Diamond buffer kits any good for preamp?

PauloPT · 13th November 2011, 10:20 PM

Hi,

Some years ago I bought from eBay these two diamond buffer kits and now I was thinking in using one of them as a unity gain preamplifier. What I'd like to know is if any of them would suit as a high-quality unity gain preamp and if so, wich one is the best. I see one has a DC servo and the other is simpler. The one with the servo has polyester caps wich perhaps is not good. Maybe put some polypropylen? The one without the servo - is it dangerous to use it dc coupled with the amp?
Would a 100k pot fit any of them as volume control?

Many thanks for your answers!
Diamond Buffer - DIY Zone.jpg

HDAM Buffer DIY Zone.pdf

PauloPT · 14th November 2011, 02:25 PM

I've been experimenting with the DC servo one and seems to blur a little the music. Also, removing the OPA2132 (the servo) the sound seems more detailed and higher in volume. Is this normal?

Thanks.

AndrewT · 14th November 2011, 02:26 PM

No.
The servo is maybe not designed properly.
There is an excellent thread on servos from a couple of years ago. Gootee was deeply involved and developed a simulator model.

PauloPT · 14th November 2011, 03:36 PM

Quote:

No.
The servo is maybe not designed properly.
There is an excellent thread on servos from a couple of years ago. Gootee was deeply involved and developed a simulator model.

Thanks, I was suspecting the same thing. I'll google it. Anyway, is the servo mandatory for this kind of circuit?

Thanks.

DF96 · 14th November 2011, 03:45 PM

Servo or coupling caps are needed for almost any circuit. One puts caps directly in the signal path. The other puts caps indirectly in the signal path, by putting them in the feedback path. You choose.

PauloPT · 14th November 2011, 06:22 PM

Can't I avoid both with carefully matched transistors? I was hoping to go capless and servoless but I can't, right?

DF96 · 14th November 2011, 07:08 PM

Can you ensure no thermal gradients too?

PauloPT · 14th November 2011, 07:32 PM

Quote:

Can you ensure no thermal gradients too?

I can thermal couple the transistors with some thermal glue but I don't know if this is good enough. I think this is what is been done with the Mezmerize buffer, at least I think they don't use a servo.

PauloPT · 14th November 2011, 08:55 PM

I just changed the 0.2uF polyester caps of the servo with one 0.1uF MKP1837. The RC constant was about 0.03 and now is 0.016 Hz. I don't know if is the polypropylen or the RC constant, but the sound improved. It's not as transparent as I hopped for but it's some improvement. Anyway, the volume goes down with the OPA in place. No servo, the volume is a lot higher. Could this be an opamp issue? - I'm using OPA2132 not the OPA2134 from the BOM I have. Could I ask someone with more knowledge than I to check the servo design for me, please?
Thanks.

AndrewT · 09:20 AM

The Servo and the Servo's Time Constant should not change the volume (output signal level).

If 0.2uF is 0.03Hz then 0.1uF is 0.06Hz, not 0.016Hz
Do you measure 0.2uF or is it marked 0.2uF? The usual E6 value is 0.22uF or 220nF or 224 (for 220000pF).

If you do opt for DC coupled through the Power Amp then you must accept the risk of damage at some time.
If you can't accept that risk then you must fit detection and protection as the least option.

Go to the servo thread. All the design and comment and simulation is in there.

13th November 2011, 10:20 PM	#1
PauloPT diyAudio Member Join Date: Jan 2010 Location: Lisboa, Portugal	Diamond buffer kits any good for preamp? Hi, Some years ago I bought from eBay these two diamond buffer kits and now I was thinking in using one of them as a unity gain preamplifier. What I'd like to know is if any of them would suit as a high-quality unity gain preamp and if so, wich one is the best. I see one has a DC servo and the other is simpler. The one with the servo has polyester caps wich perhaps is not good. Maybe put some polypropylen? The one without the servo - is it dangerous to use it dc coupled with the amp? Would a 100k pot fit any of them as volume control? Many thanks for your answers! Diamond Buffer - DIY Zone.jpg HDAM Buffer DIY Zone.pdf __________________ Kind Regards, Paulo.

14th November 2011, 02:25 PM	#2
PauloPT diyAudio Member Join Date: Jan 2010 Location: Lisboa, Portugal	I've been experimenting with the DC servo one and seems to blur a little the music. Also, removing the OPA2132 (the servo) the sound seems more detailed and higher in volume. Is this normal? Thanks. __________________ Kind Regards, Paulo.

14th November 2011, 02:26 PM	#3
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	No. The servo is maybe not designed properly. There is an excellent thread on servos from a couple of years ago. Gootee was deeply involved and developed a simulator model. __________________ regards Andrew T.

14th November 2011, 06:22 PM	#6
PauloPT diyAudio Member Join Date: Jan 2010 Location: Lisboa, Portugal	Can't I avoid both with carefully matched transistors? I was hoping to go capless and servoless but I can't, right? __________________ Kind Regards, Paulo.

14th November 2011, 08:55 PM	#9
PauloPT diyAudio Member Join Date: Jan 2010 Location: Lisboa, Portugal	I just changed the 0.2uF polyester caps of the servo with one 0.1uF MKP1837. The RC constant was about 0.03 and now is 0.016 Hz. I don't know if is the polypropylen or the RC constant, but the sound improved. It's not as transparent as I hopped for but it's some improvement. Anyway, the volume goes down with the OPA in place. No servo, the volume is a lot higher. Could this be an opamp issue? - I'm using OPA2132 not the OPA2134 from the BOM I have. Could I ask someone with more knowledge than I to check the servo design for me, please? Thanks. __________________ Kind Regards, Paulo.


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14th November 2011, 03:45 PM	#5
DF96 diyAudio Member Join Date: May 2007	Servo or coupling caps are needed for almost any circuit. One puts caps directly in the signal path. The other puts caps indirectly in the signal path, by putting them in the feedback path. You choose.

14th November 2011, 07:08 PM	#7
DF96 diyAudio Member Join Date: May 2007	Can you ensure no thermal gradients too?

15th November 2011, 09:17 AM	#10
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	The Servo and the Servo's Time Constant should not change the volume (output signal level). If 0.2uF is 0.03Hz then 0.1uF is 0.06Hz, not 0.016Hz Do you measure 0.2uF or is it marked 0.2uF? The usual E6 value is 0.22uF or 220nF or 224 (for 220000pF). If you do opt for DC coupled through the Power Amp then you must accept the risk of damage at some time. If you can't accept that risk then you must fit detection and protection as the least option. Go to the servo thread. All the design and comment and simulation is in there. __________________ regards Andrew T. Last edited by AndrewT; 15th November 2011 at 09:20 AM.

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