I've been staring down my hand-drawn schemo for a Univibe. It says all transistors are 2SC828, with the exception of Q1 (2SC529). As every tranny in the bloody thing is NPN (I count 12 828's), and given the OVERabundance of the wholly INexpensive 2SC828 tranny it calls for (COMPLETE sarcasm), I am wondering what the outcome of a 2n2222 substitution might be...
Would I have to redo the entire circuit? or would the crazy thing even work properly, let alone, at all?
Thoughts?
Hi
2N2222A subs for a lot of things. Rarely fails. But you might want a lower noise device like a 2N3904 or 2N5088. Also, the PN100 is designed to be the "universal" SS NPN.
Do you have a link to the 2SC828 datasheet?
cheers
Quote from: Brossman on August 22, 2010, 12:25:52 AM
I've been staring down my hand-drawn schemo for a Univibe. It says all transistors are 2SC828, with the exception of Q1 (2SC529). As every tranny in the bloody thing is NPN (I count 12 828's), and given the OVERabundance of the wholly INexpensive 2SC828 tranny it calls for (COMPLETE sarcasm), I am wondering what the outcome of a 2n2222 substitution might be...
Would I have to redo the entire circuit? or would the crazy thing even work properly, let alone, at all?
Thoughts?
You'll be fine with 2222's or 3904's, better quality build with 5210's and 5088's.
Brett,
Here's a link to a couple of dif datasheets for 2SC828...let me know if they don't work and I'll see what i can do...
http://www.datasheetcatalog.org/datasheets/700/489181_DS.pdf
http://www.datasheetcatalog.org/datasheets/185/489180_DS.pdf
Just for kicks, I thought I'd post the datasheets for the other NPN's y'all have recommended...
2n2222a - http://www.datasheetcatalog.org/datasheet/SGSThomsonMicroelectronics/mXyzzyw.pdf
2n3904 - http://www.datasheetcatalog.org/datasheet/fairchild/2N3904.pdf
2n5088 - http://www.datasheetcatalog.org/datasheet/fairchild/2N5088.pdf
2n5210 - http://www.datasheetcatalog.org/datasheet/fairchild/2N5210.pdf
NOTE: I'd recommend not using Firefox, as my FF browser doesn't let me open these pdf's. If you have no trouble, disregard this, haha.
I use Firefox. I'm using 3.6.8 right now, and it opens all the PDFs just fine.
I agree with using 2N5210 and 2N5088.
Just a heads-up about Fairchild 2N5210's.
I bought a load of them from Mouser about 6 months ago (I don't have the Mouser part number handy) and they are overly sensitive to base current input.
We had to raise the 22K input resistor to 28K to stop a blatty distortion problem when you hit whole chords hard on the guitar.
That sounds a lot like the problem I had: Everything sounds ok but loud chords are distorted. Only in my case it was caused by oscillation of the input stage... I solved it by installing transistors with a hFE lower value. I wonder if what you did would have worked in my unit.
Hi same problem here oscillation of the imput stage
I had three 2N5089 Hfe around 560 same batch
i have changed Q1 for a 2N3904 Hfe 195
and it's perfect now !
Mich P.
Mine were about 280 (2n5088s maybe, not that important) and I changed them to about 190 (2n3904). But I've just bought some 2n3904s with an hFE of about 290... The input buffer was designed very poorly: Not one which would have worked, not two which might have been better but three transistor connected in a weird cross linked way.
That weird way was called a boot-strap arrangement like the FuzzFace used.
Looking into more detail of the datasheets for 5088/89's, I've discovered they may be low noise but can have a gain of 350-1400...
It seem to me this is much too high. Better quality build, maybe. But will this produce a better effect? And, come to think of it, who's to say what's "better", except the beholder...
Rather than go through the painstaking task of trying to decide which ones sound better (having to buy a dozen of each kind and swap them out in tranny sockets), may I ask a recommendation?
Based on the fact that 5088's have a noise factor (NF) of 2dB, and median gain ~800, while the 2222a has a NF of 4dB, with a median gain of ~200, I would think less gain is better overall...
Reverting to n00bage, would the fact of having quadruple the gain factor affect the audio signal too terribly much (i.e. more/less distortion)?
OR
Is it better to take a hit building with slightly noisier components?
Thanks for all your help guys!
Quote from: Brossman on August 30, 2010, 11:37:18 PM...Rather than go through the painstaking task of trying to decide which ones sound better (having to buy a dozen of each kind and swap them out in tranny sockets), may I ask a recommendation?...
Been there, done that, that's why I recommended the 2N5088.
I've tried most of the usual suspects: 2N2222, 2N2369, 2N3904, 2N4401, 2N5088 and 2N5089, 2N5210, 2SA1015, 2SC1815 etc etc etc.
Well, the only reason I ask is that people have said something about getting oscillation from higher gain tranny's...
Why did you pick it over the rest? Did anything in particular stand out from the rest? Or is this your preference?
Quote from: Brossman on August 30, 2010, 11:37:18 PM
It seem to me this is much too high.
Can you expound on *why* it seems too high? :icon_biggrin:
QuoteBased on the fact that 5088's have a noise factor (NF) of 2dB, and median gain ~800, while the 2222a has a NF of 4dB, with a median gain of ~200, I would think less gain is better overall...
Can you expound on *why* less gain is better overall? :icon_biggrin:
Quotewould the fact of having quadruple the gain factor affect the audio signal too terribly much (i.e. more/less distortion)?
The rhetorical questions above were a tongue-in-cheek way of saying that almost all transistor designs rely on making the variation between parts not matter by using circuit techniques that make the gain variations immaterial as long as you have enough. Having to select parts means either that (a) you can't get good enough parts consistently no matter what you do or (b) you are for some reason unable to design one which eliminates the sensitivities to part variation.
Put it another way: if you have enough gain, it's easy to reduce the gain by feedback and get more predictable performance. It is rare that having too much gain is a problem in a transistor if you have enlightened design techniques.
QuoteIs it better to take a hit building with slightly noisier components?
It is never better to take a hit building with noisier components if you can get higher gain, quieter ones unless there is some very special purpose.
The Univibe circuit after the first three transistors is practically immune to transistor variation as long as you have enough. In fact, the two-device cascades are there because single device gains were not high enough. You can replace the two-transistor darlington connected pairs with single darlington packged devices like the MPSA12 or MPSA14 at very little change to operation. The three transistor front end has some quirks because the design had to be done with transistors available at the time. Replacing all with 2N5088 has been done many times, and quite successfully.
Quote from: Brossman on August 30, 2010, 11:55:25 PM
Well, the only reason I ask is that people have said something about getting oscillation from higher gain tranny's...
Why did you pick it over the rest? Did anything in particular stand out from the rest? Or is this your preference?
Keen's Second Law is "When in doubt, use a 2N5088.".
This is a distillation of
(1) modern transistors are very, very good, and mostly any NPN will work for any other NPN as long as
(2) the gain is high enough, and over 300 is a good place to start
and
(3) the 5088 is a high gain, high frequency, low noise device which does almost everything well. And you can get them for $5.00 per hundred. What's not to love?
Hence Keen's Second Law. :icon_biggrin:
The exceptions are where current handling or voltage handling is too high for the 5088; this is almost never a problem in effects.
Quote from: Brossman on August 30, 2010, 11:55:25 PM
Well, the only reason I ask is that people have said something about getting oscillation from higher gain tranny's...
Why did you pick it over the rest? Did anything in particular stand out from the rest? Or is this your preference?
There has got to be something else going on with the oscillation problem. I've built well nearly 50 now and a greater portion of them have been with 2N5088 and haven't had a single one have oscillations problems in the front end. Maybe it's my layout I don't know, sometimes layout can be a problem.
I know that it's real common to mis-place the 47K and 4K7 resistors, and have had many try to use a 33pF cap where the 330pF one goes, and substituting a 1k2 where the 1M2 goes gives one fits. Another thing to check is if you have a ground plane under the board, sometimes with your board on the bench w/o a ground plane under it things can get goofy. I mounted a proto-board into a 6" x 9" peppermint tin and jsut toss the PCB into that when experimenting on the bench.
Who was having oscillation problems in the front end?
WOW, great! Thankyou very much...
now to get my hands on a batch of 5088's...as I lack a commonly necessary tool for almost anything these days...a credit card.
BAH!
THANKYOU!
Quote from: Mich P on August 26, 2010, 01:30:04 PM
Hi same problem here oscillation of the imput stage
I had three 2N5089 Hfe around 560 same batch
i have changed Q1 for a 2N3904 Hfe 195
and it's perfect now !
Mich P.
RedHouse I believe this is what your looking for...
Ok thanks
Quote from: Brossman on August 31, 2010, 12:09:44 AM
Quote from: Mich P on August 26, 2010, 01:30:04 PM
Hi same problem here oscillation of the imput stage
I had three 2N5089 Hfe around 560 same batch
i have changed Q1 for a 2N3904 Hfe 195
and it's perfect now !
Mich P.
RedHouse I believe this is what your looking for...
Reducing forward gain does stop oscillation if the circuit has an oscillation problem to begin with. I've posted a couple of times about the 330pF to ground from the collector of Q2 causing a blip up in response at high frequencies, and changing this to 30pF from Q2 collector to Q2 base being much better theoretically.
That being said, I've built and seen many built with 2N5088 exclusively that worked fine. There are differences in batches and between manufacturers of 2N5088 - as there are with all transistors. I've measured hfe400 2N3904s, too. I heavily suspect the implementation and wiring in that example. But there is always variation to be coped with.
Quote from: R.G. on August 31, 2010, 12:14:21 AM... I've built and seen many built with 2N5088 exclusively that worked fine. ...
Same in my experience, I've bult dozens with 2N5088's exclusively and had no problems either.
Brad, I just took a look at your website, and I have to say I'm seriously considering scrapping my project altogether...
I must admit...the VB7 looks rather enticing!
Quote from: RedHouse on August 31, 2010, 12:06:56 AM
Who was having oscillation problems in the front end?
I had those problems with the Neovibe board ordered from GGG. I replaced the transistors with
lower gain 2n3904s (190). But the latest batch of 2n3904s I bought have a gain of 290. It might be that I soldered a wrong resistor in there, I would have to check that. But the board layout should not be the problem as I didn't design it myself.
Quote from: jasperoosthoek on August 31, 2010, 05:41:29 AM
Quote from: RedHouse on August 31, 2010, 12:06:56 AM
Who was having oscillation problems in the front end?
I had those problems with the Neovibe board ordered from GGG. I replaced the transistors with lower gain 2n3904s (190). But the latest batch of 2n3904s I bought have a gain of 290. It might be that I soldered a wrong resistor in there, I would have to check that. But the board layout should not be the problem as I didn't design it myself.
Ah, I see.
Quote from: jasperoosthoek on August 31, 2010, 05:41:29 AM
I had those problems with the Neovibe board ordered from GGG. I replaced the transistors with lower gain 2n3904s (190). But the latest batch of 2n3904s I bought have a gain of 290. It might be that I soldered a wrong resistor in there, I would have to check that. But the board layout should not be the problem as I didn't design it myself.
It is always tempting to say that whatever caused something to work again must have been what caused the problem to start with. Tempting, but open to error.
Oscillation in something that normally amplifies is what is called gain-phase oscillation or Nyquist oscillation, after the guy who did some of the early work on negative feedback. There are two things which are necessary for a negative-feedback amplifier to oscillate. These are (1) a gain through the amplifier and then back through the feedback loop attenuation that is greater than one and (2) a phase shift in the amplifier plus feedback network which causes the 180 degree phase inversion of the amplifier to get turned around to 360 degrees so that the feedback reinforces the input, not opposes it. If you have those two things, it oscillates. Eliminate either one, and it quits oscillating.
Accordingly, if something oscillates, you can make it quit by either (1) lowering the forward gain of the amplifier (2) increasing the attenuation of the feedback path so it feeds back less to the input or (3) messing with the phase shift properties of the amplifier to get the phase shift down or (4) messing with the phase shift properties of the feedback network to get the phase shift down. And note that "gain" here is voltage gain unless you're way out in the tall grass messing with current mode amplifiers and feedback.
In the Univibe, the voltage gain of Q3 is unity, because of that unbypassed emitter resistance. So the voltage gain that matters for stability is all in Q1 and Q2. For this to be unstable, either Q1 or Q2 has too high a voltage gain, or they both do, or one or both has too much phase shift. Then there's always the possibility of wrong/misplaced components, soldering, etc. But the voltage gain of a bipolar is NOT equal to the hfe. That's the current gain, and is highly variable. The voltage gain depends on the value of the resistances connected to the transistor AND the current gain. High current gain *lets* you think about high voltage gain. Proper design *lets* you use high current gain either for high and variable voltage gain or lower but more dependable voltage gain depending on the circuit.
It was recognized back in the 1950s that reliable design of transistor amplifiers used local feedback to stabilize the gain of a transistor over variations in hfe, temperature, leakage, and so on. In a well designed bipolar transistor circuit, you can stick in just about any transistor of the right polarity with enough gain and the circuit will work properly.
Here a thread from last year talkin' about Q1, Q2 and Q3
http://www.diystompboxes.com/smfforum/index.php?topic=69918.msg607080#msg607080
Mich P.
Quote from: Mich P on August 31, 2010, 04:21:12 PM
Here a thread from last year talkin' about Q1, Q2 and Q3
http://www.diystompboxes.com/smfforum/index.php?topic=69918.msg607080#msg607080
Mich P.
The distortion issue is different than the oscillation issue.
When you have the blocking distortion problem all you (normally) need to do in increase the 22k input resistor to like 28k or so that usually fixes that even with Fairchild 2N5088's.
Quote from: R.G. on August 31, 2010, 10:49:30 AM
It is always tempting to say that whatever caused something to work again must have been what caused the problem to start with. Tempting, but open to error.
Very true. Of course a wrong component or faulty layout can cause oscillation too which is then solved by changing the transistors. :)
I have a tried and tested layout (by GGG) and have rechecked all components of the input buffer on the board. They all have the correct value according to the GGG PDF, even the 330p capacitor. At least, they were all new components and the color codes and descriptions match. Also, Mich P reported the same problem on page one of this thread. He also fixed it with changing the transistors. This means that at least two people have reported this now.
There
is a discrepancy though: The resistor at the base of Q3 has to be a
3.3k according to the information on your site. However in the GGG layout it is a
3.9k. Maybe not a spectacular difference but this does increase the feedback slightly. Was it was put there on purpose to have more similar gain from both sides of the phase splitter?
Quote
Oscillation in something that normally amplifies is what is called gain-phase oscillation or Nyquist oscillation, after the guy who did some of the early work on negative feedback.
I am aware of the Nyquist theory. But, of course, the theorem is based on a perfect differential amplifier with some voltage gain A which is completely independent on frequency voltage and whatnot.
Quote
Accordingly, if something oscillates, you can make it quit by either (1) lowering the forward gain of the amplifier (2) increasing the attenuation of the feedback path so it feeds back less to the input or (3) messing with the phase shift properties of the amplifier to get the phase shift down or (4) messing with the phase shift properties of the feedback network to get the phase shift down. And note that "gain" here is voltage gain unless you're way out in the tall grass messing with current mode amplifiers and feedback.
So I lowered the "gain". ;D
QuoteIn the Univibe, the voltage gain of Q3 is unity, because of that unbypassed emitter resistance. So the voltage gain that matters for stability is all in Q1 and Q2. For this to be unstable, either Q1 or Q2 has too high a voltage gain, or they both do, or one or both has too much phase shift. Then there's always the possibility of wrong/misplaced components, soldering, etc. But the voltage gain of a bipolar is NOT equal to the hfe. That's the current gain, and is highly variable. The voltage gain depends on the value of the resistances connected to the transistor AND the current gain. High current gain *lets* you think about high voltage gain. Proper design *lets* you use high current gain either for high and variable voltage gain or lower but more dependable voltage gain depending on the circuit.
I admit I used the term gain too freely. I know what hFE means, I've spend some hours explaining this stuff to undergraduate students ;D. I'm not an expert but at least I have some idea what we're talking about 8).
Quote
It was recognized back in the 1950s that reliable design of transistor amplifiers used local feedback to stabilize the gain of a transistor over variations in hfe, temperature, leakage, and so on. In a well designed bipolar transistor circuit, you can stick in just about any transistor of the right polarity with enough gain and the circuit will work properly.
Also true, but as you say this assumes that the circuit is designed well and that local feedback is used. But just take a look at the emitter of Q2. What's that capacitor doing there? I smell a complete lack of local feedback there. Clearly a part of the circuit where the voltage gain of the combination of Q1 and Q2 is directly related to the bare transistor characteristics (hFE is some sort) :-\. Of course the combination of the 47k and 330p should stop feedback but I can imagine that if Q2 is completely open that the 'resistance' of collector/emitter pair will be much smaller. Definitely the transistor is loaded capacitively for positive input swings.
I think that you or probably anyone else here would have never designed that buffer like that.
I spent some time today performing circuit simulation of the input buffer. I could not change the gain freely in my spice program. I was not able to get the circuit to oscillate, even with darlington transistors so in 'theory' it should be stable. So that's one point for the Univibe.
But at least two people have reported oscillation of the input stage, both with the same solution. I think that maybe stray capacities play a role. Just things that are harder to predict. My unit also sounded great except for distortion/clipping at relatively high input levels. That's how I found out. It could have slipped under the radar undetected...
Quote from: jasperoosthoek on September 01, 2010, 11:12:38 AM...I think that maybe stray capacities play a role...
I would agree with that.
I once tried to reduce a FuzzFace into a 1"x1" PCB thinking I could fit that nicely inside a guitar control cavity without taking up too much space.... bbbbzzzzzttt! wrong. No matter what I did it wouldn't stop oscillation, I gave up on the idea but it was a nice lesson (to me) in how physical layout (trace and component proximity) can effect a circuit.
Quote from: jasperoosthoek on September 01, 2010, 11:12:38 AM
I have a tried and tested layout (by GGG)
Yeah. Actually, that's my layout, sold under license. :icon_biggrin:
Quoteand have rechecked all components of the input buffer on the board. They all have the correct value according to the GGG PDF, even the 330p capacitor. At least, they were all new components and the color codes and descriptions match. Also, Mich P reported the same problem on page one of this thread. He also fixed it with changing the transistors. This means that at least two people have reported this now.
OK. Two of them have had this problem
There
is a discrepancy though: The resistor at the base of Q3 has to be a
3.3k according to the information on your site. However in the GGG layout it is a
3.9k. Maybe not a spectacular difference but this does increase the feedback slightly. Was it was put there on purpose to have more similar gain from both sides of the phase splitter?
Quote
I am aware of the Nyquist theory. But, of course, the theorem is based on a perfect differential amplifier with some voltage gain A which is completely independent on frequency voltage and whatnot.
The idea of a perfect amplifier in the theory is just to allow you to model imperfections external to the "perfect part" of the model for separating them out. Imperfections in the amplifier do not invalidate the theoretical application. Rather the perfect amplifier part lets you model imperfections in the amplifier you actually have and correct or modify the imperfections.
QuoteSo I lowered the "gain".
Yes. However, lowering the gain of any oscillating amplifier will stop always it from oscillating at some point. Obviously with a gain of less than one, no amplifier can oscillate. But simply fixing things by lowering gain also sacrifices the advantages that higher gain and feedback give you, at the very same time. Keeping the gain high AND making it stable at the same time is an advantage.
Since the circuit in question has worked properly and not oscillated with all higher-gain devices, this is a big suggestion that lowering one transistor's current gain is not the single and only way to fix it. It's like stopping your teenagers from talking or texting all their waking hours. You can do that by tying them to a chair out of reach of the phone/computer. But that may possibly not be the best of all possible ways to stop the behavior.
On the other hand, if it produced results you liked, that's fine too. If it works and you're happy with it, great. Making any one pedal work to your satisfaction is fine. But generalizing from one - or two! - pedals to every pedal is an easy to misunderstand how the electronics works.
QuoteI admit I used the term gain too freely. I know what hFE means, I've spend some hours explaining this stuff to undergraduate students ;D. I'm not an expert but at least I have some idea what we're talking about 8).
OK. That's good!
Quote
Also true, but as you say this assumes that the circuit is designed well and that local feedback is used.
Yep. That was my point.
QuoteBut just take a look at the emitter of Q2. What's that capacitor doing there? I smell a complete lack of local feedback there.
Yep. That smell is the deliberate use of a bypass cap to eliminate local feedback. My point is that not all circuits do this, or do it well. And not all circuits which have overall feedback need local feedback at every point. IC opamps for instance don't necessarily use local feedback on every point.
There is no substitute for knowing the details.
QuoteClearly a part of the circuit where the voltage gain of the combination of Q1 and Q2 is directly related to the bare transistor characteristics (hFE is some sort) :-\.
Yep. That's where the raw voltage gain for the overall feedback around all three of the first transistors is developed, Q3 being a combination buffer/phase splitter. And in this circuit the combination of gains in Q1 and Q2 is what's making the raw voltage gain. And the parasitic capacitances of those two devices plus Q3, plus oddities in layout and wiring, make the parasitic components which would make the amplifier unstable if it's not properly compensated by gain/phase compensation techniques. The whole point of overall feedback from the resistors in the emitter of Q3 and the gain from Q1 and Q2 is to form an overall feedback loop around all three. It can be done so it makes the individual characteristics of all three transistors not matter much as long as there's enough gain, and as long as the compensation gets the feedback loop gain under unity by the time the phase shifts add up to enough to make the feedback turn to positive, as Nyquist said.
QuoteOf course the combination of the 47k and 330p should stop feedback
Yeah. Actually, it's a single dominant pole to cut the gain under unity before the other phase shifts make the thing oscillate. I found in simulation runs that it also makes for a resonant peak that's not quite oscillatory out at a couple of MHz. A 30pF cap from Q2 C to Q2 B is much more effective, and does not have the resonant peak. But both sound the same.
Quotebut I can imagine that if Q2 is completely open that the 'resistance' of collector/emitter pair will be much smaller. Definitely the transistor is loaded capacitively for positive input swings.
It's capacitively loaded for both positive and negative swings.
QuoteI think that you or probably anyone else here would have never designed that buffer like that.
I'm confused - Q2's not a buffer. Q3 is. No, I'd not do a circuit like this, given today's state of knowledge about components and circuits. But Mieda-san didn't have that advantage some forty-plus years ago.
QuoteI spent some time today performing circuit simulation of the input buffer. I could not change the gain freely in my spice program. I was not able to get the circuit to oscillate, even with darlington transistors so in 'theory' it should be stable. So that's one point for the Univibe.
Yeah, I get pretty much the same results. My simulator lets me turn up the gains on transistors at will for a given run, and I couldn't get the thing to oscillate until I put in current gains of nearly ten thousand. That is another thing that makes me think that changing the 2N5088 for a 2N3904 may have lowered open loop gain, and may have stopped the oscillation, but that it could be something about the transistor that was replaced or the solder joints or PCB condition that made the first one oscillate, not simply that it was a high gain device. It is quite difficult to ensure that simply because something got "fixed" when you changed something that it was the part *type* that you replaced that fixed it. Could have been a bad/nontypical part you replaced, could have been a number of other things.
QuoteBut at least two people have reported oscillation of the input stage, both with the same solution.
OK. And more than two have reported all 2N5088s work fine. I've also found that all 2N3904s work fine. The sheer number of counter examples lead me to believe that there is more to it than using all 2N5088s is a problem, or all high gain devices is a problem. Not that you're not seeing and reporting correctly - just that I suspect that there's more going on than is apparent.
QuoteI think that maybe stray capacities play a role.
I agree 100%.
QuoteJust things that are harder to predict. My unit also sounded great except for distortion/clipping at relatively high input levels. That's how I found out. It could have slipped under the radar undetected...
Good that you caught it then.
Thanks R.G. for your free lecture in Univibology! :icon_mrgreen: I'm going to need a phase splitter for the funnel diode fuzz I'm designing. I might breadboard this one and see if I can get it to oscillate again. :D
Hey all,
Glad to see everybody was so interested in learning more about the 'Vibe while I've been out! School has been keeping me very busy (as in, very without a life other than studying, haha)...
I have recently received my trannys and perfboard via post, so I'm ready (and totally pumped) to begin laying it out. Upon sitting down to lay this badboy out, I realized I don't exactly know where to begin...Yes, I want to do this on PERF.
Sometimes I get overwhelmed by the end product and can't take a step back and look one step at a time...anybody have some words of wisdom to help me out a little bit? ...point me in the right direction, if you will...?
Thanks in advance,
- Britt
Doing a 'vibe on perf is not too taxing. There are no high-gain sections where you get into trouble, with the possible exception of the feedback on the first three transistors.
Here's an off-the-top rundown of the commonest Neovibe problems as I remember them without an actual count.
1. Wiring errors, especially on the speed control.
2. Part orientation of transistors and electro capacitors.
3. LFO won't oscillate (Q11 and Q12) for various reasons, including miswiring, orientation, etc.
4. Bulb won't light up/flash right; this is usually from issues with the depth wiring, but includes driver parts, and the bias trimmer on the driver transistor.
5. Other stuff. This includes a few where the input triple oscillates.
Overall, the 'vibe is a very forgiving circuit.
If I were doing one on perf, I would use a drawing program to lay out where each part and wire goes first, and print out both top-side and bottom-side drawings as a cheat sheet for the actual wiring. I would then build it one section at a time, and then power it up and test each section as I went. That way, nothing gets fried, and errors/problems are limited to whatever you did last. So I'd do the perf layout entirely as a drawing, either on a drawing program or what I personally did decades ago, on graph paper, in pencil, so I could erase and move things. As an aside, figure out where your wires come out and where the mounting post holes are going **before** you start putting parts down. You'll be a lot happier in the end.
When you get to soldering, wire up the power supply first, and get it working 100% before you do anything else. That's because you'll use the power supply in testing all of the remaining circuits. Then do the LFO, Q11 and Q12, the speed and depth controls, and the bulb and driver. These are completely separated from the audio path except for the light going into the LDRs and the power/ground, so when they work, they work and can be ignored for the rest of the build.
Then, place and solder the input preamp, Q1, Q2, Q3 and surrounding parts right up to the capacitors that come off Q3's collector and emitter. And solder up the volume pot and input/output jacks. You can now put a guitar signal into the input jack and temporarily run a wire from either of the the Q3 collector capacitor or emitter capacitor to the volume pot and hear the audio at both places by moving the wire from one to the other. This makes the circuit into its own audio probe.
When the first stage is working OK, build the first phase stage, Q4/Q5. Do the same "audio probe" trick with the outputs from the collector and emitter of Q5. When this works, do Q6/Q7, etc. till you get to the emitter of Q10. At this point, all the circuits work and all you need is the wiring to the output switch and volume pots updated.
This all relies heavily on already knowing where each part goes to come out right. It's also a good, foolproof way to build up the PCB for the project as well. It takes longer to build, but much less time to debug.
Thanks, RG!
I'm actually doing the layout by hand on paper. I custom made graph paper on EXcel with thin translucent lines. I have it matched with the exact size of my perf, by way of hole X hole dimensions.
I will take your approach for doing it sectionally, thanks. But...does this require a voltmeter? I have several analog multimeters...these aren't voltmeters are they? haha..
You're all over it. Go man.
I see in the old schemo where the cancel switch is, but I cannot determine where the other side of the switch is...however, in the old pedal, there was no true bypass, so is this the spot where signal was shunted with a SPST switch?
Also, taking a side-by-side of this and the Neovibe schemo on GEOFEX, I cannot seem to figure out where the option of having the speed controlled pedal is...were there not some Univibes that had the foot-controlled speed as an option? I assume that would redirect the signal to a jack, where upon signal would be routed to (and then from) the rocker pedal via a stereo cable (likely hardwired to the rocker itself). I guess the trick the would be getting the signal to use a knob on the pdeal as standard, then bypass it when the footpedal is plugged into the jack.
Now as for pulling this one off, I'm completely clueless. I mean, I could use a DPDT switch to go between the two different speed knobs, but that would be...let's just say, a terrible inconvenience and not worth the effort (especially at a live gig)...
Any hints?
[Edit:] here are the links to the different schemos...
http://www.univox.org/pics/schematics/univibe.gif
and apparently, nvm about the neovibe schemo...I cant find a link, but I think you can find it at geofex somewhere...
Quote from: Brossman on October 11, 2010, 08:19:05 PM
I see in the old schemo where the cancel switch is, but I cannot determine where the other side of the switch is...however, in the old pedal, there was no true bypass, so is this the spot where signal was shunted with a SPST switch?
Kind of. The original Univibe had no bypass, true or otherwise.
What it did was to cancel the sweep by shorting the LFO signal to ground, forcing the bulb to stay at a constant light. The signal was always beset with the frequency filtering that was left over by the driver not getting any LFO signal.
QuoteAlso, taking a side-by-side of this and the Neovibe schemo on GEOFEX, I cannot seem to figure out where the option of having the speed controlled pedal is...were there not some Univibes that had the foot-controlled speed as an option?
It was not an option. The original Univibes all had a foot controlled speed rocker. They did not work *at all* without that pedal. The pedal contained the speed pots that made the LFO run. No option. Some of the units may have oscillated at a very slow fixed speed with the pedal not plugged in, but none of the ones I've messed with do.
QuoteI assume that would redirect the signal to a jack, where upon signal would be routed to (and then from) the rocker pedal via a stereo cable (likely hardwired to the rocker itself). I guess the trick the would be getting the signal to use a knob on the pdeal as standard, then bypass it when the footpedal is plugged into the jack.
As I said, the rocker was a fixed part of the LFO. No rocker, no sweep. And the signal never went to the rocker. The cancel switch was activated by rocking the pedal fully back. That shorted the "cancel" pad to ground and killed the sweep internally.
QuoteNow as for pulling this one off, I'm completely clueless. I mean, I could use a DPDT switch to go between the two different speed knobs, but that would be...let's just say, a terrible inconvenience and not worth the effort (especially at a live gig)...
There are ways to pull it off, but none of them are how the originals worked. You can use special switching jacks to switch between the internal and an external speed pot, but the number of wires gets you quickly. All of the three speed pot terminals you need are floating - none of them is ground. You have to run a ground wire to the rocker/cancel switch to work cancel, as well as yet a fifth wire to actually short the cancel pad. You're up for at least five wires to the rocker. A DPDT won't do it unless you're willing to float the whole rocker pedal sheet metal on the common line of dual pots. That's not a good idea from a hum and noise standpoint.
Your only mistake is thinking that the Univibe had some of the modern conveniences (mod cons in the UK) that we think are normal for pedals today. It didn't.
>Your only mistake is thinking that the Univibe had some of the modern conveniences (mod cons in the UK) that we think are normal for pedals today. It didn't.
Taking a few second glances at the schemo, I see how that lays out now. However, do I need the "cancel" switch if Im modding for DPDT? Wouldn't I just wire the switch to go between itself and the board in/out?
And what about the transformer in the original circuit? do I need to include some kind of inductor into this casing, as well? Or am I better off with LM317 (or the like) acting in place of this?
Quote from: Brossman on October 11, 2010, 10:59:24 PM
However, do I need the "cancel" switch if Im modding for DPDT? Wouldn't I just wire the switch to go between itself and the board in/out?
My preference is for a real bypass, not the frozen-in-place filtering that the univibe does when it's supposed to be cancelled. I'm not sure what mod you're doing for DPDT; if it's true bypass, yes, do that and ignore "cancel" entirely. I would.
QuoteAnd what about the transformer in the original circuit? do I need to include some kind of inductor into this casing, as well? Or am I better off with LM317 (or the like) acting in place of this?
Putting a mains transformer in a low-level effects pedal is a sure way to get the possibility of hum where there was none before. The original Univibe transformer was solidly encased in thick steel end bells and frame to help shield it, and the enclosure was big enough to get a little distance from the circuit. Transformers are for making DC power (in the way we use them mostly) and don't have anything to do with inductance in this case at all.
My advice: use an external 15-18Vac or 18-24Vdc wall adapter and wire it so it powers only the vibe clone, wired into the power in pads on my schematic. Do not try to use its power supply for anything else in your pedal chain.
If you insist on wanting to run a univibe clone from the same 9V adapter as the rest of your pedals, you can do that with an LT1054 charge pump converter to make 17-18Vdc from 9V and feed that into the 7815 that regulates the power for the rest of the circuit.
And while we're on power supplies, don't use the R-C filtering from the original schematic. You get better performance from a full wave rectifier bridge and a 7815 three terminal regulator, in terms of both hum and noise. That is, use the Neovibe power section, not the "vintage" Univibe power section.
IMHO.
where exactly does the power section end? after the diode/resistor/cap array? before the lamp and tranny 13?
well, nvm about that...I guess I'm too quick to say "huh" and beg for explanation rather than figuring things out on my own...which I did :o so...I'm looking into price listings for all of the other goodies involved...
I plan to be very, hmm how shall I say...deliberate (?) in my movements in production of this...It's probably my favorite effect ever produced. I really don't know what it is, but something about the woo-wee-woo-wee of a 'Vibe that just makes the guitar feel so lively...GAH!
All I'm sayin' is that I don't wanna screw this up...too badly :P
One of the huge advantages of building your own is that if you built it yourself, you're the best-prepared person in the world to fix it or enhance it.
So take heart from the idea that there is really very little you can do that is not fixable even if you do make a mistake. Every thought and every action you take toward completing the circuit not only goes into the effect, it goes into your head and your hands, and YOU get better as a result.
There is a phrase I remember seeing in the book "The Sensuous Gadgeteer" that stuck with me: the finished product is just the garbage of doing the work.
Even if the finished thing doesn't work at all, the worker is now in a position to do the (more) perfect thing. In the welding trade, for example, it's very much standard practice to do a few practice welds on the materials being welded before trying the actual production welds, just to get the feel of the material and how it responds. In machining or manufacturing, it's common to PLAN to throw away the first few articles made as "learner" items, to tweak the process in to being perfect.
By all means, plan, consider, and prepare. But don't think any mistakes are irreparable. They are - this is something that I rely on! :icon_biggrin:
Well, schooling has taken to the forefront of my pedal endeavors. However, this is still churning (or...burning...?) away through my head every day.
New Idea - taking a look at Roger Mayer Voodoo-Vibe, and another DIY project labeled "Tri-Vibe" (very VERY cool, btw), it seem possible to obtain a trem, as well as the standard chorus and Vibrato.
How can I potentially add this Tremolo to my 'Vibe? (I still havent constructed anything, let alone bought parts yet, so dont worry if its gonna totally overhaul everything... I havent forgotten any lessons i've learned here...)
Hey all,
I've been thinking about some more things I can implement into me design, since it's taking me so long to get everything together. I have some new ideas, but more questions than answers...
I've decided to use 4p5t switch to change out some phase caps. Any recommendations for some values? I like the idea of 'Vibe, Phase 45/90, and something new :icon_twisted:
I've noticed that there are some diodes arranged after the dual speed control pot... I've no idea what's going on here (help?). How are these affecting the signal? (If so, mods?)
One more... I was wondering if it's possible to have 2 separate footswitches for bypassing... I see it like this:
- include 'cancel' switch for when effect is engaged (as per Univibe)
- one 3pDt for true bypass of entire signal (regardless of 'cancel' position)
- there will be a separate (foot) unit for speed control (housing for the 'cancel' as per Univibe)
Thanks in advance,
- Britt
Quote from: Brossman on January 23, 2011, 07:24:48 PM
Well, schooling has taken to the forefront of my pedal endeavors. However, this is still churning (or...burning...?) away through my head every day.
New Idea - taking a look at Roger Mayer Voodoo-Vibe, and another DIY project labeled "Tri-Vibe" (very VERY cool, btw), it seem possible to obtain a trem, as well as the standard chorus and Vibrato.
How can I potentially add this Tremolo to my 'Vibe? (I still havent constructed anything, let alone bought parts yet, so dont worry if its gonna totally overhaul everything... I havent forgotten any lessons i've learned here...)
]
Look up the schematic for the RT-18, the univibe's predecessor.
Quote from: Brossman on February 16, 2011, 02:17:02 AM
I've noticed that there are some diodes arranged after the dual speed control pot... I've no idea what's going on here (help?).
Technology of the Univibe, http://www.geofex.com (http://www.geofex.com) Those limit the voltages across the LFO modulator generator.
Quote
How are these affecting the signal?
Not at all. They have no connection to the signal, other than keeping the LFO in bounds at all speeds.
Quote(If so, mods?)
We have noticed chronic disease that pops up from time to time. We call it BUMS - Blind Urge to Mod Syndrome. One of the most obvious symptoms is someone asking for mods without having any idea what they want the mods to do. Collecting random mods is a good way to be back here saying " I built this and it worked great, and the I put on the hyperspace doppelganger mod and it won't pass audio any more..." If you don't know where you're going, any direction is as good as any other, and staying in one place is also equal to the other directions.
QuoteOne more... I was wondering if it's possible to have 2 separate footswitches for bypassing... I see it like this:
- include 'cancel' switch for when effect is engaged (as per Univibe)
- one 3pDt for true bypass of entire signal (regardless of 'cancel' position)
- there will be a separate (foot) unit for speed control (housing for the 'cancel' as per Univibe)
Sure. That'll work.
Quote from: R.G. on February 16, 2011, 02:53:58 PM
We have noticed chronic disease that pops up from time to time. We call it BUMS - Blind Urge to Mod Syndrome. One of the most obvious symptoms is someone asking for mods without having any idea what they want the mods to do. Collecting random mods is a good way to be back here saying " I built this and it worked great, and the I put on the hyperspace doppelganger mod and it won't pass audio any more..." If you don't know where you're going, any direction is as good as any other, and staying in one place is also equal to the other directions.
Well said.
I'd like to add (if I may) it's most often the best plan to get a basic unit of whatever kind up-n-running, then worry about mods. Pre-emptive mod planning is good for daydreaming and such but without a basic, functioning unit, you really have no idea what/how the mods effected your effect.
Many want to jump-in to a fully modded state and can't figure out what went wrong, when something does go wrong.
Sorry to sound like a buzz-kill, but it will save you (and others) more time than you may realize.
Modding should be reserved for the case where you want to change something specific because it doesn't work for you or you thick it can be done better in a certain way. Don't mod just for the sake of modding just to be different. Don't fix what ain't broke. Statistically, if all you do is random mods that the most likely outcome isn't a better pedal. Bright minds design the best they can.
I slightly disagree with R.G.'s road analogy. In case of modding stuff: If you don't know where you are going or why you are even moving then just stay put!
Or, just call it circuit bending cause that's what it is ;D.
QuoteSure. That'll work.
Does the cancel switch still color the sound when engaged if the whole is not bypassed? I like the slight tonal shift of this coloration, and I'd like it available to me, but not a permanent feature.
QuoteWe call it BUMS - Blind Urge to Mod Syndrome.
Quote...because it doesn't work for you or you thick it can be done better in a certain way. Don't mod just for the sake of modding just to be different.
I don't want to mod it to make it "better," nor is my approach *completely* blind. As soon as I learn how different things work, I'd like to be able to change how they work, regardless of efficiency. I am a tone freak through and through. However, I am not 'searching' for something specific. Rather, I'd like to be able to let these sounds find me. I enjoy swapping out components to hear the tonal shift - switches, knobs, assorted controllers - if I can change it and hear it, I might be able to find a use for it.
Though, regardless of how I feel, I will take a more careful approach. I've enjoyed learning everything that has caused delays in my design and build. I'm making a lot of mental progress thanks to all of you. RedHouse, R.G., and Mark have been especially helpful, as well as the Geofex page. And I cannot forget everybody else's two cents (or pence)... It's been a total mindflip. I'm having a lot of fun with this - c'mon, can't a guy dream?
@Brossman
Modding for the sake of modding is stupid. As I said modding should be done with a specific plan in mind. Why is irrelevant to me. You clearly know what you are doing and are willing to learn. Also you know what you want. So mod all you want to get the sound YOU want ;D. I am in no position to tell people what to do and why. But I see that some people do dumb things to circuit or even worse to original vintage effects and instruments. It's their business but I'm allowed to call it stupid :).
I've run into some problems laying this one out... turns out 2sc828's are ECB, and 2n5089's are EBC. Can I just effectively use the same layout, just bend the leads around to the correct spot in the socket? Should I then shield one of these leads? I know his seems simple, but I hear tranny-pinouts give people more trouble than anything else...
Same layout as what?
Just bend the legs, no isolation necessary - just make sure they don't touch.