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Simple Stereo Preamp

post #1 of 8
10/19/09 at 3:04pm
Thread Starter 
I've got a couple of old integrated amps kicking around and what I'd like to do is make a simple preamp. I really want to make a "preamp" and not an "attenuator" i.e. I want it to be "active".

I've opened up one of the amps (Arcam Alpha II) and I spy a few wee op-amps:

2x NE5532N's
2x NE5534N's

I'd has a few pots (volume, bass, treble).. all 20k.

Couple of voltage regulators:

1x 7815
1x 7915

Nice toroidal supply, diodes for the bridge rectifier, etc.. so maybe I can make the supply out of it as well.

I can use the RCA sockets etc.

I've got plenty PCB kicking around and all the rest of the usual stuff (resistors, capacitors, etc).

Basically I'm just looking for a nice clean, simple schematic to build a stereo pre amp using these op-amps. I dont need balance, bass, treble controls - just volume.

Thanks!

(just trying to keep myself busy and it'll be handy when I get my power amp as I can ditch my integrated altogether, which would be good as the volume control is scratchy and rather rubbish to be honest).
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post #2 of 8
10/19/09 at 3:50pm
Quote:
Originally Posted by KevDo View Post
I've got a couple of old integrated amps kicking around and what I'd like to do is make a simple preamp. I really want to make a "preamp" and not an "attenuator" i.e. I want it to be "active".
You say you want it to be "active," but do you also want it to have amplification?

se

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post #3 of 8
10/19/09 at 3:54pm
Thread Starter 
Well, I just didn't like the idea of a passive pre-amp. Read that it can cause problems due to high/low impedance, cables, etc, etc..

I just thought using a proper, lets say, powered pre-amp would be better.


I've seen a few schematics now. I'm assuming adding the volume pot in between pins 3 & 5 (separately of course for both channels) of an NE5532 and ground would be how to control the volume? I'm assuming that's just pulling down/attenuating the input signal some? If that's the case, it should be fairly simple.
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post #4 of 8
10/19/09 at 3:56pm
Simple preamp schematic on opamp = CMoy.
Instead of rail splitter and battery, build bipolar PS from your toroid, diodes and 7815,7915.
For volume use volume pot from your amp.
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post #5 of 8
10/19/09 at 4:01pm
Thread Starter 
Ah the CMOY! heard of it (obviously) but never looked in to it.. Will go look for a schematic now.
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post #6 of 8
10/19/09 at 5:07pm
Quote:
Originally Posted by KevDo View Post
Well, I just didn't like the idea of a passive pre-amp. Read that it can cause problems due to high/low impedance, cables, etc, etc..

I just thought using a proper, lets say, powered pre-amp would be better.


I've seen a few schematics now. I'm assuming adding the volume pot in between pins 3 & 5 (separately of course for both channels) of an NE5532 and ground would be how to control the volume? I'm assuming that's just pulling down/attenuating the input signal some? If that's the case, it should be fairly simple.
Ok, if you don't actually need any amplification, you could just strap your 5532's as unity gain buffers and use them after your volume control. They're internally compensated for unity gain, but if you use the 5534's instead, you'll need to add a 22pF compensation cap for use at unity gain.

se

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post #7 of 8
10/19/09 at 5:27pm
Thread Starter 
Sorry to be a pain but I think you're on to a winner with that suggestion - Could you supply a quick sketch by chance? I've had a little look at the 5532 & 5534 differences and it seems like the 5534's would be a better choice? (I only have two though, so not sure if i'd need more for the circuit you're talking about).

I'm really just looking to use it as a preamp between say a CD player/Squeezebox to a power amp. Shouldn't really need any/a lot of amplification as you say.

I've stripped the case off the amp and I'm doing a cut & shut on it so it'll only be 6.5" wide (mostly to accommodate the transformer.)
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post #8 of 8
10/19/09 at 7:34pm
Here you go.



The 5532's a dual device so you can do both channels with one chip. The 5534's a single device so you'd need two of them. And you'd need to add the compensation capacitor and wouldn't be a bad idea to add the nulling circuit as well.

se

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