default mods to preamp?

[gy21]

are there any default mods that can be done to a preamp? I have a nad 1300 and I would like to upgrade it a bit, better opamps etc etc.

Does anyone have some tips?

 

[Jan Dupont]

First thing to look at is the power supply and all the caps used in the preamp.

 

[gy21]

here is the schematic for the nad1300, can anyone point me out some areas and maybe how to improve them

nad1300schematic

I replaced the opamps ic207 and ic208 (jrc2043) with ad823 opamps wich i had from this thread http://www.diyaudio.com/forums/showthread.php?s=&threadid=77540 .

the ad823 are know for a bit agressive highs, wich i liked in the nad1300, beacause of my current a bit darker sounding speakers.

i wil also try out ad8620 in this area.

 

[Jan Dupont]

Hotlinking not permitted ???
Can you download and post the schematic here ?

 

[gy21]

Nad1300 schematic

i'm sorry, this is the correct link.

 

[AndrewT]

Thanks for sorting the link.
I begin to wonder what comes out after passing through all that circuitry and switches? Is it still music?

 

[gy21]

it is still music, i use the switches to bypass everything that is possible, so no tone control and infra circuit is also bypassed.

 

[AndrewT]

That then begs the question:-
what discrete opamps and IC opamps are still in use?

 

[gy21]

i agree, that's what I would like to know as well.

I would like to cleanup the signal path, but I'm not sure howto.

 

[gy21]

my guess is that only ic201 and ic 207 and ic208 are in use if you activate all the bypass switches.

 

[gy21]

I removed several opamps (ic201, ic202, ic209), the whole ic201 circuit is bypassed with a wire, simply removing ic201 is not working, the other ic's could be simply removed.

so the only working ic's now are ic207 and ic208 (tone circuit ic's are bypassed with switch)

Does anyone know what the ic201 circuit does?

 

[carlmart]

I removed several opamps (ic201, ic202, ic209), the whole ic201 circuit is bypassed with a wire, simply removing ic201 is not working, the other ic's could be simply removed.

so the only working ic's now are ic207 and ic208 (tone circuit ic's are bypassed with switch)

Does anyone know what the ic201 circuit does?

Well, it looks as if ic201 is the line input amp.

But I agree with the comment: what do you get after all those switches? Distortion and dirt too, probably. Too many small inductors too, probably to tame oscillations.

I can't quite get what you bypassed where. That preamp really looks like a complicated way to deal with a signal. Cleaning some switches and caps away might improve things a lot.

I don't think you should use a preamp to to tame dark speakers, but if it works for you...

 

[gy21]

so it would be a good idea to remove some switches from the circuitry?

do you need a line input amp in a preamp?

ic202 is for the null circuit (don't need it)
ic209 is for the bass boost (don't need it)

it was not my intention to tame dark speakers, just to upgrade the essential opamps, as benefit it suits my speakers a bit better, i actually already moved away from the bright ad823 to the more neutral ad8620.

 

[carlmart]

Yes, you need at least a line amp and/or a buffer on a preamp. If not you don't really need the extra step between your source and the power amp.

What amp are you using after the Nad? If it has an input stage, with a buffer, you may feed your signal directly, just using a switch to select the source.

I must confess I got a bit lost trying to follow the Nad's signal path and how to improve it. I believe in simple paths, perhaps using just a buffer for volume/balance isolation or a 5x or 10x amplifying.

So I think you should see what stage serves you better and bypass the rest, including passive parts before the chips. Perhaps using a cable with clips on one side and an RCA on the other, feeding the power amp.

Sorry if this sound too radical.

 

[gy21]

i think, but correct me if i'm wrong, that ic207 and ic208 also act like an amp and/or buffer circuit. i'm not exactly sure what ic201 does extra in that other then that the infra circuit is attached to it.

i had this info form this thread, that person also had only the ic207 as active part in the preamp.

http://www.diyaudio.com/forums/showthread.php?s=&threadid=77540

the amp's i use after it are two nad 2600pe power amps.

 

[gy21]

I think I found out what ic201 does, it functions as line amp/buffer to drive the tape decks, the actual preamp line comes after the tape deck switches and connectors and goes to ic207.

so the best thing to do is to bypass all the tape deck switches and connectors by bypassing this whole are and connect straight to ic207.

one question on the coupling caps c217 and c279 (for example), since there are elctrolytes in the signal pat can i just bypass them, or is it better to replace those with higher quality caps?

 

[AndrewT]

Hi,
bypass the coupling electros with 2u2F PES film soldered under the PCB direct to the electro pads.
If you use PP film then they are much bigger and you may have difficulty getting even 1uF to fit.

 

[gy21]

bypass the coupling electros with 2u2F PES film soldered under the PCB direct to the electro pads.

ok thanks, is that better then completely bypassing them? can you explain?

anyway thanks for the help.

 

[AndrewT]

Hi,
will you ever want to use the majority of facilities in this pre-amp?

I am wondering if the case and PSU becomes a support for a new much simplified active pre-amp with the fewest facilities that you need.

 

[gy21]

Hi,
will you ever want to use the majority of facilities in this pre-amp?

I am wondering if the case and PSU becomes a support for a new much simplified active pre-amp with the fewest facilities that you need.

your right, most facilities i don't need in this preamp and are going to be removed out of the circuitry.

and again your right it, the basic preamp designs stays, only with simplified (less options) design and better components, that's my goal for this one.