Whilst composing the previous reply you seem to have reached a similar conclusion
I have to agree with your opinion of the sound’s character via the direct output option.
The gain is unity though so it will sound softer than via the active output’s
The original output buffers are absolute rubbish IMO. Replacing them could only help
The only problem is that, if memory serves the power supplies were uni-polar most of the good op-amps are happier running off a bipolar (split) power supply.
I have to agree with your opinion of the sound’s character via the direct output option.
The gain is unity though so it will sound softer than via the active output’s
The original output buffers are absolute rubbish IMO. Replacing them could only help
The only problem is that, if memory serves the power supplies were uni-polar most of the good op-amps are happier running off a bipolar (split) power supply.
Hi,
If you are right, then the designer seems to have made a decision to save on the PSU and AC couple all the stages.
I suspect his solution was not cheap.
If you plan to add a buffer for the pre output then consider a discrete opamp. They are reputed to sound a lot better, even though the specs do not match a good quality, expensive opamp.
5532 being a dual is a bit compromised for two output buffers and worse if you decided to bias the output stages into ClassA.
this would explain why there are so many caps installed all over the board.
If you are right, then the designer seems to have made a decision to save on the PSU and AC couple all the stages.
I suspect his solution was not cheap.
If you plan to add a buffer for the pre output then consider a discrete opamp. They are reputed to sound a lot better, even though the specs do not match a good quality, expensive opamp.
5532 being a dual is a bit compromised for two output buffers and worse if you decided to bias the output stages into ClassA.
Hi,
Yes, my preamp has the two sets of outputs also - buffered/direct. After listening to both I think the buffered outputs really do sound better. So, I'll need to do something about the situation. I believe you're right about the single supply.
I had hoped that the MC circuit opamps would have had a split supply but unfortunately they don't. The transformer is external, but not the entire power supply. If brings in AC ~30v and that gets rectified on the main board. I would imagine it's possible to generate a split supply quite easily from this?
The other option is simply replace the existing buffer transistors with something a bit flashier. the buffer circuit (from the top of the board at least) looks like a transistor, a resistor, a poly cap and an electrolytic so it should't be hard to replace them all if needs be. I think I'd rather put a niceish opamp in though.
Correct me if I'm wrong, but I think you could run the opamp from a single supply, biasing the input (I did this in a guitar effect pedal). Though, would the DC blocking cap have an effect on the muscialness?
Yes, my preamp has the two sets of outputs also - buffered/direct. After listening to both I think the buffered outputs really do sound better. So, I'll need to do something about the situation. I believe you're right about the single supply.
I had hoped that the MC circuit opamps would have had a split supply but unfortunately they don't. The transformer is external, but not the entire power supply. If brings in AC ~30v and that gets rectified on the main board. I would imagine it's possible to generate a split supply quite easily from this?
The other option is simply replace the existing buffer transistors with something a bit flashier. the buffer circuit (from the top of the board at least) looks like a transistor, a resistor, a poly cap and an electrolytic so it should't be hard to replace them all if needs be. I think I'd rather put a niceish opamp in though.
Correct me if I'm wrong, but I think you could run the opamp from a single supply, biasing the input (I did this in a guitar effect pedal). Though, would the DC blocking cap have an effect on the muscialness?
AndrewT said:
Thanks Andrew,
I'm in the process of buying a Marantz CD63 (that I also plan to modify 🙂 ) would copying the HDAM circuit be a good starting point? The HDAM is supposedly a discret opamp circuit.
Ashley
Hi,
you can run a chip opamp or a discrete opamp from single supply rail.
But you need to block any unmatched DC levels from stage to stage. Which is why you have all those 1uF and 220nF caps around the PCB.
A simple EF buffer should work and fairly quietly at that.
I think you should try replacing the transistors with new equivalents, just in case they have been damaged in the past. The outputs could have been shorted and upset the transistor characteristics.
you can run a chip opamp or a discrete opamp from single supply rail.
But you need to block any unmatched DC levels from stage to stage. Which is why you have all those 1uF and 220nF caps around the PCB.
A simple EF buffer should work and fairly quietly at that.
I think you should try replacing the transistors with new equivalents, just in case they have been damaged in the past. The outputs could have been shorted and upset the transistor characteristics.
Thanks again Andrew,
I'll pop the old transistors out at the weekend and see what I've got to replace them.
I'll pop the old transistors out at the weekend and see what I've got to replace them.
Hi,
Just add that for a CD players its hard to beat no circuitry
at all for performance versus cost. Depending on the topology
of the pre-amplifier and the value of the volume potentiometer
(which could be reduced and upgraded at the same time) and
keeping the cabling short it should be possible to make the
CD input / output entirely passive and better than the buffered
output.
Changing the transistors in the buffer will not change its
inherent linearity (assuming its as simple as stated) but
depending on the circuit noise may be improved.
🙂/sreten.
Just add that for a CD players its hard to beat no circuitry
at all for performance versus cost. Depending on the topology
of the pre-amplifier and the value of the volume potentiometer
(which could be reduced and upgraded at the same time) and
keeping the cabling short it should be possible to make the
CD input / output entirely passive and better than the buffered
output.
Changing the transistors in the buffer will not change its
inherent linearity (assuming its as simple as stated) but
depending on the circuit noise may be improved.
🙂/sreten.
Thanks. Noise was the first issue. Now I'm using the direct outputs they are quiter on the noise front but just don't sound as good. I'm going to try swapping the transistors first, to see how that affects things. then perhaps I'll build an opamp buffer.
Hi,
Without a full overview of the topology and the volume pot value its
hard to be accurate. Fully passive should be your best option for CD.
🙂/sreten.
Without a full overview of the topology and the volume pot value its
hard to be accurate. Fully passive should be your best option for CD.
🙂/sreten.
I'm talking about the preamp outs being active or passive. Not the inputs, so I see what you're saying that in terms of CDP to pre connectivity, less is more so to speak. But the transistors I was on about changing are for the outputs, I don't see that is would make any difference to the input. Or am I missing something??
Thanks again 🙂
Thanks again 🙂
Hi,
presumably the line inputs are passive connected i.e. direct to
the volume control (via the input selector), then either active
(noisy) or passive (no noise) to the output.
So overall its passive or active for CD.
For passive the volume potentiometer value matters.
🙂/sreten.
presumably the line inputs are passive connected i.e. direct to
the volume control (via the input selector), then either active
(noisy) or passive (no noise) to the output.
So overall its passive or active for CD.
For passive the volume potentiometer value matters.
🙂/sreten.
Ah ha. I see.
Well, I've not looked specifically at the input side of the circuit but it doesn't look like they're buffered inputs. I presume that, in this case, the pot value matter because it defines (in part?) the input impedance, thus the loading on the outputs of the CD player ?
You can see part of the amp here: http://hoshy.co.uk/~hoshy/amp/p3a.jpg
The metal rod is the input selector, the op amps are for the MC circuit (now removed) - just beneath there are two more transistors and assoc. circuitry, I don't know if that's an input buffer for all of the inputs, or part of the MC circuit. I think at some point I'm going to need to make a schematic of this amp. That will be an undertaking and a half for me (uber newbie 🙂 )
Well, I've not looked specifically at the input side of the circuit but it doesn't look like they're buffered inputs. I presume that, in this case, the pot value matter because it defines (in part?) the input impedance, thus the loading on the outputs of the CD player ?
You can see part of the amp here: http://hoshy.co.uk/~hoshy/amp/p3a.jpg
The metal rod is the input selector, the op amps are for the MC circuit (now removed) - just beneath there are two more transistors and assoc. circuitry, I don't know if that's an input buffer for all of the inputs, or part of the MC circuit. I think at some point I'm going to need to make a schematic of this amp. That will be an undertaking and a half for me (uber newbie 🙂 )
Hi,
A schematic is going to be hard work for a "newbie".
Best to start off with a "block diagram", psu block(s), tape buffer
block (pre volume control), volume + balance block, MC step up block,
MM RIAA block and line stage block. May also be a muting block.
Most of the routing for these can be gained by inspecting the tracks.
I suspect what you think is the output buffer may be muting.
🙂/sreten.
A schematic is going to be hard work for a "newbie".
Best to start off with a "block diagram", psu block(s), tape buffer
block (pre volume control), volume + balance block, MC step up block,
MM RIAA block and line stage block. May also be a muting block.
Most of the routing for these can be gained by inspecting the tracks.
I suspect what you think is the output buffer may be muting.
🙂/sreten.
I'll try a block diagram first, sounds more within my grasp.
On the photo you can't see as it's in the shadow, but, at the top right of the picture you can see the two outputs, and the muting relays. I didn't suspect that the transistors were part of that circuit but you could be right. Clearly, this requires more investigation 🙂
I'll try and make a start this evening (2h40m remaining at work 🙂 )
Thanks again,
Ashley
On the photo you can't see as it's in the shadow, but, at the top right of the picture you can see the two outputs, and the muting relays. I didn't suspect that the transistors were part of that circuit but you could be right. Clearly, this requires more investigation 🙂
I'll try and make a start this evening (2h40m remaining at work 🙂 )
Thanks again,
Ashley
Hi,
that last thought does seem more feasible.
The transistors are controlling the muting relays?
that last thought does seem more feasible.
The transistors are controlling the muting relays?
Hi,
VQ1000J - checked specs last night - no use at all regarding noise
as the specs are essentially for a low Ron switch - you'll have to
assume MF knew what they were doing.
🙂/sreten.
VQ1000J - checked specs last night - no use at all regarding noise
as the specs are essentially for a low Ron switch - you'll have to
assume MF knew what they were doing.
🙂/sreten.
Interesting. they did the same with the power amp. They used LM318 op amps, after I replaced them the amp really opened up.
Any options that I can try in replacement of the VQ1000Js ?
Any options that I can try in replacement of the VQ1000Js ?
preamp 3A
Hi there from France,
I carefully read all was written here about the preamp 3A. I am the owner of one and have the same issue with important level of noise audible when power amplifier is connected to the active output. I agree to say this active out is more musical than passive output, so I prefer to use it as well.
The last forum discussion ended with the AQ1000J I.C. which seemed to be the heart of the noise issue. Have you improve furthermore your investigations on it ? Do you find a close replacement IC since ? Any info is very welcome.
I use Rega P3 / Rega planet 2000 / MF Preamp 3A / Cayin 4xEL34 power amp
Hi there from France,
I carefully read all was written here about the preamp 3A. I am the owner of one and have the same issue with important level of noise audible when power amplifier is connected to the active output. I agree to say this active out is more musical than passive output, so I prefer to use it as well.
The last forum discussion ended with the AQ1000J I.C. which seemed to be the heart of the noise issue. Have you improve furthermore your investigations on it ? Do you find a close replacement IC since ? Any info is very welcome.
I use Rega P3 / Rega planet 2000 / MF Preamp 3A / Cayin 4xEL34 power amp
Hi Diclem,
that is the wrong conclusion.
Hoshy seemed convinced that only the buffered output had a noise problem.
This appeared to be down to those two transistors or the muting relays.
I hope he confirms what solved the problem.
The VQ1000j dil may be a switch, possibly to do with bringing in the vinyl pre-pre stage.
that is the wrong conclusion.
Hoshy seemed convinced that only the buffered output had a noise problem.
This appeared to be down to those two transistors or the muting relays.
I hope he confirms what solved the problem.
The VQ1000j dil may be a switch, possibly to do with bringing in the vinyl pre-pre stage.
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