When I used the 844, and I have used it a number of times, that never happened with me - I stopped that saturation and upped the headroom. Very little current (only some) goes into Pin 2. It sounded just great.
Input Z equal to 15 stacked 844s.
Cheers, Joe
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I think you need to go back and try stacking yourself, with a multibit dac.
It was either Pejda Rodic, Abraxilito, or Charles Hansen (the latter I think) that said, it is very easy to current starve the 844 in this i/v situation, maybe that's why he use 4 or 8 paralleled in one of the Multibit Ayre cdp's.
You can clearly hear the dynamics improve markedly when 2 are stacked for the PCM1704 which has very small output compared to the TDA1541 which others say improve in dynamics with 3 stack, as a few here have proved to themselves and also Mick from Supratek.
Cheers George
It was either Pejda Rodic, Abraxilito, or Charles Hansen (the latter I think) that said, it is very easy to current starve the 844 in this i/v situation, maybe that's why he use 4 or 8 paralleled in one of the Multibit Ayre cdp's.
You can clearly hear the dynamics improve markedly when 2 are stacked for the PCM1704 which has very small output compared to the TDA1541 which others say improve in dynamics with 3 stack, as a few here have proved to themselves and also Mick from Supratek.
Cheers George
Yes, you have to be very careful with the 844.
I used the 844s way back in the 80's - trust me, I don't current start it at all - indeed with the way I used it, stacking would hardly improve it, at all. Now I know what you are going to say, that I haven't tried it, but think of it this way, you really only need a race harness when you race and a set belt is not required if the car is not moving... it's a case of prevention rather than the cure and stopping the horse from bolting and keeping the gate shut and... better stop there...
I have done my sums, with 4mA p/p coming out of my DAC, it will see 3R3 in parallel with 50R and hence the AC signal voltage seen is about 11mV. Then 3.7mA goes to ground and 0.2mA into Pin 2 of 844, and that is a worse case scenario. Pin 3 is high Z, so if you have a DAC with diff-outputs, it looks even better as you put another 3R3 there and halve the problem again. You also have a number of ways to tweak it, that you would not otherwise have.
This is elegance rather than brute force design.
Cheers, Joe
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If you do it your way with the PCM1704 that only has 1.2mA output, more noise will be probably be outcome, because you will have to boost the daylights out of the TZ pin gain resistor it to get 2v outout of it.
With the the 1541 it maybe not be as bad beacuse you've got 4.6mA to start with, but the outcome will be the same, more noise.
Here's the 1541 PDF do your thing with the 844 for it, I'm sure of of these 1541 guys will give it a go.
Cheers george
With the the 1541 it maybe not be as bad beacuse you've got 4.6mA to start with, but the outcome will be the same, more noise.
Here's the 1541 PDF do your thing with the 844 for it, I'm sure of of these 1541 guys will give it a go.
Cheers george
Pedja's discrete diamond I/V
I used Pedja's circuit as he published it. No substitutions were made with regards to the active transistors. In the output cap position I was able to drop that from 10 uF to 0.1 uF the output goes directly to a BUF03 with super high input impedance. I used an "Aunt Corey's" BUF03 board that George found on Ebay. Mostly because it was easier then making boards. I don't have a lot of time for DIY these days.... I did have a small 12 mV offset that could not be eliminated so I kept the coupling cap. I have pondered if parallel discrete circuits would have a similar effect to stacking 844's. I have a bunch of the recommended transistors on hand so I suppose at some point it might be worth a try.
I used Pedja's circuit as he published it. No substitutions were made with regards to the active transistors. In the output cap position I was able to drop that from 10 uF to 0.1 uF the output goes directly to a BUF03 with super high input impedance. I used an "Aunt Corey's" BUF03 board that George found on Ebay. Mostly because it was easier then making boards. I don't have a lot of time for DIY these days.... I did have a small 12 mV offset that could not be eliminated so I kept the coupling cap. I have pondered if parallel discrete circuits would have a similar effect to stacking 844's. I have a bunch of the recommended transistors on hand so I suppose at some point it might be worth a try.
844
Hi George, For those of us stacking 844's the results are obvious and clear. I got bored with a single 844 and eventually gave up on it. After I found your thread I started stacking and will never go back. Use a BUF03 across the TZ resistor and it is even better. I noted on the various threads someone always chimes in they have a better way and put up simulations and never a circuit diagram. Like it's a big secret. Joe I hope you show us your way.
Hi George, For those of us stacking 844's the results are obvious and clear. I got bored with a single 844 and eventually gave up on it. After I found your thread I started stacking and will never go back. Use a BUF03 across the TZ resistor and it is even better. I noted on the various threads someone always chimes in they have a better way and put up simulations and never a circuit diagram. Like it's a big secret. Joe I hope you show us your way.
which is quite the same as the various opamps do in their role as I/V
Some interpret I/V better than others, due to their speed, accuracy (and vocabulary... bandwidth?) of interpreting..
In a word, no.
As you know my CDP that has this 2 x AD844/BUF03 in it, is the old 2004 Cary 303/200. which has the PCM1704K dacs and PMD200.
I've compared it now to many "state of the art" units that are so highly regarded and stupid high money, on speakers like the Wilson Alexia's, and have been so happy with what it sounded like compared to those cdp's I have not felt the need to do anything more to it.
Not only that it sounds absolutely flawless with well recorded cd's, it's even given a new lease on life to what I thought were grungy old badly recorded discs, to the point of thinking they have been somehow cleaned up, maybe this zero global feedback 844 I/V doesn't get "negatively" excited by the grunge as much as other feedback type of I/V's do?.
All I know there's something special about it, it adds analogue type body to everything (especially the midrange) yet still remaining tight, controled and very dynamic with no bloom or overhang.
Cheers George
I used Pedja's circuit as he published it. No substitutions were made with regards to the active transistors.
I've built a few versions of the Pedja discrete circuit now, for a different flavour the 2SA970 & 2SC2240 used in place of the BC devices are more delicate in the treble and more 'resolved' generally, if softer in the bass. The BC combination sounds 'faster'.
Could you link Pedja's circuit? Don't have a lot of spare time right now, but would like a quick look. Thanks.
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Just wondering Tim.
Did Pedja disclose the input impedance of his buffer if you used it as well?
As the output of the TZ pin of the AD844 is very high output impedance and tests I did it lost a bit of output when driving into a 1megohm load which meant it was getting loaded down, and would be far more comfortable driving into a high impedance (many megohms) fet input like the BUF03, yet it still retains the beauty of a bi-polar output for low impedance and great current drive, and it's dc coupled as well!!
Cheers George
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And don't forget a key point that the 844 has the same footprint as a normal single opamp so you can retro fit the 844 to many DACs that use a singles as the I/V (tend to be the higher end ones)!
Super DIY friendly!
Yes same footprint but not plug and play (removing the existing feedback ect) but one needs to do some surgery to the PCB and that can be a headache if it's multilayered.
Cheers George
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