Hello everybody,
this is my first posting on this forum, however I've read a lot from this forum in past years. So please be patient with me 😱
I've just bought a project CD player, Pioneer PD-7700, to start to improve the sound from this unit, which is one of lower rank of Stable Platter units (below 8700 and 9700 etc.).
It has single DAC unit, PD2026A, which I really want to hear in it's "glory", as from what I've read, it should not be bad sonically afterall. Now the sound of CDP is something which is not worth mentioning. It has only one PCB and is quite easy to work. Right now I'm on tight budget, so I will not install clock or build secont power supply for it (like 8700 and 9700 has).
Plan: First replace opamp NJM5532 with LM4562 and two capacitors after it, replace some nearest caps of DAC too, and then remove unwanted muting transistors.
The muting transistor schematic is very complicated, and I wanted to have some input from you how to proceed with it? Completely remove all Q401-Q404 and Q453/Q454 ?? Or just install new RCA connectors and wire to them directly after opamp IC402 ?
Please check this and give me input, as all other Stable platter players are very different in this analog output section.
this is my first posting on this forum, however I've read a lot from this forum in past years. So please be patient with me 😱
I've just bought a project CD player, Pioneer PD-7700, to start to improve the sound from this unit, which is one of lower rank of Stable Platter units (below 8700 and 9700 etc.).
It has single DAC unit, PD2026A, which I really want to hear in it's "glory", as from what I've read, it should not be bad sonically afterall. Now the sound of CDP is something which is not worth mentioning. It has only one PCB and is quite easy to work. Right now I'm on tight budget, so I will not install clock or build secont power supply for it (like 8700 and 9700 has).
Plan: First replace opamp NJM5532 with LM4562 and two capacitors after it, replace some nearest caps of DAC too, and then remove unwanted muting transistors.
The muting transistor schematic is very complicated, and I wanted to have some input from you how to proceed with it? Completely remove all Q401-Q404 and Q453/Q454 ?? Or just install new RCA connectors and wire to them directly after opamp IC402 ?
An externally hosted image should be here but it was not working when we last tested it.
Please check this and give me input, as all other Stable platter players are very different in this analog output section.
Everyone will have their own ideas on this... so here are mine.
I would suggest trying an OPA2604 opamp as well as the LM4562 because the 2604 being FET input might behave a little better (audibly) with the hf hash from the DAC. And out of all the devices available it really is one that has a "different" non aggressive sound.
The muting circuit is simple 🙂 The four devices on the right are all in parallel as regards their drive circuitry. If you remove them its up to you if any pops and thumps are tolerable. The other two (left hand ones) are driven independently and that suggests this is an older player that catered for all the possibilities the red book standard allowed such as being able to select different soundtracks on L and R channels etc. I note they are PNP devices too. Again its up to you if the loss of functionality is acceptable.
You could look at replacing the transistors with FET's if the drive voltage was suitable but that's a bit more advanced.
I would suggest trying an OPA2604 opamp as well as the LM4562 because the 2604 being FET input might behave a little better (audibly) with the hf hash from the DAC. And out of all the devices available it really is one that has a "different" non aggressive sound.
The muting circuit is simple 🙂 The four devices on the right are all in parallel as regards their drive circuitry. If you remove them its up to you if any pops and thumps are tolerable. The other two (left hand ones) are driven independently and that suggests this is an older player that catered for all the possibilities the red book standard allowed such as being able to select different soundtracks on L and R channels etc. I note they are PNP devices too. Again its up to you if the loss of functionality is acceptable.
You could look at replacing the transistors with FET's if the drive voltage was suitable but that's a bit more advanced.
Thank you very much Mooly!
As a novice I got many new hints from your message. I will try OPA2604 on this CD. I will put DIP socket on the board, so I can try also OPA2107 on this too. There is also spare 627 from Audio-GD dac somewhere as couple different HDAM's from them.
Muting circuit is indeed simple, thank you for pointing this out. I was just surprised to find so many transistors, but the age of the device indicates that it must have been to comply with Red Book specs as you kindly noted out.
I'm willing to try without muting stuff, but I will check FET versions too for future reference.
First I have to concentrate on power supply too. Low ESR capacitors are ordered already.
Cheers,
hiisku
As a novice I got many new hints from your message. I will try OPA2604 on this CD. I will put DIP socket on the board, so I can try also OPA2107 on this too. There is also spare 627 from Audio-GD dac somewhere as couple different HDAM's from them.
Muting circuit is indeed simple, thank you for pointing this out. I was just surprised to find so many transistors, but the age of the device indicates that it must have been to comply with Red Book specs as you kindly noted out.
I'm willing to try without muting stuff, but I will check FET versions too for future reference.
First I have to concentrate on power supply too. Low ESR capacitors are ordered already.
Cheers,
hiisku
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