A few months ago i found this CD player in a scrap metal shop.I bought it with 0.2 pennies /kg...It wasn't working.I found a dead -5v regulator giving -4v , some dried capacitors too and one dead optical coupler .Yesterday i changed one HCPL2631 for a HP4661. Today i replaced both optical couplers for data/clock/le to be identical, as hp4661 looks superior , the third one being for de-emphasis.
As you can see in the schematic they use a different type of low pass filter than most players do.
You have here the only meaningful review Google could find me on this item
NEC CD-810 CD-player review, test, price
Now I'm going to recap the whole thing if needed, but most important i need to make a different external i/v stage to pcm56 although, to be honest this player sound is quite good as it is.
There's even one bigger surprise : the headphones amp done with upc4570c has an unexpectedly good sound and I have the impression of a wider stereo imaging than the one i have when i use my tpa6210 headphones amp on line output which is interesting!
Actually i have a lot of respect for this small op-amp made by NEC too and used in very critical places with better performance than many well known op-amps.
I replaced the ne5532 with njm2043 just because i could , but there's no reason behind it other that i didn't know where i put the old ne5532.I'd probably go with LM4562 for the filters and buffers.
I have a good idea for an i/v stage, but now I'm elaborating on it.By tomorrow i might come back with a solution.
PS:
as a small note, the 680pF capacitors in the second filter are actually 620pF
As you can see in the schematic they use a different type of low pass filter than most players do.
You have here the only meaningful review Google could find me on this item
NEC CD-810 CD-player review, test, price
Now I'm going to recap the whole thing if needed, but most important i need to make a different external i/v stage to pcm56 although, to be honest this player sound is quite good as it is.
There's even one bigger surprise : the headphones amp done with upc4570c has an unexpectedly good sound and I have the impression of a wider stereo imaging than the one i have when i use my tpa6210 headphones amp on line output which is interesting!
Actually i have a lot of respect for this small op-amp made by NEC too and used in very critical places with better performance than many well known op-amps.
I replaced the ne5532 with njm2043 just because i could , but there's no reason behind it other that i didn't know where i put the old ne5532.I'd probably go with LM4562 for the filters and buffers.
I have a good idea for an i/v stage, but now I'm elaborating on it.By tomorrow i might come back with a solution.
PS:
as a small note, the 680pF capacitors in the second filter are actually 620pF
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Well...after i discovered the Technics class AA buffer stage i wanted to try it the best possible way for me and here is the result.
I clearly didn't go the usual way trying to simplify everything.I kept the original filters and buffers , replaced the ne5532 with lm4562 although the slightly higher current noise of the lm4562 in this schematic does add some noise but not one that i can hear right now...
I used the op-amp inside the PCM 56 to offer the ground for the i/v stage and used external feedback resistor unlike the Technics solution as the internal resistor in both pcm56 was different in value: 3k67 vs 3k9.I used slightly higher value, a 4k3 as i had higher power supply for the external op-amps(+-12v...actually 11.7...11.5 after the trc filter ).
I also corrected a small mistake i did in the first schematic. and made both optical couplers the same and better than the original, the HPmcp4661, faster version .I also added better decoupling on their pins on the pcb back as the player manufacturer didn't take care about it and obviously that was the cause of one optical coupler failure.It had just 10nf decoupling where the datasheet saud 100nf would be needed for the slower version, the original 2631.Now i have about 600nf as decoupling.
Now i need to take care of the original case as i want to make a different upper lid giving some more air to the electronics inside .I'll probably build a grill over the electronics area and completely enclose only the transport-transformer area.
This is truly a good sounding player .I just can't find anything wrong in it for the moment as i just finished the analog part work a few hours ago.
I also need to find the power button plastic cover which i lost somewhere...I'll probably build a new one and glue it in place.
I just foud 4 x pcm61 in a broken denon dn 2000 and i wonder if there would be any benefit in replacing each pcm56 with two paralleled pcm61 or transform the single ended version in a balanced one...For now i just enjoy it as it is.
I clearly didn't go the usual way trying to simplify everything.I kept the original filters and buffers , replaced the ne5532 with lm4562 although the slightly higher current noise of the lm4562 in this schematic does add some noise but not one that i can hear right now...
I used the op-amp inside the PCM 56 to offer the ground for the i/v stage and used external feedback resistor unlike the Technics solution as the internal resistor in both pcm56 was different in value: 3k67 vs 3k9.I used slightly higher value, a 4k3 as i had higher power supply for the external op-amps(+-12v...actually 11.7...11.5 after the trc filter ).
I also corrected a small mistake i did in the first schematic. and made both optical couplers the same and better than the original, the HPmcp4661, faster version .I also added better decoupling on their pins on the pcb back as the player manufacturer didn't take care about it and obviously that was the cause of one optical coupler failure.It had just 10nf decoupling where the datasheet saud 100nf would be needed for the slower version, the original 2631.Now i have about 600nf as decoupling.
Now i need to take care of the original case as i want to make a different upper lid giving some more air to the electronics inside .I'll probably build a grill over the electronics area and completely enclose only the transport-transformer area.
This is truly a good sounding player .I just can't find anything wrong in it for the moment as i just finished the analog part work a few hours ago.
I also need to find the power button plastic cover which i lost somewhere...I'll probably build a new one and glue it in place.
I just foud 4 x pcm61 in a broken denon dn 2000 and i wonder if there would be any benefit in replacing each pcm56 with two paralleled pcm61 or transform the single ended version in a balanced one...For now i just enjoy it as it is.
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I needed to come back to say something that bugles me for a while...This is the second player where, when i use a lm6172 i have the impression that the base is thinner than when i use any other op-amp and i mean ANY OTHER op -amp!
I just replaced the lm6172 with various op-amps and all of them have a better base presentation, not a huge difference, but clearly a difference.
I replaced lm4562 and op2132(two different stages-i/v and voltage buffer) in my favorite Denon dcd1560 with lm6172 and the base is gone .
Came back at opa2132 and lm4562 and the base is back.Its very true that lm6172 is the best at reproducing highs, but i think now that a circuit using lm6172 needs a base boost or something...I used it in i/v for tda1541 , it performed the same, lower base and it cannot complain of not being given a low enough input impedance.
Now i'm trying every single op-amp i have in the load bootstrap section figured by the lm6172 in my schematic and i'll come back with the best config i can evaluate.You shouldn't take my advice as the norm though...I'm just one in 7 billion people who's spending a very beautiful Saturday rolling op-amps.
I just replaced the lm6172 with various op-amps and all of them have a better base presentation, not a huge difference, but clearly a difference.
I replaced lm4562 and op2132(two different stages-i/v and voltage buffer) in my favorite Denon dcd1560 with lm6172 and the base is gone .
Came back at opa2132 and lm4562 and the base is back.Its very true that lm6172 is the best at reproducing highs, but i think now that a circuit using lm6172 needs a base boost or something...I used it in i/v for tda1541 , it performed the same, lower base and it cannot complain of not being given a low enough input impedance.
Now i'm trying every single op-amp i have in the load bootstrap section figured by the lm6172 in my schematic and i'll come back with the best config i can evaluate.You shouldn't take my advice as the norm though...I'm just one in 7 billion people who's spending a very beautiful Saturday rolling op-amps.
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For the second op-amp on Technics class AA stage I tried njm2043, njm2114, njm4562, lm4562, ne5532(TI), opa2132, lm833, op275, lm6172, opa2228.
Lm4562 and lm833 stood out , but i really regret for the lm6172 not being able to deliver on the base side as it surpasses every other op-amp except at deep base reproduction. Lm4562 is very good at unity gain as i said for many times.
lm6172 is simply incapable of scrambling the highs, but seems to have no talents below 50hz in my circuits which is really weird given the output capability on 100ohms.
ne5532 was the worst sounding of all except opa2228 which is not unity gain stable, unless all the music used for tests was crap and ne5532 is true .
By the way...to give pure objectivists a chance on ne5532(new Texas Instruments purchased 3 months ago from Mouser) , i used Christina Aguillera Back to basics and Shania Twain Come on over for my subjective tests.
Lm4562 and lm833 stood out , but i really regret for the lm6172 not being able to deliver on the base side as it surpasses every other op-amp except at deep base reproduction. Lm4562 is very good at unity gain as i said for many times.
lm6172 is simply incapable of scrambling the highs, but seems to have no talents below 50hz in my circuits which is really weird given the output capability on 100ohms.
ne5532 was the worst sounding of all except opa2228 which is not unity gain stable, unless all the music used for tests was crap and ne5532 is true .
By the way...to give pure objectivists a chance on ne5532(new Texas Instruments purchased 3 months ago from Mouser) , i used Christina Aguillera Back to basics and Shania Twain Come on over for my subjective tests.
Back to bass-ics 
I started with a first of 4 sims i thought would solve the lm6172 poor rendering of bass region so i modified the feedback network of i/v stage accordingly.The second op-amp in the sim is lm6172 while the first is opa2132 .I just used readily available fet-bipolar op-amps from Spice library as it was easier for evaluation.
Now i can enjoy Kate Bush...Aguillera simply killed my ears, but it was a good record for bass evaluation that i knew already.
The bass is a bit more than i need now, but acceptable for the moment.I'll probably go for milder boosts than the first one(4k9 -470nf).
And yes...i eat on my laptop...it's real food on it ! And i'm paranoid too , covering its camera...Guilty as charged!
Well...this laptop lived with me in a tent and on a touring bike for six months too, three years ago.It's a real soldier.
Army dreamers...
I started with a first of 4 sims i thought would solve the lm6172 poor rendering of bass region so i modified the feedback network of i/v stage accordingly.The second op-amp in the sim is lm6172 while the first is opa2132 .I just used readily available fet-bipolar op-amps from Spice library as it was easier for evaluation.
Now i can enjoy Kate Bush...Aguillera simply killed my ears, but it was a good record for bass evaluation that i knew already.
The bass is a bit more than i need now, but acceptable for the moment.I'll probably go for milder boosts than the first one(4k9 -470nf).
And yes...i eat on my laptop...it's real food on it ! And i'm paranoid too , covering its camera...Guilty as charged!
Well...this laptop lived with me in a tent and on a touring bike for six months too, three years ago.It's a real soldier.
Army dreamers...
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Thought of trying milder bass boost and tried 100nfm200nF-8k2(NO WAY!) and 450nf-8k2...a bit too soft, now listening in progress for 6k49-450nF(muse electrolitic real value)
I can say that with the 450nF-4k9 combination the bass is really deep , just that you can't fully enjoy some jazz with very low chord vibrations, too much bass in that case.Let's say i can listen Norah Johnes with 470nF-8k2 and Aguillera on 470nF-4k9.
So i settled in between with 6k49-470nF .That's where Loreena McKennitt and most of the good music sits for my ears.
Most probably i'll be having a variable bass boost in the heart of the i/v converter, a 3k9 resistor series with a 5k pot and 470nf for the wildest dreams.
I don't know why so few manufacturers implemented the de-emphasis filter in the feedback of I/V stage...that stage is perfect to be used to implement all the filters you might think of especially if you have a fet op-amp but probably at the time when these players were on the wave there was no fet-op-amp good enough for the job.In a way there aren't perfect fet op-amps for the job today either.
So Lm6172 isn't a disaster at bass reproduction, but you need this bass boost with this op-amp for sure.The rest is simply perfect with it.It will reproduce anything in the mid-highs area perfectly if i haven't said that enough
I can say that with the 450nF-4k9 combination the bass is really deep , just that you can't fully enjoy some jazz with very low chord vibrations, too much bass in that case.Let's say i can listen Norah Johnes with 470nF-8k2 and Aguillera on 470nF-4k9.
So i settled in between with 6k49-470nF .That's where Loreena McKennitt and most of the good music sits for my ears.
Most probably i'll be having a variable bass boost in the heart of the i/v converter, a 3k9 resistor series with a 5k pot and 470nf for the wildest dreams.
I don't know why so few manufacturers implemented the de-emphasis filter in the feedback of I/V stage...that stage is perfect to be used to implement all the filters you might think of especially if you have a fet op-amp but probably at the time when these players were on the wave there was no fet-op-amp good enough for the job.In a way there aren't perfect fet op-amps for the job today either.
So Lm6172 isn't a disaster at bass reproduction, but you need this bass boost with this op-amp for sure.The rest is simply perfect with it.It will reproduce anything in the mid-highs area perfectly if i haven't said that enough
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Thank you!Unfortunately my experience in both phono mm preamps and cassette tapeheads(pioneer ct-777) reversed those lines for opa2132 and opa1642 as i tried them both.The lowest noise were njm2043 , 2114 and m5220 in all configurations with both cassette tape preamps and phono mm preams! Yes, BJT input op-amps were lower noise than their fet counterparts with relatively high input impedances even though it appeared that they choosed those op-aps only for their output drive capabilities on low impedances to aquire low noise.njm2068 is the weakest of them, but with higher gains they perform very well. The fact that most good cassette players used m5220 should speak for itself.
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Was just reading through this thread thinking that the 2068 might be worth trying, is always one I try along with the 2114 when replacing the fuzzy sounding ne5532.
Have you tried the 1612 yet?
Some bipolar opamps work better when decoupled using a small .01uf film across the rails only, and then the typical 10-47uf from each rail to ground.
Have you tried the 1612 yet?
Some bipolar opamps work better when decoupled using a small .01uf film across the rails only, and then the typical 10-47uf from each rail to ground.
Never tried opa1612 in my own circuits, just once in the past and i remember it was very good, but expensive at the time. I'm using floating ground now in every single circuit i make .Just some good capacitors with a 51...100k resistor across them after the rectifier bridge to give enough current for any op-amp bias, then a first order rc filter made with 10...33 ohms resistors series on rails with one low esr capacitor between +_ rail pins on every op-amp and that's all. 2114 dark sound is one of the sweetest one. Dark and silent knight. There are some more op-amps i like , as upc4570 but i don't want to make a case for op-amps here.
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