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DIY High or Low Ouput Moving Coil Phono Stage

HypnoToad said:
1 x OPA27GP = 3.3ma
1 x AD797 = 8.2ma

So yeah they do draw a lot more current.

What voltage are the LiPo's? Looks like a neat setup.
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That explains it then.
These LiPo's are 11.1v nominal, 3 cell, 1200mAH packs. Full charge is around 12.5 volts. They're a nice size to fit in the Fry's box, so we'll see how the hours work out, I'm guessing 60 or so. The nice thing about Lithium Polymer batteries is that they can be recharged in an hour and don't discharge when sitting idle. They also can handle 24 amp draw (20C) so the load in this instance is irrelevant. I have some larger 4 cell 2500mAH packs around here too I'll try as well.
 
jimreeves said:
That explains it then.
These LiPo's are 11.1v nominal, 3 cell, 1200mAH packs. Full charge is around 12.5 volts. They're a nice size to fit in the Fry's box, so we'll see how the hours work out, I'm guessing 60 or so. The nice thing about Lithium Polymer batteries is that they can be recharged in an hour and don't discharge when sitting idle. They also can handle 24 amp draw (20C) so the load in this instance is irrelevant. I have some larger 4 cell 2500mAH packs around here too I'll try as well.
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I just checked my lantern batteries and after a few weeks they still read over 24v total.

Have you tried listening through your SDA's as I find that the SDA effect is better with the new stage. Well everything sounds better, in fact it just shows me what I was missing out on before.
 
I jumped into measuring my caps today. Almost every one, labeled 1nF, measures 1.45nF. Hmmm, I will try to find some others. Two will pretty well replace the three in parallel but I will need some closer to 1nF to replace the single cap.

Of course that assumes that my meter is accurate.
 
I just heard something that sounds better than the stock unit, the Jim Reeves recommended op amp swap. I put in the AD797's in the output stage and wow.

This thing really sprang to life, I thought it couldn't get any better but I was wrong.

It gives it even more separation, more depth to the sound stage and much tighter bass. I did like the smooth laid back sound of the OPA27's but the AD797's have smoothness, warmth and tightness. They have a reputation of being very good and they show it in spades, I wonder what other recommendation's op amp Jim has to offer?
 
I think I prefer the AD797's in the output stage to anything else so far, but I haven't tried all the combinations just yet. If you are a BB fan it may be best to keep the OPA27's in the input stage. As I mentioned earlier, the BB's don't really 'do it' for me, in my setup. I kinda like the AD711's in the input stage, I think they reinforce the AD797 character, particularly the deep bass. OTOH, the LME49710's seem to bring out even more detail as inputs along with the AD797's as outputs. With LME49710's in all 4 positions it sounds a bit too analytical, no warmth. Remember the LM4562's all-around in the 640P 'toad?

Then again, the AD711's in the outputs with OPA27's as inputs may make a good combo if you want to keep the current draw down for 9v batteries.

So many possibilities and they all sound good! I didn't order any AD843's though, don't you think they run kinda hot (current-wise)?
 
I have the LME4970's so will try those in the input stage.

Will probably pick up some AD711's as well. The AD843 is similar to the dual circuit AD823 from what I have read.

I really like the AD797's for there openness and warmth they have higher gain than the others as well.:thmbsp:

Looks like I am keeping the lid off this one for a while.:D
 
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I decided to change out the Nichicon Polyester RIAA caps in the PC3 in my bedroom system.

I thought it sounded a little edgy compared to the one in my main system, I swapped them out for Wima FKP2's and now I have them in both stages.

Even though they are not burnt in yet it sounds much smoother, I got hold of some soft Jazz and it's uncanny how good it sounds.

I tried Jim Reeves idea of putting AD797's in the output section of one as well, it really opened it up the OP27GP's give it a tube like sound but the AD797's give it a very open sound. Either way it's the best I have heard.
 
I see that all the iterations stay with the dual-mono of the original ckt, why not dual-channel chips instead? The separation will still be much better than any cart that would be used thru it.
 
HypnoToad said:
I tried Jim Reeves idea of putting AD797's in the output section of one as well, it really opened it up the OP27GP's give it a tube like sound but the AD797's give it a very open sound. Either way it's the best I have heard.
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Have you tried the 797s in both stages? I expect it would be even better with it's lower noise and openness. The Oracle Paris uses 797s and it is supposed to be outstanding. I am thinking about getting the RJM boards and using the 797s in both stages.
 
Noob Tube said:
Have you tried the 797s in both stages? I expect it would be even better with it's lower noise and openness. The Oracle Paris uses 797s and it is supposed to be outstanding. I am thinking about getting the RJM boards and using the 797s in both stages.
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Unfortunately many have tried the AD797 in the input stage but it won't work, Richard Murdey the designer had this chip in mind but could not get it to work either. I haven't bothered but apparently there is no gain so it must be incompatible with this circuit.
 
The LME49710/AD797 combo seems to me to be the most 'open' sounding, if at the expense of some 'warmth' or 'smoothness'. The Burr-Brown choices at the inputs combined with the AD797 at the outputs is a good compromise for added warmth.
 
jimreeves said:
The LME49710/AD797 combo seems to me to be the most 'open' sounding, if at the expense of some 'warmth' or 'smoothness'. The Burr-Brown choices at the inputs combined with the AD797 at the outputs is a good compromise for added warmth.
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I am running the OPA27GP/AD797 combo in my main rig, it's not completely burnt in yet but sounds amazing. Thanks to Jim the Op Amp King. :banana:
 
As much as I want to roll OAs (and need a functioning set as well, I reversed the negative supply) my parts purchasing caught up with me. My wife saw the bill for multiple CNCs and this phono preamp. Not to mention my major project the four tubed Eros, I bought a $80 bag of upgrade parts for it.

I think I will be surfing Digi-Key for first class mail packages after the end of the month. Thanks to Fasterdamnit for the suggestion.
 
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Grainger49 said:
As much as I want to roll OAs (and need a functioning set as well, I reversed the negative supply) my parts purchasing caught up with me. My wife saw the bill for multiple CNCs and this phono preamp. Not to mention my major project the four tubed Eros, I bought a bag of upgrade parts for it.

I think I will be surfing Digi-Key for first class mail packages after the end of the month. Thanks to Fasterdamnit for the suggestion.
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I have some spares just laying around I'd be happy to send you gratis, I'm at work now but will take a look at what I have when I get home if you like. PM me later.
 
Fascinating thread!

Now let me ask the potentially dumb-question-of-the-day: Would it make any sense to build a precision stereo L-pad to drop a MM cart down to LOMC level in order to utilize this preamp? Or perhaps, the better question is, is there a MM DIY preamp of this equivalent quality?

Thanks all;
Artie
 
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