Vox - Repeat Percussion (V 809)  [schematic]

Discussion regarding early stompbox technology: 1960-1975 Please keep discussion focused and contribute what info you have...
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tabbycat
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Post by tabbycat »

if anyone has an unboxed version of this circuit that they know works
http://4.bp.blogspot.com/-k1MS42zlbeI/U ... ied+II.png
or are uk-based and would be prepared to make me a working populated board for a charge (i can post you all the bits as one of the transistors isn't that common) i would be grateful if you could pm me.

the one i built and posted in this thread (image taken pre-boxing) didn't work. i have spent hours and hours this weekend fiddling around with it, researching every possible problem online, taking it apart and putting it back together a hundred times, desoldering-resoldering, all to no avail, and it has finally made up my mind that i don't want to build vero layouts anymore. it's not worth my frustration.
i know it's me and not the layout as others have built it successfully. the layout is good. i am the faulty component.

when i built my first pedal (superfuzz) my concentration was sharp, but due to a recent serious illness (hence my absence from the site for years) i am not up to the mental task anymore, and it's bad for morale to try to push my new limitations.
from now on i will stick to easy mods on cheap pedals. one or two bits i can cope with. and when they work will post photos and details here so others can follow. that i can do.

but i would still like to have this pedal, and (since there are no commercially available clones i know of) i thought i would ask here before searching further afield. i have the box wired up properly (pots, switches, 3pdt, etc) and all ready to go. i just can't do the circuit.

many thanks, tabbycat.

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induction
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Post by induction »

The Earthquaker Devices Hummingbird is based on the Repeat Percussion, with additional Depth and Level controls, just FYI.

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tabbycat
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Post by tabbycat »

thanks for the tip, induction.

alas i'm inescapably underclass for the foreseeable re having a ton to throw at a pedal right now. am having to be creative with modded danos, joyos and behros, etc, and what i can knock up (or clearly can't) for myself. i was planning to take a break re building until such possible time as i get better anyway (re illness affecting concentration) but this was one of three unboxed builds i thought i could easily finish off before breaking. fatal error.
but i notice mark has the humming bird layout at guitar fx so will peruse to see if it is any simpler (tbh i think the average electric tin-opener has more components, which just adds to my shame).
so your thought may yet help at a future date.

tabbycat.

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tabbycat
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Post by tabbycat »

victory at last.

this was painful. a real nightmare build. probably not worth the pain it caused me to finish it but i will not be beaten. not in my nature. a stubborn little cat. so a pyrrhic victory. but it really helped me reset my perspectives re pedal building, which has ultimately been a valuable lesson.
and i can now do offboard wiring a lot better from stripping and rebuilding this, and understand schematics a lot more from comparing the various incarnations of this. which was hard won and long overdue.

main problems i had with this build were that the 2n2646 unijunction transistor ticked because it was in backwards. as it has two bases (outside legs) i didn’t think it could be in wrong (and the middle leg was set back which matched the vero layout) but i bought it from ebay so didn’t know much about it. spun it around out of sheer frustration and the thing leapt into action. also got caught up in the offboard wiring. never been good at that so was asking for trouble choosing the deluxe two switch modded layout. but cracked it through sheer bloody-mindedness.

may do an fsb post on the differences between original vox onboard repeater (starstream, etc), IvIarks layout (which i used), and acidfuzz’ modded version (as it appears in the sonic boom. some learning to share, for what it’s worth.
but apart from mods (which i’m going to get into primarily now) i don’t think i will build anything for which i can find a cheap clone that will get me within 90% of the sound i’m looking for. as things stand for me healthwise anyway. and if that doesn’t exist i will then i will look into possibilities of modding something that gets close to that up to spec.
building from scratch will be a absolute last resort until my head clears and i can concentrate properly again. absolutely no fun until. perfectionism is a good ideal but when it becomes masochism it’s time to take a step back and re-evaluate my relationship with the whole thing.

anyway, the actual finished thing sounds superb. happy with that. really choppy and time-warpy. more warpy than a basic tremolo alone. slighty 1960s science fiction. a really nice period texture to it. definitely an original. there are some things i intend to tweak when i get around to it but for now this is it.
tabbycat repeater 1.jpg
tabbycat repeater 2.jpg
tabbycat repeater 3.jpg
tabbycat repeater 4.jpg
my deviations from IvIark’s great layout (thanks IvIark) were placing the 47k from the 2n2646 transistor with a 4k7 (as shown in the original vox layout. i tried it with an 8k and a 10k as it just shifts the rate speed starting point, which you can then really change with the rate switch and rate pot.
am going to swap electro caps on rate switch for something lower. 10u and 4u7 is suggested by IvIark’ s vero, but having experimented (and read others feedback) something like 4k7 and 1u would bracket speed better. an easy swap out at a later date.
actually i tried a 20k and 50k pot in place of the 47k resistor (before swapping it) and it worked like a fine-tune rate pot. or so i remember. not hugely useful to me, but if you are a dj or in the studio and trying to fine synch this effect with something else then that mod might be worth playing with.
empty sockets on ground rail were just something i put in to give me quick ground options when breadboarding the offboard wring.

many thanks to all fsb members who chipped in contributions and ideas o get me off the ground with this. always much appreciated. you know who you are.

tabbycat.

am dedicating my build to delia derbyshire, whose astonishing ‘the dreams’(1964) was the inspiring soundtrack to the trouble-shooting phase of my build.


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Nocentelli
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Post by Nocentelli »

Looks good! Glad you finally got it working.
modman wrote: Let's hope it's not a hit, because soldering up the same pedal everyday, is a sad life. It's that same ole devilish double bind again...

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Post by kaycee »

Yes, well done indeed.

A really nice looking build too, neat work.

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Calambres
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Post by Calambres »

I've done this circuit. It works but the output us much higher than the bypass sound. I've read in this and other threads about the opposite and some mods to make it louder but in my case the output is so big that almost distorts.

I'm using the classic schem, no depth mod, BC108/BC109 couple (tried a pair of MPSA18 too) and 2N2646. The only difference with the original schematic is that I prefer a 100K rate pot.

:scratch: :hmmm:

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tabbycat
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Post by tabbycat »

Calambres wrote:I've done this circuit. It works but the output us much higher than the bypass sound. I've read in this and other threads about the opposite and some mods to make it louder but in my case the output is so big that almost distorts.

I'm using the classic schem, no depth mod, BC108/BC109 couple (tried a pair of MPSA18 too) and 2N2646. The only difference with the original schematic is that I prefer a 100K rate pot.

:scratch: :hmmm:
hey calambres, i built the basic vox one (from a vero layout at guitar fx layouts, i used the all options layout) using the mpsa18 and the 2n2646.

viewtopic.php?f=19&t=2687&start=120#p244261
http://tagboardeffects.blogspot.co.uk/2 ... ssion.html

vol is a shade louder than bypass but i think that suits it as it makes it 'pop' in the mix a bit more clearly. i tweaked the trim in my my dano cool cat trem to have a slight vol boost for the same reason. if its loudest is bypass volume then the repeater sounds more like a dropping out than a punching in, if you understand what i mean. like the silences between the noise (the falling away of volume) become the feature, rather than the increasing noise (punching in between the silences).
but both have their uses.

after an agonising build (don't know why this one was such a pain, have built more complicated things before and since without headaches), i'm actually about to start retworking it. the depth control is needless really. like you am going to get rid and jumper to full on. going to fine tune the rate caps as there is too much overlap. would like a wider range. would like to add a stomp and rate cap mods that allow me to double the repeat rate at a stomp, if that's feasible.

you say you built with both bc108/109 and the mpsa18, was there any difference in the final result?

but to get back to the vol issue, maybe compare your resistor and cap values with the one in the vero link i posted. maybe a diference that tames that?

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Calambres
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Post by Calambres »

Regarding the BC108/109 against MPSA18, I have not found a significant difference but I have not spent much time with the later pair as I noticed there was no difference in ticking, very low with RG's split grounds trick, nor in the output level. I decided to stick with the BCs.

The output in my build is TOO loud. I've scoped it and it is much higher than the input... I'll post a pic of the scope's screen later this afternoon. I've decided to breadboard a new instance of this circuit to play with some values to tame it out. At first I planned to add up a voltage divider in the output, a volume control, but as I said in my previous post, the output is almost distorting. I do not think a trem should distort at all! The cap and res values in the link you posted are for "more output" which is exactly the opposite I want. I used those values in the first try and went back to the otiginal values but still with too much output. I've checked the values and they're all fine. I cannot figure why it is so loud when most of the people complains just for the opposite.

And I totally agree with you that the depth control is needless in this particular circuit.

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Post by induction »

Calambres wrote:The output in my build is TOO loud. ...

I've checked the values and they're all fine.
Post photos and we'll double-check for you.

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tabbycat
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Post by tabbycat »

Calambres wrote:The output in my build is TOO loud. I've scoped it and it is much higher than the input... I'll post a pic of the scope's screen later this afternoon. I've decided to breadboard a new instance of this circuit to play with some values to tame it out. At first I planned to add up a voltage divider in the output, a volume control, but as I said in my previous post, the output is almost distorting. I do not think a trem should distort at all! The cap and res values in the link you posted are for "more output" which is exactly the opposite I want. I used those values in the first try and went back to the otiginal values but still with too much output. I've checked the values and they're all fine. I cannot figure why it is so loud when most of the people complains just for the opposite.
hey calambres,

did you notice this post?
"put a 3.3K resistor in series with lugs 2 and 3 to ground where the volume pot was so the volume stays even throughout. Move the volume control to the end of the circuit by replacing the 1M resistor at the output with a 500K audio pot.
https://www.freestompboxes.org/viewtopic ... 00#p192793

though it doesn't explain why your build is so much louder than other builds based on the same schematic/layout is may be something to try?

original onboard guitar repeater schematic http://d13ucm2atqlvn6.cloudfront.net/16 ... fc5100.jpg
acid fuzz's modified schematic for the sonic boom https://www.freestompboxes.org/download/ ... &mode=view

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Post by Calambres »

Note to self: Never double-check... always triple check :oops:

1K resistor from B2 of the 2N2646 was 10K. I swear that orange looked so reddish! :roll:

Now, with a real 1K resistor, the output is somewhat tamed although I cannot explain why as this is not the audio path :scratch: Also the VFO fequency decreased. Now a 10uF cap from emitter from the 2N2646 to ground is sloooooow and 4.7uF is still too slow. 2.2uF or 3.3uF may be the ticket. I think I still have something wrong in this build.

Other modification I've just done is that I prefer a 22nF input cap. Not too thin (4.7nF) and not too boomy (100nF).

Just for the record, this is a scope shot before discovering the wrong resistor. Channel 1, up, is the input wave (500mV scale) and the second channel, below, the output (1V scale). Phase is also inverted.
Attachments
VRPscope.jpg
VRPscope.jpg (45.77 KiB) Viewed 3759 times

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Post by tabbycat »

Calambres wrote:Note to self: Never double-check... always triple check :oops:

1K resistor from B2 of the 2N2646 was 10K. I swear that orange looked so reddish! :roll:

Also the VFO fequency decreased. Now a 10uF cap from emitter from the 2N2646 to ground is sloooooow and 4.7uF is still too slow. 2.2uF or 3.3uF may be the ticket. I think I still have something wrong in this build.
hey calambres, good to hear you cracked it in the end. human error = factor x.

sometimes i think the small builds try to trick you into a false sense of security. you think 'well i don't have to concentrate much because it's so small, what could possibly go wrong?'...
and then they've got you.

here's the final specs of the my build (as shown in my build post above, somewhere):
"my deviations from IvIark’s great layout (thanks IvIark) were placing the 47k from the 2n2646 transistor with a 4k7 (as shown in the original vox layout. i tried it with an 8k and a 10k as it just shifts the rate speed starting point, which you can then really change with the rate switch and rate pot.
am going to swap electro caps on rate switch for something lower. 10u and 4u7 is suggested by IvIark’ s vero, but having experimented (and read others feedback) something like 4k7 and 1u would bracket speed better. an easy swap out at a later date.
actually i tried a 20k and 50k pot in place of the 47k resistor (before swapping it) and it worked like a fine-tune rate pot. or so i remember. not hugely useful to me, but if you are a dj or in the studio and trying to fine synch this effect with something else then that mod might be worth playing with.
empty sockets on ground rail were just something i put in to give me quick ground options when breadboarding the offboard wiring."
https://www.freestompboxes.org/viewtopic ... 20#p244261

maybe useful notes in trying to speed yours up?

interesting to see the scope image. i don't really understand the fine print of scoping but it looks like it doubled or tripled input vol. a bit annoying.

such a neat tone these things have. magical.

tabbycat.

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Calambres
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Post by Calambres »

Thanks, Tabbycat. I experimented yesterday with rate caps and definitely 1uF is much too fast but I'm using a 47K resistor as per the IvIark layout instead of the original 4k7.

More on this for this afternoon.

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Post by Calambres »

All went well. I opted for the original design with 22nF input cap. As soon as I returned to a 4K7 resistor and 4.7uF cap the circuit behaved as supposed.

Thank you all for your support.

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Post by Duckman »

Hey, Calambres, no le saquen el pie del acelerador a Pisotones!
Es uno de los pocos sitios serios (Dios! dije serios???) en español que hay.

Gran abrazo y felicitaciones!

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Post by Calambres »

:D :horsey:

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Post by R.G. »

Design note on the RP:

The repeat percussion works by shunting a lot of the input signal to ground. In that sense, the circuit is a "tremolo down" or "cut only" circuit. It would be much quieter than the original signal for that reason if there was not a post-tremolo amplifier to bring the signal level back up.

If the post amplifier is not enough gain to regain what the shunt circuit took away in averaged-to-the-ear signal level, it sounds quieter to the ear than the original signal. If there is too much gain in the post-amplifier, it sounds louder to the ear than the original.

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Post by tabbycat »

R.G. wrote:Design note on the RP:

The repeat percussion works by shunting a lot of the input signal to ground. In that sense, the circuit is a "tremolo down" or "cut only" circuit. It would be much quieter than the original signal for that reason if there was not a post-tremolo amplifier to bring the signal level back up.

If the post amplifier is not enough gain to regain what the shunt circuit took away in averaged-to-the-ear signal level, it sounds quieter to the ear than the original signal. If there is too much gain in the post-amplifier, it sounds louder to the ear than the original.
hey rg, many thanks for the authorative explanation re the 'cut-only' circuit.

i think i grasped that 'cut-only' by instinct and feel, and have a vague understanding of how tremolo is a wave thing and there can be different textures and depth of wave that offer tremolo. but hadn't yet understood (technically) why the repeater sounds more 'sucky' and 'concave' than other tremolos that are more 'pulsey' (excuse the abstract terms but am from an art not tech background).
tabbycat wrote:vol is a shade louder than bypass but i think that suits it as it makes it 'pop' in the mix a bit more clearly. if its loudest is bypass volume then the repeater sounds more like a dropping out than a punching in, if you understand what i mean. like the silences between the noise (the falling away of volume) become the feature, rather than the increasing noise (punching in between the silences).
https://www.freestompboxes.org/viewtopic ... 20#p248391

i really like the repeater because it has that spooky fluttering shattering feel. slightly otherworldly. maybe because it also has aspects that remind me a bit of reverse delay effects somehow. again i don't understand why but that's just how i fit it into my personal sound filing system (in my head).

for example, though i'm not 100% sure (james c, get on here and tell us) i'm sure the intro to this is a repeater ramped up with wah.


for the record, are there any other vintage tremolos that fit into this circuit category and sounsdcape that you are familiar with? for example the jordan vico-vibe? that's non-optical pre-digital. that has a lush fender rhodes kind of tremolo tone to it, also very nice (in my opinion anyway). am considering double-reboxing my repeater with either a vico or magnavibe trem (though mag is optical).

and are there any mods that lend themselves particualrly well to this 'cut only' circuit that you would recommend or suggest?
i am about to de-depth-control and de-rate-switch my repeater build as they aren't really worth the fiddle.
(i built the last all-mod-cons version here: http://tagboardeffects.blogspot.co.uk/2 ... ssion.html)
however i do like the tone switch on this. the repeater stays lush across the frequencies, so may extend the range of that (add more tone caps on a rotary switch) or experiment with some tone stacks. swtc or a scoop on a trim pot.

by the way, are you the rg, as in rg keen? if so many thanks for your stuff across the net and at geofx mission control. am a big fan of your work. and live my stompbox building life accoring to your 'keens laws'. you're like the stomp box moses.

tabbycat.

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Post by R.G. »

tabbycat wrote: i think i grasped that 'cut-only' by instinct and feel, and have a vague understanding of how tremolo is a wave thing and there can be different textures and depth of wave that offer tremolo. but hadn't yet understood (technically) why the repeater sounds more 'sucky' and 'concave' than other tremolos that are more 'pulsey' (excuse the abstract terms but am from an art not tech background).

i really like the repeater because it has that spooky fluttering shattering feel. slightly otherworldly. maybe because it also has aspects that remind me a bit of reverse delay effects somehow. again i don't understand why but that's just how i fit it into my personal sound filing system (in my head)
The EH Pulsar does a similar thing, attenuating the signal, but with a pulsed control signal, not a sawtooth signal.
The repeat percussion is unique as far as I know in that it does not simply pulse the signal on and off, but actually does some loudness shaping on each "on" cycle, giving it a high initial peak which trails down before the next peak. The Pulsar is mostly on/off.

I think your feelings about the signal might be a response to that kind of shaping it into many "notes".

As Freud said "It's a theory..." :D
by the way, are you the rg, as in rg keen? if so many thanks for your stuff across the net and at geofx mission control. am a big fan of your work. and live my stompbox building life accoring to your 'keens laws'. you're like the stomp box moses.
Guilty. :D

I'm glad if some of that stuff has been a help.

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