Gut shot of 80's OD-250 on Ebay.

[nightingale]

For the OD-250 guys/gals out there.
I was never quite sure if they had GE or SI diodes. I have only looked inside a couple of older ones,  but they had the SI diodes.
Good sounding little circuit for sure IMO.

http://img.inkfrog.com/click_enlarge1.php?image=dod1.jpg&username=sparestuff

[markm]

The OD250 is my all-time favorite overdrive for sure.
Not that I'm not looking for other OD circuits to mess with but,
the 250 is a winner for me.
For Country, it can add just the right amount of grit.
I'm also very pleased with Drangonfly's SparkleBoost but,
that's for a different thread.
Thanks for the pic!!

[nightingale]

a couple more:

http://cgi.ebay.com/Vintage-DOD-Overdrive-Preamp-250_W0QQitemZ180000512551QQihZ008QQcategoryZ41416QQrdZ1QQcmdZViewItem

http://cgi.ebay.com/1980-dod-overdrive-preamp-250-fat-tube-tone_W0QQitemZ320001397916QQihZ011QQcategoryZ41416QQrdZ1QQcmdZViewItem

[burnt fingers]

I got one from the early 80s that has a bad switch.  prloblem is, any swithces I have wont fit with the battery.  I made a freind one to grey box specs.  I guess I'll get around to building myself another soon.  I love that little yellow bugger.

Scott

[JHS]

My personal fav is the early '77 version with the 4001 diodes, very tube like sounding, hard to fine a better OD for a Strat and a Marshall.
To me the '78 version w 914 diodes sounds like crap compared to the '77, way more compressed and less dynamic w mushy bass and less headroom.

To be fair, the '78 version w 741 sounds much better compared to the newer OD-250s or a Dist+ , but it's to soft for boosting a brit amp.

JHS

[analogmike]

JHS,

I always enjoy your posts, you have the same tastes in tone that I have. Send me an email sometime maybe we can work together?

I dont remember seeing 4001 diodes in an OD-250, were they the black ones?

[JHS]

@analogmike
A few weeks ago there were a good board pic of a very early grey unit on ebay.
The seller said the diodes are 4001 and the mylar caps 2,2n, every thing original. the circuit is somewhat different to the later grey units.
Someone in the German forum posted the link, it was not sold because the limit of 500€ was not reached, that started the whole thing.

After some googling I found very good board pics on the site of a vintage FX dealer, early '77, '78 and present chinese type.

From that info I built a '77 and '78 prototype, a member in the German forum did the same, the '78 sounded really good but the '77 was a killer, w tight focused bass and clear articulated highs. Changing the diodes in the '78 to 4001 was disapointing, the goal to great tone is the different circuit of the '77 w altered cap values + 4001. They use ceramic caps in the old unit, they give a bit more grit and clarity than the mylar caps in the later units.

I send you the ebay pic and the traced schem. Chip manufactures is unkwown, can't identify the logo, but they put in what the just got in the early units, even the cap values and the layout were different from unit to unit.

When I have some time left I will build two more prototypes of the '77 250 with 5%/2W CC and polypropylen caps an the other with a discrete circuit instead of the 741. A pal from the German Forum uses the Davisson diode compressing discrete Op-Amp, acc. to him the OD sound is similar to a small tweedamp, I must try this too.

To me the OD-250 is one of the best basic OD-circuits ever made, can be altered to nearly everything, fuzz, OD, distortion.

JHS

[markm]

Do you have a layout for the '77 OD250??
I'd love to get my hands on the layout and schem if possible......PLEASE!

[JHS]

The circuits of the '77 and '78 are nearly identical, so every  Dist+ or 250 board and layout can be used for a build.

'77 details:
=========

No 10uF cap in the BIAS-divider

I-cap is 10n ceramic type
I-cap to ground is 2,2n green Mylar

47n cap is ceramic type
4,7uF is 22uF
cap parallel to the diodes is 2,2n green Mylar

diodes are 1N4001

gain pot is 500k lin
vol pot is 100k lin

1M, 470k, 2x10k like on the normal OD-250


On the prototype I use multilayer ceramics and a RC1458 for a bit more gain, a 5% plain foil electrolytic and 2W 5% CC. The prototype has 1% 2W 22k MF in the BIAS devider to make it really symetrical.
I replaced the 500k lin with a 250kC for better adjustment and the 4001 w 4003 (a bit less harsh than 4001 and more musical sounding).

JHS

[markm]

Thanks for that bit of info.
NOW I have to build one!
I'll add it to the list of projects. 

[Ed G.]

How's the OD-250 stack up to the Ross distortion? It's another variation of the same basic circuit. A friend had one, we cranked it through a big-ass Bassman 135 and it sounded brawny, just a tight muscular crunch sound. He had the black Ross, I think they were made overseas instead of Kansas (not in Kansas, anymore...) I remember Philip at Fuzz Central posted a schem for his take on the Ross model.

[aron]

Hilarious. Back then, the MXR was famous, but most people thought the Ross might have been better. The OD250 was considered not as good 

[Ed G.]

The Ross had it all over the MXR and DOD with their cool enclosures.

[markm]

The circuits of the '77 and '78 are nearly identical, so every  Dist+ or 250 board and layout can be used for a build.

'77 details:
=========

No 10uF cap in the BIAS-divider

I-cap is 10n ceramic type
I-cap to ground is 2,2n green Mylar

47n cap is ceramic type
4,7uF is 22uF
cap parallel to the diodes is 2,2n green Mylar

diodes are 1N4001

gain pot is 500k lin
vol pot is 100k lin

1M, 470k, 2x10k like on the normal OD-250


On the prototype I use multilayer ceramics and a RC1458 for a bit more gain, a 5% plain foil electrolytic and 2W 5% CC. The prototype has 1% 2W 22k MF in the BIAS devider to make it really symetrical.
I replaced the 500k lin with a 250kC for better adjustment and the 4001 w 4003 (a bit less harsh than 4001 and more musical sounding).

JHS

Looks to me like the PCB layout over at the GGG site has provisions for the "mods" you describe!
Cool --

[burnt fingers]

I'm lovin this.  It's about time those little yellow boxes got some respect.  This just got bumped to the top of my build list.

Scott

[Yun]

i allways loved the Ross distortion (i had a tan coloured one).  That thing had A LOT of feel.  Not as Bright sounding as the MXR dist +, but i wouldn't say that it was "creammy" either.....

i've never played through the OD 250 .  However; i have played/owned many vintage Dist+ 's and 1 Ross distortion.  Can anyone give me a link to the Ross distortion schematic eh?

If i remember correctly; The ross had germ diodes by the way....

[JHS]

www.home-wrecker.com/ ross.html

JHS

[Yun]

www.home-wrecker.com/ ross.html

JHS

HEY!!!  thanks, man!  Much obliged, dude 

[aron]

The black one has some very cool ideas that we would use now! Look at the diodes and the IC type etc...

[Yun]

The black one has some very cool ideas that we would use now! Look at the diodes and the IC type etc...

What do you mean by the black one eh?  Are you refering to the ross Distortion eh?