| 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. |
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| Nuuk |
| Don't wait - read ! ;) |
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| AndrewT |
| go with Pedja Rogic's FET buffer. |
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| ionomolo |
| I havn't tried the Pedja Rogic fet buffer, but i can tell that opamps at unity gain do sound bad. |
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| 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. |
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| Dxvideo |
Finally I have decided to make Pedja's.. And finished in one weekend :D
Now its ready for departured! But I have a problem with the power supply. Which is;
http://www.diyaudio.com/forums/show...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... |
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| AndrewT |
| get a 20-0, 20-0Vac transformer and you won't need a regulator/s |
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| Nuuk |
| Or replace the 1083 regs with another pair of 317/337 to see if that cures the problem. |
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| Dxvideo |
| quote: | Originally posted by AndrewT
get a 20-0, 20-0Vac transformer and you won't need a regulator/s |
But Pedja advices regulated supply in his web site...
| quote: | Originally posted by Nuuk
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! |
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| Nuuk |
| quote: | | 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 . ;) |
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| 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. |
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| Nuuk |
| For the cost of another small traffo and rectifier bridge etc, I would build a separate supply for your buffer! :att'n: |
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| 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? |
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| Nuuk |
| Without 317/337? It won't be regulated then. Or do you mean to keep in the 1083's? |
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| 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? |
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| 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... |
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| 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.. |
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| thoronx |
| Dxvideo , can you post your pcb of LM3875 Amp with Pedja's buffer, thx. |
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| BWRX |
| Now build one with the AD797 and see which one you think sounds better instead of letting everyone else decide for you. |
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| Dxvideo |
| quote: | Originally posted by thoronx
Dxvideo , can you post your pcb of LM3875 Amp with Pedja's buffer, thx. |
Do you want as PDF or the originals? (Eagle) |
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| thoronx |
| I have Eagle installed, so it might be a better idea to have it in Eagle format, Thanks again. |
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| Dxvideo |
Enjoy it...
By the way, mine is "some" cracked 4r16 version. Hope yours can read.
:D |
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| thoronx |
| thanks, I will try it at home... |
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| Dxvideo |
| quote: | Originally posted by BWRX
Now build one with the AD797 and see which one you think sounds better instead of letting everyone else decide for you. |
I will...
After having a couple of AD797 of course. |
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| thoronx |
| Dxvideo, nice eagle file, initially I can't open it, but with a little help of Eagle_LegaliZer it was a piece of cake, but I have found some unrouted nets, and I'd like to ask You once again if You can please post Your PDF version, the PCB is nice and I don't want to modify it, just to make a proto, and the pdf will be sufficient for this. |
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| Dxvideo |
I think you must make Ratsnets to rebuild the groundplane on the left side. But after that if you will insist on PDF files the I will send.
Good luck. |
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