Maestro Ring Mod Build Report, question.

[Ry]

Hooooooooray!  After a two weeks of working on it, my Maestro Ring Modulator works like a charm!  Thanks to Jsleep and Zero the Hero for making this one possible.

It sounds quite evil and is a LOT of fun.  I found the layout to be a little too compact for my tastes, but it needed to be tight to fit all of the components on such a small board.

I built a different power supply from the one on Jsleep's site.  I couldn't get the +/- 12 volts using the schematic (it dropped down to about 7 volts using the resistors as show), so I got one each positive and negative 12 volt regulators and made another circuit just like the +/- 15 volt one.

It has a bit of modulation bleed through, which has me thinking about how to reduce it.  I was wondering how it would work out if I took a copy of the modulation signal, inverted it so that it is out of phase, then mixed it into the final signal as the last stage prior to going out of the box?  Wouldn't this remove the modulation bleedthrough and leave the original signal, sum and difference signals?

Now to wire up all the external jacks and put it in a box!

Ry

[bwanasonic]

Hooooooooray!  After a two weeks of working on it, my Maestro Ring Modulator works like a charm!

Sweet! I would love to tackle this one someday, but I'd really want an electric piano to go with it  One of my favorite sounds!

Kerry M

[Paul Perry (Frostwave)]

It has a bit of modulation bleed through, which has me thinking about how to reduce it.  I was wondering how it would work out if I took a copy of the modulation signal, inverted it so that it is out of phase, then mixed it into the final signal as the last stage prior to going out of the box?  Wouldn't this remove the modulation bleedthrough and leave the original signal, sum and difference signals?

Maybe, but you might find, depending on the origin of the bleedthru, that there is a different amplitude and phase of the bleedthru at different oscillator frequencies. If you are REALLY unlucky, it will vary with temperature as well! Plus, it likely contains harmonics as well, esp. 3rd.
But, a heroic effort to get this sucker going, I dips me lid!

[Zero the hero]

Cool, man!
Did you find it difficult to set all those trimpots?

[Ry]

Did you find it difficult to set all those trimpots?

It was easy to set the ones that actually worked.  I used a cheap o scope that a friend gave me and a multimeter.  I replaced TR1 and TR3, thinking that they might be broken, but they still didn't do anything to the signal.  I'm not sure why because I measured the output after replacing them and it is varying as you'd expect (from -15 to ground for TR1).  TR2 also did not have any effect on the sound, as you wrote in your instructions.

I eventually changed out the 100k resistor off of the wiper of TR1 with a 56k, expecting that it would bring the signal closer to ground.  Nothing changed.  I will continue to look at it.

Thanks again!

Ry

[bioark]

please wath´s replace 2n4360??
help me!!!

[Zero the hero]

2N3820
When I'll be at home I'll look for other suitable FETs.

[Brunetto Latini]

I bought the Ready To Solder Board from GeneralGuitarGadgets.com and I have a few questions regarding a few components.

First off, what the hell are these things:
PT1        50k audio
PT2        50k linear
PT3        150k dual gang audio

Actually that's it for now, but the site I got it from is taking too long to e-mail me back with an answer.

[RickL]

Those are the pots.

[jsleep]

Hi Brunetto,

Actually that's it for now, but the site I got it from is taking too long to e-mail me back with an answer

I emailed you back the answer to your question almost immediately. I'm not sure why you didn't get my reply.

JD Sleep

[Brunetto Latini]

http://www.generalguitargadgets.com/v2/diagrams/maestro_ring_mod_ps.gif


I PMed jsleep about this but I'll take anyone's suggestions on this one.
I'm at the stage of building a power supply. What I've been looking for is a 35V transformer with somewhere between 2A to 5A. I just got a PM back from jsleep stating this:

"Where did you get that specification? This unit takes 9 volt bipolalr power I think. 5a is way more than you need also. 35v?"

How are we supposed to get +/-15V and +/-12V from a 9V bipolar supply?

I already bought a 20VCT at 2A. I'd love to be able to return this and get something cheaper...more importantly I want the right one, so what did you guys use?

[Paul Perry (Frostwave)]

Is that power supply circuit correct? I would expect that the 35v center tapped transformer would be connected to ground from the center. That gives you 17.5v to be rectified.
In my Blue Ringer, I just use a 15 or 16v AC tranny (not tapped). I ground one side of the AC & have half wave rectifiers (single diode) for the raw + and - lines, which go to 15v + and - regs. I expect the Maestro might have slkightly more current draw, but mine is only 200ma or so, so I can't see the need for a HUGE tranny.

[Ry]

I used a 16v, 1A AC wall wart from Jameco.  It works very well.  I couldn't get the circuit to work per the schematic, so I used +/-12 volt regulators to get the correct voltage directly from the transformer (just like the +/- 15v circuit) rather than putting resistors directly in line with the 15v supplies to get 12v.

I actually used the power supply schematic for the infinitphase (I don't have the link readily avalible right now) because I knew that it was dead quiet.

Hope this helps.

Ry

[Zero the hero]

MY FAULT!
People, that Poewr supply is not the one I used in my Maestro.
Sorry for that, I'll re-design a new one when I'll have a bit of time.
Use this one instead: http://www.diystompboxes.com/sboxforum/viewtopic.php?t=23268

Use 15v transformer and 7815, 7915 regulators. For +-12v use the resistors of the old power supply schematic or (as Ry suggested) another couple of 7812 7912.

[Brunetto Latini]

MY FAULT!
People, that Poewr supply is not the one I used in my Maestro.
Sorry for that, I'll re-design a new one when I'll have a bit of time.
Use this one instead: http://www.diystompboxes.com/sboxforum/viewtopic.php?t=23268

Use 15v transformer and 7815, 7915 regulators. For +-12v use the resistors of the old power supply schematic or (as Ry suggested) another couple of 7812 7912.

Do really need +/-15V?

I see on the schematic that the 741 chip requires 15V. We looked up the specs on the 741 chip, it only needs 12V. Of course, there are other chips on the board that require 15V, and we haven't looked those up yet, but are teh specs on the 741 a typo?

One other thing is that the new power supply you've linked me too only has an output 12V. So how is this useful for us when there are several components that require 15V?

[Brunetto Latini]

O yea and one more question:

the trimpots TR1-TR5, once they're tuned they won't be touched again? Or will they be constantly messed around with? I'm thinking only PT1-PT3 will be used for constant adjustment.

[Ry]

The trimmers will be set once and then not touched.  On that note, I HIGHLY recommend using 25-turn multi-turn pots.  I just got mine tuned correctly.  It was very difficult to zero in on cancelling out the modulation signal even with the multi-turn pots.  I can't imagine getting it right with single turn trimmers.

A word of advice about the trimmer procedure:  I did everything according to the factory instructions (with a multimeter and a scope).  I found that trimmers 1, 2 and 3 didn't do anything.  Trimmer 5 is very helpful in setting up the oscillator level.  I adjusted trimmer 4 by ear to cancel out the oscillator signal on the output.  

As far as the voltage circuit goes, the schematic that Zero the hero posted is for +/-12V, but the same schematic can be used to get +/-15v, just replace the +/-12v regulators with +/-15v ones.  I think you need all four voltages to get this pedal working correctly.  I built two power supply circuits, one each for +/-12 and +/-15.  Just connect the transformer output to the input of each.

It sounds fantastic.  Build it, you won't be sorry.  Yell with any more questions.

Ry

[Brunetto Latini]

I just asked for 5k multi-turn trimmers at teh shop. I hope they facilitate this tuning procedure. It sounds like a real bitch to do.

So that schematic I was originally looking from teh GGG site, isn't necessarily incorrect is it? I just want to know if there is a way to build only one power supply for all four voltages.


About the 741 chip, though. Was that a typo?

[Brunetto Latini]

I'm trying to look up specs on the other ICs, namely the IC741 and IC1458 and they all say they require 12V and not 15V.

http://www.emba.uvm.edu/~oughstun/pdf/lab-07.pdf

It also says in the instructions that the MC1495 uses 12V.

I'm obviously having problems finding a 15V transformer, so I'm doing all I can to get this thing done with a 25VCT tranformer.

[Brunetto Latini]

I am not getting what thes imput/output jacks are. I know there should be one input for the instrument(J1), a quarter inch plug, and the same for the output to the amp(it must be the one at the top, right hand corner in the schematic).

So what is this stuff about an Oscillator Output(j5), Pitch pedal input(j4), External Carrier(j3). and Modulation Pedal input(j2)?

Are they just for trimming? Does this mean I have an expression pedal for this thing?

I hope everyone's not taking their vacation just yet.