smallsound/bigsound - mini  [traced]

General documentation, gut shot, schematic links, ongoing circuit tracing, deep thoughts ... all about boutique stompboxes.
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bubstance
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Post by bubstance »

Some preliminary gutshots to get things rolling. They're not the best, but it's what I can do at this precise moment. I only have the pedal for another day or two, so ask all the questions you can.

https://s44.photobucket.com/user/bubsta ... oads/story

Q1= 2N5089
Q2= J201
Q3= 2N5457
Q4= J201
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smallsnd/bigsnd
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Post by smallsnd/bigsnd »

i got u. even cleaned up the schematic from the original so it's easier to read... :hug:

Image

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bubstance
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Post by bubstance »

Damn, Brian, you really are the actual fucking man, aren't you? :hug:

So what's going on in the "high gain/scramble/octave" mod on these? I've seen you offer up info for the DIY inclined, but never had a mini to look at for comparison.

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smallsnd/bigsnd
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Post by smallsnd/bigsnd »

bubstance wrote:Damn, Brian, you really are the actual fucking man, aren't you? :hug:

So what's going on in the "high gain/scramble/octave" mod on these? I've seen you offer up info for the DIY inclined, but never had a mini to look at for comparison.
nah just figured i'd save everyone some time.
uuuh let me get back about the scramble mod - i have it written down at my shop and i'm not there at the moment.

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destro
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Post by destro »

YES!! This is awesome. Thanks, Brian. Christmas in July!!

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smallsnd/bigsnd
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Post by smallsnd/bigsnd »

destro wrote:YES!! This is awesome. Thanks, Brian. Christmas in July!!
:cheers

maybe i should make up a PCB for DIY folks?

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karter2000
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Post by karter2000 »

smallsnd/bigsnd wrote:
destro wrote:YES!! This is awesome. Thanks, Brian. Christmas in July!!
:cheers

maybe i should make up a PCB for DIY folks?
Count me in for one. Thanks a bunch for the schematic!

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destro
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Post by destro »

smallsnd/bigsnd wrote:
destro wrote:YES!! This is awesome. Thanks, Brian. Christmas in July!!
:cheers

maybe i should make up a PCB for DIY folks?
:scratch: :hmmm: .... it's a trick. Get an axe.

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bubstance
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Post by bubstance »

smallsnd/bigsnd wrote:
destro wrote:YES!! This is awesome. Thanks, Brian. Christmas in July!!
:cheers

maybe i should make up a PCB for DIY folks?
Hell yeah. I'd buy several.

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maortojn
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Post by maortojn »

smallsnd/bigsnd wrote:
destro wrote:YES!! This is awesome. Thanks, Brian. Christmas in July!!
:cheers

maybe i should make up a PCB for DIY folks?
Really cool to post the schematic, and I would definitely be up for a pcb.

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smallsnd/bigsnd
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Post by smallsnd/bigsnd »

alright, sounds like there is interest. i'll get on it this week. the layout i use is a little weird so i'd rather make something new that's more DIY-friendly. i can make one with 2 PCB mounted pots like the way i already do it - then you wire 3 off-board pots. in my experience, a 125B is the best choice for size vs overall ease of build.

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287m
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Post by 287m »

hello
the gain pots is dual gang pots?
and what criteria for jfet?
thanks :thumbsup

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hozy31
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Post by hozy31 »

Verified a vero layout of this on Guitar FX layouts posted by Anders in the contributions section. Awesome overdrive. Thanks Brian for the schematic.

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smallsnd/bigsnd
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Post by smallsnd/bigsnd »

hozy31 wrote:Verified a vero layout of this on Guitar FX layouts posted by Anders in the contributions section. Awesome overdrive. Thanks Brian for the schematic.
cool! oh sorry there is one small error in the schematic which is important - BIAS in the schematic is a 10k TRIMPOT.
the actual BIAS control that is panel-mounted should connect the wiper to the intersection of the drain of Q3/C4 and lug 1 to pin 1 of the 10k trim. sorry about that! you might want to update the vero. i'll update the schematic in a few minutes.

also - i use J201 for Q2 and Q4, 2N5457 for Q3.

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storyboardist
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Post by storyboardist »

Thanks Brian for sharing with us! Here's a perf and PCB layout for those interested. All pots can be board mounted and you might be able to squeeze it into a 1590B (though I agree with Brian, 125Bs are best).

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EBRAddict
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Post by EBRAddict »

I'd socket the drain and source resistors, measure the component values and pick the values based on what 2N5457 I have. The 2N5457 has a 0.5-6V Vgs swing and Idss is 1-5mA. You'd grow old and/or broke trying to find the right through-hole JFET. My experience with SMD JFETs is they are fairly uniform so picking through them is not very productive.

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smallsnd/bigsnd
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Post by smallsnd/bigsnd »

storyboardist wrote:Thanks Brian for sharing with us! Here's a perf and PCB layout for those interested. All pots can be board mounted and you might be able to squeeze it into a 1590B (though I agree with Brian, 125Bs are best).
nice!
EBRAddict wrote:I'd socket the drain and source resistors, measure the component values and pick the values based on what 2N5457 I have. The 2N5457 has a 0.5-6V Vgs swing and Idss is 1-5mA. You'd grow old and/or broke trying to find the right through-hole JFET. My experience with SMD JFETs is they are fairly uniform so picking through them is not very productive.
that's what the trimpots are there for although you won't go broke or old if you handpick... i select all three JFETs for each pedal using a little test rig and it only takes a few minutes. ymmv though of course.

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johnk
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Post by johnk »

I etched and built up storyboardist's PCB and it works great so it's verified.
what bias voltage are we looking for on the Jfet's.
I have an original 125B MINI but i'd prefer not to take it apart to measure them since the legs on them are so short.

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smallsnd/bigsnd
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Post by smallsnd/bigsnd »

johnk wrote:I etched and built up storyboardist's PCB and it works great so it's verified.
what bias voltage are we looking for on the Jfet's.
I have an original 125B MINI but i'd prefer not to take it apart to measure them since the legs on them are so short.
cool! yeah it's a simple little build so it shouldn't be too difficult for anyone.
now that i think about it for Q2 i actually choose the transistor for a resistance value in my test build so that the range of the bias is correct.
for voltages, i like:
Q1 - 5.1V +/- .2V
Q2 - i go for approximately half supply at noon on the bias knob.
Q3 - 4.5-4.7V

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smallsnd/bigsnd
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Post by smallsnd/bigsnd »

no worries! just fyi if you change the bias points of the first and/or second jfet specifically, you may or may not have issues with the main bias knob at lower settings and/or with low bass settings. :secret:

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