Jcm 900 dual reverb

Kalimna

To play devils advocate *slightly*, I have no doubt that Timmysoft does hear a difference. However, that is entirely different to saying that there *is* a difference. To use an analogy - I could pour a measure of wine into a thin-walled crystal glass and also, from the same bottle (avoiding any sediment), into a glazed pottery mug. Assuming equilibrium is reached with temperature, the two drinks will taste different, despite being absolutely identical. Tis the same way with sound, it really is *all* in the mind, for that is where senses are processed, and the slightest thing will affect that processing. And because you *hear* it, you become absolutely *certain* that what you are hearing is a solid reflection of reality, when actualy it isn't.

Adam

fretmeister

Kalimna said:

To play devils advocate *slightly*, I have no doubt that Timmysoft does hear a difference. However, that is entirely different to saying that there *is* a difference. To use an analogy - I could pour a measure of wine into a thin-walled crystal glass and also, from the same bottle (avoiding any sediment), into a glazed pottery mug. Assuming equilibrium is reached with temperature, the two drinks will taste different, despite being absolutely identical. Tis the same way with sound, it really is *all* in the mind, for that is where senses are processed, and the slightest thing will affect that processing. And because you *hear* it, you become absolutely *certain* that what you are hearing is a solid reflection of reality, when actualy it isn't.

Adam

I don't think anyone is claiming that it doesn't appear different to him.

It's just that his hypothesis would fail in a properly conducted double blind experiment. 

Kalimna

fretmeister said:

Kalimna said:

To play devils advocate *slightly*, I have no doubt that Timmysoft does hear a difference. However, that is entirely different to saying that there *is* a difference. To use an analogy - I could pour a measure of wine into a thin-walled crystal glass and also, from the same bottle (avoiding any sediment), into a glazed pottery mug. Assuming equilibrium is reached with temperature, the two drinks will taste different, despite being absolutely identical. Tis the same way with sound, it really is *all* in the mind, for that is where senses are processed, and the slightest thing will affect that processing. And because you *hear* it, you become absolutely *certain* that what you are hearing is a solid reflection of reality, when actualy it isn't.

Adam

I don't think anyone is claiming that it doesn't appear different to him.

It's just that his hypothesis would fail in a properly conducted double blind experiment. 

Agreed

fretmeister

The OP has gone on a break according to the Mod interventions page.

EDIT - it's Timmysoft. My bad.

I did like his reasons though!  

poopot

fretmeister said:

The OP has gone on a break according to the Mod interventions page.

Not the op... he is still here... timmysoft is on a break...

ICBM

Just to be clear, I'm also not saying that it can't make any audible difference - just that if it does, the difference is purely due to a small change in volume and not to some magic that the FX loop circuit is adding.

I've been aware of this myth for a long time, after someone brought me one for repair, and there was a jumper cable in the FX loop. I assumed that was because the FX loop switch contacts had got dirty - which is common on many amps, and causes random volume changes or the amp to cut out, and is most easily fixed from outside the amp by putting a patch cable in the loop - so I cleaned the contacts and made sure it was working properly as well as fixing whatever else was wrong with it. I told the owner that I'd done the loop as well, and he said 'no, it was fine - it's because it makes the amp sound better'. So I checked, and it doesn't.

I suppose if you run the amp with the master volume up full then it could make a difference that you can't achieve otherwise, but I don't know anyone who does that!

Voxman

I am not a techy - I can barely read (let alone read a schematic!! )

I have a JCM2000 DSL401 and there's a very noticeable difference in volume and clarity/punch when I jump the FX loop (the FX loop has an FX mix control so is parallel I think?). I'm assuming that this is because the circuitry is therefore quite different to the JCM900 in this regards? 

ICBM

Voxman said:

I have a JCM2000 DSL401 and there's a very noticeable difference in volume and clarity/punch when I jump the FX loop (the FX loop has an FX mix control so is parallel I think?). I'm assuming that this is because the circuitry is therefore quite different to the JCM900 in this regards? 

Yes, completely different. There's an IC driver and return amplifier, and a whole lot more circuitry which does genuinely boost the signal level when the mix is turned up.

poopot

If one was to try this “mod” what would be the best length of cable to use?

fretmeister

38.7 feet.

poopot

fretmeister said:

38.7 feet.

Bugger... I’m .7 foot too short or .3 foot too long...

will never know now

Edit****

if I tie a knot in the longer one that should work no?

fretmeister

poopot said:

fretmeister said:

38.7 feet.

Bugger... I’m .7 foot too short or .3 foot too long...

will never know now

Edit****

if I tie a knot in the longer one that should work no?

Don't see why..... knot!

BOOM BOOM!

Voxman

ICBM said:

Voxman said:

I have a JCM2000 DSL401 and there's a very noticeable difference in volume and clarity/punch when I jump the FX loop (the FX loop has an FX mix control so is parallel I think?). I'm assuming that this is because the circuitry is therefore quite different to the JCM900 in this regards? 

Yes, completely different. There's an IC driver and return amplifier, and a whole lot more circuitry which does genuinely boost the signal level when the mix is turned up.

This seems to be a pretty useful design then. I was just wondering why Marshall didn't use this on the JCM900 and other models?

ICBM

Voxman said:

This seems to be a pretty useful design then.

It's technically a poor design. Really, an FX loop shouldn't alter the signal level or tone at all, and in a parallel loop the mix should go smoothly from 0% to 100% effect with no change in anything other than the relative amount of wet and dry.

The reason for it in the DSL appears to be that the parallel bypass is very crude and just done with a single resistor, which has to be a rather high value to avoid feedback via the loop, so actually the non-loop sound is weaker than it should be.

Voxman said:

I was just wondering why Marshall didn't use this on the JCM900 and other models?

Because the 900s came earlier and they hadn't developed it yet .

The 900 loop is a vast improvement over the 800 and Jubilee loops too, which aren't properly buffered at all and interfere with both the level and tone. At least the 900 one is buffered properly.

What's puzzling is why Fender can use such a perfect loop in the Hotrods - without unnecessary complexity, it's just a single IC, but is fully buffered and has almost no detectable effect on the tone - and hardly anyone else seems to be able to get it right. Although to be fair, Marshall's add-on loop circuit which comes as stock on the 1987X and 2203 reissues is very good too.

simonbeckwith

I'm with @timmysoft on this one, my last 900 dual reverb sounded bigger, more low end a change in the mids with a patch cable in then fx loop. Wasn't a difference in volume, but a change in eq.

whether there are components in there or not, there was a definite difference. 

ICBM

simonbeckwith said:

I'm with @timmysoft on this one, my last 900 dual reverb sounded bigger, more low end a change in the mids with a patch cable in then fx loop. Wasn't a difference in volume, but a change in eq.

whether there are components in there or not, there was a definite difference. 

This is exactly what psychoacoustics does. A small change in volume is perceived as a change in tone and not a change in volume.

This is a very well-known effect and makes it quite difficult to compare two sounds unless you’re certain they’re very accurately matched for volume.

(Sorry, edited a bit that was maybe too dismissive.)

p90fool

I bunged a Metro Amps loop in my JCA 20 and that seems to work as well as my HRD loop, well-buffered but transparent-sounding. 

It's probably a worthwhile mod for some amps which already have a loop tbh.

http://i67.tinypic.com/rhv220.jpg

RiftAmps

@ICBM is absolutely correct here.

olafgarten

poopot said:

fretmeister said:

38.7 feet.

Bugger... I’m .7 foot too short or .3 foot too long...

will never know now

Edit****

if I tie a knot in the longer one that should work no?

This is misinformation, you need to use a cable that is exactly φ times as long as the length of the plug. It's important. 

Fenderish

RiftAmps said:

@ICBM is absolutely correct here.

How are your loops designed, then  ?