ISP Decimator G-String II

[megaup987]

Have you tried putting any other pedals in the loop? Or just use a jumper cable in between send and return and see if you're having the same problem?

If you're not having this issue when the Loop is ON, but the Decimator is OFF, then I'm worried that the problem may be with the pedal.

Also, I can recommend trying the following setup to rule out the Decimator problem. Guitar - Decimator Guitar IN - Decimator Guitar OUT - Muff - Decimator Dec IN - Decimator Dec OUT - Amp in. And see whether the Decimator works as intended or not.

[Dave Sloven]

I'm going to try putting some green insulation between the three cables going into the right side of the pedal to see if it might be a problem with the cables connecting via the metal jacks touching one another.  It seems like a long shot but worth checking out.

[Dave Sloven]

I'm pretty sure the problem was the cables touching one another.  I did wrap tape around the ends of the two cables from the loop but I didn't have enough to make much difference.  What helped was laying the cables down so that one goes to the front and the other to the back with the centre patch lead vertical so that nothing touches.  I'm pretty sure something was short-circuiting due to one at least of the cables not being sufficiently insulated.  If you look at the photos they all have metal ends.

I put the Decimator after the overdrive etc.  Didn't seem to make much difference, sounded the same either way.  The only thing that might be influenced by that is the clean sound.  The clean sound with the ISP pedal engaged was not that good.  Maybe if I put it straight after the guitar it will be better?

[Dave Sloven]

Have you tried putting any other pedals in the loop? Or just use a jumper cable in between send and return and see if you're having the same problem?

If you're not having this issue when the Loop is ON, but the Decimator is OFF, then I'm worried that the problem may be with the pedal.

The problem is there when the loop is on even without the Decimator on.  I haven't tried it with just a patch from send to return yet, that will be my next step, cheers

[megaup987]

Any luck figuring out what the problem was?

[Dave Sloven]

Any luck figuring out what the problem was?

I tried it just now replacing the cables for send and return to the ISP with a simple patch cable joining send and return.

i.e.,

6534+SEND-->DECIMATOR G-STRING-->6534+RETURN

to

6534+SEND-->6534+RETURN

With the long cables to and from the pedal the amp makes a horrible fizzy noise whenever the loop is engaged by the footswitch, whether the pedal is on or not.

With the short patch cable from send to return there is no difference between when the loop is engaged and when it is not.

From this I have to assume that the issue is something to do with either how the cables are routed or the cables themselves.  Or, the fact that a 20ft cable either way might need some kind of buffer between send and the pedal?  Maybe an EQ pedal?  I could try putting the Metal Muff in the loop before the Decimator as I am pretty sure it is not true bypass (it is the early model) and could therefore act as a buffer.

[Dmoney]

The Send from the amp is probably buffered.
If it's easy to test the cables themselves I'd do that first.

[Dave Sloven]

I eliminated those leads and connected the Decimator with short patch cables, still the same problem, and if anything becoming worse.  I am starting to wonder if my 6534+ has a defective inverter valve in the pre-amp.  I connected the Metal Muff in the loop before the Decimator as a buffer and no improvement.  The same whether the pedal was on or off.  Either the pedal sucks tone and volume both while playing and turned off or there is an issue with the amp.

[Dmoney]

I'm a bit lost now. Soz.

forgetting all the pedals...
1. You get gain hiss from the head if your guitar is plugged directly into the front and you get some drip drip noise from somewhere.

2. When the ISP is in the loop only w/ Long Cables, you get a horrible fizz if the loop is engaged whether the ISP is on is off. What if the loop is off? At all threshold levels on the ISP?

3. When the ISP is in the loop w/ Short cables, you get a horrible fizz if the loop is on or off? (no mention of the pedal being on or off itself). If you have a pedal in the loop doing something, then turning the loop on or off should make a difference. In this case if the ISP is actually having a gating effect then I would imagine turning the loop off would increase hiss as the ISP would be bypassed.

It's probably not a bias issue and preamp valves are reasonably tough. Have you researched something in particular that make you think its the PI? Can you post a recording of the drip drip noise? I've heard amps make irregular little pops and noises, but I can't imagine what your describing. The jacks having metal ends at the ISP should only matter if those sockets are isolated internally in some combination. It would be a pretty poor design to have that not be the case and to have jacks at one side create wacky ground loops if they touch.

I'd forget all your pedals and go back to basics. Set it up as per the manual and see how it sounds and take it from there. play around with the dial on the ISP.

Indicently, the 6534 manual says only non-gain effects should be in the loop, which makes total sense.

[Dave Sloven]

1. You get gain hiss from the head if your guitar is plugged directly into the front and you get some drip drip noise from somewhere.

Yes and yes.  I've added a filter to the power, which I thought might be the cause of the drip drip sound, but I'm still getting it, although it is sometimes faint.  It's possible it's a tube.  I can't think of another cause

2. When the ISP is in the loop only w/ Long Cables, you get a horrible fizz if the loop is engaged whether the ISP is on is off. What if the loop is off? At all threshold levels on the ISP?

Yes, I get a fizz and a volume drop, with long cables or short cables whenever the pedal is in the loop, whether the loop is on or off.  It happens at all threshold levels and whether the pedal is on or off. When you switch the loop off it stops.  The only time it doesn't happen with the loop engaged is if you run a short patch cable from send to return.  Then it acts normally, the same as if the loop is switched off.

3. When the ISP is in the loop w/ Short cables, you get a horrible fizz if the loop is on or off? (no mention of the pedal being on or off itself). If you have a pedal in the loop doing something, then turning the loop on or off should make a difference. In this case if the ISP is actually having a gating effect then I would imagine turning the loop off would increase hiss as the ISP would be bypassed.

Yes with short cables too, whenever there is a pedal and the loop is on.  When loop is off all is fine. The ISP does reduce noise when engaged but the overall problem of the volume drop and the tone suck is still there whether its on or off.

It's probably not a bias issue and preamp valves are reasonably tough. Have you researched something in particular that make you think its the PI? Can you post a recording of the drip drip noise? I've heard amps make irregular little pops and noises, but I can't imagine what your describing. The jacks having metal ends at the ISP should only matter if those sockets are isolated internally in some combination. It would be a pretty poor design to have that not be the case and to have jacks at one side create wacky ground loops if they touch.

Thanks, I will have to look into all these things.  At the moment I am cleaning everything with contact cleaner and will try again after dinner.

I'd forget all your pedals and go back to basics. Set it up as per the manual and see how it sounds and take it from there. play around with the dial on the ISP.

Incidentally, the 6534 manual says only non-gain effects should be in the loop, which makes total sense.

I've been using the gain stuff only before the amp.  The only time I put a gain pedal in the loop was with everything set to 12 o'clock and distortion at zero just to see if it would buffer the loop.

Cheers for your help.  It's certainly frustrating!

[Dmoney]

Ok hmm.
Do you get more hiss if you engage the loop with no pedals or patch lead (straight from send to return) in the loop? It sounds like if you have the loop off you have no additional hiss, then if you turn the loop on you get more hiss, but putting a patch lead from send to return reduces the hiss again. Is that correct?

If you do get more hiss with the loop on and no pedals in it, how much more hiss is there? A little? Or lots!


My thoughts are...
Is the ISP true bypass? If not, it would always have some suck to it whether it's on or off depending on the design of the buffer in the pedal. I can't find any info to say it IS true bypass, which is unusual since it's normally used a marketting point with other devices. I'm wondering if this explains the reason why having the pedal on or off makes no difference to the volume drop. I assume the pedal does gate the hiss when it's on though?

Secondly. If the pedal is working as a gate while in the loop and actually cutting the signal going into it from going out again (say you have it in a really brutal cut off threshold for instant silence) then it's probably fair to say additional hiss is probably getting into or after the pedal. If turning the loop on with no pedals in and no patch lead also adds the same noise I'd suggest it isn't the pedal adding the noise, I'd suspect something in the return end of the loop. If however, putting a patch lead in the send and return stops that noise then that seems odd. Send and Return jacks with nothing in tend to connect to each other internally when not used, so adding a single patch lead normally doesn't rule anything out other than the jacks sockets themselves.

After your FX return, the signal won't go directly to the PI valve. The loop valve with be split into two with one triode driving the send jack and one acting as a return stage (after the return jack) to drive the signal from your effects into the PI. The loop bypass function might cut out this whole valve (two stages). Some additional hiss could be expected from engaging the loop if this is the case as youre adding two stages to the preamp, but why a patch lead would reduce that hiss I don't know.

EDIT: I'm guessing this loop config is the case based on the amount of preamp valves and the 5150/5150II schem. I'm guessing there isn't any or not much solid state in the loop. I don't have a 6534+ schem.

2. When the ISP is in the loop only w/ Long Cables, you get a horrible fizz if the loop is engaged whether the ISP is on is off. What if the loop is off? At all threshold levels on the ISP?

Yes, I get a fizz and a volume drop, with long cables or short cables whenever the pedal is in the loop, whether the loop is on or off.  It happens at all threshold levels and whether the pedal is on or off. When you switch the loop off it stops.  The only time it doesn't happen with the loop engaged is if you run a short patch cable from send to return.  Then it acts normally, the same as if the loop is switched off.

I guess this is an error and you mean wether the pedal is on or off not loop?

[Dave Sloven]

I meant the loop being on or off with the effects button on the footswitch.

Anyway I went over to the Marshall forum as part of my searches for people who have had similar problems with an ISP Decimator G-String and I found this interesting bit of information:

According to ISP Technologies technical support --->

The G-string was never intended to run on batteries. The battery in it is there for test purposes only. It won't last a set, let alone a gig. Use an AC adapter

This, together with your suggestion that the pedal is not true bypass, made me think that the fact that it keeps getting worse (even though the pedal seems to be working in terms of noise reduction) means that the issue might be a battery going flat.

Seems like this pedal REALLY chews through batteries.  So I cleaned all the contacts - including on the footswitch jacks - and installed a brand-new 9V battery.  It's working okay now, but I'm guessing not for long.  I will have to get a 9V adapter but I really want to get a proper pedalboard rather than getting a heap of individual 9V adapters.

This battery issue combined with the fact that it is not true bypass would explain (1) why the problem kept getting worse & (2) why it happened whenever the pedal was in the chain, even if it was turned off.

The drip drip noise is another issue.  It didn't do it tonight but it has been doing it most days long before I got the loop set up. It seems to be better or worse at different times of day.  It might be a tube going microphonic.  I should call my dealer as the tubes are still under warranty.

Cheers for all your help.  I was pretty lost as to what the cause was.  I don't have a 9V adapter so I didn't test that out.

One good thing about it is that I just kept playing pentatonic scales listening to the amp while making small turns to the pickup height on my Nailbomb and finally found that sweet spot I'd been looking for (I also raised the pole pieces quite a lot).  I got the Cold Sweat set up pretty well too, with the pole pieces up one half turn.  Generally it sounds pretty good now, although obviously the amp could do with some EQ changes for different styles I just hammered through various riffs with the existing settings in clean, crunch, and lead modes. A bit of old Priest, some Sabbath, some AC/DC, some Rose Tattoo, some Iron Maiden, and some Accept.  8)

[bucketshred]

I had a DigiTech delay a few years back which ate batteries. You could get about 20 minutes out of it tops.

If you're looking into a power supply, I highly recommend the T-Rex ones. I've got one of the small ones and it really is bombproof! I used to use a cheapo one for years that was really noisy and dodgy. Its really worth investing in one, like a decent tuner pedal, they last forever!

Paddy

[Toe-Knee]

I know a fair few people who have had issues with the 5150 loop. I belive its 0dB rather than +4dB or -10dB like normal.

The g-major has terrible issues with hum and hiss when used with the 5150 loop even tc electronics advise that its best to run the guitar into the g major then the g major send into the front of the amp which is barely standard procedure.

This could be whats causing your issues. I know a guy with a few amps including a 5150 that uses a decimator g string ill check if he had any issues with it.

[Dave Sloven]

I did see someone recommend as a last resort placing the G-string first in the chain and then all the noisy pedals after it (e.g., overdrive, distortion) and then into the DEC IN and out the DEC OUT on the G-String again before the amp.  This is only one small step up from the standard Decimator in front of the amp and hardly worth the extra $100+ just for that tracking feature if it doesn't handle the pre-amp hiss as well (as placement in the loop should).  In any case mine seems to working okay until the battery wears down (which doesn't take long at all).  I will probably just put it aside until I can get a powered board, as $10 an hour for batteries is not so cool.