AD797 Phono Stage Build and Help Desk Thread

It should be obvious: DCR will drop from infinite to near zero whenever you make a connection with the switch. (Reminds me; I need more and better DMM probes; my clippy ones always pop off right just as I’m trying to take a reading.)
 
Hi guy's I have just received a pair of Burson V6 for trial. On inserting them into my AD797 phono in place of the AD797 I got no sound, which was not a surprise as I had read that this most likely would be the case. However when dropping them into the second op-amp slots I got sound but very, very quiet. I increased the gain on the pots to there max, but the sound was still quiet, say background levels only. As I use a passive preamp I cannot increase the volume via normal means.
However I have a second phono amp, the Graham Slee fanfare that I use with AD797's. With this unit inserting in the Burson's gave much higher sound levels, but still diminished a little from normal.

Any ideas

Straight out the box the V6's sound fantastic in the Fanfare.

Cheers Derek
 
Interesting. I have a pair of Sonic Imagery 992's I'm hoping to hear from, but I need to figure out my power switch first. They draw more amperage, but should operate fine with the 12V rails - or so I hear.
 
Hi guy's I have just received a pair of Burson V6 for trial.

I have the Burson V5i in the second stage of mine and have found no reduction in sound levels. The gain of the second stage is set by the two resistors R10 / R11 which are 390 ohms, reducing the value increases the gain, you could try adding another pair of 390 ohm resistors in parallel to see if it helps, this would increase the gain a lot. But I doubt this will correct the problem as there shouldn't be that much reduction. I have tried OPA637's in those spots as well and they don't work properly at all so maybe it's an incompatibility issue.

Another thing you could check is the voltage at the supply pins (pin 4 is neg & 7 is pos) of the op amp sockets, make sure there not over +- 16.5vdc which is the limit of the V6 according to Burson.
 
Last edited:
Hi All,

I wanted to purchase the latest AD797 board but am unable to find it on Bartertown. What am I missing, and yes I am a subscriber?

Thanks!
John
 
Someone built it with all premium parts
34584Jo.jpg

J1EvMya.jpg

kdsl8v3.jpg


Regards
Sachin
 
This is the circuit. It also has some modifications to the way the RIAA is performed. The best, theoretical, way to implement an RIAA is to do all of the equalization in the first gain stage- I won't go into why as it's a lengthy explanation- but that's not so good when the first amp is an AD797. As an alternative the best approach is to put the 75us pole first- and in some ways it could be argued that it's actually better- and that's what I did. The gain is 72dB and it's compliant to RIAA within +/-0.1dB 20-20kHz.
The DC offset is designed to be less than 10mv worst case...

View attachment 1306519

I built this and It seems to work well, but I haven't checked it sufficiently to see if I "just got lucky".
The DC offset values are the max values based on my cartridge/phono cable combo which has a 16 ohm DC series resistance.
wyn, is the circuit you posted the one that we are talking on this threat?
index.php


Not the basic circuit that hypnoToad posted in #1338, 3 post behind you?
Schem-1.png


The basic phono circuit that HypnoToad posted is very, very low end. But the one that you post is a real high end circuit. There is a world of difference between the two.
 
Last edited:
Here is an extensive discussion of that second design. The thread provides some corrections for RIAA value miscalculations on that schematic. That design forms the basis of the CNC phono stage talked about frequently on this forum.
Hi, absolon, the link you provided is for a MM phono stage with passive RIAA. We are talking about a phono stage for low output MC cartridge. It is like talking vapor ware without an actual schematic. The circuit that HypnoToad showed has a high gain linear first stage and an all active RIAA second stage. Is it really a good approach for LOMC?? :(
 
wyn, is the circuit you posted the one that we are talking on this threat?
index.php


Not the basic circuit that hypnoToad posted in #1338, 3 post behind you?
Schem-1.png


The basic phono circuit that HypnoToad posted is very, very low end. But the one that you post is a real high end circuit. There is a world of difference between the two.
I don't know about the world of difference, but clearly there are differences and the fully modified design isn't particularly compatible with the AD797 MCPRE board as it includes active offset reduction, but if you ignore that section then, yes, it can be used to replace the original AD797 design for MC cartridges and it can be built using the current board with a bit of kludging and yes it does have superior overload characteristics, which theoretically could matter.
 
Hi, absolon, the link you provided is for a MM phono stage with passive RIAA. We are talking about a phono stage for low output MC cartridge. It is like talking vapor ware without an actual schematic. The circuit that HypnoToad showed has a high gain linear first stage and an all active RIAA second stage. Is it really a good approach for LOMC?? :(
If the input stage has a gain which is equal to the 1kHz gain difference between the MC and MM stages then the designs have equivalent overload characteristics and somewhat inferior noise characteristics. Using an opamp with a high gain bandwidth product reduces the effect on the frequency response. Adding a passive supersonic pole in between the stages improves the HF overload characteristic, while moving the 75us pole to the first stage in addition improves the high audio and low supersonic frequency overload characteristics.
 
I don't know about the world of difference, but clearly there are differences and the fully modified design isn't particularly compatible with the AD797 MCPRE board as it includes active offset reduction, but if you ignore that section then, yes, it can be used to replace the original AD797 design for MC cartridges and it can be built using the current board with a bit of kludging and yes it does have superior overload characteristics, which theoretically could matter.
It would be nice if someone will pick up your design and make a PCB set for it. I like your passive/active RIAA topology and the servo feedback. They are idea for a 2 stage opamp based phono stage for LOMC.
 
Happy new year to all !!Not to disrespect to anyone but I am completely agree with HT. I think Phillip already tried few recommended values. The difference wasn't audible. There are so many builds and so many happy users. I have listened to so many high end design, but this always came out winner.

Regards
Sachin
I considered for some time whether to respond to this.
So here goes.
It has been demonstrated, conclusively and unequivocally, that trained listeners can hear differences (over fairly broad regions of the audio spectrum) of less than 0.25dB.
I have conducted the tests myself and I can hear variations of 0.25, but not 0.125dB.
I have a friend who is an audio reviewer who in many ways has inferior hearing to me, but he can hear differences as low as 0.125dB.
The way the test is defined and performed the results are not open to subjective bias and they are conducted a statistically significant number of times until a valid conclusion is reached.
Incidentally, my reviewer friend also has slightly superior pitch resolution to myself as determined by similar tests, although both of us have greater than average ability.
There is evidence to suggest that these abilities are to some extent trainable, so the concept of the "golden eared listener" has some validity.
So, yes, I would say that to some listeners the difference between +/-0.1dB variation in RIAA compliance and +/-0.4dB will be apparent, but for most it will not be the case.
However, whether you care or not, even if you can indeed hear the difference, particularly in light of the relatively massive variations in audio band frequency response of mechanical cartridges, is another matter entirely.
In addition, the original AD797MCPRE has demonstrably relatively poor overload characteristics in the supersonic and hypersonic ranges which the additional pole I added improved.
This kind of issue has been shown to be a problem in historical Hi-Fi designs and improving that characteristic has been a goal of RIAA amp designers for many years.
The effect of this overload is subtle- in essence supersonic/hypersonic information is intermodulated and downconverted into audio band signals. These audio band signals manifest themselves in various, and sometimes surprising, ways. If you don't believe me try putting ultrasonic test tones or upconverted music through your RIAA path and see what happens. You might be lucky, but when I did this I was astonished at the result- the biggest culprits by far were the Rogue M180 power amps that I use- especially in Triode rather than ultra-linear mode. My RME ADI-2PRO FS ADC/DAC has zero audible effects, but the RIAA stage without an ultrasonic filter was audible. I used the RME's headphone output to avoid the effect of the power amps. The RME designs are extremely low distortion and are great as references.
(As an aside, this test suggests that the problem with many amps is not too much feedback but too little in conjunction with an inadequate full power bandwidth...)
By the way, ultrasonic can mean just that- for example frequencies of say 30 and 31kHz can produce an audible 1kHz tone. It does not have to be in the >>20kHz region, although that too will work.
The two greatest sources of this problem are generally the RIAA amp and the power amps. It is highly recommended that the gain stages be limited in bandwidth in a way that would minimize the presence of ultrasonic and higher information in these stages.
 
Last edited:
If the input stage has a gain which is equal to the 1kHz gain difference between the MC and MM stages then the designs have equivalent overload characteristics and somewhat inferior noise characteristics. Using an opamp with a high gain bandwidth product reduces the effect on the frequency response. Adding a passive supersonic pole in between the stages improves the HF overload characteristic, while moving the 75us pole to the first stage in addition improves the high audio and low supersonic frequency overload characteristics.
You summarize the advantage of a passive-active RIAA topology very well. It is what I read in most of the low noise opamp application note and Erno Borbely's publication. I would expect a high end design to use this topology unless there is other overriding consideration. Can you share a higher resolution file of your schematic?

Your suggestion on how to optimize the noise performance of this topology in your answer to Sachu is much appreciated.
 
Last edited:
I PM sachu, but did not buy. Sachu cannot share the schematic of the PCB that he is selling. For DIYers, it is very strange.
Did I force you to buy? I already told you in my first conversation that I don't have schematic and that's the truth.

Regards
Sachin
 
Last edited:
You summarize the advantage of a passive-active RIAA topology very well. It is what I read in most of the low noise opamp application note and Erno Borbely's publication. I would expect a high end design to use this topology unless there is other overriding consideration. Can you share a higher resolution file of your schematic?

Your suggestion on how to optimize the noise performance of this topology in your answer to Sachu is much appreciated.
The schematic for the AD797MCpre is pretty straightforward. Essentially it is as you posted earlier plus the RC filter elements.
It is well known that no complete schematic is available from Hypnotoad and Sachin and it hasn't been a significant issue.
It's pretty easy to trace from the board, which is single sided. I did it in a short time. I didn't keep the schematic plus component identifiers as, frankly, it was of minimal interest to me as it's a copy of a data sheet app. Don't get me wrong, that's perfectly fine- it's just not very interesting to me.
I have posted .asc files of the old and modified schematics before. I suggest that you dig through the posts to find them.
The design that I suggest is, I believe, unusual, and is supported by extensive simulation.
It has the (perhaps) flaw that, in essence, simulation for a particular gain distribution is necessary and it is very hard to get right "from first principles" as some of the pole/zero constellation elements are in actuality composite. I'm not suggesting that this is anything but trivial, by the way.
 
Did I force you to buy? I already told you in my first conversation that I don't have schematic and that's the truth.

Regards
Sachin
If I offended you, I apologize. I did not say that you forced me to buy. But it is unusual to sell PCB without a schematic for DIY use. It is just MHPO. All power to you if you sold many PCB without schematic. You can argue that the average user cannot hear the noise, RIAA accuracy and distortion that wyn palmer is talking about, may be neither do I. But I still prefer to build the optimized phono stage that wyn palmer describes. Building a DIY phono preamplifier is neither cheap nor easy and I choose to go for the best.
 
Last edited:
I have posted .asc files of the old and modified schematics before. I suggest that you dig through the posts to find them.
The design that I suggest is, I believe, unusual, and is supported by extensive simulation.
It has the (perhaps) flaw that, in essence, simulation for a particular gain distribution is necessary and it is very hard to get right "from first principles" as some of the pole/zero constellation elements are in actuality composite. I'm not suggesting that this is anything but trivial, by the way.
I will go hunt for .asc files of the old and modified schematics. The phono stage will be used for a Dynavector Ruby 23R cartridge and that only. So I know the specific input impedance and total gain I need to have. I will probably start with one of the commercially available PCB and see how it goes from there. If you have a suggestion, please, PM me. I really enjoy reading your posts.

I built PCB for many projects before, but no longer have the facility to do that in my current home.
 
The schematic for the AD797MCpre is pretty straightforward. Essentially it is as you posted earlier plus the RC filter elements.
It is well known that no complete schematic is available from Hypnotoad and Sachin and it hasn't been a significant issue.
It's pretty easy to trace from the board, which is single sided. I did it in a short time. I didn't keep the schematic plus component identifiers as, frankly, it was of minimal interest to me as it's a copy of a data sheet app. Don't get me wrong, that's perfectly fine- it's just not very interesting to me.
I have posted .asc files of the old and modified schematics before. I suggest that you dig through the posts to find them.
The design that I suggest is, I believe, unusual, and is supported by extensive simulation.
It has the (perhaps) flaw that, in essence, simulation for a particular gain distribution is necessary and it is very hard to get right "from first principles" as some of the pole/zero constellation elements are in actuality composite. I'm not suggesting that this is anything but trivial, by the way.
I did a search for posts with string ".asc" by wyn palmer and got a few hits. Most of them are in the thread titled "Converting the AD797 MC Phono Pre to a MM Phono Pre - A Mixed Design". I cannot tell which one is for moving coil cartridge with your mod. Most of them seem to be for MM. Do you have note to show which one is the LOMC design .asc?

I am sorry to keep bothering you.
 
Back
Top Bottom