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Plague Bearer low-output woes
MUFF WIGGLER Forum Index -> Flight of Harmony Goto page Previous  1, 2, 3  Next [all]
Author Plague Bearer low-output woes
Soy Sos
I just finished the mod with a 100k trimpot. Works great and I
learned something too! The PB 3.1 sounds great, different from
the original in an interesting way. Now I have one of each in my system.
gde & Soy Sos: Excellent! You have no idea how stoked I am that it all worked out. smile

A minor caution: According to my 'scope, a 10k resistor sets the overall (Vout/Vin) gain to ~1 when the controls are 3/4, 3/4 3/4, 1/2 (high to input respectively). I tried to get it to 1 during normal/moderate usage, but the output can go over ±5V when: the input is cranked or driven very hot, or the filter is oscillating.
Hey flight. Question for you. I am using the cv'd gain (front panel mod) a lot on the PB 3.1. I really like the sound the increased q and gain gives.

The thing is and we discussed this before. It works in reverse to most cvs. Meaning I need to give it a negative ADSR envelope, and furthermore I need to use my Model 14 to push the voltage more negative to get this to be optimal.

I'd really like to be able to take the model 14 out of the picture and be able to send a normal positive cv pulse (positive ADSR).

I noticed on the Polivoks that it has a really sweet bipolar +/- control on it's cv input.

Is it possible to easily reverse the response polarity, so it responds to more + instead of more -? My rudimentary electronics skills want to just reverse the leads on the plug, but it can't be that easy.
Let me ponder this for a bit (I've been meaning to anyway) and I'll get back to you.

Also: I apologize to everyone for not commenting as much as normal, I've been very busy filling orders. I hope to have a chance to catch up and listen to all the samples soon.
flight wrote:
Let me ponder this for a bit (I've been meaning to anyway) and I'll get back to you.

Also: I apologize to everyone for not commenting as much as normal, I've been very busy filling orders. I hope to have a chance to catch up and listen to all the samples soon.

*cracks his whip*

screaming goo yo

You Quadders just have to be patient, I'm trying to get to the frac Choices still! And the damn INMs that have been hanging since November!

So there. wink

Anyway, I looked at the PB, and there is no simple way to do an on-board mod for positive-acting gain CV. The pot is even wired backwards, so changing the CV in would make the pot act backwards, etc. And any component change would drastically affect the sound.
However, there is another way - a little work perhaps, but without damaging the board or the sound: an ancillary board, just big enough for an opamp wired as a single-supply inverter. Connect the power leads to the open power connector holes at the base of the PCB, mount the board on two standoffs in the holes on the edge of the PCB, run the CV jack to the inverter and from the inverter to the original CV input.
I'll try it out when I have a chance & maybe whip some boards up if there's enough interest.
Ah, opamp...yeah makes sense.

It's the quad that really makes me worry about this since where to find 4 sources of negative ADSR and voltage. Maybe the quad just has the 4 opamps mounted together somewhere's. whip crackin...hopefully more PB sounds this week.
Excellent point, I'll do that on the quads.
You know the funny thing about the low-output problem? I don't feel like mine is giving a low output. And I'm finding the sweet spots with the way it is currently, so I am kind of nervous to make the change. I guess the trim pot is what I'll do and if I don't like that, I'll just remove it.

This shouldn't really be called a filter though. It's more of a waveshaper, harmonics exciter, thinga-ma secret sauce gadget.

I almost always use it in conjunction with a more traditional filter now to add timbre and harmonics. Check these out. I ran noise and a triangle oscillator through the PB and then into a DMF-2 lowpass with the resonance, freq cutoff modulated by ADSRs and the woggle bug along with ADSR retriggering via same. VCA key'd off ADSRs. I also cv'd the gain on the PB but I can't remember with which one.

I don't know why, but these tones only come through when the PB is involved, it must add some freq content that the DMF keys off of. If I take the PB out of the chain, it sounds boring. I can't explain it cause I have no idea what I am doing.
Those sound good, especially the last one!

You don't need to worry that boosting the output will affect the character of the filter. The output is just a buffer and is not part of the filter circuit.

I agree about the filter/waveshaper issue, but it really just defies classification. Secret Sauce Gadget works, I like that.
It does add a LOT to a sound (depending on setting of course). It is quite interesting to watch on an oscilloscope. I wish I had a spectrum analyzer to see what happens in the frequency domain! With the right settings, you can create chorus effects, phase effcts, overtones, undertones and all kinds of weird shit.
Hi flight, finally assembled my barebone (see my hordes of chaos thread).
regarding the low output - i figured out that without any resitors (no R6 and nothing in CN2) I got the highest output level. however, I placed a 10K res to be on the save side. Now I am thinking to revert back to the no resistor solution to get the most out of my PB.
actually I have no idea what I am doing there - so, do you recommend runing the PB without any resistors in the buffer circuit?

thanks, hel
Thanks for the heads up about your build, I like the look! What case is that, a Hammond?

PB: R6 is the feedback resistor that sets the output level. The formula is Vout=Vin(Rfeedback/Rinput).
Leaving Rfeedback out sets that term to infinity, which means that you are running the opamp "open loop" at maximum amplification. This is as loud as it gets! But it will also add a lot of noise and distortion, and clip the output very easily. Sounds nice and nasty, but you loose a lot of the subtle goodies. :(
It also means that your output will often be at full supply voltage (±12V), which is a lot hotter than most circuits expect.

So, I recommend 10k. 20k if you really need higher output. The best for your situation would be a trimpot so you can adjust it to your preferred flavor. wink
HI Flight,

thanks! the pult is a (S)Hitpult from Conrad electronics (part supplier in germany and austria).

Thanks for the schematics and the explaination - everything clear now. I will add a 100k trim then. Didn't have one around.

i feel like a jackass since i havent really had time to play with the 3.1 since I got it... with my dad being in the hospital I just havent been home. My 3.1 is really low to. i thought it was just me but... a/b to the old version i have sitting ontop of it... it's low. So where do I put a 100k trim pot to fix this? smile
There's three holes on the right side of the PCB just next to the chip and above the metal can. You will need to remove the SMT resistor that is between the holes and the IC.
computer controlled
I'll be getting a PB in a trade this week. How will i know what version it is? Is it marked on the PCB anywhere?
so remove that smt part and put the 100k trim pot in its place?
@ computer controlled: Yep, It is either silkscreened onto the PCB (r2.3) or etched into the copper (r3.1, r3.2). To verify that the upgrade has been done, check to see if the resistor to the right of the IC is marked "1002"

@ tragedybysyntax: Yup!
computer controlled
Thanks. Looking forward to bastardizing something with this!
kevin, thanks bud! I guess i didnt really catch the prob because i was running this and the 2.1 in series, lol. Man am I fucking pumped to fix the 3.1 and start tearing off heads!!!! Can't wait to hear what it's supposed to sound like! Tomorrow evening.... it is my plans after work!!!!! =)
Let me know what you think when it's done - there are a few other little changes to bring it fully up to the 3.2 revision, but if you like how it sounds I wouldn't bother with them. If the sound isn't quite what you'd like I'll still swap it out no charge.
computer controlled
I got my PB today. It's a rev2.2. Weird power connector on it. Now all i need it for my case to arrive and to order my power supply.
Ah, one of the very early ones! I had originally thought "why use a dual-row connector when it only needs a single-row". Standardization won out, of course.
FIXD!!! This thing sounds sick! lol. CUrious as to what other mods you say will bring it up to the newest version. Easy fixes i could do?

Simple, yes. Easy? Not as much so. These all (aside from removing the transistor) involve replacing SMD.

Removing the transistor makes a HUGE difference in the tone. It is responsible for most of the difference in character vs. the r2.3, and is only used when a negative CV is applied. The rest of the time it just muddies up the sound.

The 2MΩ resistor may have a capacitor sitting on top of it, and it may not be 2MΩ, since I started replacing these with 1MΩ early on. This is one of the feedback resistors for the filter section, and it sets the maximum distortion amount - bigger resistor = more distortion. I felt it was adding too much.
The 10pF cap is the same one that may be soldered on top of the above resistor and is necessary to stop extremely excessive oscillation. I just moved it to an open spot on the board since that's just a better way to co it.

The 15kΩ that gets changed to 49k9Ω is the wiper resistor for the Gain CV pot. In short, removing the transistor makes the circuit MUCH more sensitive on the high end, which made it so that, when turning the knob, you could hear the wiper scraping across the resistive element (due to the innate rough surface of the carbon-film track). Increasing this resistor reduces the response of the VC Gain to filter this out.

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