Noise problem with Engl Screamer

[Tamar]

Hi,

I would be very grateful for any help in diagnosing a noise problem with an Engl Screamer valve amp.

The amp exhibits additional noise, but only when a note is played. No guitar signal and no noise. In all other regards the amp is behaving fine, I haven’t noticed any deterioration in volume or tone etc or background noise. The noise is like that of rustling paper, a bit crackly or a bit like a flabby speaker.

I’ve done the obvious things and gone through all the valves with no change or improvement. This included the pre-amp and power amp valves. I’ve tried different guitars and the behaviour is the same. The noise is certainly more prominent in the lower notes and almost goes on the higher notes, and also increases in volume with the general amp volume if the master volume is increased.

I’ve also noticed that the noise is present on the effects loop send signal, and interesting, if I only input to the amp via the return the noise is also present on the audible output.

As a bit of history, this amp has recently had the PSU capacitors replaced. Two of the three caps showed signs of leaking and this work was initiated by noticing a general hum noise from the amp that was constant and independent of the master volume. (A different type of noise altogether to that now occurring).

Could there be another PSU related problem? I really would be grateful for any pointers or suggestions from the more experienced.

My thanks in advance…………..

[Chuck H]

how old is this amp?

[Tamar]

how old is this amp?

It would be 5-6 years old and has been used regularly during its life. Kept in lounge rather than garage or similar. Use would be for 2-8 hrs/week on average.

[Gtr_tech]

Sounds like cracked solder to me....

[Chuck H]

I asked because that's not very old to have bad power filters. The noise you describe like cracked solder, dirty tube pins or microphonic tubes, but you replaced those (with known good ones?) Could also be a parasitic oscillation if any lead dress was changed in prior service.

[Tamar]

Update

I wanted to give an update to the noise problems.............

The issue seemed to be intermittent; after the initial post I took the amp to a band practice and it behaved perfectly. Brought it home and the noise was back – this lead me to think that something must have moved internally from the transport vibrations. I took the amp apart and tried to find something loose, played through it whilst tapping components and wiring etc. This was all without success.

I did notice however, that the amp has no series grid resistor from the guitar to the valve, which I understand to be not recommended. Out of desperation and interest I added a 47k and this really helped with the noise problem, but also gave high frequency attenuation making the amp sound much duller.

Sort of gave up on it at this point, but whilst browsing the forum came across this post:
http://music-electronics-forum.com/t20533/
The MP3 sound clip noise was exactly like the problem with my amp and the poster concluded that it was due to incorrectly grounded copper tape acting act an antenna within the amp. This reminded me that I have a good quality planet waves cable that always makes noises when used with the Engl amp. I’ve since checked operation with my other leads and as it happens this was the cause! I’ve used the particular offending cable for many years without problem (it is a good quality Neutrik & Van Damme) and this cable is fine with other amps. The intermittent occurrence of the noise issue was purely down to which cable I happened to be using.

Sorry the explanation is a bit long winded, but I hope the information may be of use to others.