Ampeg V4 Noise Floor

I have a new V4B, it does hum a little (regardless of volume and other settings). The hum is quieter than the cooling fan on my previous amp, though, so it doesn’t bug me too much.

 

I have/have had a few older models, not a modern one, but they’re generally pretty quiet when running up to spec. I’ve had issues with one where the isolation washers on the speaker outs were missing which caused some induced hum, but other than that mostly just normal tube related issues if any.

The catalogs for the old V4B and others are in the portaflex wiki, they say 80db signal to noise ratio.
Sales Literature and Advertisements | TalkBass.com

The new amps say the same
https://ampeg.com/data/6/0a020a41e58d5e0b91edd46ce/application/pdf/Owner’s Manual - English .pdf

 

I had an older model with 7027A power tubes.
Probably owned it 20+ years and it was super quiet.
Sold it with the original tubes.
Probably the best sounding bass amp I've ever owned but 100 watts was not enough clean headroom with a 2x15 cabinet.

 

Do you have one that hums or hisses?

 

Closely related to hum itself is the problem of the hum mixing with notes from the bass, especially low notes on the E string, to produce "sum and difference products" - beats. Sounds a little like tremolo. I suggest this as something to listen for (in the context of the thread) because I don't notice the hum, but do hear these beats. In my case it's worst on G, E string 3rd fret.
I don't have a V4B but my SVT-CL does this a little. I have no idea whether or not this small amount is normal for this amp.
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Also closely related - if the V4B has the toroidal inductor for the mid control and I think it does - at least one (apparently technically advanced) member here replaced that toroid in an SVT-2 with a better one to reduce hum being picked up in the inductor (like an antenna). There was a service bulletin (I think that's what it's called) covering this for at least one model of Ampeg amp with that inductor. That's all I remember.

 

C2012 model V4B RI here.

And as far as I recall, it's pretty much silent. I s'pose it's got a hum like they do. But I've not noticed it... that I recall

 

A tube is a possibility and a good place to start. Wire layout to the tone switches and pots should be looked at. Check the shielded wires inside the amp, if they were moved something may have broke. Pay close attention to the ext amp jack and wire. Unsoldering it on the PCB can be revealing.

Your tech should be able to trace through the circuit to locate the source of the hiss. Could be a bad component or solder joint.

If your speaker cab has a tweeter, it can reveal hiss that wouldn’t normally be heard.

A common source of hum is the chassis input jack contacts, this is the main ground. Oxidation here can be a problem. Also, the two speaker out jacks require isolation washers.

For the record, my ‘74 is very quiet.

 

Mine's a couple years old. It's dead silent.

 

My old V4 is noisy at idle but with @beans-on-toast and @Wasnex help, I have a couple of strategies to try in the following weeks.

 

I have a 1974 V4 and the only time I get any noise is when the spring reverb is turned up (I leave it off 99.9% of the time). The bass-specific V4Bs don't have a reverb.