Carlos,
What PSU capacitors do you use for the AD815? Transformer rating?
You awoke my interest for an active.
What PSU capacitors do you use for the AD815? Transformer rating?
You awoke my interest for an active.
From what I've heard, slow diodes are the ones that do not need a bypass capacitor, but fast dioides do because of their switching noise.carlosfm said:
But apparently the parallel capacitor can introduce noise as well. That's why a 'soft recovery' fast diode without bypass is preferred.
This is just repeating what I've read, nothing more.
Bgt said:
You mean on the PSU pins of the AD815?
Philips 68uf + 100nf film.
I use a 400ma 2x17v toroid, but anything around 2x15v at 300~500ma will do.
Regulate for +/-15V.
I must warn you that if you never worked with current-feedback op-amps this will be a tough one.
demogorgon said:
As you guys have problems (???) making a search, I made that for you.
Starts here:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=40783&perpage=10&pagenumber=1
Schematic here:
http://www.diyaudio.com/forums/showthread.php?postid=480255#post480255
Don't ask me too many questions, because it's all there.
😀
PS: I'm using the direct output, without the coupling caps.
It has some DC-offset, but sounds better.
I have input coupling caps on my power amps.
Carlos, like a true gentleman, i must say.
Didn't know about that thread.
time for some info diggi'n..
Didn't know about that thread.
time for some info diggi'n..
Carlos,Hans L said:
could you address this post please? A few posts ago, you recommended fast diodes without bypasses because 'they don't need them'. What is your explenation for that?
Hans.
Carlos,
Pity you did not use an integrator to null the offset, is far more effective(=0.1mV offset). Like they use in power amps to avoid the offset caused by the resistor to ground in the negative feedback(=gain) path.
Anyway, the AD815 has a lot of offset. This has to be dealt with to avoid the coupling caps.
Pity you did not use an integrator to null the offset, is far more effective(=0.1mV offset). Like they use in power amps to avoid the offset caused by the resistor to ground in the negative feedback(=gain) path.
Anyway, the AD815 has a lot of offset. This has to be dealt with to avoid the coupling caps.
Ok, because I do my schematics on a piece of paper I can only tell you the drawing.
From the output of the power amp. take a 1M resistor to the - of the opamp, + (opamp) to ground, 470nF from - (opamp)to the output(opamp), from opamp output to the + input of the poweramp through 2x 1M8 resistors in series where in the middle of the 2x 1M8 resitors is a 100Nf to ground to take all the spurious HF components away. Don't forget to put 2 prot. diodes on the - of the opamp to protect it from going to the full supply rail voltage of the power amp. Opamp can be any modern 741 like type.
Bgt said:
I did my best to keep DC-offset low, without killing the sound.
Understand that it's hard to use this chip alone for audio applications.
I don't like servos...
Hans L said:
Hans, a diode can be "fast" but have soft recovery.
Normal diodes may benefit, but even with those I don't use caps.
As I said somewhere, I always get the feeling I'm injecting AC into the PSU.
I see, you said fast dioides but you meant soft recovery diodes as well.carlosfm said:Hans, a diode can be "fast" but have soft recovery.
Normal diodes may benefit, but even with those I don't use caps.
As I said somewhere, I always get the feeling I'm injecting AC into the PSU.
It does not do anything negative to the sound, it just improves because you have no big electrolyte sitting in the negative feedback loop.
First I mus say , I dont like praralel caps on any kind of diodes becouse they can produce new spikes. It is becouse of capacitance that store some energy an after AC voltage swings to opposite of voltage that is stored in capacitor, the cap can relase that voltage in some delay time.
Secound , question . Did someone try to use a BUF634 after OP to incrase the output current drive capability of OP.
What is the sound signature of BUF634 buffer?
Secound , question . Did someone try to use a BUF634 after OP to incrase the output current drive capability of OP.
What is the sound signature of BUF634 buffer?
Gasho said:
I personally didn't ,but my friend does. He told me combo opa627+buf634 is the best for headphone amplifiers.Very good fast sound.He also used buf634 in one of his dac's as out buffer,and he mentioned BUF634 can kill any difference between cinch cables.He was a bit unsatisfied,because cheap chinch and Acrotek for 500 bucks sound same with buf634🙂 .
... can kill difference ...
No, make difference between cables insignificat, what is correct 😉 - kill the cabelmania 😀 .
No, make difference between cables insignificat, what is correct 😉 - kill the cabelmania 😀 .
In the cases I have seen it here (PMA, Carlosfm, ...) the BUF634 was within the feedback loop of the driving op amp.
If I am going to use a BUF634 outside feedback loop (eg because the driving device has the loop within the chip - PGA2310, INAxxx), what would be the (sonical) result? Has anyone experience with such an open loop implementation of BUF634?
Thanks for any comments
Ciao, Tino
If I am going to use a BUF634 outside feedback loop (eg because the driving device has the loop within the chip - PGA2310, INAxxx), what would be the (sonical) result? Has anyone experience with such an open loop implementation of BUF634?
Thanks for any comments
Ciao, Tino
opa627/buf634 is ok for headphone amplifiers. There are way better designs though, even using opamps as gain stage. A discrete diamond buffer is more transparent by example (see the old jung article).AnthonyAsh said:
I've used the buf634 outside the feedback loop in a headphone amp (with OPA2132). The sound was a tad warmer and less focused than with the op2132/buf634 in multiloop.zinsula said:
Btw, you can use the buf634 in the feedback loop of an INA134, just look at the application designs of the datasheet.
00940 said:
I agree opa627+buf634 is definitely not the best,but from good ones I think this design is easiest to implement (except Cmoy) 🙂.
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