Topic: Well I'm Stumped!

Hey guys,

I was experimenting with the effects loop in my Marshall JCM900 last night and encountered something I just can't get my head around..

Basically at the moment all my effects are in front of the amp, but I've created a loop in my pedals so it looks like this:


Guitar -------- Noisegate (NS-2)---------Delay (DD3)--------------------------Amp
                      l                     l           
                      l                     l                                     
                      l                     ---------------------------------¬
                    Tuner (TU-2)----Dunlop Wah----Tube Screamer (TS-9)     

Apologies for the rubbish diagram!

Now what I tried to do was take the delay out and put it in the effects loop, but when I did I had a massive drop in volume. I'm talking with the amp on around 5 or 6 you could barely hear it. Could my effects loop be broken?

Any ideas?

Re: Well I'm Stumped!

Can you switch your effects loop between 10dB and -4dB (I've possibly got the negative in the wrong place)? Effects loops are usually designed to cater for both rack mount and stomp box effects.

Ensure that you have the correct loop setting for your effects.

Is the volume drop present with and without the delay pedal being engaged? If so, you might have a dodgy cable in your loop. I had this when I bought my Vintage Modern 2 summers ago.

Re: Well I'm Stumped!

I'll try that out after lunch, cheers man smile

Re: Well I'm Stumped!

I don't want to worry you more by telling you this but, in the studios I practice in, every one of their 900s have broken loops. I don't know why, but thats the problem I had with all of them too, the volume drops down to nearly nothing and its very buzzy. It's nothing to do with the db level on the loop though, cause I altered that and nothing worked.

Re: Well I'm Stumped!

Yeah, i know they are famous for broken loops hmm

However, shes off to Marshall in a few weeks for a revalve and a service so i'll get em to check it I think!

Re: Well I'm Stumped!

Just to ask something quickly - which exact model is it?

I have owned six 900s over the years and all of the dual reverbs and 50w ones have not been the greatest. Loop failings, pots dying on me, odd bits and bobs.

The best ones by far (for me - for tone and reliability) have been the older MK3 models 100w.

I found on all the 900s (much more than other amps with the same feature) the step-down switches were awful and took the life out of the amp - lack of low end, mushy top end and just things missing.

That's my two cents. tongue

Re: Well I'm Stumped!

Yeah im finding that more and more Dave, I think a lot of it is the fact it needs some new valves. Mine is the 100w JCM900 4100 Dual Reverb. Its quite old I think though and the pots are all fine, other than the trouble I'm having with the loop now its never ever let me down!

Re: Well I'm Stumped!

The 4100 is definitely one of the better ones! cool

Good luck with that and let us know how it all pans out with the service etc.

Ive never had an official service by any manufacturer - somehow just don't trust them...

Re: Well I'm Stumped!

It was the first valve amp I ever bought years ago.. It's never failed, never broken.. not even got a scratchy pot. Over the last four years or so its been through a lot! When I was playing quite a lot it was run for 4 hours every week at practise and sometimes 2 maybe 3 gigs at the weekend for about a year! Plus I used to practise through it at home too, without knowing how to power up or power down properly.

As for trusting the Marshall I only live a short skip and hop from their HQ in London wink I'm the other way around to be honest, I know a local tech guy but he's so stoned all the time I wouldn't trust him to remember my name! Amazing guy though, plays just like Hendrix and once built a 15w head based on a JCM 800 circuit that was just incredible.. anyways I'm getting slightly off topic and rambling..it's late!

I'll post up once I get the cash together and get it looked at. Thanks for the help!

Re: Well I'm Stumped!

The jack socket of the fx-loop get dirty & become oxidised, creating a bad contact and lowering sound quality &/or volume especially if you havn't used them for quite a while.

SOLUTION - just spray some electrical switch cleaner (not WD40) into EVERY jack plug socket, and push a jack-plug in/out several times. This will clean the socket, and release any 'sticking' jack plug. If your amp is older you may need to repeat a few times to get the contacts clean.

It's also a good idea to spray some switch cleaner into your guitar jack socket and tone/volume pots if you haven't done this for a while too!

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Marshall JVM 210H, Marshall JCM 900, Hughes&Kettner Statesman Dual EL34   
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