DS-1 (Japanese) Mod Gone Wrong... :(

[themdla]

so i decided to mod a friends' Japanese DS-1 (TA7136AP) based on a schematic i used to successfully modify a newer M5223 based model.

unfortuantely the mod has failed...
the distortion pot only creates distortion when it's turned 85% clockwise.
all the distortion happens from 8-10, and nothing happens but volume increase from 1-8.

i have included a schematic showing all the parts i have replaced (in red & blue).
i also had to modify the original schematic to include the japanese op-amp and attached circuitry.

i'm assuming this has something to do with the values of one of the 3 componets i replaced that have red dots next to them.

any help would be greatly appreciated i'm a bit of a noob and totally stuck on this one 

[themdla]

bump!

40 views and no responses hmmm...

[MikeH]

It sounds like you may have changed the clipping threshold somehow, and you could bo on to something with the dotted components.  The only real way to know would be to change them back and see if the problem goes away.

For future reference: Every time I mod a pedal I plug it in and check it's functioning after every component added/replaced/removed.  It's the only way to know for sure which mod is mucking things up.

[PRR]

> i decided to mod a friends' Japanese DS-1 (TA7136AP)

Is there a spec-sheet or schematic for this TA7136?

It appears to be one of those odd 5-transistor preamp chips, made in great varieties back in the 1970s before large analog chips arrived.

What works for one such chip may not work for another. (Which may be why you got no comment.)

[themdla]

@PRR

the pinout has been added to the schematic along with operating voltage.. will this suffice?
yes you are correct... what work for one chip will not work for another...

however, in this instance what are the normal operating parameters of this (made in japan, TA7136) distortion circuit?

has anyone ever modded one of these?
can anyone compare the circuit i have to a similar circuit (DS-1 clone with a single op-amp) and tell me what reduces the distortion so much typically?

i.e. what part of this negative feedback circuit would increase distortion based on what i currently have? (values or design)


@MikeH

thx mike i think your right, i agree that one of these componet changes has affected the clipping threshold ... unfortunately the original componets have since been lost...

based on your experience which of the three componets in my example would have the most affect on distortion threshold?

[themdla]

@PRR

here is a spec sheet i found... sadly it's in japanese lol.

[themdla]

anyone???

if this boils down to something i need to read i will... but any suggestions at this point would be awesome 

thx guys

[MikeH]

I would start by returning the values that you have dotted back to stock.  If you need to buy more parts, that's just the way it's going to have to be.

[themdla]

@mikeh
i agree with you mike but i dont have the original values or a schematic that tells me what they are... i have plenty of extra parts but no idea of what values i should use to create the desired effect.

@world
hypothetically, in distortion circuits based around single op-amps....

what is a common method (i.e. boss, mxr, etc...) for creating distortion?
what values in one of these circuits change distortion characteristics?
based on my example (see schematic) what values would i change to create more distortion?

or

(see schematic) what is wrong with this picture?

[themdla]

just to mention i have changed all parts in red and blue... the dotted ones are just the ones i believe are causing the issue but i could be completely wrong 

[5thumbs]

Here's a copy of the BOSS-original schematic for the pre-1994 DS-1 pedals (of which you have a specimen):

(Many thanks to Brian Wampler for hosting this image on his site.)

None of the changes you made should have had a dramatic effect like you're describing, so my gut feeling is that you made a solder bridge somewhere.  Inspect your work carefully and see if you can find any soldering mistakes such as that.  After that, look for shorting wires (either from wear-and-tear or from contacting the enclosure when the pedal is rehoused.)  Old pedals that have been opened up a lot (or if you weren't gentle with them when modding) can and will have the pedal wires short out sometimes.  If the pedal works when opened up, but not when rehoused, look for shorted (internally/externally) wires and/or other components.

If all that doesn't work, replace all the original components in their original locations (use the attached schematic to help you) and retest the pedal.  If it works, you can go ahead and repeat the mod steps one at a time, testing the pedal after each component change.  That should allow you to repeat the mod steps, but hopefully identify any mistakes as you make them.  If that doesn't work, then you'll have to use the Search feature on this site to find out how to make and use an Audio Probe to locate the point-of-failure in your pedal.

Good luck!

[themdla]

dude you are the @#$%ING SHIT!!!

thx man!! i thought i was SOL on finding this schematic but the internet is apparantly the greatest show on earth!

[tech bill]

if i may ask,

what are the results of this mod supposed to be?

i have a stock ds-1 that might see some bench time.

thanks!

[themdla]

this is all the keely mod... it sounds amazing on my modern ds-1 circuit (M5223), it worked perfectly the first time! 

i did both the all seeing eye and the ultra mod, seriously very impressive, but almost an exact copy of what keeley has done.

but this japanese circuit has a single op-amp so i wasn't sure if it would work the same and unfortuantely it hasn't.

here's a couple good links to the mods i did, the first one looks like it was actually written by keeley and it tells you how he does the mod, the second is pretty much the exact same thing but with schematics! enjoy!

http://www.robertkeeley.com/audio6l6/dstech.html

http://urso94.free.fr/techniguitare_com/Boss%20DS-1%20us.pdf#search='boss%20ds1%20schematic'

[5thumbs]

I'm familiar with Keeley's DS-1 mods.  Some of those mods simply put caps back in place that were in the original, hence part of the reason his mod sounds better than the stock, post-1994 DS-1 pedals.  Even if you follow his mods to the letter, you shouldn't cause any failure in the operation of the pedal.  There just might be parts that are specified to be modified, but are not in the older, MIJ DS-1 pedals.

Looking for solder bridges, shorted cables, or enclosure-contact-when-closing-case issues would be my next suggestions for your build.  After that, if you still haven't fixed it, audio probe, audio probe, audio probe.  Audio probing has been very useful in diagnosing "dead" DS-1 pedals that get brought to me (usually after someone tried to unsuccessfully mod it.)  APing the pedal might help you find the point of failure that might elude your visual inspections.

Good luck!