Hi Folks,
I'm new to this forum, know precious little about electronics, and have a query about replacing the opamps in my ancient Adcom GCD575 cd player.
Reading the forums it seems that a useful sonic gain can be had by substituting the existing opamps with something a bit posher. I've ordered a pair of BB OPA627's since they seem, by many folks reckoning, to be the ducks nuts with regard to sonic value. I like the Burson discrete op amps too but feel that my old Adcom might not be worth the outlay, so for now I'll try the 627's in sockets so I can roll later.
The question I have is this... Is the BB OPA 627 a single or dual op amp? It says on the front of the amp that dual DAC's are used. Does that mean 2X dual opamps, or 2X single op amps, or are the DAC's something else entirely?
Is it possible, if it is the latter, that there might be a useful sonic benefit if I was to fit a double-up socket to carry 2 of the 627's per side ( 4x 627's in total)? Is that either possible, or necessary, or would it be best just to stick with the original plan of straight swaps?
I'm an absolute beginner in all this, so go easy anyone who is inclined to reply. We all have to learn🙂
Cheers, Martin
I'm new to this forum, know precious little about electronics, and have a query about replacing the opamps in my ancient Adcom GCD575 cd player.
Reading the forums it seems that a useful sonic gain can be had by substituting the existing opamps with something a bit posher. I've ordered a pair of BB OPA627's since they seem, by many folks reckoning, to be the ducks nuts with regard to sonic value. I like the Burson discrete op amps too but feel that my old Adcom might not be worth the outlay, so for now I'll try the 627's in sockets so I can roll later.
The question I have is this... Is the BB OPA 627 a single or dual op amp? It says on the front of the amp that dual DAC's are used. Does that mean 2X dual opamps, or 2X single op amps, or are the DAC's something else entirely?
Is it possible, if it is the latter, that there might be a useful sonic benefit if I was to fit a double-up socket to carry 2 of the 627's per side ( 4x 627's in total)? Is that either possible, or necessary, or would it be best just to stick with the original plan of straight swaps?
I'm an absolute beginner in all this, so go easy anyone who is inclined to reply. We all have to learn🙂
Cheers, Martin
hi Martin, Adcom is using proprietary opamp for their player, and imo is good enough and
for this kind of tweaking best to have schematic or service manual, check out hifiengine.com, 627 is single, and if memory serves me right so does the adcom opamp
wish you luck with this fine player
for this kind of tweaking best to have schematic or service manual, check out hifiengine.com, 627 is single, and if memory serves me right so does the adcom opamp
wish you luck with this fine player
You need to find out what kind of OpAmps you have - single/dual, if they are SMD or trough hole mounting...
There are adaptors (Brown Dog is one) that can fit 2 singles to provide dual connections, if you are set for the 627.
In my experience (other model, GCD600) they are using some single thru-hole OpAmps, labeled "6AA". I would bet those are relabeled NE5534...
There are adaptors (Brown Dog is one) that can fit 2 singles to provide dual connections, if you are set for the 627.
In my experience (other model, GCD600) they are using some single thru-hole OpAmps, labeled "6AA". I would bet those are relabeled NE5534...
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GCD-575 has 6A which is LT1056.
6AA is AD711. 7A is LT1057, and as you can guess, 7AA is AD712.
Cheers,
6AA is AD711. 7A is LT1057, and as you can guess, 7AA is AD712.
Cheers,
I am curious where did you get that information - not that I won't belive it.
If 6AA is AD711, that is listed by AD as "With a slew rate of 16 V/ms and a settling time of 1 ms to ±0.01%, the AD711 is ideal as a buffer for 12-bit D/A and A/D Converters...". They continue with "Common-mode rejection of 88 dB and open loop gain of 400 V/mV ensure 12-bit performance even in high-speed unity gain buffer circuits."
LT1056 is slighty better (maybe one bit higher), but a far cry from something like LT1028...
Kind of sad...
On a positve note, being JFET, they can use for the OPA627 as replacements.
If 6AA is AD711, that is listed by AD as "With a slew rate of 16 V/ms and a settling time of 1 ms to ±0.01%, the AD711 is ideal as a buffer for 12-bit D/A and A/D Converters...". They continue with "Common-mode rejection of 88 dB and open loop gain of 400 V/mV ensure 12-bit performance even in high-speed unity gain buffer circuits."
LT1056 is slighty better (maybe one bit higher), but a far cry from something like LT1028...
Kind of sad...
On a positve note, being JFET, they can use for the OPA627 as replacements.
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Here is where I found the info:
http://www.diyaudio.com/forums/digital-source/177180-opamp-used-adcom-6aa-opamp.html#post2404817
But one thing to consider, this CD player is close to 20 years old. They (Adcom) probably didn't have too much choice at that time. Yeah, mine is due for a refresh
of more modern parts as well 🙂
Cheers,
http://www.diyaudio.com/forums/digital-source/177180-opamp-used-adcom-6aa-opamp.html#post2404817
But one thing to consider, this CD player is close to 20 years old. They (Adcom) probably didn't have too much choice at that time. Yeah, mine is due for a refresh
of more modern parts as well 🙂
Cheers,
I am filling my DigiKey order for a bunch of caps for the Adcom oldies: GCD-575, GDA-600, and GCD-700. Thanks to Martin to remind me that I still have these treasure, LOL. Yeah, will pick up a couple LM4562 along the way.
Thanks for the replies guys,
Being short on expertise means I rely on suck it and see; do the mod, switch on and hope for a miracle. I have yet to get up to any mischief with it though...got the new sockets but still waiting for the 627's. (EBay rocks!)
I've hung on to the Adcom but only just started reusing it after a number of years now I have most of my hearing back. I guess I've kept it rather than forked out on a new machine out of nostalgia, and having read the various forums I hope I'm right.
I also have an Adcom power amp ( I used the variable output from the GCD575 which saved the expense of a pre-amp, and the system worked very well till I retired the power amp...under the bed with the GCD575). A new though quite modest SET tube amp sits patiently waiting for me to flail into it with replacement signal caps (Russian pio's), and once I've done the various mods, we shall see, or hear...
The GCD 575 was a very good player in its day I understand, an '89 model which I bought preloved around '92, and I haven't had the remotest urge to let it go, so if I can improve things a little, maybe even replace a few of the tired old electrolytics on the way, and it goes up in smoke, I would be sad, but life is too short, and I would wing my way back to the excellent hifi emporium from whence it came, and buy another machine, maybe a middle range NAD or something.
Nothing ventured, nothing gained, as they say, so here's hoping...
I'll report back in due course...
Cheers, Martin
Being short on expertise means I rely on suck it and see; do the mod, switch on and hope for a miracle. I have yet to get up to any mischief with it though...got the new sockets but still waiting for the 627's. (EBay rocks!)
I've hung on to the Adcom but only just started reusing it after a number of years now I have most of my hearing back. I guess I've kept it rather than forked out on a new machine out of nostalgia, and having read the various forums I hope I'm right.
I also have an Adcom power amp ( I used the variable output from the GCD575 which saved the expense of a pre-amp, and the system worked very well till I retired the power amp...under the bed with the GCD575). A new though quite modest SET tube amp sits patiently waiting for me to flail into it with replacement signal caps (Russian pio's), and once I've done the various mods, we shall see, or hear...
The GCD 575 was a very good player in its day I understand, an '89 model which I bought preloved around '92, and I haven't had the remotest urge to let it go, so if I can improve things a little, maybe even replace a few of the tired old electrolytics on the way, and it goes up in smoke, I would be sad, but life is too short, and I would wing my way back to the excellent hifi emporium from whence it came, and buy another machine, maybe a middle range NAD or something.
Nothing ventured, nothing gained, as they say, so here's hoping...
I'll report back in due course...
Cheers, Martin
Well, I've done the mod; swapped out the Adcom opamps for sockets, and then bunged in the OPA637's. Any difference? Hard to tell. There is an element of my wanting there to be a difference of course but I can say that there seems to be a little more mid range detail and bass has a little more authority. Nothing huge mind, but I believe there is some sonic difference. Enough to justify the change? Dunno, but it really doesn't matter either way. I enjoyed the small challenge it presented and the sound is certainly no worse, so at the very least I didn't end up with a dud player.
I'm tempted, after owning the player for nearly 20 years, to purchase a NAD, a brand I've always liked, or maybe even a Chinese player. I'm hardly rolling in cash so a budget of $500-600 is all I'll be able to get past the missus probably. I definitely don't have the budget, or the desire to own really high end gear...there is a fair bit of snake oil in hifi I feel, and hifi is a fine example of the law of diminishing returns.
Many years ago I assisted a chap starting up a high-end hifi shop here in Perth, and was exposed to some highly-desirable gear. Unfortunately I also saw many examples of smoke and mirror antics which folks with lots of cash readily swallowed, presumably for the bragging rights rather than sonic appeal. Any protests from me soon had me booted out of the inner sanctum and out the door for being a non-believer and clearly not worthy, and for having the temerity to question the dubious science behind some of the hocus pocus presented to folks with more money than sense. Anyway, that's another story, and I certainly don't want to start a religious war with the true believers....
Moving along, I think I'll hang on to the Adcom a little longer and see how it fairs when partnered up to my new SET tube amp, but I'm sure it will be replaced soon.
All in all, good fun... something gained, and nothing lost🙂
Cheers, Martin
I'm tempted, after owning the player for nearly 20 years, to purchase a NAD, a brand I've always liked, or maybe even a Chinese player. I'm hardly rolling in cash so a budget of $500-600 is all I'll be able to get past the missus probably. I definitely don't have the budget, or the desire to own really high end gear...there is a fair bit of snake oil in hifi I feel, and hifi is a fine example of the law of diminishing returns.
Many years ago I assisted a chap starting up a high-end hifi shop here in Perth, and was exposed to some highly-desirable gear. Unfortunately I also saw many examples of smoke and mirror antics which folks with lots of cash readily swallowed, presumably for the bragging rights rather than sonic appeal. Any protests from me soon had me booted out of the inner sanctum and out the door for being a non-believer and clearly not worthy, and for having the temerity to question the dubious science behind some of the hocus pocus presented to folks with more money than sense. Anyway, that's another story, and I certainly don't want to start a religious war with the true believers....
Moving along, I think I'll hang on to the Adcom a little longer and see how it fairs when partnered up to my new SET tube amp, but I'm sure it will be replaced soon.
All in all, good fun... something gained, and nothing lost🙂
Cheers, Martin
Thanks for the report, Martin.
Quite frankly, we all hearing sensitivity, memory, and preference.
I have heard some mod perceived as day and night by others that I embarrassingly couldn't tell much of a difference 🙂
I will recap and socket my GCD-575 soon. Let see I will hear anything 🙂
Quite frankly, we all hearing sensitivity, memory, and preference.
I have heard some mod perceived as day and night by others that I embarrassingly couldn't tell much of a difference 🙂
I will recap and socket my GCD-575 soon. Let see I will hear anything 🙂
Now, it all depends also of the rest of audio chain. If you amplifyer is tube based, you might not hear a difference - it will "cover" the resulting change with the lower signal/noise ratio, higher distortion levels, reduced bandwith (depending of the output transformer).
Try a good pair of headphones directly on player output, to see what I mean.
Try a good pair of headphones directly on player output, to see what I mean.
Change Op amps in Adcom GCD-575?
I recently purchased an Adcom GCD-575 and are interested in the Burr Brown OP amp upgrade - Unit shows to have dual opamps (IC 203,204)
They are labeled: "Adcom 6A 8905", and "Adcom 6A 8903" respectfully.
Cost of Op amps?😕
Thanks,
Steve
I recently purchased an Adcom GCD-575 and are interested in the Burr Brown OP amp upgrade - Unit shows to have dual opamps (IC 203,204)
They are labeled: "Adcom 6A 8905", and "Adcom 6A 8903" respectfully.
Cost of Op amps?😕
Thanks,
Steve
Finally, I am done with recapping my GCD-575 which has passed 22 years old (was born in Sept '89). The result is very satisfactory, and I am still using the same Adcom 6A opamps (LT1056 rebadge). Here are the mods that made the major improvement:
1. Replaced the caps in the power supply chain with the higher capacitance.
2200uf/25V x 2 => 3300uF/35V x 2
2200uF/16V => 4700uF/16V
3300uF/16V => 4700uF/16V
470uF/16V x 2 => 1000uF/16V x 2
220uF/16V x 2 => 470uF/16V x 2
2. All caps are Panasonic FC, except C223 and C224.
These 2 x 22uF/63V are the output caps after the active LPF.
I replaced them with Silmic II 10uF/35V.
3. At each power pin of the opamp, I added a 120uF/25V cap.
I also added a 0.1uF across pins 4 and 7 to anticipate of dropping
in the opa627 and LME49990.
I also unplugged the head amp and the variable output as I don't use either.
The most noticeable improvement is the mid and the bass. The bass slam is tight and authorative. For about $30 of parts, I will say this is a well worth effort if you one of these player sitting in the closet 🙂
Wrong.
You need one between EACH pin and ground. Otherwise is not efficient, you are pushing HF noise from one rail to another (because transitors in the final stage work alternatelly).
Decoupling 101 - by Analog Devices.
OpAmps proper decoupling - by Analog Devices.
Look at figure 3 on this above document.
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I actually searched this topic quite a bit. My understanding is that the film cap across pin 4 and 7 is to prevent oscillation. The 0.1uF bypass from the power supply pins to ground are not needed if decent caps (especially low ESR caps) are used and soldered near the pins. I will find it out myself whether I will need the bypass to ground.
I can't quantify which change provides the best bang for the bucks. Even with the stock LT1056 opamp, it sounds very good. When I posted last night, it was only 3 hours after I finished the work. If caps break-in does exist, then there should be more improvement to come .....
To honest, the newer and faster opamp will sound different for sure, but I don't have high hope as the current circuit really isn't optimized for these opamps, e.g. the feedbacks network are not optimized.
There is no need for "feedback optimization". Just better power supply rails (since the faster opamps tend to draw more curent).
And no, a cap between 4 and 7 (when the opamp load is connected to the ground) will just increase the garbage on the power rails.
The engineers that wrote those App Notes are those that designed the OpAmps and definitely are not stupid (like some people on this site tend to belive).
And no, a cap between 4 and 7 (when the opamp load is connected to the ground) will just increase the garbage on the power rails.
The engineers that wrote those App Notes are those that designed the OpAmps and definitely are not stupid (like some people on this site tend to belive).
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