A guy who calls himself carlosfm wrote in a chipamp forum:
At request of several families , my PM is full of questions , here's the trick.
It's easier than you think.
On some op-amps you notice better sound by doing this, on other ones you don't.
But the OPA627 really NEEDS this to sing properly.
As simple as a resistor from V- to output, biasing the op-amp in to class-A at between 5 to 10ma.
For +/-18v PSU I use 2k, and for +/-15v PSU I use 1.8k.
You can use anything that bias it from 5 to 10 ma, it's not critical, although I usually go for around 10ma.
No need to use jfets to do this, just try it with a resistor at around these values and be amazed.
And now my question. I want to try OPA627 as I/V converters in my Denon DCD3560 CDP. The original opamps for I/V conversion are uPC4570C, see diagram. IC512/514 originally NE5534 are also now OPA627 in DIP version, they fit directly in the PCB.
Does the above classA trick work for OPA627 as IC511 I/V converters?
I should say that the OPA627 I am going to use here are not the DIPs, they are single and do not fit into the PCB where the double opamps PC4570 are. I have made some tiny modules with the OPA627 SOI versions that are soldered to a small PCB so that the leg positions are going in correctly.
Will they gererate heat biased in classA? Is the trick dangerous from other points og view?
Any experience appreciated!
At request of several families , my PM is full of questions , here's the trick.
It's easier than you think.
On some op-amps you notice better sound by doing this, on other ones you don't.
But the OPA627 really NEEDS this to sing properly.
As simple as a resistor from V- to output, biasing the op-amp in to class-A at between 5 to 10ma.
For +/-18v PSU I use 2k, and for +/-15v PSU I use 1.8k.
You can use anything that bias it from 5 to 10 ma, it's not critical, although I usually go for around 10ma.
No need to use jfets to do this, just try it with a resistor at around these values and be amazed.
And now my question. I want to try OPA627 as I/V converters in my Denon DCD3560 CDP. The original opamps for I/V conversion are uPC4570C, see diagram. IC512/514 originally NE5534 are also now OPA627 in DIP version, they fit directly in the PCB.
Does the above classA trick work for OPA627 as IC511 I/V converters?
I should say that the OPA627 I am going to use here are not the DIPs, they are single and do not fit into the PCB where the double opamps PC4570 are. I have made some tiny modules with the OPA627 SOI versions that are soldered to a small PCB so that the leg positions are going in correctly.
Will they gererate heat biased in classA? Is the trick dangerous from other points og view?
Any experience appreciated!
Attachments
I've tried that with opa604
Hi there...
I've tried class A polarisation at 9mA with the opa604 placed in my Arcam Alpha 7SE in the output section and also in the I/V conversion.
The opamp runs a little bit warmer so the resistors. I placed the resistors a bit away from the pcb for better heat dissipation.
Sounds mutch more airy , spatial , powerfull and cleaner...and just with 4 resistors!!! ( why don't they do that from factory???).
with OPA627 the result will be surelly similar but...that's just my opinion... The better thing is to try with and without...trust your hears!
Hi there...
I've tried class A polarisation at 9mA with the opa604 placed in my Arcam Alpha 7SE in the output section and also in the I/V conversion.
The opamp runs a little bit warmer so the resistors. I placed the resistors a bit away from the pcb for better heat dissipation.
Sounds mutch more airy , spatial , powerfull and cleaner...and just with 4 resistors!!! ( why don't they do that from factory???).
with OPA627 the result will be surelly similar but...that's just my opinion... The better thing is to try with and without...trust your hears!
I'd like to point out that disturbing DC potential at OPs’ pin 7 is going to disturb DC potential of DACs' I out pin via R538 to unknown result. And we are talking here about low I out, good (is it 16bit?) precision, fast settling times and similar....
I suggest that you pick one of the I/V converters available here on forums. I particularly do not like C525 placed across I out to ground. The muting circuitry’s been implemented in questionable way as well. I out gets switched, where you should really short the analogue output to ground.
Regards,
Extreme_Boky
I suggest that you pick one of the I/V converters available here on forums. I particularly do not like C525 placed across I out to ground. The muting circuitry’s been implemented in questionable way as well. I out gets switched, where you should really short the analogue output to ground.
Regards,
Extreme_Boky
Hi Extreme
I am an illeterate when it comes to diagrams and the ability to see what is -
"muting circuitry that is implemented in questionable way and why I out gets switched, where you should really short the analogue output to ground."
Could you explain i little? Any simple tricks that could improve the existing circuitry? Why do you not like C525 placed across I out to ground?
I read your comment to the classA biasing as: Do not do it with just a resistor between pin 7 and pin 4 of IC511?
A search for I/V converter here brings up several 100 threads and I get lost!
🙂 Klitgt
I am an illeterate when it comes to diagrams and the ability to see what is -
"muting circuitry that is implemented in questionable way and why I out gets switched, where you should really short the analogue output to ground."
Could you explain i little? Any simple tricks that could improve the existing circuitry? Why do you not like C525 placed across I out to ground?
I read your comment to the classA biasing as: Do not do it with just a resistor between pin 7 and pin 4 of IC511?
A search for I/V converter here brings up several 100 threads and I get lost!
🙂 Klitgt
Extreme_Boky said:
OK, I guess I have figured out what you mean by "The muting circuitry’s been implemented in questionable way as well."
You mean the IC510 (TC74HC4066AP) through which the signal passes on its way to I/V converter IC511?
But I still do not understand the problem with C525.
I will appreciate your comment on this!
😕
;-) Klitgt
C525 is a brutal way to get rid of high frequency rubbish after your DAC. We have here a large number of very fine current “steps” that change in level with time, and DENON decided to apply a capacitor across this current, straight to ground. The value is moderately small – however, it will still cause phase shifts and affect the slew rate.
You can choose one of the current to voltage converter designs posted here on forums, or you can opt for ready-made I/V converter – it’s up to you.
Or, you can do a bit of modifications yourself and who knows – you might even be satisfied with results:
1. Short pin 8 and 9 on IC510. You’ll probably get a bit of “clicks” when turning the CD player ON and OFF. If you get worried for your speaker cones, remove the link.
2. Replace IC513 with AD826
3. Replace IC512 and IC514 with AD797 or AD817
4. Replace IC511 with OP2134. This is going to work very nicely in your CD player. Funny, DENON decided to use only one half of this IC (???). However, just replace it with OP2134 and do not worry….
5. Remove C538 + C539 and C242 and couple the analog out signal via WIMA 4.7uF / 400V (MKP4 or MKP10), or even better, via AURIcap 4.7uF/200V. Each of these 3 capacitors has its own character and you should try them all.
These mods are simple but effective. I avoided SMT parts and adaptor boards bearing in mind that you where after: ”simple tricks”.
I can not suggest any power supply mods because you posted only a part of circuit diagram.
I have a full data sheets on uPC4570c if you are interested. It’s around 400kB in size. It is a dual OP similar to NE5532, just faster and quieter a bit. It should definitely be replaced with one of fet input IC with low input bias current, like OP2134.
Regards,
Extreme_Boky
You can choose one of the current to voltage converter designs posted here on forums, or you can opt for ready-made I/V converter – it’s up to you.
Or, you can do a bit of modifications yourself and who knows – you might even be satisfied with results:
1. Short pin 8 and 9 on IC510. You’ll probably get a bit of “clicks” when turning the CD player ON and OFF. If you get worried for your speaker cones, remove the link.
2. Replace IC513 with AD826
3. Replace IC512 and IC514 with AD797 or AD817
4. Replace IC511 with OP2134. This is going to work very nicely in your CD player. Funny, DENON decided to use only one half of this IC (???). However, just replace it with OP2134 and do not worry….
5. Remove C538 + C539 and C242 and couple the analog out signal via WIMA 4.7uF / 400V (MKP4 or MKP10), or even better, via AURIcap 4.7uF/200V. Each of these 3 capacitors has its own character and you should try them all.
These mods are simple but effective. I avoided SMT parts and adaptor boards bearing in mind that you where after: ”simple tricks”.
I can not suggest any power supply mods because you posted only a part of circuit diagram.
I have a full data sheets on uPC4570c if you are interested. It’s around 400kB in size. It is a dual OP similar to NE5532, just faster and quieter a bit. It should definitely be replaced with one of fet input IC with low input bias current, like OP2134.
Regards,
Extreme_Boky
Extreme_Boky said:
Thank's for reply!
Should I remove C525 or use a smaller value to reduce the damage to phase shifts and slew rate? Why did Denon put it there, any idea? Denon do many strange things, among those using dual opamps in positions where singles are sufficient!
1. I will try to short pin 8+9 on IC510 with volume turned down and listen to the clicks, then turn up and see what happens.
2. As to IC513 I have an opamp Denon call SM2139. Some say it is custom made by AD for the Denon top CDP models. I doubt that, it is mentioned in the datasheet here
http://crio.mib.infn.it/wig/electronics/Componenti/Analog/Operazionali/ad797.pdf
Denon spare part dept. in DK sell them to anyone who asks for them.
3. Agree
4. Agree
5. Agree, but I have 4 of 2,2uF 400V, I take 2 in parallel per channel.
I have the sheet for uPC4570c, thank's.
Why select an opamp with low input bias current, like OP2134, what is the importance of low input bias current in the I/V converter position?
Thanks a lot if you can answer Q about C525 and input bias current🙂
I am here to learn! My illiteracy in audio electronics is doing better and better!😀
Regards
Klitgt
1. "clicks" will be noticeable only when you turn the power to the CD player ON or OFF. Please make sure that you do all mods with mains power switched OFF.
2. AD826 is much better OP. Alternatively, if you find AD826 too accurate and clinical, try OP275.
You can try high quality WIMA polypropylene (little square green-caps, 63V DC I think) for C525, 526, 530, 529, 535, 533, 536. Re: to remove C525 or not to remove - I advise against it, however you can try and see for yourself. Better use the little WIMAs.
Re: I/V conversion and importance of low input bias current and low offset, check the file attached.
Regards,
Extreme_Boky
2. AD826 is much better OP. Alternatively, if you find AD826 too accurate and clinical, try OP275.
You can try high quality WIMA polypropylene (little square green-caps, 63V DC I think) for C525, 526, 530, 529, 535, 533, 536. Re: to remove C525 or not to remove - I advise against it, however you can try and see for yourself. Better use the little WIMAs.
Re: I/V conversion and importance of low input bias current and low offset, check the file attached.
Regards,
Extreme_Boky
Extreme_Boky said:
1. That is always a good rule. I once soldered on a PCB with the power on by a mistake. No damage, but that was luck!
2. As to which opamp to pick there is much debate! Some Danish hifi freaks writing in Danish forums say that NE5532/34 are the only opamps that should have access to analog stages of CDPs. They say that bipolars are preferrable to fets because bipolars are more musical, dynamic and leave a black hole of silence when there is silence. Fets are too nice, smooth and boring!
They even say it is not a matter of taste, it is the truth!!
Regards and thank you for providing useful information
Klitgt
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