New DISPRE preamp, successor to previous popular version

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#627
Hum reduction

Hi Pavel,

I have completed the preamp about two months ago, without any problems.
It sounds excellent to my ears and is probably the strongest component in my audio chain.
I am using OPA2134 for dc servo.
The volume pot (Noble, 10k) is grounded, as suggested.

I am using a pretty good power supply (SuperTedyReg, can be found at Teddy Pardo home of TeddyCap TeddyXPS power supply for Naim Audio replaces HiCap and XPS) and all components are mounted on an mdf plate.
Input and output connectors a mounted isolated, on aluminum L profile. The profile is not connected to pcb ground (I have tried it connected but think this way is better).

The only issue I have is a higher degree of noise which is detectable with my ear relatively close to tweeter, comparing to my previous diy opamp preamp.
Both pairs of interconnects are of shielded type and I don't have any ground issue worth mentioning.

What could I do to further reduce the level of noise?

Thanks, Baki
 
#629
Baka said:
The only issue I have is a higher degree of noise which is detectable with my ear relatively close to tweeter, comparing to my previous diy opamp preamp.

....

What could I do to further reduce the level of noise?

Thanks, Baki
Click to expand...

Hi Baki,

thank you for your feedback. IMO Dispre 2 has quite reasonable noise for a line level stage, though it is not a very low noise design, and it would not be enough as a microphone preamp or phono preamp.

Dispre 2 uses high value degeneration resistors in the input differential pairs. This was decided to obtain excellent slew rate and high range of input differential voltage. In fact it is impossible to dynamically saturate the input stage. The price for this decision and design is slightly higher noise. Normally it is undetectable, but it may happen that with high gain power amplifier and sensitive speakers you may hear some noise with your ear close to the tweeter.

Regards,
 
#630
Hi Pavel,

LM3886 chipamp with discrete regulated supply has a high gain - 33 and the sensitivity of my speakers is around 85 db.

I thought that putting the preamp in aluminum case could contribute to a little bit lower noise.

DISPREII is excellent preamp anyway.

Thanks,

Baki
 
#637
From others. I see the designers comments on listening tests (and I think one other person.) Thanks!

I'm trying to pick a DIY (term used very loosly to mean assembly, I see in this forum DIY is more likely to reflect mad skilled designers!)

In addition to this design/kit, on the non passive side, so far for consideration I have:

a) Perander's kits
b) Starfish (seems a bit complicated for a first DIY build attempt)
c) NJ boards for existing pre
d) RelaiXed (very little info, project "dead"?)


With respect to Dispre II I'd love any ideas on:

a) replacing pot with remote resistor-shunt type attenuator

b) simple to build or have madeup case



Thanks!
 
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