Metropoulos Forum

Jofipe wrote:Is the Zero Loss loop completely bypassed when it's not in use? I'm considering it for my '78 JMP... i LOVE the tone of it, and don't wanna change that for recording... but I need a loop for gigging it.

The loop circuit is fully bypassed/out of the amp circuit when loop is switched off/out.

Just a heads up for people that may not have seen the announcement, but George is having a Thanksgiving/Black Friday sale on the ZL loops. $20 off for a very limited time, happy Thanksgiving to all.

http://metroamp.com/store/index.php?mai ... cts_id=499" onclick="window.open(this.href);return false;

I have the version 3A pedal level effects loop. What components do I need to change to what values to make it a line level loop? I'm getting a lot of white noise in my non master volume amp (Zwreck clone) and I'd like to try a rack mount reverb/effects unit to see if there's less noise.

Hi all,

A similar problem to another guy on the forum. I am reading 432 V on my 50 Watt plexi. I have the Rev 3A board, can I use 68K resister or should I use the 75K resistor? it seems the 2 versions of instructions I have seen differ.

Many thanks,

Silly72

I just picked up a Marshall SL5, which doesn't come with an effects loop. It's a 5-watt (switchable to 1-watt) Class A 2-channel amp. Anybody have any idea if the Zero-Loss FX Loop kit would work in this amp, or is it only made for the big 50w/100w amps?

hello i have buy one fx loop 02/05/2014
order 11495
statut Build In Progress
is there a problem with my loop ?
i have no response by mail
thank you

boby6kiler wrote:hello i have buy one fx loop 02/05/2014
order 11495
statut Build In Progress
is there a problem with my loop ?
i have no response by mail
thank you

I believe George posted recently that there was going to be a delay on Loops.

Found it! http://forum.metroamp.com/viewtopic.php?f=2&t=43082" onclick="window.open(this.href);return false;

Silly72 wrote:Hi all,

A similar problem to another guy on the forum. I am reading 432 V on my 50 Watt plexi. I have the Rev 3A board, can I use 68K resister or should I use the 75K resistor? it seems the 2 versions of instructions I have seen differ.

Many thanks,

Silly72

Sometimes Marshalls/kits, particularly 50 watters, have the B+ line wired up a bit differently, connections are "reversed" to a couple decoupling resistors near the start.

Take a look at the pics below. Both are exact same thing/prinicipal, just a couple typical Marshall style board options commonly seen, hopefullly one or the other makes it easy to see where your PI node is.

Typically you want to use use the PI node to feed the loop as it'll be at lower voltage, can use the pics below to determine where it is in your amp, what the proper loop decoupling resistor value should then be to use it, and even which turret you may want to attach loop board decoupling resistor to.

That all said, you could opt to just use the screen node (which is likely going to be the 432V reading node you tested before -if the amp is running normally/all tubes in when you tested/ and the amp doesn't have a very high B+ overall), but running the loop off the PI node instead will mean a smaller loop decoupling resistor value is needed. That in turn means less power needs to be dropped/less heat need be dissipated by the loop resistor, which, in general, is a good thing to aim for in electronics.

Again, is OK to use the screen node here. In this case though, since you fall in near the top end of the acceptable voltage range (would need to use a 75K resistor to power the loop from the screen node), that means your PI node will measure at the midddle or lower end of the loop voltage chart (depending on the circuit you 50 watter has). Hence the decoupling resistor value needed would be much smaller if you used the PI node instead. Just makes life a tad bit easier on a things overall, though not technically necessary, again is always just a good general practice.

Don't know why you are seeing two versions of instructions/loop decoupling resistor charts, but correct instructions for any loop version are here: http://home.comcast.net/~mamp17/Unsorted%20Pics.html" onclick="window.open(this.href);return false;

Thanks SDM, very useful information , I will try your suggestions and see how I go. Thanks for the support!

I have the metro loop installed in my Wizard Modern Classic, when I engage the loop the amp jumps in volume, it doesn't seem right. Could it be a wrong value for the resistor or does the internal trim pot need to be turned down? I'm not a tech, the amp was purchased with the loop in there already. I read the installation instructions and it seems there is more to it than just slapping the loop in there after drilling the holes... you have to make calculations regarding the value of a resistor on the board based on readings you obtain from the amp. I have no clue if the tech actually took the time to adjust this properly? what are all the possible reasons for the extra gain when the loop is engaged? thanks guys!

lespaul6 wrote:I have the metro loop installed in my Wizard Modern Classic, when I engage the loop the amp jumps in volume, it doesn't seem right. Could it be a wrong value for the resistor or does the internal trim pot need to be turned down? I'm not a tech, the amp was purchased with the loop in there already. I read the installation instructions and it seems there is more to it than just slapping the loop in there after drilling the holes... you have to make calculations regarding the value of a resistor on the board based on readings you obtain from the amp. I have no clue if the tech actually took the time to adjust this properly? what are all the possible reasons for the extra gain when the loop is engaged? thanks guys!

This is a hard question to answer as the circuit is pretty well guarded and I've never had a Wizard Modern Classic on the bench. So, with info provided, have no way to know if things are installed correctly, if the loop is tapped into the optimal part of the circuit for starters.

That said, it is pretty basic to get the voltages right to the loop, deal with the calculation aspect and such. Not going to be hard for most any tech to get that right, so that is unlikely to be a issue here. Loop wouldn't be working at all if that was mucked up horribly either.

A more plausible concern is incorrect placement of the loop in the circuit. That shouldn't be too difficult for a decent tech either, though it could possibly be installed in a non optimal spot. Perhaps level adjusted high to make it work better/compensate for inappropriate signal to noise ratios.

Is also possible the loop may have simply been set to give the amp a boost on purpose, also possible it was just adjusted improperly, can only guess without more info here.

With so little to go on, only thing I can suggest here is to take a look at the loop instructions, and adjust the loop board trim pot as described in the "Level Adjustment" section. You cannot hurt the amp or loop adjusting the trim pot, so give it a go.

If adjusting the trim pot doesn't resolve things properly, would need more info to be able to help out further.

thank you very much for the reply... I will do the adjustment per the instruction and see what happens. appreciate the help with this!

How much is the impedance of ZeroLoss' send signal? Is it high or low impedance? Is there a way to measure it with a simple multimeter?

Send is low impedance. Depends on the config of the loop, and frequency, but on average around 600ish Ohms across the audio band.

One could measure/calculate with a resistive load, a multimeter, and a signal generator, but you'd just see near the output impedance stated above for audio frequencies.

I'm happy this forum is back

In the meantime, the problem I was having (a huge loos of volume) occurred when I connected my Marshall JMP with zero-loss to the insert loop (that's where you should connect preamps) of my GSystem; what happens is that GSystem' insert loop only works with low impedance signal, max 24000 ohms; its other loops instead can receive higher impedance signals (1M ohms). When I've connceted the JMP's preamp to other loops it worked great. So it looked like an impedance issue, even if George stated that zero-loss send impedance is pretty low.

So I've boutght a MXR/CAE 406 buffer, and everything worked great - and more important, with my other 2 amps too.