Modding a SS preamp

[Slim-Shaddy]

I have an Onkyo P-308 preamp that I would like to modify. What modifications would you recommend? One idea that crossed my mind was adding a set of tube outputs. I don't know if this is feasible, or even possible, but if I could have a set of tube and a set of SS outputs, that would be cool. I've never really modified anything before, so any suggestions would be helpful.

Sparky.

[OldiesButGoodies]

that sounds risky.  that pre is using opamps in the output stage that maybe you can upgrade (ad744jn I think).  if they are soldered in Tomas can remove them and put a few sockets on the board.  I entertain myself buying different opamps on ebay for the c-19 and seeing how they sound.  inexpensive.  you could also get a tube buffer stage (like a musical fidelity) to put in between the pre and the power amp but that be adding a stage which may be an issue if you are a purist. I imagine you could try replacing the op amps w a tube output stage,  though that sounds like an Anders level task. I say play with op amps or upgrade the coupling caps,  and avoid the sargent solder syndrome whereby any part near a replaced coupling cap gets heat-treated  .

pepe

[schwarcw]

Sparky, Pepe is offering some good advice on the tube buffer.  Personally, I would go directly to a tube preamp, and a solid state amplifier.

I would like to ask, what is it that you are wanting to hear that is prompting this idea for a tube output stage on your preamp?  What are you trying to accomplish?  The reason that I am asking is that tubes might not give you what you want.

[Slim-Shaddy]

I like the sound of this preamp a lot, but it's older, and I think it could benefit from some upgrades. If I could soften the sound a tad, it might be an improvement, but I can't say for sure unless I hear it. That's where the idea of having both tube and SS outputs comes in. Plus it would be cool to have the ability to switch between the two on the same preamp. It's really just an idea. As far as other, much simpler mods or upgrades, I'm open to ideas.

[Sir Thrift-a-Lot]

I like the sound of this preamp a lot, but it's older, and I think it could benefit from some upgrades. If I could soften the sound a tad, it might be an improvement, but I can't say for sure unless I hear it. That's where the idea of having both tube and SS outputs comes in. Plus it would be cool to have the ability to switch between the two on the same preamp. It's really just an idea. As far as other, much simpler mods or upgrades, I'm open to ideas.

Try one of those $500 power cables.   They seem to work well with gear that already sounds nice.

[F1nut]

  I've never really modified anything before, so any suggestions would be helpful.   

First question, can you solder? Second question, do you have the schematics?

If so, I would suggest starting with something simple such as replacing the power supply caps and diodes with audio grade versions of the same values. It all starts there. If you're still game after that, realizing that you've probably spent more on parts than the pre amp is worth, you could remove the headphone amp section and remove or bypass the tone controls to clean up the signal path. At this point you should let the caps burn in for a few hundred hours, then give it a good listen to see where you're at.

[Slim-Shaddy]

Yes, I can solder. I have the schematic downloaded.
I'll start with what you suggested. How much are you thinking PS caps and diodes are going to cost? I'm not trying to be cheap, but I didn't thing they would cost as much as the preamp is worth...

[F1nut]

I don't know what the values are, so kind of hard to say what the actual cost would be, but using Mundorf audio grade caps and Fairchild diodes I could see it easily exceeding the $100 or so value of the pre amp.

[Anders]

I'm really not into helping people mod their own stuff because i usually end up having to fix them.
I would suggest having someone modify it that has the experience and knows which parts to change that would give the most improvement.

[ataudio]

You could start with coupling caps, upgrade the volume control to an ALPS or Noble, etc.  Picking which brand of caps could be crap shoot unless you
research what sonic signature you are after.  Volume controls are usually low quality parts.  I've used Alps Blues and vintage Noble (no longer made) with great success.  I would start there and final output caps (if this pre has them).  The tube buffer might soften things up. 

[Slim-Shaddy]

What are coupling caps? Sorry for being a novice.

[SunnyDaze]

A coupling capacitor is a capacitor that is used to join two points on a circuit or network.

When used in an amplifier, a coupling capacitor in series between two points (or nodes) can behave as a one way "gate" allowing only the AC portion of an audio signal to pass while blocking the DC portion of said signal.

Coupling caps also behave as high pass filters; the filter mechanism depends on the output impedance of the first stage (DC stage) and the value the capacitor in series between the first (DC stage) and second stage (AC stage).