Dear Friends,
after having succesfully repaired and upgraded my ML335 and ML336 amps a couple of years ago (other post), with your valuable assistance, I am planning to upgrade also my ML380S, although it is in good working stage.
After 20 or more years, i believe it is time for this.... While i was planning to change only the electrolytic capacitors (with Rubycon ZLJ series), I noticed the significant number of old opamps used in this circuit, most of them already obsolete or not state-of-the-art.
So, a 'crazy' idea came up: to change all opamps with the best i can find nowadays.
More specific:
These are the top replacements i have found up to now. If someone has something better in mind it would be very usefull.
So, theoritically, such upgrade will give a huge 'boost' on the already very good preamp, right??
However, on a second thought, few questions came up:
So, if someone has done such upgrades before, i would appreciate a tipp.
By the way, Hans Polak i would appreciate your opinion. I remember from the past that you are 'kind of expert' on Mark Levinson designs 😀
Thank you all.
Best regards,
Theodore
after having succesfully repaired and upgraded my ML335 and ML336 amps a couple of years ago (other post), with your valuable assistance, I am planning to upgrade also my ML380S, although it is in good working stage.
After 20 or more years, i believe it is time for this.... While i was planning to change only the electrolytic capacitors (with Rubycon ZLJ series), I noticed the significant number of old opamps used in this circuit, most of them already obsolete or not state-of-the-art.
So, a 'crazy' idea came up: to change all opamps with the best i can find nowadays.
More specific:
- ADEL2020 (instead of EL2020)
- LM4562 (instead of AD823)
- OP275 (instead OPA2604)
- OPA828 (instead of OPA627) - not that easy as the OPA828 comes only in SOIC, but can be done i guess...
These are the top replacements i have found up to now. If someone has something better in mind it would be very usefull.
So, theoritically, such upgrade will give a huge 'boost' on the already very good preamp, right??
However, on a second thought, few questions came up:
- what about the gains. Unfortunately i do not have any detailed schematic, only few parts i found here. If someone has the complete schematic, please contact me.
- with the device be stable after such extended upgrades or am i going to destroy it instead of improving it...?
So, if someone has done such upgrades before, i would appreciate a tipp.
By the way, Hans Polak i would appreciate your opinion. I remember from the past that you are 'kind of expert' on Mark Levinson designs 😀
Thank you all.
Best regards,
Theodore
The AD823 is a FET opamp, replacing it with bipolar LM4562 may have issues if the ultra-low bias current of a FET amp is required in that part of the circuit.
The OP275 is another bipolar amp, so again there may be issues replacing the FET OPA2604.
In general different opamps have different decoupling requirements, and stability margins, so there is always a risk changing to a different device could lead to oscillation, some testing is required with access to a 'scope.
The OP275 is another bipolar amp, so again there may be issues replacing the FET OPA2604.
In general different opamps have different decoupling requirements, and stability margins, so there is always a risk changing to a different device could lead to oscillation, some testing is required with access to a 'scope.
Hello and thx for the tipp.
In fact Analog Devices provides that OP275 is "Bipolar/JFET". See specs.
Although there is no internal schematic, this could probably replace both OPA2604 and AD823.
I would not change the opamps in this preamp. Recap the electrolytics by all means but the opamps will have been carefully selected for their specific tasks. You are not going to make dramatic improvements in performance or sound quality by opamp rolling like this. On the contrary, you will prob tend up with a sub-optimal preamp.
The LM4562 has known serious burst noise problems for starters (google it) and as Mark just pointed out, the OPA275 is a bipolar input opamp that should not be used to replace a FET input device which would have been used for low bias current and/or low input current noise.
😊
The LM4562 has known serious burst noise problems for starters (google it) and as Mark just pointed out, the OPA275 is a bipolar input opamp that should not be used to replace a FET input device which would have been used for low bias current and/or low input current noise.
😊
Hmmm maybe you are right... What about OPA1642? Looks very good... not excellent in noise like eg AD8599 i have used in another preamp, but still fine and with JFET input...
This could be used instead of both AD823 and OPA2604 (with SOIC adapter).
Bonsai, i have already in mind your point and potential risks... But the whole story is to try to do the 'good' even 'better'. Curiocity let's say...
I understand the desire to tinker. Just taking a step back, Mark Levinson is not known for being a cost-cutting company; if a more expensive part was better for the job, their engineers would likely have specified it and bragged about doing so. Actually, they may have already evaluated the parts in question and decided they chose the best one for the job; we don't know!
Your changes would be more of the intent to voice the preamp to suite "your" tastes, assuming it doesn't introduce undesired issues as Bonsai pointed out. You really have to be careful with applying the newer parts; they're not all the same as far things like compensation & supply bypass needs, etc. , let alone the obvious characteristics like input technologies, unity gain stability, etc.
Your changes would be more of the intent to voice the preamp to suite "your" tastes, assuming it doesn't introduce undesired issues as Bonsai pointed out. You really have to be careful with applying the newer parts; they're not all the same as far things like compensation & supply bypass needs, etc. , let alone the obvious characteristics like input technologies, unity gain stability, etc.
If you want to tinker, there are lots of things you can build and a lot of choice with help right here in diyAudio. As an earlier poster says, if you mod this ML product, the value will go down. Don’t do it. You may gain something re-capping it carefully if the caps have dried out, but that should be it. This preamp was put together by an experienced bunch of engineers - I’m sure if there were better opamps they’d have used them.
Hi guys, thx for your tips.
I agree with both of you that Mark Levinson would use the best available components... But obviously this device was designed and built 20+ years ago!!
However, we should not forget that the available solutions in opamps (and other components) at that time is not the same as of today!! Now we obviously have more choices (some of them better, some not) than the available components 20 years ago...
You’ve been given some very solid advice, but it seems you don’t want to listen. The best opamp ever made was the AD797 and it was available 20 yrs ago.
Opamps are used in in a circuit because of their specific characteristics. You can’t go swapping these out without considering the full range of implications.
Anyway, I guess no one here is going to convince you that hacking a Mark Levinson product is not the smartest thing to do with your money or your time.
I’m outta here.
Opamps are used in in a circuit because of their specific characteristics. You can’t go swapping these out without considering the full range of implications.
Anyway, I guess no one here is going to convince you that hacking a Mark Levinson product is not the smartest thing to do with your money or your time.
I’m outta here.
Well I certainly can't agree with that for several reasons. First there is no "best" unless you know the precise set of requirements and their weighting!
If you want DC precision zero-offset opamps are "best", if you want video bandwidth, high speed opamps are "best". If you want 100 opamps, cheapest that works is "best"....
If you want low bias currents, perhaps an ADA4530-1 with its <1fA inputs (typ) is "best", or for high voltage perhaps LTC6090 is "best". If you have low supply rails the rail-to-rail opamp is probably a requirement...
The AD797 is specialized to low impedance work in the 10R to 1k impedance range, its not a general all-round performer (mainly let down by its price and current noise) It was designed for sonar hydrophones I believe, for general audio work the OPA1612 is probably a more capable low-voltage-noise part as its rail-to-rail and far cheaper as its both cheaper per-package and a dual package. The very low input offset of the AD797 is seldom needed in audio, though for DC-precision use it is very nice.
Note that 4 OPA1612 stages in parallel is cheaper and less noisy than one AD797. Cost is not a consideration to drop lightly...
And of course the "best" opamp for low-noise is anything that can bootstrap a low-noise transistor (ZTX951 etc). Cheaper and more performant by large factors...
Since you mentioned my name, here is my comment:
1) The EL2020 is merely used to bootstrap thereby reducing the Miller effect in the buffer and extending the BW to almost 5Mhz.
It has hardly a function in the audio reproduction and replacing such a high speed CGA may lead to oscillations, don’t do it.
In the ML320, which topology of the whole audio part is almost a copy of the 380S, this amp was replaced by a AD810 because instead of highly matched dual transistors in the buffer, non matched singles where used, not an improvement IMO.
2) The OPA2604 is not a bad amp but replacing it by OPA627’s gave a solid sound improvement to my subjective experience.
Unfortunetly the 627 is largely overpriced these days, but it is still an absolute top performer in this preamp.
Have no experience with the OPA828, but I would never replace a OPA627.
3) The AD823 used in the volume control was repaced in the ML320 by a AD797, which gave a better low end to the sound.
But also at this position the OPA627 was performing better, more musically and less cold than any other op-amp, again to my own subjective opinion.
There you are
Hans
The AD797 was a breakthrough opamp when it came out in terms of noise and distortion. It does suffer from high input bias currents, but DC offset is also very good at 80uV max giving it a precision ranking. Add to that CMRR of over 110 dB (130 dB in some cases) and PSRR of 110 dB or better and you can see why it still rates as a top performer and holds its own amongst the best opamps available today - that’s a testament to Scott Wurcer's (RIP) skills as a designer. There are few opamps around even today that offer all of these performance characteristics - they may be better at one or two of the parameters, but not most of them which the AD797 is. But, the main point I was making is that there were some seriously good opamps around when the ML 380 was launched - swapping them out for what one may think are better modern opamps will not necessarily bring better results, and there are other considerations around stability etc. As for the ZTX851/951 comment please see the https://www.diyaudio.com/community/threads/bonsais-x-altra-mc-mm-phono-preamp.358956/
(BTW, this preamp uses an AD797 as the main gain opamp in the line stage and I sold one to a guy with a huge collection of high-end gear here in Norfolk to replace an ML 380s - he did not like the 380s because he said it sounded 'soft'. Who am I to judge
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