DIYHiFi.org

I would like to use Jocko's discrete I/V, but it looks all too hard building 4 of them and implementing them, and I can't find a proper diagram of it anywhere anyway, but a lot of talk how good it is.
So trying the lazy way, I have subbed the 2x Ne5532 's for 4x AD825 's and it was a massive difference for the better, but with my current output Dac (PCM1738) it seems from what I've read that a current feedback opamp should be even better again.
So I've ordered 4 x THS3001 's and 4 x AD844 current feedback opamps to try, do I just use these the same way as I've subbed the NE5532 for the AD825's, or do I need to do a bit of circuit changing around the original circuit? Any help/guidance will be appreciated, below are links for the THS3001 and AD844

http://focus.ti.com/lit/ds/symlink/ths3001.pdf

http://www.analog.com/UploadedFiles/Dat ... /AD844.pdf

Cheers George

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Can't play any more, I think I hear my mother calling me.

Uh oh, Jocko hates current feedback!

In that case, he's going to love me for posting this, a tried and tested transimpedance amplifier with passive filtering and output buffer I designed a while ago for a friend. Do make sure you match within 2% and glue the transistors on the input stage together.



Cheers,

Sander.

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Indoctrinated in the ways of the dark side

Just want to try out the THS3001's or AD844's thanks, as I just want to keep it simple for now, to see what opamps can do. Any takers? or is Jocko listening (he say's quivering in his boots).



Cheers George

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Can't play any more, I think I hear my mother calling me.

I'll bite.
The most simple, cost effective and probably the best sounding solution for you and what you pretend to do is 2x THS4032.
You must try these for I/V.

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Carlos Filipe

"Any intelligent fool can make things bigger, more complex, and more violent. It takes a touch of genius - and a lot of courage - to move in the opposite direction." Albert Einstein

Thanks for your answer Carlos, but I did read your posts of these a while back and got some samples, at first I thought YES! they are very clean and distortionless and transparent, but after a while I found something missing, although cleaner and more transparent than the AD825's, they lacked in bass slam and something I call "bounce" some call it rhythm of the music, and for this fact I still prefer the AD825's.
The THS4032 were somehow dynamiclly challenged in the bottom end and rhythm department, compared to the AD825's.

Cheers George

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Can't play any more, I think I hear my mother calling me.

George,

how about the OPA861 (or OPA860 with buffer)?
Or Pedja´s AD844 I/V?

Seb.

You need at least 100uF bypass caps from each rail to ground, on the PSU pins (really, as close as you can). Panasonic FM 100uF/25V are almost mandatory, you won't go back.
And a very small cap across the rails (1nF MKT ).
You can also try latter adding snubbers from each rail to ground(0.22R+3.3nF).
This way, there's no lack of dynamics and bass slam.
IME it's an opamp that doesn't seem to add or remove anything. It has very tight, correct bass (sometimes incorrectly confused with lack of bass), but in a dynamic sort of way.

Well, anyway, it's up with you if you want to try it again.
But have in mind that the THS4031/2 are very very picky with the PSU bypass arrangement. They can sound very different, very easily.

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Carlos Filipe

"Any intelligent fool can make things bigger, more complex, and more violent. It takes a touch of genius - and a lot of courage - to move in the opposite direction." Albert Einstein

Do you really need 8 transistors to drive a 10K load?

Ok, now that you have simulated it.....and probably built it............listen to it for a while, the find a way to get rid of R_fb. Then listen to it and report back.

Or I smackah u face!

Jocko

No, but the outputbuffer put too much of an influence on the performance of the overall circuit in terms of THD, now it is virtually transparant with THD/20kHz even at 10Vpp output buried well in the noise floor (sub -130dB). And yes, it has been built not just simulated

Cheers,

Sander

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Indoctrinated in the ways of the dark side

I'm an ocean away remember, you can't touch this (plays Mc Hammer song loud!)

Cheers,

Sander

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Indoctrinated in the ways of the dark side

As you use lots of BC547/557 transistors, why not the BC847BPN?
I have a bunch of these and the problem is that they are really small.

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Carlos Filipe

"Any intelligent fool can make things bigger, more complex, and more violent. It takes a touch of genius - and a lot of courage - to move in the opposite direction." Albert Einstein

Hearing all these positive comments about THS4031/2 on I/V role, I´m looking forward to try it!

What do you think about using TL431 regulation, is the output impedance low enough? Using large AC-feedback cap (>200uF), the outp. imp. should be < 0.3 ohms @ 2Hz, for 12V output, according to simulations. See for example http://www.tnt-audio.com/clinica/regula ... ce2_e.html .

-Alexandre

I don't want to quibble too much, but don't you mean active filtering?

That impedance is still high, if you compare even to a simple 78xx reg...
But the TL431 doesn't get upset with a low ESR cap on it's output. It depends too much on it to get low impedance at low frequencies, though.

_________________
Carlos Filipe

"Any intelligent fool can make things bigger, more complex, and more violent. It takes a touch of genius - and a lot of courage - to move in the opposite direction." Albert Einstein