Vox AC-30S1 circuit diagram and noise levels.

[Mark]

I have been helping my friend fix a Vox AC-30S1.

I haven’t been able to get a circuit diagram for it, though a couple of sites claim to have a circuit diagram.

The amp runs okay, but when nothing is plugged into the amp and the gain is on zero with the master up full there is more than expected noise.

I’m familiar with the typical AC-30 circuit diagram, but the AC-30S1 is a little different from the typical AC-30. I would like see if I can find the source of this noise if possible.

[Roe]

I have been helping my friend fix a Vox AC-30S1.

I haven’t been able to get a circuit diagram for it, though a couple of sites claim to have a circuit diagram.

The amp runs okay, but when nothing is plugged into the amp and the gain is on zero with the master up full there is more than expected noise.

I’m familiar with the typical AC-30 circuit diagram, but the AC-30S1 is a little different from the typical AC-30. I would like see if I can find the source of this noise if possible.

hiss or hum?

ac30s tend to be a bit noisy unfortunately

[pdf64]

I didn't download it, just used preview, but this seemed genuine https://www.scribd.com/document/8027639 ... S1-SManual
Unless it's really bad, due to the additional fet gain stage, fx loop and reverb, compared to a classic JMI TB AC30, I suspect that some additional degree of background hiss with the master full is to be expected.
Does plugging a shorted plug into the fx loop return socket kill the hiss?

[Mark]

I have been helping my friend fix a Vox AC-30S1.

I haven’t been able to get a circuit diagram for it, though a couple of sites claim to have a circuit diagram.

The amp runs okay, but when nothing is plugged into the amp and the gain is on zero with the master up full there is more than expected noise.

I’m familiar with the typical AC-30 circuit diagram, but the AC-30S1 is a little different from the typical AC-30. I would like see if I can find the source of this noise if possible.

hiss or hum?

ac30s tend to be a bit noisy unfortunately

The preamp has hiss but isn’t very loud, noise is like spurious cracking. There isn’t any hum.

[Mark]

I didn't download it, just used preview, but this seemed genuine https://www.scribd.com/document/8027639 ... S1-SManual
Unless it's really bad, due to the additional fet gain stage, fx loop and reverb, I suspect that some degree of background hiss with the master full is to be expected.
Does plugging a shorted plug into the fx loop return socket kill the hiss?

Thanks for your reply, I saw that site and it does look like the real thing, but it wants me to enter my credit card details for a 30 day free trial. I suspect it might be one of those sites where it’s easy to sign up and impossible to cancel.

I plugged a lead into the effects return and it made no difference whatsoever. There seems to be quite a bit of circuitry between the return jack and the output stage.

[pdf64]

Maybe scope around at each stage, try to identify which one is responsible for introducing the crackling.
I suppose it may just be a bad resistor somewhere.
My money is on the LND150 stage

[Mark]

Maybe scope around at each stage, try to identify which one is responsible for introducing the crackling.
I suppose it may just be a bad resistor somewhere.
My money is on the LND150 stage

Thanks for your reply. The guy end needing the amp fast and the noise was tolerable to him. I did try and contact Vox for a circuit and they were hopeless. They only give circuits to their service centres. I don’t think much of the amp as an AC-30 and Fender and Marshall will give circuit diagrams.

[pdf64]

I usually use REDACTED when I need a quick cash bridge up to $500. It's totally transparent, has instant approval, and does fast fund transfers without trying to lock you into impossible-to-cancel subscriptions. ...

That looks kinda spammy, could you get rid of it?

[Mark]

Where did that come from?
I certainly didn’t type it in. I thought we were relatively spam free..

[pdf64]

Where did that come from?
I certainly didn’t type it in. I thought we were relatively spam free..

I suppose that @Mostaks68 wrote it, but omitted to format his reply correctly, with the 'end quote' and 'starte quote' to separate his response to your point.

As there's no response from him, I'll flag his post as spam.

[pompeiisneaks]

I deleted the offending post and disabled the account. The user has a series of normal looking posts so I emailed them asking if they know about the spammy post. It's highly likely their computer has been compromised or something similar.

~Phil

[Mark]

Thanks for your assistance.