Hi guy's I have just received a pair of Burson V6 for trial.
Send P.M. to sachu888 on this forum...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
wyn, is the circuit you posted the one that we are talking on this threat?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.
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??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.
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.wyn, is the circuit you posted the one that we are talking on this threat?
Not the basic circuit that hypnoToad posted in #1338, 3 post behind you?
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.
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.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??
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.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.
I considered for some time whether to respond to this.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
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?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.
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
Send P.M. to sachu888 on this forum...
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.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.
The schematic for the AD797MCpre is pretty straightforward. Essentially it is as you posted earlier plus the RC filter elements.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.
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.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
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 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?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.