what's the smallest (literally) boost stage i could hack on the end of this?

[pinkjimiphoton]

i built this sucker, got it crammed in a 1590a (almost... man its busting my stones lol, every time i try to button it up something messes up)

anyways, i gotta LITTTTTTLE room on the side of the switch.. enough to stuff a really small daughterboard i think.

i've tried breadboarding a few things, one seems to work fairly well, but my guitar volume sounds scratchy when i tweak it so not sure if its a good fit.
don't have room for much... so hoping a suggestion or two for a small transistor boost will work. never tried to tack one on an envelope filter before.

or is there a better way? i tried messing with some of the resistors around the oa to raise the gain, but not happening. i think its too simple, or i'm too stupid, or a combo of the two.

advice appreciated. i'll buy a bum a cuppa joe with your name on it.

[Keppy]

I think messing with the opamp gain will mess with the sound of the filter, otherwise you could just increase R108 to a few MegΩ and be done.

Re: guitar volume scratchiness, did you leave out R112 as indicated? That resistor to Vref would put some DC on your guitar pot, which would make it scratchy for sure. I don't see how a booster after the circuit would make the guitar knob scratchy though.

The input impedance of this circuit is pretty low, as if it was intended for a buffered bypass. Have you tried buffering the input instead of boosting the output? If you're just looking for output volume equal to input, that might do it.

I don't actually have any boost suggestions.

[Rob Strand]

I think messing with the opamp gain will mess with the sound of the filter, otherwise you could just increase R108 to a few MegΩ and be done.

Probably, I haven't checked.
You could adjust some of the parts to compensate.  (Without doing any calculations I'd guess R108=470k and C105=3n9)

However,another way to do it is to put a divider on the output.  It must DC coupled the feedback components to the opamp output.
1) disconnect R108 and C105 from the opamp output
2) place a divider say
     opamp output ->  2k2 -> 10k -> *Vref*
    or, if your Vref cap isn't very large.
    opamp output ->  2k2 -> 10k -> 4.7 or 10uF to ground.
3) Connected the floating side of  R108 and C105 to the junction of the 2k2 & 10k.
(4) The output cap stays on the opamp)


When I look at C104 it looks wrong to me!   


BTW both my examples here increase the gain by approx 20%.

[lars-musik]

You could do an LBP-1. If you leave out the input cap and the pulldown resistor, you'd end up with 4 resistors, one tranny, one cap and a small trimmer (or you just hardwire it to the desired volume). You wouldn't even need a circuit board for those few components.

https://hotbottles.files.wordpress.com/2012/02/lpb-schematic.png

[Fancy Lime]

+1 for the input buffer. The circuit sure doesn't look like it was intended to be fed a guitar signal directly and adding a buffer will be the simplest, lowest parts count thing to do without changing the sound. Any of Jacks basic buffers will do:
http://www.muzique.com/lab/buffers.htm

I would go for a dual op-amp dual buffer (input and output). That way you can easily make the output buffer a booster by adding just 2 resistors (not sure if you need/want to do that but it makes a very useful and versatile buffer daughter board for many projects and I for one appreciate the benefits of modularity). This can be made with a layout that is about twice as big in total as the op-amp itself. A single JFET input buffer will be slightly smaller and might suit your needs as well.

If I were you I would add the simplest buffer first and if that is not enough try Robs modifications on top of that. If that still doesn't cut the mustard (which would surprise me) go for the dual buffer arrangement and make the second buffer a booster (op-amp boosters have a buffered output anyway).

And by the way:

i'll buy a bum a cuppa joe with your name on it.

This is an excellent currency to pay for forum advice, although it may confuse the hell out of the coffee shop guy who writes the name on the cup in case of some forum members names

Hope that helps,
Andy

[pinkjimiphoton]

shit, looks like i'll be doing some time at the soup kitchen to pay all this great advice back.

ok... so buffer. i fell down the rabbit hole at jack's site, looked at the dr quack and see the way he implemented the buffer.

but a couple questions... won't the buffer interfere with the interaction with the guitar? i mean like the way it will f-up a fuzzface?

can i change out the 10k e resistor to a smaller one to bump up the gain a couple db if i use this?



it interacts with the guitar pretty much perfectlly now, just needs to go up about 4db louder... thinking maybe i could also use jack's page for this:


and use a dual OA, and just "sandwich" the existing vero between two stages?

really, all i need is to bump the volume up a little.

i tried playing with the value of the 390k resistor, no bueno... i can try to add the voltage divider dealio, but this vero is real close to the point of death... i think this board was a bad one, as the traces are kinda lifting really easily. its almost literally a perf build at this point i dunno how much more i can get away with!!

i will ditch the pulldown on the input, and see if that ditches the dc problem

as i recall, the input board on all these dano minis has buffered in and outs, so..... good call.

i'd still kinda like to just stick a transistor on the end of it tho...

last nite i worked up a stupid simple npn boost... literally direct coupled to the b from the existing output cap,
2.2k to ground e resistor, and a 50k trimmer to c with a 100n cap off the junction of the c and the trimmer.

gives it a nice vocal -like quality... takes it away from the envelope clarity and makes it a little more wah like.

i appreciate the help guys... will report back with whatever i end up doing.

i may have to lay out another board at this point. but with luck, the daughterboard deal should work fine.

if i go with the buffers, i just don't see how that's gonna bump up the output very much.

thanks for all the help!!

[pinkjimiphoton]

still haven't made it down to my dungeon, but worked this up...
its an lpb1 with a trimmer for volume, sans input cap (the autowah has an output cap, so....)
6x7 piece of vero, should fit anywhere.



but first i may try the "tiny boost" i worked up last nite... slightly smaller, less parts
(just barely)


it actually sounds really good after the wah... gives it a bit more "edge", volume, and fatness. the trimmer lets ya adjust the output via the bias, where as the lpb1 adds a bit more distortion i think.

more when i get done. again, thanks guys
either way should work out,  if the lpb1 doesn't work out for this maybe i'll stuff it in a guitar

[Fancy Lime]

won't the buffer interfere with the interaction with the guitar? i mean like the way it will f-up a fuzzface?

Not really. Envelope controlled filters such as the one we are talking about here are controlled by the amplitude of the signal (well I guess you new that) but they do not care all that much about the sound that goes into them. In a low input impedance fuzz, the input stage interacts with the guitar pickups and effectively kills the treble (in an interesting, dynamic way, which is part of the magic of the fuzz). The treble attenuation is necessary for the fuzz to sound good, a buffer before the fuzz prevents that, feeding the fuzz too much treble, making it sound like fingernails on chalkboard. But the high frequencies for which these things are important hardly contribute to the amplitude of the overall signal, which is why the envelope control won't care much either way. What a buffer up front will change however, is the volume attenuation caused by the guitar-output-device-input impedance interaction. That why adding an input buffer will increase the volume. By how much depends on the output impedance of the preceding stage (or guitar). And it is precisely why Jack Orman added it to the Dr. Quack and one of the more important improvements of that design over the original Doctor Q. A booster in the end works too, but a buffer on the input has the added bonus of getting consistent behavior and volume regardless of what you feed it. Without the buffer, you will get different sounds and volumes if you plug your guitar in directly or have a bypass buffered pedal or unity gain device of any kind in front. Not usually very practical.

About sandwiching between a dual op-amp dual buffer: I just suggested that because it is small, versatile and convenient. Not really necessary, a single input buffer will have almost the same effect in most situations.

Hope that helps,
Andy

[pinkjimiphoton]

thanks bro
in this case, i don't think i have the room for it. i'll lay out the orman version maybe next time.
i'm trying to squish this all in a 1590a that was already used for something else (vox repeat percussion) so i have very little wiggle room to play with.
i may have to re-do the whole vero i did to make it work. we'll see. still trying to get a break to go to my shop and play with it.
thanks for the explanations, that helped clarify stuff for me.

[digi2t]

Straight from the tail end of the Gemini III...



2N5088 for the transistor.

[pinkjimiphoton]

love it

same thing ya tacked on the suzy q, wasn't it?

so far, messing with the breadboard, a 2.2k resistor from b+ to c and a 470r resistor from e to ground with a 470n output cap seems to be winning. 4 parts. i was gonna use a trimpot, but its just a RCH too big to fit in the box.

the single 5089 and them three passives sounds really good, believe it or not. bumps it up just a little above unity. and gives it just a little edge.

ditched the 100k to vref. no more scratchyness.
input impedance seems low tho when i roll it back now, so i have a feeling its gonna end up being a complete rebuild down the road

this suckah sounds great with a fuzz

[thermionix]

but its just a RCH too big to fit in the box.

Is that a red one?  I know what the CH is.  Are the red ones thinner than standard?  I've never brought a micrometer along to the party, probably get some funny looks.

[pinkjimiphoton]

red ones are the finest measurement known to man i believe. or maybe i'm just a sucker for them



ok, now that my blatant sexism is out of the way and my prefs are established,
i got this suckah nailed.

made a small daughterboard. 5x5 piece of vero. used a 5089 as the q. 2.2k resistor from b+ to c, input from the output cap to b, and 470r resistor e to ground. 100n output cap off the c/2.2k node.

to my ear, its now unity gain when i kick it in. i had to use ky jelly and a spatula and a 10 lb hammer to fit this sucker all in the box, and i will NEVER EVER OPEN IT. cuz i think getting it to close was some kinda magickal fete, its closed, it works, i'm good!!!!!
there was JUUUUUUST enough room to cram the daughterboard on the side of the footswitch, i had to stand the resistors up and then lay them and the q down to make it work.

warms it up just a smidge too. i couldn't fit a trimmer in there, just not enough space... but for a repurposed box, i can live with it.

[Fancy Lime]

Nice! Glad to see it worked out. What is your main board: perf, strip or PCB? Makes me think if the vactrol based Minimum Parts Envelope Filter I have planned as the next project might fit in a 1590A. I might need to start using PCB's after all. Or go all the way to SMD I actually have been thinking of designing a few "utility circuits" like the sandwich buffer, minimal booster and a switching circuit as full (or partial, if certain components are not obtainable in sane quantities as SMD's) SMD boards. These tiny daughter boards (little more than two stacked USD quarter or € 20 cent coins for the buffer) would be quite useful, I think. But not trivial to make, especially since I have no experience with or any of the tools for SMD. Well, some day, I hope.

Andy

[pinkjimiphoton]

hi andy
i used vero (strip) board for most things easy. really complex stuff i get ahold of phil mowdes, he's ace with laying out boards and telling me where to get them fabb'd. i am way too dense, and it is way above my paygrade.

i am thinking of using smd electros in some builds cuzza their size, but generally stick to thru hole stuff. its much easier.

look forward to seeing your designs!! the last one looks pretty killer,  and the demo sounds great.
if ya get any funkontakt boards made, i'd love to buy one from ya.

this little sucker started on the vero posted over on tagboardeffects.blogspot.com, it was actually a smidge too big for the 1590a, i had to lop off a couple corners to get it to fit.

i think your idea of add on daughterboards is ace. be awesome to have something simple and stupid, like maybe a 5532 based dual opamp input and output buffer... sandwich the original pcb between the two, all on one tiny board. great idea, and probably kinda overdue, as i haven't seen anyone do this yet!

thanks for the help, explanation and advice, too bro. much appreciated!!
i'm really just a monkey with a breadboard and an obsession with ge fuzzes i have no particular knowledge or intelligence.
blind stupid luck and a willingness to let the magick smoke out of expensive rare vintage components has led to a few lucky things.
i really am a newbe still after all these years with just the most basic understandings of actual electronic theory.

good at distortion tho

peace!
jimi

[digi2t]

Niiiiiice.

The pedal's not bad either.

Bring on the vid!

[Plexi]

To me, the LPB is a "must be".
But! if you whan something really LOUD, and small:

[pinkjimiphoton]

bring on the video .... lol

yeah it will happen someday maybe.

i went back inside the thing, added a pulldown to the footswitch, and a 50k trimmer to ease the volume down a bit. it sounded GREAT in front of distortion, but after distortion it was significantly louder.

hard to tell with sweeping filters sometimes until ya mess with it a while... lack of bass content makes stuff seem quieter.

now it seems about the same before or after dirt. i'll mark it as done i think. for now.

really not happy with the front end tho. can't turn the guitar down without it mudding out, which is i am sure why it needs a buffer in front of it. i DO have a LEEEEETLE more room on the input side of the switch, i may just be able to squeeze another daughterboard in that sucker.

plex, thanks man.... i been meaning to try that one out for ever.

so many @#$%ing circuits, such a @#$%ing finite life span at 55, ya know?

i didn't wanna go with an lpb1 cuz i find anything with the volume at the end like that usually adds too much grit. frankly, i'm surprised the stupid little boost stage i came up with works so well with it.

accident!!! a happy one

[amptramp]

Anyone ever use the TO-92 version of the LM317 as a boost stage?  The signal input goes to the adjust pin, the source pin goes to the positive rail and the output goes to the output.  The output will be 1.25 volts above the input, so bias the input appropriately and add a pulldown resistor at the output.  Use capacitive coupling to the output and add the normal pulldown resistor.

[PRR]

Sounds like a follower, not a boost.

There is a hot little amp in there, and you can get gain, but I never explored that.