Best buffer for a chipamp?

[Dxvideo]

Hi all,

I am planning to make an unity gain stage to use for my chipamps (LM3886, LM4780 and LM3875).
Whats the best sounding buffer design?
Should I use a discrete design (i.e. Pedja Rogics JFET buffer)?
Or may I use just an OPA134 in unity gain? (I dont know if it sounds good at unity gain)
Or do you advice a better alternative?

Thanks in advance for your replies.

 

[sneih]

waiting too

 

[Nuuk]

Don't wait - read !

 

[AndrewT]

go with Pedja Rogic's FET buffer.

 

[ionomolo]

I havn't tried the Pedja Rogic fet buffer, but i can tell that opamps at unity gain do sound bad.

 

[juma]

I can't decide between Pedja's buffer and AD797 in unity gain - they are both extremely good - and if you want to drive low Z headphones too, or very long cables - go for JISBOS.

 

[Dxvideo]

Finally I have decided to make Pedja's.. And finished in one weekend

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

Now its ready for departured! But I have a problem with the power supply. Which is;
http://www.diyaudio.com/forums/showthread.php?s=&threadid=124548
I havent got any replies from Power Supply Design guys until now. May you say something? Because I am growing impatient to try my JFET buffered gainclone...

 

[AndrewT]

get a 20-0, 20-0Vac transformer and you won't need a regulator/s

 

[Nuuk]

Or replace the 1083 regs with another pair of 317/337 to see if that cures the problem.

 

[Dxvideo]

get a 20-0, 20-0Vac transformer and you won't need a regulator/s

But Pedja advices regulated supply in his web site...

Or replace the 1083 regs with another pair of 317/337 to see if that cures the problem.

Hmm... With 30v supplies, one LM3875 sink more than 3.5A, in this case, do you think 317/337 will enough, especially if you take consider my speakers sensivity is just 86dB!

 

[Nuuk]

Hmm... With 30v supplies, one LM3875 sink more than 3.5A, in this case, do you think 317/337 will enough, especially if you take consider my speakers sensivity is just 86dB!

I'm confused Ozgur! Are you using the same supply for the buffer and your amp?

As Andrew says, the ideal solution is to use a lower voltage traffo for your buffer supply. I used an 18v one for mine, followed by two stages of regulation so each stage drops about 5 volts which doesn't stress the regulators, or require heatsinks. Full details
here .

 

[Dxvideo]

I guess, the problem is using the same PSU for buffer stage.. Youre right..
Because a lot of people use that (the first stage of PSU) design for chipamps.. However using LM337 just after LT1083 may cause that problem. So I will remove the 317/337 regulators and test it again...
I hope it will work.

 

[Nuuk]

For the cost of another small traffo and rectifier bridge etc, I would build a separate supply for your buffer!

 

[Dxvideo]

I have a spare 2x15v toroid trafo... So the cost is not a problem..
I will try it. Do you think my supply will work without LM317/337 pair?

 

[Nuuk]

Without 317/337? It won't be regulated then. Or do you mean to keep in the 1083's?

 

[Dxvideo]

No meant;
If I remove the LM317/337 will it work at just +/-30v rails..
But its not an issue for now. I removed the 337 and it works fine, +/-30v is ok...
But thats really weird! It would be work with LM337 also! I am confused.. Do you have a explanation?

 

[Dxvideo]

I found the reason of that fault. The LM337 is definately dead!
Now I ve replaced it with a new one (the old one was also new!)
and it works...
I will report about the results under this topic...

 

[Dxvideo]

I've tested one of my amplifier last evening. (With this regulated supply).
I can say only one word: EXCELLENT!
Thanks Pedja, youre a real guru..

 

[thoronx]

Dxvideo , can you post your pcb of LM3875 Amp with Pedja's buffer, thx.

 

[BWRX]

Now build one with the AD797 and see which one you think sounds better instead of letting everyone else decide for you.