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Hi,
I just like to use 2 amps and one is a bit noisy. The sound of both mixes great, but the background noise of the AC15 gets a bit too loud when there is silence.
For Jazz trio / duo / solo it is too much right now. For bigger bands it is fine just as it is.
Do you think it can be fixed? I use a fender princeton reverb 65 clone which is great and a JMI AC15 as 2nd amp. The fender is wet, the ac15 is dry.
It´s hard to get new tubes in europe right now and if is is possible it is going to be expensive. Before I buy them to swap them I´d like to ask you for advice.
Thank you
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It's probably a noisy tube.
It could be a loose tube or dirty tube socket contact. You can look at that. Clean the tube pins and socket. Make sure the socket contacts are tight. The red "D5 DE-OXIT" works great; cleans and protects; it handles tube heat very well! Recommended. maxresdefault.jpg (1280×720) (ytimg.com)
I always keep a spare set of everything 'tube', just for this type of situation.
Good luck.
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Is the background noise a hum, i.e. induced by the 50Hz from the power supply?
Or it is more a hiss, i.e. in the treble range (what I suppose)?
If its the latter one, it might be due to the missing negative feedback loop in the power section which is typically for Vox amps. A negative feedback loop like in other amps (also in the Princeton) dampens the highs more than lower frequencies, which also reduces audible hiss compared to amps without that loop.
Might be the reason why the Vox has more background noise than the Fender.
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Pre-amp tubes. Good luck, but that's my guess.
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Thank you, Gregc57, bluenote61 and Jimmy Mack!
I´ll try that out.
The background noise immediatly starts when I turn the amp on. Sounds quite normal for a tube amp and gets a bit louder when tubes are getting started.
There is no standby switch. The amp is getting started and after some time it is ready to be played.
I just used a smartphone app and it shows a dark noise between 100 and 400 hz. Of course this is no professional tool. The noise is getting
higher in frequency when I turn on the volume (no instrument plugged in). But to my ears it sounds like a hum that is low end.
The AC15 makes this noise when being used in the setup with the other amp. But it performes in the same way when I use it as the only amp.
I split the instrument signal by using a stereo pedal by lehle. Instrument to pedal -> pedal has 2 outputs.
Maybe I´ll bring the amp to a technician to swap the tubes. The amp has a voltage switch built in. 240 / 230 / 115 / 100 V. It is set on 230 as I live in Germany.
It has an English power plug type G and goes to an adapter for central Europe. I never changed it and it was installed by the previous owner.
The adapter is a "commenly used" model as you can find it in hardware stores and fulfills safety standarts, but it is not made of high end quality.
Does anybody have experience with high end power supply with noise filters and quality adapters? Do you think it might be useful to buy stuff like that?
I mean the overall noise is ok-ish and I know that this amp consists of a lot of tubes and therefore it won´t perform like transistor amps.
But I really enjoy it in the setup I mentioned in my opening post. If there is a chance to get it less noisy I would appreciate to get it done.
I can record the noise if you think this would be helpful.
Thank you, respectfully,
HerrvonPoppel
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A record of the noise would be helpful to get a better idea about the kind of "noise" of the amp, if its hum or hiss or other, e.g. "campfire noise".
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I hope it works. It´s just playing something and recorded in front of the amp on my smartphonehum.mp3
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Ok, its a hum most probably caused by the 50Hz of the power supply.
To get deeper in the problem, I would like to know
1) How old is the amp?
2) Does the hum appear also in other rooms or somewhere else?
3) It is humming also with a guitar straight plugged in without any additional pedals etc?
4) You wrote about an adapter for the wall plug. The earthing is routed through that adapter?
Thx for answering.
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Hey bluenote61, thank you first of all.
1) How old is the amp?
I think it was manufactored in 2012. It is an AC15 made by JMI in England. They started building them again for a short period by hand.
I got it checked by a technician that I trust. He told everything would be ok (sometime before covid19).
2) Does the hum appear also in other rooms or somewhere else?
Yes. It makes the same noise in other rooms as well. And my other amps do not cause the same background noise in the same rooms.
3) It is humming also with a guitar straight plugged in without any additional pedals etc?
Yes, also with a different guitar. But that time it was less annoying. The other guitar´s output is higher and I did not have to turn up the amp´s volume
so much. The noise is growing with volume.
4) You wrote about an adapter for the wall plug. The earthing is routed through that adapter?
Yes I think so. I can´t test it, but it has 2 poles for electricity and 1 additional for erthing. Both. The German and the UK plug.
Thank you
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Ok, it looks like the amp produces that hum.
Could be either the filter caps in the power supply section or a tube.
If the amp is approx. 10 years old the first is unlikely but could happen in some cases.
Checking the preamp tubes could be done by pulling the preamp tubes out one by one.
But you need the tube layout with the tube numbers for correct analizing the failure. Vox amps (and I suppose the same for the JMI) have an odd layout of the tubes.
Perhaps it would be helpful to consult again that technician whom you mentioned in your previous thread.
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Thank you very much. I will ask the tech.
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While it is worth trying to chase this down, as someone else said, Voxes are prone to more hum than other brands because of their construction. I know this is true of the two Voxes I have had, though both were vintage.
Hopefully you can get it straightened out, but I suspect it is part of the amp's DNA.
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Sometimes this easy fix works, swap one preamp tube for another, works especially if it’s the first preamp
tube that’s noisy.
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Power supply hum is quite easy to recognize by its sound, you can probably find videos on youtube with examples of it.
Does the reverb knob affect it much?
Is there noise when both pre amp volume and master volume are at 0?
With pre amp volume on 0, does the noise change (much?) when you turn the master volume?
With master volume at max, does the noise chagne much when you turn the pre amp volume?
Does the tone stack shape the noise?
Does your AC15 have an EF86 and 4 input jacks or no EF86 and 2 input jacks? (I'm not very well versed in the different AC15 variants, to me it seems they either have 1 channel and 2 inputs (no EF86), or 2 channels with 2 inputs for each (4 total) and a EF86 on one of the channels.).
If it has 2 input jacks, and you plug in a guitar with the volume at 0 (same as a shorting the signal), is the noise different if you plug into the high or the low input. (The input jacks have a switch which change the input impedance, which affect the thermal noise on the grid).
If it has 4 inputs, does pulling the 1st tube in the channel you don't use reduce the noise? (you'll might need some reading to figure out wihch tube is which)
If the noise is in the first 12AX7 you can change it for the lower gain 12AY7 (lower noise and but also lower gain).
(others have already suggested swapping preamp tubes for new ones which is a good suggestion. If you have other tube amps you can temporarily try tubes which you currently in use in other amps).
If all this sounds too complicated, it's probably best to take it to a technician.
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