AD797 Phono Stage Build and Help Desk Thread

[tabarddn51]

Hi Albertli, As you can see there are no answers. i think sadly this site has now been abandoned by anyone with enough experience to help both of us.
I am however curios with your description, are you using the board in conjugation with a SUT, or was than another board you were taking about.

Cheers & good luck

 

[albertli]

Hi Albertli, As you can see there are no answers. i think sadly this site has now been abandoned by anyone with enough experience to help both of us.
I am however curios with your description, are you using the board in conjugation with a SUT, or was than another board you were taking about.

Cheers & good luck

Sachin and or Philip might not see it yet.
I know they are nice guys and willing to help.
My board is for MC cart and it marked HQMC which I brought from Sachin couple of years back. One channel is working perfectly and I just hope for some advices for the other channel which is working also but not as what I'd expect. I'm checking on all the parts with the problemed channel and see if I have put some wrong parts on it.

 

[sachu888]

Hi Albertli, As you can see there are no answers. i think sadly this site has now been abandoned by anyone with enough experience to help both of us.
I am however curios with your description, are you using the board in conjugation with a SUT, or was than another board you were taking about.

Cheers & good luck

Sorry, I have just read the posts.Sadly the Coronavirus is all the world, so not everyone in a mood to check this site regularly.This has been a case on most hifi sites of world. I hope everyone is fine here.
Albert, have you tried swapping position of LME49990 between them? There could be a dry solder, a faulty Electrolyte cap or opamp.

Regards
Sachin

 

[sachu888]

Hi, Hope you guy's can throw some light on a problem I have.
Recently got hold of an Accurphase AC-2, S/SMith re-tipped with ruby & H/Ell stylus for $600. This cart is very, very good, much better than either of my K/Rosewood and Dyna XX1.
However, it is very very low output 1.8mv, when I try using my AD797 no sound, even with Vol turned full up. Using my Pearl 2 exc sound but to much background hum. (vol turned 80% up) Humble G/Slee Fanfare with a pair of V5's fantastic wonderful sound with still a little but acceptable back ground hum/noise.

So my question is why cannot I get anything out of my Ad797, it was working with my other carts, Tried it on the bench with a single from a FM stations through a h/phone amp, signal OK (Ok it sound like crap but that's to be expected)

Any theories, is the AC-2 output just to low, using an input of +/-9.5 from battery supply

Any suggestions appreciated

Cheers Derek

Hi Derek
One of my friend is using it with one of the very low out put cart with .02mV output, sorry I forgot the name of cart. It works fine with 2X 9V batteries. Did you try increasing the gain on phonostage. Silly question, but soundsmith also sells Low output Mi carts. This phonostage will not work with them.

Regards
Sachin

 

[k**rkleclaire]

Just a suggestion, I have built 5 of these with three different power supplies. I "thought" had a distortion problem with one of them, after about 10 minutes the distortion would start first in one channel then the other. I was convinced it was just a single unit and tried all combinations of power supplies, swapping op amps, re-soldering, exchanging output caps ect... but the problem persisted and eventually it manifested itself in other units... after much trial and error ( and soldering) I eventually I realized it was a particular wall wart causing the issue and not the
amp or power supply board at all....the wall wart was working and measured fine but at some point something happened (what I do not know)....Once I stopped using it it's been smooth sailing.

As Sherlock Holmes said : "When you eliminate the impossible whatever remains no matter how improbable must be the truth"...

So please consider it might not be the unit at all and might be your power supply. Have you tried it with batteries?

Cheers!

 

[albertli]

Sorry, I have just read the posts.Sadly the Coronavirus is all the world, so not everyone in a mood to check this site regularly.This has been a case on most hifi sites of world. I hope everyone is fine here.
Albert, have you tried swapping position of LME49990 between them? There could be a dry solder, a faulty Electrolyte cap or opamp.

Regards
Sachin

Sachin,
Wish you're well, and thanks for your reply.
Yes I did swapped the 797 and the 49990 from the good functioned channel to the problem channel, but the result was the same. I checked all joints and all parts at the problem channel yesterday and 100% sure all parts were the same with the other channel.
As you can see from the pictures, the 10k square wave at problem channel is the same to the good channel at 104k but the problem channel output power is less than the good channel at 104k.
Regards
Albert

 

[albertli]

Sachin,
I took couple more shots at point of 390 ohm with ( > mark ). please see picture for location.
Both are at 100k input. The left and right channel are identical at RMS output.

 

[DCESpeedy]

Sachin & Albert,

I have been enjoying mine from years ago. It seemed fine. But now I am building a second one with a better cabinet and a few more tweaks. I just ran a baseline from one computer to another with a 20Hz to 22kHz log sweep into Audacity. Then I used Hagerman Audio RIAA (-60dB) inverter through the Emotiva XPS-1 MC and both channels are identical and match the reference Spectrum Plot and the amplitude is correct. I then ran my AD797 in the same config and the right channel cuts off on amplitude and doesn't match the Spectrum Plot.

I have carefully matched every component that I can on the new board and will test when I am done. If it still shows a drop on the right channel it may be the batch of boards itself. I know I wasn't able to hear problems, I only saw it when I ran the test.

Below are the 2 test images, the one on the left is from the AD797 and the one on the right is from the Emotiva XPS-1. I have the load at 100 Ohm and the gain at 1k.

BTW, Sachin so thankful for all the support you have provided on this forum. I pray you are safe amidst all this chaos in the world.

Sincerely,
David

 

[tabarddn51]

Hi Sahin, Thanks for your feedback with my problem.
1 - I can confirm the AC-2 is an MC, it was re-tipped by S/Smith. I works with my Pearl 2, but the Pearl does not have enough gain for this MC, I also have a G/Slee Fanfare fitted with V5's. The AC-2 works very well with the Fanfare, but a little noisy, (due to have to dial the V/C of my Pass B1 Korg all to the 5 'o' clock position.
2 - Now to my AD797 phono amps, I have two of them & when working both were quieter than either of my other two MC phono amp. However both have developed the same problem, one I build & one I bought of off a L/Heaven member. (I actually believe it was originally one on your builds Sachin, but that is no matter)
Both units only work on the L/H channel.
Both units cannot for some reason get a full signal to through the R/H 2K trimmer. On one unit I have replaced the R/H trimmer with a fixed resistor of 1.8K, (I need max output for the AC-2 cart) but still cannot get a signal to pass. I have spent a lot of time measuring & checking solder joints. All units measure from various points the same unit we get to the trimmer. On the R/H channel of both units (one has a fixed resistor of 1.8k & one with a trimmer) I get virtually no ohm's when measuring the two resistor points to set the gain. On the L/H side no problem, everything is fine & both units work normally through that channel.
3 - I can see no logic why two units from separate builders should crap out in exactly the same place. I the long run I suppose I could make a good unit from the two defective boards by just using the L/H channels from both units.

Cheers for any suggestions & Keep Safe.

Derek

 

[DCESpeedy]

Sachin & Albert,

I have been enjoying mine from years ago. It seemed fine. But now I am building a second one with a better cabinet and a few more tweaks. I just ran a baseline from one computer to another with a 20Hz to 22kHz log sweep into Audacity. Then I used Hagerman Audio RIAA (-60dB) inverter through the Emotiva XPS-1 MC and both channels are identical and match the reference Spectrum Plot and the amplitude is correct. I then ran my AD797 in the same config and the right channel cuts off on amplitude and doesn't match the Spectrum Plot.

I have carefully matched every component that I can on the new board and will test when I am done. If it still shows a drop on the right channel it may be the batch of boards itself. I know I wasn't able to hear problems, I only saw it when I ran the test.

Below are the 2 test images, the one on the left is from the AD797 and the one on the right is from the Emotiva XPS-1. I have the load at 100 Ohm and the gain at 1k.

BTW, Sachin so thankful for all the support you have provided on this forum. I pray you are safe amidst all this chaos in the world.

Sincerely,
David

View attachment 1835713 View attachment 1835714

I tested the new board and it is still the same. I am going to change the RCA connectors and wires to be shielded silver plated so nothing gets in the way. But it still sounds awesome. I will post the results tomorrow sometime.

 

[DCESpeedy]

I tested the new board and it is still the same. I am going to change the RCA connectors and wires to be shielded silver plated so nothing gets in the way. But it still sounds awesome. I will post the results tomorrow sometime.

Changing the wires to shielded silver rather than twisted silver didn't change anything. To eliminate variables I ran the right input into the right input channel with the left channel disconnected and then ran the same right input channel into the left channel with the right disconnected. It came out the same with the right channel cutting off early.

I tested how audible it was using my Office PhaseTech PC80s through my Kenwood KR-7600. I ran a test with the only one channel playing, then the other and both with the 20Hz to 22kHz sweep I captured.There was a noticeable drop on the right channel recording starting at about 4.5kHz. Anyone have an idea if this can be corrected? If not I will be left with modifying my cabinet design to include 2 boards using only the left channels.

I am also in agreement with Derek that the AD797 sounds much better than other MC phono preamps I have used. The Emotiva XPS-1 is a good reference, but I run both off of batteries and the AD797 is far superior to the XPS-1 as far as noise. I use the XPS-1 for my office, but planned to have 2 AD797's and have the XPS-1 as a backup. I only have 3 AD797 boards and was planning on making one for charity some time in the near future.

 

[DCESpeedy]

I tried one last ditch attempt and increased the R channel gain to no avail. As you see it is out of balance with the left channel and still has the drop. Right (bottom) set to 1.5k and left (top) set to 1k.

 

[sachu888]

What could be the issue here? All the PCBs are from random batches, so I don't see any problem with particular batch. I have built so many of them, lost count, never had any issues.

Regards
Sachin

 

[DCESpeedy]

What could be the issue here? All the PCBs are from random batches, so I don't see any problem with particular batch. I have built so many of them, lost count, never had any issues.

Regards
Sachin

I wounder if it was a bad batch or a few boards and Derek and I both got some. Is there a control number on those or are they all the same?

Sachin, if you have a more recent batch of those boards that are unused, I would like to reimburse you for one to test it. I have enough parts to put one together to test this. Let me know.

Thanks,
David

 

[sachu888]

Hi David,
Yes I do have some latest boards. I can send once the lockdown ends here.

Regards
Sachin

 

[DCESpeedy]

Hi David,
Yes I do have some latest boards. I can send once the lockdown ends here.

Regards
Sachin

Thanks Sachin! Please stay safe.

 

[guest147]

Gents,
I am new to this site but keen to build myself an AD797 Phono Stage. Can anyone tell me where I might get a PCB for this and also a BoM for the parts?

Garnet

 

[DCESpeedy]

Gents,
I am new to this site but keen to build myself an AD797 Phono Stage. Can anyone tell me where I might get a PCB for this and also a BoM for the parts?

Garnet

I think Sachin can help you with that. But you will need to wait until he is out of the lockdown. I have an older BoM, but it is pasted in many places in this thread.

 

[DCESpeedy]

I think Sachin can help you with that. But you will need to wait until he is out of the lockdown. I have an older BoM, but it is pasted in many places in this thread.

Also The LME49990 has been replaced with the OPA1611 (not as good as the 49990 specs but should work well since it is the second stage opamp).

 

[DCESpeedy]

Also The LME49990 has been replaced with the OPA1611 (not as good as the 49990 specs but should work well since it is the second stage opamp).

Also, this one looks pretty good ADA4898-1YRDZ. I may give it a try sometime but it seems to be back ordered on Mouser and Digikey has them in stock, but cost more. It only has a +/-16.5V instead of the +/-18V power supply max. I like the higher voltage so it can handle in in rush current better and set my supply to +/- 14V to 15V .