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Help needed with pro-ject pre box ds2 digital Headphone output.

Bohdan

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Hello everyone,

I am having a slight issue with headphone output hum and background noise. Allow me to go into more details with what I experience.
Source (10 years old sony F11 laptop) -> usb > pre box ds2 digital > 1/4 jack adapter to 3.5mm > audio-technica ath es88 > ears > brain

As soon as I turn on DS2 I start hearing hum and noise even if USB not connected and no signal sent:
- background noise
- hum like cash counting machine on a same db level
- most prominent between 7-9 nob indicator and after 3.
- the noise and hum does NOT increase or change with turning the volume nob to max. It actually gradually decreasing after 9 up until 3 ocklock and then it goes to same level as in the beginning.
- Audible it in the music.. because black is no mo black, it is grey now, subjectively speaking.

When I run ATH-ES88 from my laptop 3.5mm it is silent as it can be no noise at any volume level.
When I feed from DS2 > fixed rca out > old akai amp> headphones
. I can hear very slight noise at high power (no music being fed) nothing extraordinary.
I powered pre box ds2 into wall outlet and into surgeX, same story.
Pre box ds2 runs on 1.02 firmware and I think there are updates. I don't know it can fix this.


Some inside photos at the last page

Suggestions are welcomed.
Thank you

test track:


1639105530174.png
 

Tremolo

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If you don't have the issue with the fixed output it could be a pot failure
 

ZolaIII

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Take a look at the output graph @33 Ohm's and that it has a 2.4 Ohm's output impedance. Those are 103 dB LPS/mW and 34 Ohm's declared (0.9 V to drive them fully). But you will use a lot less. Those two really don't go good together. You should be able to hear the noise along with chanal disbalabce (analog volume control) but still I am not sure it should sound like that.
Did you try to drive those ATM trough DB2 line out (10+ dB SINAD difference at 2V).
 
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mhardy6647

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I'm flattered to be mentioned in any context at this forum :) but I got nothin' on this issue, I'm afraid.
Historically, hum (loud hum) independent of volume control setting is indicative of a bad filter capacitor in a (linear) power supply -- I am guessing that's irrelevant here (??).
I have had "chip amps" fail in such a way as to give only a low hum and no signal amplification, but I don't know why, and, again, probably not relevant to the current situation.

Sorry!
 
OP
Bohdan

Bohdan

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No need to shy away. Fame, sometimes, comes unexpectedly :)
 
Last edited:
OP
Bohdan

Bohdan

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@ZolaIII ,

DS2 headphone out and that what I hear. I tried fixed out into integrated akai amp and it does not have such problem, but I hear pop sound when I plug into my old akai. Like a base pop just once.. Quite loud, but irrelevant to this issue.

I will try variable line out into same akai this evening.

Another thing to mention is when I switch between mods, filters or inputs on ds2. There is a board click which is normal and a delay. During this delay all noise and hum dissapear for 2 seconds.

I saw Amir measurements and comments but I dont have enough experience to know the possible effects on low impedance headphones.. I probably will need to source 200+ ohms ones to see if I can hear some practical difference.
 

ZolaIII

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@ZolaIII ,

DS2 headphone out and that what I hear. I tried fixed out into integrated akai amp and it does not have such problem, but I hear pop sound when I plug into my old akai. Like a base pop just once.. Quite loud, but irrelevant to this issue.

I will try variable line out into same akai this evening.

Another thing to mention is when I switch between mods, filters or inputs on ds2. There is a board click which is normal and a delay. During this delay all noise and hum dissapear for 2 seconds.

I saw Amir measurements and comments but I dont have enough experience to know the possible effects on low impedance headphones.. I probably will need to source 200+ ohms ones to see if I can hear some practical difference.
Nope the lo impedance high efficient one's are a perfect tool (as SINAD is in a hear able range with such lo output power) to see if something is wrong. Problem is there is so much things wrong with that hedaphone amplifier module in the first place that is hard to me to say if it's really broken (and should be horrible for such hedaphones even if it isn't). For a love of God never put unattended line input (while that line is in use) into the working amplifier even on moderate load, your twitters will be most grateful. And even if you had 200~300 Ohm ones it would drive them just good). It would drive sensitive high efficient hedaphones considerably better from the line out and for the purpose of driving a line out 2V (it does it up to 2.4) its perfectly OK.
 
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Bohdan

Bohdan

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If you don't have the issue with the fixed output it could be a pot failure
So I ran it through variable into stereo amp and into heaphones and that specific hm/noise is gone... there is some but it does not change whether ON and OFF pro-ject ds2. (probably stereo amp itself creating some).
Looks like ds2 headphone amp is faulty more likely or maybe 1/4 slot itself..
Will bring it to authorized service for some surgery.
 
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Bohdan

Bohdan

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so ended up to be nothing wrong with it.
It is the poor performance with low impedance headphones what I hear. When I plug high impedance headphones it has pitch black background.
I guess confirmed what Amir measured.
 
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Bohdan

Bohdan

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Take a look at the output graph @33 Ohm's and that it has a 2.4 Ohm's output impedance. Those are 103 dB LPS/mW and 34 Ohm's declared (0.9 V to drive them fully). But you will use a lot less. Those two really don't go good together. You should be able to hear the noise along with chanal disbalabce (analog volume control) but still I am not sure it should sound like that.
Did you try to drive those ATM trough DB2 line out (10+ dB SINAD difference at 2V).
yes. it is the poor performance with low impedance phones.now i know how bad numbers on the chart sound :)
 
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