Weird

e_fortier · 25th June 2008, 12:02 AM

Hi,

Can't get much info on this over the net so here is my question;

I have some very nice quality log stereo pot (10kohm) that I would like to use with the Sure Elec PCB amplifier that comes with TA2024.

My problem is that when connected in the circuit it does not work at all with my source, without the pot it works great but of course I can 't control the output.

What I find weird is that the original T-Amp uses a 50kohm pot (probably) linear and a 10kohm resistor is connected in parrallel to the pot so that it creates a log pot, still the overall impedance seen by the amp is equal or smaller than 10kohm but it works with my current set-up

I have tried my MP3 player or my Sony CD player as source and both do not work.

Both the Sure Elec and T-amp are configured in Inverting amp therefore the impedance of the input resistance (for the gain) and the value of the pot are part of the overall gain of the amp.

What would you recommend so I can use these very nice pot.

Regards,
Eric

e_fortier · 2nd July 2008, 10:56 PM

Hi,

No buffer needed even with a pot of 10kohm.

Problem fixed

Eric

gurley123 · 3rd July 2008, 09:54 PM

How was it fixed?

I'm also looking at this board and now there is talk of improvement with the addition of a unity gain buffer.

e_fortier · 4th July 2008, 01:16 AM

Hi,

With the small input caps to gnd (100pF) nothing was working, I simply removed one channel at a time (C3 then C24) and then everything worked.

I have also changed the gain with Rf still 20Kohm but Ri is 20k parallel with a 27kohm (don't ask, this is what I had handy) this way I did not have to remove any of these small resistors. The overall gain is now 20k / (20k//27k) or 20.9V/V or 26.4dB which is the same gain as Amp6.

I have also removed R3 and R16. The pot I'm using is a stereo log 10kohm.

For your DC offset to go even lower I have read (but not tried) that adding a resistor equal to Rf (R7 =20k) in parralel to C23 would help.

Regards,
Eric

25th June 2008, 12:02 AM	#1
e_fortier diyAudio Member Join Date: May 2001 Location: Eastern Canada	Weird Hi, Can't get much info on this over the net so here is my question; I have some very nice quality log stereo pot (10kohm) that I would like to use with the Sure Elec PCB amplifier that comes with TA2024. My problem is that when connected in the circuit it does not work at all with my source, without the pot it works great but of course I can 't control the output. What I find weird is that the original T-Amp uses a 50kohm pot (probably) linear and a 10kohm resistor is connected in parrallel to the pot so that it creates a log pot, still the overall impedance seen by the amp is equal or smaller than 10kohm but it works with my current set-up I have tried my MP3 player or my Sony CD player as source and both do not work. Both the Sure Elec and T-amp are configured in Inverting amp therefore the impedance of the input resistance (for the gain) and the value of the pot are part of the overall gain of the amp. What would you recommend so I can use these very nice pot. Regards, Eric

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2nd July 2008, 10:56 PM	#2
e_fortier diyAudio Member Join Date: May 2001 Location: Eastern Canada	Hi, No buffer needed even with a pot of 10kohm. Problem fixed Eric

3rd July 2008, 09:54 PM	#3
gurley123 diyAudio Member Join Date: Oct 2007	How was it fixed? I'm also looking at this board and now there is talk of improvement with the addition of a unity gain buffer.

4th July 2008, 01:16 AM	#4
e_fortier diyAudio Member Join Date: May 2001 Location: Eastern Canada	Hi, With the small input caps to gnd (100pF) nothing was working, I simply removed one channel at a time (C3 then C24) and then everything worked. I have also changed the gain with Rf still 20Kohm but Ri is 20k parallel with a 27kohm (don't ask, this is what I had handy) this way I did not have to remove any of these small resistors. The overall gain is now 20k / (20k//27k) or 20.9V/V or 26.4dB which is the same gain as Amp6. I have also removed R3 and R16. The pot I'm using is a stereo log 10kohm. For your DC offset to go even lower I have read (but not tried) that adding a resistor equal to Rf (R7 =20k) in parralel to C23 would help. Regards, Eric