Gabdx1 said:Pcm56 is popular lol, I wish I can do it.
I have problems with the 3 mv 60hertz parasite at the output
I have a bass problem : can't hear much bass
Still, with everything done correctly ?
What player do you use ?
Voltages on pin 1, 3, 8, 16 ok ?
Sounds a bit like something freaky... ground connection on output missing ?
Did you best pick output ground on pin 12 ?
I did a drawing.
I have some 40 mv at output even when player is turned off and some noise 60 Hz persisting loudly at the output ONLY when connected to my other amplifier (the other one is not so much sensitive I guess). That was after the modification. Both channels hum.
Probably that I did not do the ground correctly I think it is not supposed to be connected on the dac right ? ! LOL please look my picture !
I have some 40 mv at output even when player is turned off and some noise 60 Hz persisting loudly at the output ONLY when connected to my other amplifier (the other one is not so much sensitive I guess). That was after the modification. Both channels hum.
Probably that I did not do the ground correctly I think it is not supposed to be connected on the dac right ? ! LOL please look my picture !
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Gabdx1 said:I did a drawing.
I have some 40 mv at output even when player is turned off and some noise 60 Hz persisting loudly at the output ONLY when connected to my other amplifier (the other one is not so much sensitive I guess). That was after the modification. Both channels hum.
Probably that I did not do the ground correctly I think it is not supposed to be connected on the dac right ? ! LOL please look my picture !
1. Why do you still use that 18 ohm / 100n ?
Please try my drawing.
2. A coupling cap is not necessary, there is no DC offset.
3. For the hum, connect your chinch cables to the CD player output as usual, cut the traces on the chinch signal pins and route the signal from Iout to the chinch signal pins.
That means , just bypass everything between the DAC chips and the chinch jacks.
4. What player is it ?
Hi Bernhard, you reply very fast, nice to have you on the forum !!!
Helping newbie’s and sharing knowledge is great!
I'll answer all your questions:
1. I don't have the inductors, ill try to find some, I also have a 27K volume pot resistor (ri_amp?), not 100k maybe it changes the schematic?
2. I am paranoid
but ill remove it
3. I had taken the pain to insert new RCA connections lol, but I think you're right, the old jacks seems free of parasites. Ill do that.
4. it’s an old dbx5, cheap and still working.
Cheers
Helping newbie’s and sharing knowledge is great!
I'll answer all your questions:
1. I don't have the inductors, ill try to find some, I also have a 27K volume pot resistor (ri_amp?), not 100k maybe it changes the schematic?
2. I am paranoid
but ill remove it 3. I had taken the pain to insert new RCA connections lol, but I think you're right, the old jacks seems free of parasites. Ill do that.
4. it’s an old dbx5, cheap and still working.
Cheers
Gabdx1 said:Hi Bernhard, you reply very fast, nice to have you on the forum !!!
Helping newbie’s and sharing knowledge is great!
I'll answer all your questions:
1. I don't have the inductors, ill try to find some, I also have a 27K volume pot resistor (ri_amp?), not 100k maybe it changes the schematic?
2. I am paranoid
1. I think you mean capacitors.
Look, maybe you find some film caps in the analog filter section of the player that you can use, 10n + 3 x 1n , all parallel.
If you have only 10n or 12 n, use that.
2. PCM56 has near zero output current without signal.
Even if it should fail which is nearly impossible, it is very unlikely to have any other voltage than 0V on the output.
Just to clarify things up : 4x os. I need to cut completely the sampling frequency and I don't mind if the filter cuts 1 db at 20khz.
I found the schematic for free on dbx website.
Bernhard what I am going to do is to route back the output through the original RCA socket.
Ill also try just one around 50nf in // just to make sure no filtering frequency get to my amplifier which would result in a disaster. My amplifier is DC coupled and flat in response up to 350Khz, I have no high frequency limiter in my XO at the speakers also = disaster if sampling frequency get through !@@!
I found the schematic for free on dbx website.
Bernhard what I am going to do is to route back the output through the original RCA socket.
Ill also try just one around 50nf in // just to make sure no filtering frequency get to my amplifier which would result in a disaster. My amplifier is DC coupled and flat in response up to 350Khz, I have no high frequency limiter in my XO at the speakers also = disaster if sampling frequency get through !@@!
Hi, Bernhard a question if I may
I run my 2 x 4 PCM56P K's into the Transimpedace amp attached, it is hard to find out the input impedance of it, the designer says close to zero, I have a feeling when listening to very loud recorded cd's that either the amp or the dac is going into slight distortion, if it is the dac can I try say a 100ohm resistor in series with the dac output/ will this then lower the load the dac sees or lower the input to the I/V amp?
Cheers George
I run my 2 x 4 PCM56P K's into the Transimpedace amp attached, it is hard to find out the input impedance of it, the designer says close to zero, I have a feeling when listening to very loud recorded cd's that either the amp or the dac is going into slight distortion, if it is the dac can I try say a 100ohm resistor in series with the dac output/ will this then lower the load the dac sees or lower the input to the I/V amp?
Cheers George
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Hi George,
if you put 100 ohm in series with the DAC outputs you will have more voltage swing on the DAC outputs, but as the DACs are CCSs, still the peak current into the amplifier will be 4mA...
I would as first step measure the pp voltage on the DAC outputs with a scope and 0 dB test CD.
Second, look if the amplifier output is clipping.
Third simulate the amplifier.
Also this is a 4 stage amplifier, the input signal has a max. 350 ns rise time, maybe try passive ?
You could do passive balanced + transformer with gain
or
passive >> filter >> buffer with gain. So the active stage wouldn't have to deal with staircase signals.
if you put 100 ohm in series with the DAC outputs you will have more voltage swing on the DAC outputs, but as the DACs are CCSs, still the peak current into the amplifier will be 4mA...
I would as first step measure the pp voltage on the DAC outputs with a scope and 0 dB test CD.
Second, look if the amplifier output is clipping.
Third simulate the amplifier.
Also this is a 4 stage amplifier, the input signal has a max. 350 ns rise time, maybe try passive ?
You could do passive balanced + transformer with gain
or
passive >> filter >> buffer with gain. So the active stage wouldn't have to deal with staircase signals.
Thanks Bernhard I will check tommorrow the voltage swing of the dacs output with 0db 1k sine, I'm also worried that the i/v transimpedance amp and it's single ended A class output stage is all run on just 10volt rails as well.
Now that I think about it, all the very loud discs that I feel have a slight distortion on them are all remasters that are nearly twice as loud as normal disc they replaced before remastering cd became popular, this could be the problem itself.
Cheers George
Now that I think about it, all the very loud discs that I feel have a slight distortion on them are all remasters that are nearly twice as loud as normal disc they replaced before remastering cd became popular, this could be the problem itself.
Cheers George
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