I'm working on my LM3886 based amp and was thinking that after I should make a preamp for it. I'm almost done my amp modules and have to wait for my transformers so maybe now would be a good time to work on a preamp, the thing is what design to use. I'd like to keep it simple and use a single IC based idea (as is my amp) whlie not trading sound quality. Any ideas would be apreciated. Since my amp boards are almost done I'd like to start the preamp in a week or two...
I'd recommend something very simple with an audio grade op-amp like the TI OPA2134. Selector switch, volume control, op-amp with gain of 5 or so. Do you want/need tone controls? Balance control? Remote control (!)?
You can use a stepped attenuator instead of a potentiometer for volume if you wish.
There are many DIYers at headwize.com that have done evaluations of different op-amps, you may want to browse around there for a while. Use an IC socket and you can plug in different types to see if you can hear the difference.
You may be able to get away with no opamp at all if your source is, say, a CD player.
You can use a stepped attenuator instead of a potentiometer for volume if you wish.
There are many DIYers at headwize.com that have done evaluations of different op-amps, you may want to browse around there for a while. Use an IC socket and you can plug in different types to see if you can hear the difference.
You may be able to get away with no opamp at all if your source is, say, a CD player.
No, I don't need tone controls, or balance controls, just selection and volume. I'll probably use mainly a CD or PC soundcard, so I know I could probably not even use a preamp (which is what I was originally planning), but I'd like to build one and use an opamp so that if ever I wanted to expand and use different devices I could.
I was looking at the LM358, would that workout fine?
I was looking at the LM358, would that workout fine?
LM358 is an older design that is probably very poor for audio, at least by today's standards. LM833 would be better.
But I think both are duals. Build it with a 358, get it working, then plug in an 833 (or OPA2134) and see if you can tell the difference.
Pick an op-amp that is unity gain stable; while you're not using it at unity gain it will give you more stability at small gains as well.
But I think both are duals. Build it with a 358, get it working, then plug in an 833 (or OPA2134) and see if you can tell the difference.
Pick an op-amp that is unity gain stable; while you're not using it at unity gain it will give you more stability at small gains as well.
JoeBob
There is a design for a pre-amp at http://www.linkwitzlab.com/images/graphics/preamp1.gif using OPA2134. Elsewhere on the site, you can find formulae for changing the design.
I have built this on 1" of veroboard. You could omit the polarity and tilt sections. The only thing I didn't like about it was the volume control range. SL has used a linear pot (much better than log pots) to get a linear dB adjustment, which is great, but over a very narrow range, not so great.
Be very careful about the power supply. I'd strongly recommend that you don't have mains (i.e. including the mains transformer) in the same box as your pre-amp. Part of the mains buzz I was (and partly still am) experiencing on my system was due to this.
Jamie
There is a design for a pre-amp at http://www.linkwitzlab.com/images/graphics/preamp1.gif using OPA2134. Elsewhere on the site, you can find formulae for changing the design.
I have built this on 1" of veroboard. You could omit the polarity and tilt sections. The only thing I didn't like about it was the volume control range. SL has used a linear pot (much better than log pots) to get a linear dB adjustment, which is great, but over a very narrow range, not so great.
Be very careful about the power supply. I'd strongly recommend that you don't have mains (i.e. including the mains transformer) in the same box as your pre-amp. Part of the mains buzz I was (and partly still am) experiencing on my system was due to this.
Jamie
For the preamp power suply I'm probably going to use an E-I transformer (since I get them free), could I put this in the same box as my power-amp power suply (two toroidals, seperate from power-amp)? Or would magnetic interference play a role then? I'd also like to add a +/- 12v power suply in there (again E-I) to power the soft-start switch as well as my 12v fans (need those fans
), would that be too many transformers in the same enclosure?
), would that be too many transformers in the same enclosure?- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.