
 
You guys are validating what I said and we can't blame it on the DAC yet. Run it with any other input and in fact a phone is almost ideal. I don't know off hand the output voltage of a phone media player but it is easily adjusted for volume (voltage). Test it low and high and see what the results are.
 
" I changed the amplifier to another from the 80s. After several days left channel began to "click", hiss, etc."

Sounds like the source to me if you changed out the amp. Check speaker connections, what speakers are you running.
 
lico said:
" I changed the amplifier to another from the 80s. After several days left channel began to "click", hiss, etc."

Sounds like the source to me if you changed out the amp. Check speaker connections, what speakers are you running.
Click to expand...

Still proves nothing. He has still not taken the DAC out of the equation and tried another source to compare the results. Why is this a hard thing to try?
 
Montycat said:
Still proves nothing. He has still not taken the DAC out of the equation and tried another source to compare the results. Why is this a hard thing to try?
Click to expand...

"I've connected repaired amplifier with DAC - after a few dozen same problems occurred. I've changed speakers for another pair - problem still persists. I changed the amplifier to another from the 80s. After several days left channel began to "click", hiss, etc."

2 different amps, 2 different sets of speakers, same problem. Has to be DAC. Agree another source would be the way to test.
 
charles 1973 said:
I suppose there is a remote possibility you have a problem with your AC power, Perhaps over voltage or a faulty ground. I've heard that can create problems. Also make sure the amp/receiver is clean and well ventilated and double check your connections, Especially the speaker connections
Click to expand...
The electrical installation in my apartment (and the entire multi-family building) was completely changed a few years ago and meets all European and national standards. Final measurements showed this. Also, the urban power transmission is in good condition. Other electrical and electronic devices work perfectly.

lico said:
Sounds like the source to me if you changed out the amp. Check speaker connections, what speakers are you running.
Click to expand...
All conections (power, aux in, speakers sockets, etc.) I've cleaned with isopropyl alcohol. No slack in the sockets, the speaker terminals are also firmly tightened.
I used two pairs of speaker: old Pioneers (I don't remember) and nowadays JBL L100.

Montycat said:
Still proves nothing. He has still not taken the DAC out of the equation and tried another source to compare the results. Why is this a hard thing to try?
Click to expand...
I must admit honestly that other sources have been connected to the amplifier but for quite a short time - so I can not tell if they could also generate a problem. I recall that I connected the borrowed CD player and the problem did not occur during its operation (several tens of hours). So it seems that the DAC is making a "mess". Especially, that the problem also appeared on another amp.

In conclusion: there are few signs that the DAC generates a problem. At present I don't have the possibility to borrow another one (DAC). I can only buy (n few weeks), but here I have a question - what to look for in the parameters to avoid the described problems?
Besides, if Dragonfly generates the correct voltage, in what could be the problem? In amperage, resistance? Please note that Dragonfly doesn't have a dedicated RCA output, only headphone - maybe it has different current parameters?
 
Very well could - line level inputs are high impedance (usually 10K or more), some headphone outs can be designed for lower impedance loads. I think the impedance mismatch mentioned above sounds likely. Dragonfly black is not recommended for high impedance headphones (just reading about it - the Red is). I've heard hiss/pops before using headphone outs into line ins before - just not after several hours usually you hear it right away.
 
My tech bench tested a personal player to see what it would do at max output. He told me that when it clips, it overloads the input of the amp which is not good. If I have to use a mini player, I start with zero gain and turn it up just enough for the preamp or the amplifier gain control to take over. I use the preamp for volume control and run the mini player at as low an output as I can. Don't trust the little buggers one bit with my vintage.
 
Since the terminals were damaged, what's the impedance of your speakers? Perhaps your speakers killed two amps and it had nothing to do with the dac (should be fine with a modern dac since these amps were built in the age of cds unless it's a chinese dac, dan dan daaan)
 
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