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AD797 Phono Stage Build and Help Desk Thread

I received one of these from Sachin a couple of months ago and have been tricking about with power supplies etc. I wanted to wait until I felt I had got as much performance out of it as possible before making any comments.... and I'm gad to say it has exceeded my expectations a lot. I'm using it with a modified Lenco TT, Schroeder clone arm and a Benz L2. I am using a supercapacitor PSU which I know is probably not the norm but has brought significant improvements to these and friends with educated ears. I ended up using Bennic caps for the outputs, which on listening I felt gave the best blend of detail with smoothness YMMV.

The separation, resolution, bass response, absence of harshness etc is the reward. In short I'm a vey happy camper!!
 
Hi Woodturner, Interesting your power supply (a supercapacitor PSU) could you post some pictures & maybe a link on it's construction.
I'm currently using a DIYaudio "Silent switcher" which is very quiet , but only when used with a 5V mobile phone battery booster as it's feed power source. Lasts about 5 days of listening but easy to charge up. Without the battery supply it's much noisier than my Omishra supply, which is still very quite & I think would suit 95% of users. Unfortunately I am using a very low output MC, so it makes my noise requirements much more critical.

Cheers & Happy Listening
 
maco said:
...when I connect to Phonopre the Voltage measures different 19.8V and -7V on the negative rail. Measurement made at the zhe input of the Phonopre. If I disconnect the Phonopre and measure the output of the OPS I get +/- 14.50V on both rails. ....
Click to expand...

I know this post is a little old, but just in case it helps, I had a similar issue when I started. Connecting the phono stage would draw the - side of the OPS down to low voltage. In my case it was because I used a "mic cord" to connect the two devices that had the shield of the cord wire internally connected to the pin I was using for the - power. Since my cord sockets were connected to the case and the case to ground through some dubious connections, the cord was drawing the - side of the power supply down.

Only yesterday did I discover that I think the - leg 10mH inductors were damaged by overheating at that time. The OPS powers the phono stage ok, but the inductors on the - side only measure 2.7 ohms where the other 4 measure 6.7 which is right at spec. Luckily I found a couple identical inductors so I won't have to replace all 6. I'm running the 'stage on 9-volts for a bit and have to go find the instructions to set up the OPS again. :)

I hope I didn't do other damage running it as it has been. I might have other parts to replace. But it has sounded fine throughout.

Hope you already solved your problem long ago, Mario!

Best wishes,

-Dave G.
 
Hi all,
I recently finished one of these from boards I purchased about 1 1/2 years ago (thanks Sachin!), I think it sounds wonderful, so I purchased another one to use with my MC20 (haven't got it yet). I hooked up my completed board to my Ortofon MC20 yesterday and I wish it had more gain. I went through this thread and noticed that another member had the same cartridge (MC20), which has a very low output (.07mv), however he just wanted to use this as a head amp, without using the RIAA EQ part at all (most of this information is on page 63, and 64 of this marathon thread). I was hoping that someone here could help me understand the solution given. It appears that changing a few of the resistor values will give the extra gain I'm looking for, however I DO want to use the RIAA section. In the solution that Wyn Palmer came up with, it looks like he recommends changing the variable resistor (gainR, gainL) to a fixed value 330 ohms, and the negative terminal to ground (R15, R16) to 6.8 ohms. There is also the recommendation to change ImpR, ImpL to a fixed value of 47K ohms, I'm pretty sure that this change was because this was being used as a head amp and plugged into a separate phono preamp. I have attached the technical specs of the cartridge, just in case. I guess my question is do I just need to change the gainR and gainL, along with R15 and R16, or do I also need to change the ImpR and ImpL. Just FYI, I bumped the gainR and gainL up to 1.6K, still it could use more gain. I would appreciate any insight that could be provided.

index.php
 
india42 said:
... I went through this thread and noticed that another member had the same cartridge (MC20), which has a very low output (.07mv), however he just wanted to use this as a head amp, without using the RIAA EQ part at all
Click to expand...
That was probably me, so I might be able to help.

This design is basically a head-amp (AD797) followed by an RIAA stage.

As designed, with 2k trimmer centered at 1k, and 47R shunt, the AD797 provides @ 26dB gain (useful range of adjustability @ 18-32dB), the RIAA stage another @ 36dB.

The MC20 needs at least another 8dB.

Wyns recommendation of 330/6.8 ohm brings the AD797 gain up to @ 34dB, and the low resistor values keep the noise low.

If you want to retain some adjustability, use say a 1k trimmer & 10R shunt, but fixed resistors will provide the lowest noise, and that's important with the ultra-low MC20 output.

There is also the recommendation to change ImpR, ImpL to a fixed value of 47K ohms
Click to expand...
That was based on incorrect info in the MC20 datasheet, since resolved. The MC20 works with 75-100 ohms.
 
HalfApt said:
That was probably me, so I might be able to help.
Click to expand...
Thanks for the response HalfApt, I appreciate it. I was just playing with it a bit more, I set the Impedance to 60 ohms, maybe I should bump it up a little. I'm working on a Mouser order, I guess I'll add some resistors and mess around with it a little bit. I really could get by with the gain as it is, it's not that bad. It is an improvement over the phono section in my Carver C-1, so I'm pretty happy about that.
Thanks again,
PK
 
india42 said:
... I was just playing with it a bit more, I set the Impedance to 60 ohms, maybe I should bump it up a little.
Click to expand...
May or may not make a difference. Ortofon set their STA-76 head-amp (designed for the MC10/20) at 75 ohms, so that's what I use. I suspect anything from 50-100 should be fine.
 
Hi to all I'm a long time lurker but never posted due to poor english and technical skill. I bought one board a year ago from Sachin and finally i've finished but i'm facing a problem.
Only one channel is working (right) while the other is deadly silent.
I've swapped the inputs but no change, sound come out only from the right side, checked with DMM the input voltage (15-0-15) and is ok, checked the connections between the board and the RCA and is ok, the inputs impedance is set to 100 ohms while the gain impedance is 1K. Any idea how to catch the issue?

Thank you in advance for your help.
Giuseppe
 

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Has anyone tried a passive RIAA between the opamps? Other options for opamps, like OPA1611 since LME49990 are no longer? Also looking for good active/reg power stage...don't want to use batteries.

Jeff
 
Hi,
- Sorry Cannot answer about the RIAA part of your question, but using the Burson's V5 or V6's give a better result than your two mentioned op-amps.
- Quietest P/S I have found is the ''Linear Audio Silent Switcher V3'' from DIYaudio, but only when used with a 5 VDC mobile Power Pack.
However the P/S offered by Sachin gets very close the the Silent Switch, especially if you use a decent R-Core.

Cheers Derek
https://diyaudiostore.com/collectio...ssories/products/linear-audio-silent-switcher
 
I'm stuffing the new Sachin board and it appears to have 10uf 50V caps connected between the V+ and V- rails, one at each opamp. Is that correct? Never seen this...can anyone answer why? Is there a schematic that shows these...maybe I'm wrong.
 
Hi, I have just finished a CNC and the AD797. The CNC works fine but the AD797 plays very softly. The volume does respond to the gain pots.
All the components are from Mouser. I have double checked all the resistors and caps. The +/-15v powers both CNC and ad797. Output caps are the Rrussian ones from Sachu. Can someone tell me what voltages to expect at the opamp pins?
I am using OPA1611 on dip converters and AD797 opamps. The orientation of the opa1611 seems to be correct. The leg near the dot has continuity with pin 1 on the dip pin.
Thanks,
kffern
 

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I aligned the white dot on the 1611 with the dot on the converter board. With probes on pin 1 of the 1611 and pin 1 of the dip8 I read continuity. Is that right?
Kffern
 
MM cart use. Interestingly i have just read a note on DIYaudio that if the op-amp AD811 is used ILO the AD797, this phono amp can be used with MM cartridges.

Cheers derek
 
tabarddn51 said:
MM cart use. Interestingly i have just read a note on DIYaudio that if the op-amp AD811 is used ILO the AD797, this phono amp can be used with MM cartridges.

Cheers derek
Click to expand...
Why would you wish to use a bipolar transimpedance opamp for this application? An OPA1641 or OPA1656 is much preferred for MM.
 
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