Crumar Performer- ripe for all kinds of mods

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Crumar Performer- ripe for all kinds of mods

Postby Mattew96 » Wed Aug 16, 2017 4:52 am

Hello forum!

I've had the pleasure of working on a Performer for the last few weeks. I'm getting fairly familiar with its operations and wanted to share the one mod I am doing to it as well as the untapped potential this synth has.
First, some background:
I got the synth with a very crackly power supply as well as its sliders. So I did the usual, recap and deoxit. (There's weird random RF noise in my house that gets picked up by my oscilloscope and all of my synths with a filter that made me think there was a more systemic issue with the synth, but then I noticed that the noise still appeared on my oscilloscope with the probe completely unplugged and the synth off, as well as my SH-101, so that's weird)
One of the per-key sustain caps failed to a resistive short (it is a tantalum after all). I couldn't find another tantalum at 4U7, so I replaced it with a 10U 10V and changed the bleed resistor to fix the time constant, from 1M to 470K. Now the key works and sounds just like the others!
During my time with the synth I noticed a lot of quirks and strange behaviours which could be expanded upon quite easily...
Chorus bypass, filter input, filter drive, chorus input, filter release control, filter sustain control, maybe a few others I'm not remembering. I can't do those because it's not my synth and the owner prefers no new holes in his panel, however there is one mod that seems super simple on the surface but due to the nature of the synth it is actually fairly difficult... This is the one I am tackling as, IMO, it's really cool and makes the synth operate with more versatility and how I would expect it from the factory in the first place.
Basically, it goes like this:
When Strings are on by themself, the sustain control is active.
When Brass is on by itself, the sustain control is also active (and the crescendo control does nothing).
But when they are on together, the crescendo control works and the sustain control is disabled.
There is a really interesting reason for this:
When strings are on alone, the crescendo control is directed towards the per-key envelope generators, and the sustain control allows the keys to fade out individually. However, when the brass is enabled the sound generators can't fade in since the brass sound relies on the tone generators going through the filter at full volume. So they give up fully polyphonic envelopes and when strings and brass are enabled together, the brass switch and string switches together make a connection which bypasses the sustain slider, effectively setting it to 0. The brass switch also directs the crescendo control to a single VCA which paraphonically controls the crescendo on the strings. In summary: Strings only, polyphonic VCA with crescendo and sustain. Brass only, polyphonic VCA with sustain (there is no way to add crescendo to the brass since there is no paraphonic brass VCA, and the crescendo on the polyphonic VCA destroys the GATE signal that triggers the filter envelope). Brass and strings together, paraphonic VCA with crescendo only on the Strings, and no sustain.
The brass and strings combination bothered me, so I set out to keep both crescendo and sustain active. Now, the trivial way of doing it makes the synth behave like when brass only is selected: Remove pin 13 from the brass switch connector and bridge pins 12, 13, and 14. This is somewhat useful, as it re-enables the sustain knob. However the paraphonic VCA is still active, and it cuts off the sustaining notes anyways so that you get a cool effect pretty much the same as the brass filter cutting off the sustained notes (with those notes reappearing at the next trigger when the VCA/VCF reopens even though you didn't press them). Classic paraphonic sound.
Well I want to go one step further. I want a paraphonic crescendo and a polyphonic sustain. My solution is a gate-triggered sample and hold circuit. Six wires, a dual jfet op-amp, a mosfet, and a capacitor. The idea is when gate goes high, the sample and hold circuit follows the envelope open. Then when the keys are released, the gate goes low, the sample and hold circuit holds the paraphonic VCA open, and the polyphonic sustain circuit works its magic. Then the next time the gate is triggered, the sample and hold circuit follows the envelope again from closed to open. This circuit would be in series between R50 and T4 on the strings board.
Preliminary tests are extremely promising. I will post an update tomorrow once I finish fully testing. My favourite thing is that it potentially adds so much functionality without needing to cut any holes in the synth. Also, a significantly easier modification alternative. If you prefer having a sustain control during brass and strings on at the sacrifice of the crescendo control, all you have to do is remove pin 13 from the brass switch connector, and bridge 12, 13, and 14 as before, and also remove pin 10 and bridge 8, 9, and 10 on the same connector. This bypasses the paraphonic VCA entirely for the strings, but since brass needs the gate signal, there can also be no crescendo for the strings.
Anyways, I'm out for testing tonight! I'm excited to see how this goes!
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Re: Crumar Performer- ripe for all kinds of mods

Postby Mattew96 » Wed Aug 16, 2017 1:25 pm

It totally works! I'll be posting some details including pictures and schematics of the mod tonight!
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Re: Crumar Performer- ripe for all kinds of mods

Postby adhmzaiusz » Thu Aug 17, 2017 8:52 pm

Cool. I remember sound doctorin made a video about this but a schematic would be easier to follow if you can post it!
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Re: Crumar Performer- ripe for all kinds of mods

Postby Mattew96 » Thu Aug 17, 2017 10:44 pm

As far as I'm aware Sound Doctorin just did a switch modification which gives you either crescendo control or sustain control, but not both. Mine would give you control over both! :) I'm trying to put together a good detailed post which is why there's a bit of a delay. More soon!
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Re: Crumar Performer- ripe for all kinds of mods

Postby Mattew96 » Mon Aug 21, 2017 5:58 pm

Okay, I'm ready to post about this mod finally.
Image

It's actually very simple, and requires some parts that are fairly common.
At a bare minimum, you'll need three parts:
A high impedance input Op Amp (I used TL062CP)
A low leakage MOSFET (preferably without a Source-Drain bypass diode, but I do not actually know of a MOSFET without this) (I used MTP10N15L)
A low leakage (film is best) capacitor between 1uF to 4.7uF, and a 16V minimum rating (If you decide to use a polarized cap, positive must go to ground) (I used a 1uF 63V film capacitor)
Please note that this circuit is not perfect and does not solve all problems. There are benefits to doing this mod, and there are benefits to doing the switch modification Sound Doctorin details. I recommend putting in a toggle switch so that you can use either. My mod, however, does not destroy the original functionality of the synth. This only affects the settings when Strings and Brass are on together, and if you set the "Sustain" control to zero, it behaves exactly as it would behave stock. What this does is make the "Sustain" control active at all times so that you can use it for artistic effect as you see fit.
What it does:
When Strings are turned on with Brass, rather than being given their own envelope on a per-key basis, due to a few different reasons they end up getting a pure gate. On with key on, off with key off. The reason that crescendo still works is that the crescendo control is routed to a VCA which paraphonically controls the volume of all of the strings voices. In practice, you don't notice the difference between this and normal mode, other than the fact that sustain controls are disabled, both because the individual envelope generators instantly cut off, and the VCA also cuts off at the same time. However I believe that there's a better way to control the strings.
My idea: Re-enable the Sustain control for Strings. My first attempt, before I knew about disabling the VCA, was just to re-enable the Sustain control by removing pin 13 from the Brass Switch connector, and shorting the three pins of the switch where connector pins 12, 13, and 14 lead. Since pin 15 is unused on the connector, I found it simple to just move the wire from pin 13 to pin 15 so that it's not hanging loose in the case.
This worked, but not well since the VCA was still muting the Strings section. So now I had to come up with a solution for the VCA. I know that the strings cannot have a per-key crescendo since the brass requires the sharp attack of the gate signal. But nothing says they can't have a polyphonic sustain. So therefore the VCA must do the crescendo to full volume, and then stay at full volume while the per-key envelope generators fade out. Since there is a Gate signal in this mode, this sounds to me like a job for Sample and Hold! And that is exactly the circuit I built.
Note that there is an artefact with my design. The Sample and Hold circuit does not maintain full VCA volume, but rather it cuts to about 75-80% and then holds there while the envelope generators fade out. This, in practice, is not a huge problem and sounds unique. I actually like it more this way because it's kind of like an accent, and it just adds extra character to the Strings in this configuration. If you don't like it, there might be a better Sample and Hold circuit you can build instead of mine. The important bit is the connections you need and the signals that will be sent to the circuit.
Image
My circuit needed six connections:
+12V
-12V
Gnd
Gate (0 - +6.1V)
S&H IN (0 - -6.1V)
S&H OUT (0 - -6.1V)

Please note that at the optimal point for grabbing the signal, the envelope is inverted such that 0V is off, and -6.1V is full volume! When designing your circuit account for working in the negative region!

I attached my power lines directly to the power supply (Red to red, black to orange, green to green, see pictures).
Image
Image
The gate signal I tapped off of the pad right next to pin 2 of J2 on the strings board (on the bottom of the board. Note that in this picture I was tapped directly onto the connector instead of the safer pad to the left):
Image
The IN and OUT signals were supplied by lifting up the leg of R50 on its output side (on the top of the strings board). IN was soldered to the leg of R50 and covered with heat shrink, and OUT was soldered to the pad where R50 was formerly attached. (Note that I have since neatened up these connections from the ones in the pictures)
Image

That's actually pretty much it!
All of the power wires fit in the provided wire ties inside the synth. For the signal wires I wrapped them like vines around the cable assembly on the control board. They tucked nicely underneath the pot mounting rails so that no cutting was required to get to the top board.
Since I used stiff solid core wire and a small prototype board, my solution for mounting was just to tie all six wires very close to the board and leave it loose in the synth. It doesn't move or rattle this way.
Image

Here's my case as to why you might want to switch between this mod and the sound doctorin mod. I actually discovered that mod independently while I was working on this problem.
If you keep the VCA permanently open by modifying the switch across pins 8, 9, and 10, you lose control over crescendo. But in some cases this is good. With my mod, every time you retrigger the gate, all of the strings cut out momentarily even at crescendo set to 0, since the VCA momentarily clamps down and then reopens. It's a cool effect, but not always a desired one. I think the coolest way you could overcome this is by mounting a small momentary switch horizontally across the base of the crescendo slider so that when you move it all the way to zero it automatically switches to the alternative mode where the VCA is clamped open. Unfortunately I cannot develop this as this is not my synth and it's time to return it home to its owner. However it shouldn't be too hard to create and it would be a very badass way of making the Crumar look stock but behave in a much more useful way!

Anyways, I'm out for now. Sorry for the delayed post, but definitely feel free to ask me any questions! I do have plans to add some more pictures of the finished product, so feel free to ask for any pictures not yet included.
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Re: Crumar Performer- ripe for all kinds of mods

Postby grunderone » Tue Aug 22, 2017 3:58 am

My only question is : who's near me? Whats the cost ? Take my money!
Although I can follow this , it's like reading music - I could do it but I'll probably mess it up. I'm not a tech and I don't have golden screwdrivers ...
I'm nearly onto a Performer or an Orchestrator and am very much into making them play and sound the best they can .
If you're not able to , maybe I can get Ken Rich to modify them for me , he probably has done this to some Crumar at some point in history .
Anyway guys I really loved reading your enthusiasm and not only solving problems but innovating as well . It's inspiring .
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Re: Crumar Performer- ripe for all kinds of mods

Postby Pro5 » Tue Aug 22, 2017 5:02 am

I've got a performer, thanks for the interesting post will save it and re-read on a rainy day. I may need to fix it first as I've not used it for a short while and think there was a sound issue creeping in last time... should be an easy fix on such a machine though (easier than the 2 polysix battery damaged synths I fixed anyway)
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Re: Crumar Performer- ripe for all kinds of mods

Postby Mattew96 » Tue Aug 22, 2017 5:38 pm

Here's a picture of how I modified the Brass switch. The wire shorting the pins is actually the leg off of one of the capacitors I had just put into the board (On the left you can see where I previously had tried the sound doctorin style mod):
Image
Note that one wire (purple) which was in pin 13 is now residing in the N/C pin 15 slot:
Image
Here are some images showing how I wired the harness (note that there actually is no tension on those cables even though it looks like there might be. Also note how the purple GATE wire is now attached to the pad I was talking about before:
Image
Image
I didn't want to take the panel off again (but if you ask really nicely I guess I could... that octave switch is a real PITA to install) but here's the idea behind tucking those IN and OUT wires underneath the pot mounting rail:
Image
Here's a better picture of the board:
Image
And finally... Here's a really crummy video I made at 2 AM showing off the mod:


Also, I have a picture of the key fix that I did:
Image

As far as doing the mod, it's actually insanely simple and I think that this is a very good entry project for any inspired synth enthusiast. The parts are cheap, it's a simple circuit, and really the only way you can mess it up is by getting the drain and source backwards (and then the mod won't work), or killing the MOSFET with static (and then, of course, the mod still won't work). Otherwise the circuit is dead easy to build and mount in the synth. It really is a charm to work on this thing.

And as for me grunderone, I'm in the GTA in Canada, so if you're in the area, great! If not, I'll leave it up to you if you want to spend the shipping money ;) Honestly though I encourage you to do it yourself.

I did some testing last night. If anyone wants to try the momentary switch at the bottom of the crescendo control, all you need to do is connect the switch between pins 8 and 9 on the brass switch and it will work like a charm.

Anyways in case you can't tell, I really think this synth could do a whole lot more if someone were to seriously look at tricking it out. There's a gap under the power supply heat sink where you could run an umbilical with all of your modification controls so you don't have to cut holes in the case when you experiment with it and mod it. Full envelopes are possible, along with drive and lots of other tricks here and there!
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Re: Crumar Performer- ripe for all kinds of mods

Postby fh991586 » Tue Aug 22, 2017 9:47 pm

Too bad you can't find them anymore for cheap... Had one with multiple issues (almost every switch needed replacing, PSU loose, etc.), and I finally let it go because I had a Roland RS-09 in pristine condition which covered almost the same bases. Still a nice sound!
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