Hey all,

Does anyone know a really solid preamplifier design using only OpAmps as the active components??  Doesn't matter how many chips or amps it uses, ideally I'd like it to have just like volume and 3 band eq, that sorta simple thing.... ideally running from like +/- 12 or 15 volt rails... needs to feed a high power (~400W) SS amp so it has to be super clean.... pleasepleaseplease help me!

Thanks in advance!!!

Check out the "Pocket Rockit" build article on Hammer's site.  Remove the distortion stage.  Adjust caps for voltage if necessary.  Convert to bipolar power supply.  You're done (I hope)!

Guys, if I screwed something up, be kind!

http://sound.westhost.com/projects-2.htm

checkout the preamps on there .... from memory there isn't any mids control, but it uses a common tone stack where you can shoe-horn a mid control in. PCBs available also!

Mike

Look for either a Roland JC-120 schematic, or a schematic for the old Peavey Session amps.  The JC-120 is basically a SS Twin Reverb, the old Sessions are fabulous for cleans (steel guitar players love 'em).

thanks guys, great help!

RDV

Thanks Rick,

I'm so lost on how those tone stacks work, anyone have time for an explanation???

EDIT:  Rick, do you think this would work as well if I changed the feedback resistor for a gain adjustment, and used +/- 15V rails on the opamps?  

Oh I have another question too - do preamps generally amplify the signal as much as it can in terms of potentials?  IE to the limit of the power supply rails, as permitted by the op amps?

Just leave out the voltage divider circuit and attach the +15v to where I've got 9v. Attach the -15v to where I've got the ground symbol. The feedback resistor is a 100k trim pot anyway, so just make it a panel mount pot. This is a very simple cicuit that may not be enough for what you want. However; it's not so elaborate that you'll be out much $ to build it. I would definitely use a serious opamp like a Burr/Brown.

RDV

I like the 2262 for ultra-clean stuff :mrgreen:

Rick,

For the schem you gave me:  this works, except for the input cap to the second op-amp.  If I take it out, it works fine, if I leave it in it thrashes the signal.  Tried different caps, different amps;  anything you can think of?

Quote from: freebird1127Rick,

For the schem you gave me:  this works, except for the input cap to the second op-amp.  If I take it out, it works fine, if I leave it in it thrashes the signal.  Tried different caps, different amps;  anything you can think of?

With a supply like you're using, you don't need that one. Sorry, I didn't include that in my post. I thought about it later, but I've always dealt in 9v supplies with a divider. I hope it does what you're wanting it to. Of course those two 100k to Vr are not needed either cause there's no Vr.

RDV

Oh okay good, I get it now.  Yeah everything works great!  I like that tone stack!

You mean you've tried driving that 400watt SS amp with it and it works? What are you using it to amplify? Bass? That's just a Marshall tone stack from Joe Davisson's site.

RDV

NO no no no sorry sorry sorry... didn't mean to cause unjustified excitement... got the preamp working, I'm quite pleased with it.  And actually, I added the TS clipping and tone sections to the circuit with true bypass to see what it would sound like, but havent hooked it up to a speaker since... I'm scoping it but getting a weird triangle-ish wave... as noted in my newest post.  

Thanks Rick for the schematic.