Moving Master Volume In A Ceriatone Chupacabra For Effects Loop Installation

[ledvedder1972]

I purchased a Metro zero loss effects loop to replace the "unusable" effects loop in my Chupacabra. But, I'm being told that it won't work correctly because the master volume is before the tone stack. Some have said it will work if I move the master volume after the tone stack. I'm just starting to learn about the ins and outs of amp modding. Will this work? Can it be done? If it can be, can someone share some information.

I've attached the Chupacabra schematic.

[Enzo]

Hi, wselcome.

That which you have attached is not a schematic, it is a layout drawing. Do you have an actual schematic to post too? I hope?

[Mick Bailey]

Your FX loop insertion point is immediately before the phase inverter, so your send/return is positioned right at the end of the preamp stages. At the moment you have master>tone stack>FX loop>phase inverter.

If you relocate the master, you get tone stack>master>FX loop>phase inverter.

The important thing about the FX loop is that your signal level on the 'send' is still dependent on the tone and master controls, whichever way round you position them. I can't see any rationale behind moving the master volume control, unless I'm missing something. Who told you it won't work like it is and what's the explanation?

Have you tried the setup as it stands?

[d95err]

In general, effect loops should always be before the master volume. Otherwise, the master volume will affect the loop signal level, resulting in poor signal-to-noise ratio unless the master volume is at max.

You can just remove the current master volume and put it after the Metro loop return stage instead.

[ledvedder1972]

In its current stock form, as soon as I plug anything into the loop, it loses all dynamics and a lot of highs. I get that "blanket over the speakers" sound. I've tried this with both single pedals and a multi effects unit that had level adjustment. With the multi effect unit, I was able to match the volume level, but the amp still sounded unlively. I'd like this to operate just as my DSL's loop works. No tone loss and it isn't affected if I have the amp loud or quiet.

The maker of the amp has told me the metro loop won't work well unless other changes are made.

A few other folks have said something like this will work (attached drawing).

I'd love some help/pointers, if you guys wouldn't mind.

[ledvedder1972]

Hi, wselcome.

That which you have attached is not a schematic, it is a layout drawing. Do you have an actual schematic to post too? I hope?

I don't. It's not on Ceriatone's site.

[ledvedder1972]

In general, effect loops should always be before the master volume. Otherwise, the master volume will affect the loop signal level, resulting in poor signal-to-noise ratio unless the master volume is at max.

You can just remove the current master volume and put it after the Metro loop return stage instead.

How do I do this?

[Enzo]

Shouldn't we also consider the signal levels? He has it going into the phase inverter. Isn't his signal level way higher than line level? And would the returning FX signal have a hard time moving the PI?

[ledvedder1972]

Ceriatone is telling me I have to use their Klein-ulator Klein-ulator | Ceriatone, but I don't want to have another piece of gear to lug around.

[Gregg]

First of all these types of amps were never meant to have an FX loop because they rely on PI and power tubers overdrive to get "that" tone but since you intend to add one some compromises will have to be made.
The ZL loop is usually placed between the TS and Master but this isn't the only way to use it. The main reason for that is you have a pretty consistent signal level after the TS which is then attenuated to line levels and the Master goes after the FX return stage.
Now think Mesa DR for example. The loop is after the channels' masters and it has a Send level pot which one usually would set up in a certain position and not play with it too much anymore. The ZL loop has a trimpot instead. So if you don't intend to footswitch the loop in and out I see two solution to your problem:
1/ Add one more master after the return stage which will become you "global" master ala Mesa DR. This is a good solution if you're going to footswitch the loop in and out.
2/ Use a switch to "place" your master after the loop as per the picture you posted. This is the equivalent of your master before the TS set to max and placing it after the return stage. I don't know how the amp reacts to a TS-PI coupling versus the most common Master-PI so how this will affect the tone (if at all) is a matter of experiments.

[ledvedder1972]

First of all these types of amps were never meant to have an FX loop because they rely on PI and power tubers overdrive to get "that" tone but since you intend to add one some compromises will have to be made.
The ZL loop is usually placed between the TS and Master but this isn't the only way to use it. The main reason for that is you have a pretty consistent signal level after the TS which is then attenuated to line levels and the Master goes after the FX return stage.
Now think Mesa DR for example. The loop is after the channels' masters and it has a Send level pot which one usually would set up in a certain position and not play with it too much anymore. The ZL loop has a trimpot instead. So if you don't intend to footswitch the loop in and out I see two solution to your problem:
1/ Add one more master after the return stage which will become you "global" master ala Mesa DR. This is a good solution if you're going to footswitch the loop in and out.
2/ Use a switch to "place" your master after the loop as per the picture you posted. This is the equivalent of your master before the TS set to max and placing it after the return stage. I don't know how the amp reacts to a TS-PI coupling versus the most common Master-PI so how this will affect the tone (if at all) is a matter of experiments.

How complicated is option 1? I wouldn't be switching the loop in and out. I basically need a reverb on most of the time, and a delay and boost to turn on and off for solos, etc.

I'm not sure I understand the difference between option 1 and 2.

[d95err]

First of all these types of amps were never meant to have an FX loop because they rely on PI and power tubers overdrive to get "that" tone

Not really. The Chupacabra is a high-gain amp in sthe style of Jose, Friedman and so on. It is designed mainly for preamp distortion, not poweramp crunch.


My suggestion:

Replace the current (pre tone stack) master volume pot with a fixed 1M resistor. Install the Metro Zero Loss FX loop after the treble pot viper. Add a new master volume between the output of the loop and the PI input.

This picture is for the Tube-Town FX loop, but it will be pretty much the same for your amp (after you've removed the pre tone-stack master).

[ledvedder1972]

Not really. The Chupacabra is a high-gain amp in sthe style of Jose, Friedman and so on. It is designed mainly for preamp distortion, not poweramp crunch.


My suggestion:

Replace the current (pre tone stack) master volume pot with a fixed 1M resistor. Install the Metro Zero Loss FX loop after the treble pot viper. Add a new master volume between the output of the loop and the PI input.

This picture is for the Tube-Town FX loop, but it will be pretty much the same for your amp (after you've removed the pre tone-stack master).
[ATTACH=CONFIG]46046[/ATTACH]

Is this possible? What happens to the "Era" switch that goes to B and C?

[Chuck H]

The amp is basically a hot rodded Marshall with the TS and master reversed in the wiring. Reversing this arrangement to the more typical TS-master design may change the tone noticeably when the diode clipper is engaged since it will make the load constant as if the master were set full. That load is somewhat variable with the master setting. I don't think it would be too significant or objectionable though. I would try feeding the tonestack straight from the lead currently going to the ungrounded outer leg of the master pot. I really don't think you need to add a 1M resistor load for this. Then feed the Metro effects loop from the treble pot output (center tab) just like the stock loop. Then wire the master volume to the output of the Metro loop. The master feeds the PI. I believe this will adequately preserve existing signal levels and the loop should operate as prescribed this way.

As to the stock tone stack... Little advantage from the low impedance output of the cathode follower is preserved after the tone stack. This is why the tone gets muddy and weak when the stock effects loop is used. Also, the stock effects loop is almost certainly level incompatible with some effects and processors at all but low master settings. Attempting to force the issue with level controls would almost certainly result in poor performance anyway. Including that loop in a design for sale or public use demonstrates a poor understanding of the principals at work on the part of the designer IMNSHO.

This was already suggested above (except I don't think you need to replace the master pot with a fixed resistor). Consider this my endorsement

[ledvedder1972]

The amp is basically a hot rodded Marshall with the TS and master reversed in the wiring. Reversing this arrangement to the more typical TS-master design may change the tone noticeably when the diode clipper is engaged since it will make the load constant as if the master were set full. That load is somewhat variable with the master setting. I don't think it would be too significant or objectionable though. I would try feeding the tonestack straight from the lead currently going to the ungrounded outer leg of the master pot. I really don't think you need to add a 1M resistor load for this. Then feed the Metro effects loop from the treble pot output (center tab) just like the stock loop. Then wire the master volume to the output of the Metro loop. The master feeds the PI. I believe this will adequately preserve existing signal levels and the loop should operate as prescribed this way.

As to the stock tone stack... Little advantage from the low impedance output of the cathode follower is preserved after the tone stack. This is why the tone gets muddy and weak when the stock effects loop is used. Also, the stock effects loop is almost certainly level incompatible with some effects and processors at all but low master settings. Attempting to force the issue with level controls would almost certainly result in poor performance anyway. Including that loop in a design for sale or public use demonstrates a poor understanding of the principals at work on the part of the designer IMNSHO.

This was already suggested above (except I don't think you need to replace the master pot with a fixed resistor). Consider this my endorsement

I highly appreciate everyone's feedback. But, as I'm just starting to learn about this stuff, it would be very helpful to me if someone could provide a layout of these suggestions. Perhaps just editing the layout that I posted earlier?