An externally hosted image should be here but it was not working when we last tested it.
two questions:
- can anyone tell me what the red surrounded transistor circuit does?
- can around ic207 and ic208 things be improved?
another question
can R223 and C261, R224 and C262 be bypassed.
Since you already have coupling caps for the inpuit of the ic's (C217 and C218). The opamp ic207 gets the signal now straight from the source instead of via ic201 in the original schematic.
can R223 and C261, R224 and C262 be bypassed.
Since you already have coupling caps for the inpuit of the ic's (C217 and C218). The opamp ic207 gets the signal now straight from the source instead of via ic201 in the original schematic.
Hi,
is the red area an auto mute?
and it gets disabled by moving the switch to the upper position.
is the red area an auto mute?
and it gets disabled by moving the switch to the upper position.
The thing is I cannot find sw601 anyware, I traced down where the switch should be connected on thepcb layout in the service manual, but from there a jumper wire is running. So i need to open the preamp tonight to have a look again.
Meanwhile while i'm in there tonight, should i bypass (wire) R223 and C261, R224 and C262?
Anyway Thanks for your help.
Meanwhile while i'm in there tonight, should i bypass (wire) R223 and C261, R224 and C262?
Anyway Thanks for your help.
I think I found it, sw601 is part of the power supply, maybe it is the power on switch, does that make sense for the red circled area?
I bypassed c217/c218 and removed R227/R228.
All the other coupling caps i bypassed with a 1uF wima mkt film cap (6 in total) .
All the other coupling caps i bypassed with a 1uF wima mkt film cap (6 in total) .
My guess now is that the red area is indeed a muting circuit. Does this have the same impact on sound like a muting circuit on the output of a cd player has?
So then it can better be removed from signal path, correct?
So then it can better be removed from signal path, correct?
Hi,
the FET passes the audio signal.
I think it would be better if it didn't.
A changeover relay could do the job better.
or just a shorting single pole relay is probably best of all if the source can stand the short to ground.
the FET passes the audio signal.
I think it would be better if it didn't.
A changeover relay could do the job better.
or just a shorting single pole relay is probably best of all if the source can stand the short to ground.
I bypassed the whole mute circuit this morning and when I listened to it felt like another curtain dissapeared from the sound, more detail, natural high's and a bit better bass.
can it do any damage nog the mute circuit has been bypassed? I don't hear any plops when I turn off the preamp while the power amp is still working.
can it do any damage nog the mute circuit has been bypassed? I don't hear any plops when I turn off the preamp while the power amp is still working.
One more question, I woul dlike to replace the volume control by a dact attenuator, but the closest value available is then 20k instead of the original 25k pot.
Is the value of 20k ok for this circuit as volume control?
Is the value of 20k ok for this circuit as volume control?
Hi,
there is little difference between the 25K and 20K pot values. go ahead if you think this is a good value experiment.
But, before you fit it compare the passive Dact with the active NAD. That comparison might give you some sound references to work with.
there is little difference between the 25K and 20K pot values. go ahead if you think this is a good value experiment.
But, before you fit it compare the passive Dact with the active NAD. That comparison might give you some sound references to work with.
you mean to try out a passive preamp situation?
I already connected my cd player straight up to my power amplifier. This is also my reference sound for the mods to the nad 1300 pre.
The nad 1300 is now sounding nearly the same as a passive situation, it is just a bit more veiled. But the bass has more slam. So it's a compromise.
I already connected my cd player straight up to my power amplifier. This is also my reference sound for the mods to the nad 1300 pre.
The nad 1300 is now sounding nearly the same as a passive situation, it is just a bit more veiled. But the bass has more slam. So it's a compromise.
An externally hosted image should be here but it was not working when we last tested it.
This is the input of my power amp. Since it has dc blocking on the input would it be an idea to remove some dc blocking caps from the preamp?
Hi,
if C109 is better quality than the Pre-amp DC block then get rid of the poorer quality cap. You don't need both.
But, what if you change your equipment. A switchable or pluggable short across the cap gives more flexibility.
if C109 is better quality than the Pre-amp DC block then get rid of the poorer quality cap. You don't need both.
But, what if you change your equipment. A switchable or pluggable short across the cap gives more flexibility.
Both caps are the same quality (yec), so i will remove the ouptut cap from the preamp.
Making it switchable is actually a good idea, mm just have to see how to sort that out nicely on this pre.
The cap in between the opamps, is that also an option to remove?
Making it switchable is actually a good idea, mm just have to see how to sort that out nicely on this pre.
The cap in between the opamps, is that also an option to remove?
Hi,gy21 said:
measure the DC at the cap and after the second opamp.
The circuit may demand DC blocking here.
Try temporarily shorting it and measure DC again.
I replaced C279/C280 by a wire. When I measure dc at those wires I measure 0.9 and 0.4 mV.
At the positive side of cap C266/C265 I measure 0.8mV and 1.2mV.
So not a lot of dc offset I think.
One other thing. When I inserted 4 AD843's (on browndogs) tonight I get atrsnage crackling noise (quite loud) when I turn the volume all the way down, this happens at the lowest part of the volume control.
I out the opa2132's back in and the issue is gone. I found out that only a AD843 couple in IC208 position is causing it.
Any idea what this can be?
At the positive side of cap C266/C265 I measure 0.8mV and 1.2mV.
So not a lot of dc offset I think.
One other thing. When I inserted 4 AD843's (on browndogs) tonight I get atrsnage crackling noise (quite loud) when I turn the volume all the way down, this happens at the lowest part of the volume control.
I out the opa2132's back in and the issue is gone. I found out that only a AD843 couple in IC208 position is causing it.
Any idea what this can be?
yes but only when an ad843 couple is in ic208. With every other opamp i've tested there is zero crackling.
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