Original DOD 250 Grey Spec layout,and layouts with mods and transfer images

[Steve Mavronis]

Here's a picture found on a Japanese site showing some of the  Analogman "mojo" mod with a 741 installed on a reissue DOD 250 PCB. Too bad he didn't use an IC socket and wire that jumper underneath!

[zombiwoof]

Here's a picture found on a Japanese site showing some of the  Analogman "mojo" mod with a 741 installed on a reissue DOD 250 PCB. Too bad he didn't use an IC socket and wire that jumper underneath!

Interesting, it seems there is a resistor change I wasn't aware of in the mod (R8, the carbon comp in the pic).  I thought all you had to do was change the input cap and IC.

Al

[Steve Mavronis]

Interesting, it seems there is a resistor change I wasn't aware of in the mod (R8, the carbon comp in the pic).  I thought all you had to do was change the input cap and IC.

Yeah I saw that too. According to what comes on the pedal to get it to gray spec you'd remove the 25pF C2, change the 0.001uF input cap C3 to 0.01uF, and go at least to a 1458 (dual 741) op amp, and if you actually do the "mojo" mod to a regular 741 you'd have to do some trace and wire re-routing to compensate for the different pinout. If you did change out the op amp you should add an IC socket too.

[zombiwoof]

Interesting, it seems there is a resistor change I wasn't aware of in the mod (R8, the carbon comp in the pic).  I thought all you had to do was change the input cap and IC.

Yeah I saw that too. According to what comes on the pedal to get it to gray spec you'd remove the 25pF C2, change the 0.001uF input cap C3 to 0.01uF, and go at least to a 1458 (dual 741) op amp, and if you actually do the "mojo" mod to a regular 741 you'd have to do some trace and wire re-routing to compensate for the different pinout. If you did change out the op amp you should add an IC socket too.

I didn't think the Yellow 250 RI has the 25pf cap, I thought that's only on the YJM308(?).  Maybe that pic IS the 308 (I thought they used the same board).   Anyway, I know about all of those mods, what I'd like to know is what is the deal with the carbon comp resistor in the pic?.  Is it a change of value, or just of resistor type?.  I know AnalogMan uses carbon comps in his TS mods, I'm wondering if there is a similar resistor mod he does in this case.

Al

[Joe Hart]

Anyway, I know about all of those mods, what I'd like to know is what is the deal with the carbon comp resistor in the pic?.  Is it a change of value, or just of resistor type?

That is odd because the original grey pedals (to know knowledge) never used carbon comp resistors! It just must be marketing crap? You know, "we even downgraded the resistors to ones that are more expensive and less useful!" Maybe they can even toss some dust into the pots to make them scratchy and intermittent?
-Joe Hart

[tednet]

http://www.aronnelson.com/gallery/main.php?g2_view=core.DownloadItem&g2_itemId=43214&g2_serialNumber=1

On the last version with mods, the one with the many switches, what values for C9 and C10 could you recommend? Also, could you draw on the picture how exactly the switches are connected, especially SW 3 and SW 2, as there is no schematic provided and I have yet to find out how the on off on switches work =)

Best Regards

[Steve Mavronis]

I didn't think the Yellow 250 RI has the 25pf cap, I thought that's only on the YJM308(?).

Both boards have a C2 in the feedback loop. Maybe the yellow reissue has a different value cap there?

Here is some info found on the net about reissue yellow vs yjm308 that I'll condense here. I'd have to see a side by side parts comparision to see which one overall would be less work to mod to grey specs:

The YJM is the same circuit as the original "Yellow" Dod 250 but with a .001uf input cap (vs. .01uf on the original). Also, the reissue 250 has a 100k resistor feeding the clipping diodes; the original and YJM have a 10k.

you can mod the re-issue yellow and the yjm308 to grey specs! - change the .056 cap to .047 - remove the 25pf cap - change the 100k resistor to 10k - change the .001 cap to .01 - remove the 4558 chip,install a socket and a 1458 chip [its basically a dual 741]

Heres the specs of the yellow reissue late 90's model, Board number 80-6211-A (Please note some of the resistor readings could be inaccurate as it was really hard to tell White from yellow plus im not the best reader of the codes).

R1. 4.7K
R2. 1M0
R3. 10K
R4. 100R
R5. 22K
R6. 470K
R7. 22K
R8. 100K

D1 & D2 CANT READ THE LITTLE WRITING.

C1. 2A 563 J Large green
C2. 25J SMALL ORANGE CAP
C3. 2A 103 G Medium sized green
C4. 10uF Black
C5. 4.7uF 35V Black
C6. 2A 102 K Medium sized green

U1. KA4558
522C
(this is exactly how its written on the chip with the other numbers and letters underneath.)

P1. C500K with the ink code 9739
P2. W100K " " 9807

[zombiwoof]

That explains it, that resistor is R8, which has to be changed to 10k from 100k.  The carbon comp is just an AnalogMan thing, he always seems to use carbon comps in his mods, it has nothing to do with what was in the originals.  It just stood out in the pic, as it was the only carbon comp there.

Al

[Brymus]

http://www.aronnelson.com/gallery/main.php?g2_view=core.DownloadItem&g2_itemId=43214&g2_serialNumber=1

On the last version with mods, the one with the many switches, what values for C9 and C10 could you recommend? Also, could you draw on the picture how exactly the switches are connected, especially SW 3 and SW 2, as there is no schematic provided and I have yet to find out how the on off on switches work =)

Best Regards

On SW2 the center post (SPDT) is connected to C6 (should be .047uf not pf) then the two outer posts would be connected to C9 and C10 this would be to add them to C6 so C6 is your smallest value cap and then the other two caps are added seperatly to make higher values.
As far as values, the larger the cap value (combined or single) the greater the bass response will be.
A good ide IMO would be to make C6 smaller than stock so that adding C9 would equal the stock value then adding C10 would make the combined value rather larger than stock.(sockets for all 3 caps here is a good idea, so you can find the values you like most)
To start you could try making C6 and C9 both .022 uf and make C10 .1uf   SW settings = stock,(less bass than stock=middle) ,more bass than stock
Or another good combo would be C6 .047uf C9 .022uf and C10 .047 - .1uf  SW settings = more bass than stock,(stock=middle),even more bass than stock

SW3 is similiar (SPDT) the center post would connect to the unused pad on the top most trace.The outer two posts would connect to the unused pads at D5 and D3
If you use an ( on,off,on ) type switch then the middle postion would be a clean boost (no diodes in use) ,and all the clipping would come from the op amp.
If you use an ( on,on ) switch then you would just be changing between the two sets of diodes.(one set of 2 diodes the other a set of 3 diodes)For two different clipping sounds.
LEDs , 1n914/4148 , small zeners , and 1n34 or other Ge types  are good choices to experiment with (use sockets if you arent sure which to use)
(I drew in LEDs for the set of two and 1n914 for th eset of 3 as these are my favorites for this set up.)

SW1 Connects to the unused pads by D6 it is a simple (SPST)(open or closed) switch it closes to short out (remove) the second diode in the pair that are in series.(D5+D6)
With the switch closed (shorting out D6 ) you have symetrical clipping.
With the switch open the second diode (D6) is in series with the first (D5) and you get asymetrical clipping.
I hope that explains it well enough ,if not I will try to draw a pic for you  



@Carbon comp resistor
Isnt that the 1M resistor in the FBL ?
Perhaps he thinks it will add some of the distortion that carbon comps are known for in tube amps to the distortion of the pedal.
If so he hasnt read the GEO article which states the voltage needed is way higher than that present in a FBL of an op amp.
At any rate a sound test would be in order to see if you can notice any flavouring worth keeping ,or if its just adding more noise.
It still got you guys talking though ,so it at least has shock value if nothing else  

[tednet]

Thanks Brymus, I can't express how grateful I am for everything =)

[Steve Mavronis]

At any rate a sound test would be in order to see if you can notice any flavouring worth keeping ,or if its just adding more noise. It still got you guys talking though ,so it at least has shock value if nothing else  

Just some obvervations relating to noise and tone with 250 circuits and component values used over the different versions of this pedal. The only comparision I have first hand is between my stock YJM308 and the late 70's grey clone I built, of which you would expect not just mine, but anyone's such clone to sound pretty close to the gray pedal it is modeled after. So for the sake of discussion I'm going to equate everyone's "gray spec" clones with the original gray 250 itself and assume they all sound the same if built from the same component values. I'll use the parts labeling of the YJM308 to make a comparision list between it and a late 70's gray spec clone:

Component	Late 70's Gray 250	YJM308
U1 (Op Amp)	LM741CN	KA4558
R1	4.7K	4.7K
R2	1M	1M
R3	10K	10K
R4	100	100
R5	22K	22K
R6	470K	470K
R7	22K	22K
R8	10K	10K
P1 (Gain)	500K Reverse Log	500K Reverse Log
P2 (Level)	100K Audio	100K Audio
C1	.047uF	.047uF
C2	N/A	25pF
C3	.01uF	.001uF
C4	10uF	10uF
C5	4.7uF	4.7uF
C6	.001uF	.001uF
D1	1N4148	1N4148
D2	1N4148	1N4148

In later posts I'll update this table with more columns to include the other 250 variations.

The first thing I noticed between a YJM308 and a gray 250 when playing through it is tone. The YJM308 sounds more like a treble booster whereas a gray 250 has more midrange tone. Does anyone have tone difference experience with the reissue yellow 250 and a gray spec clone? The other thing I noticed is noise output. The YJM308 is very noisey at higher gain levels. My clone 250 is not as noisey. I don't have a scientific measurement but I see a difference with my Boss NS-2 Noise Suppressor pedal. It has a threshold knob with a red LED that lights when noise reduction turns itself on to eliminate the hiss. I can use less noise reduction with my clone (with threshold set at 2:30 position vs almost 5:00 with the YJM308) so my note sustain is longer before it decays and cuts off. With the YJM308 there is a strange and annoying "sizzle effect" heard the longer you hold a note before it decays.

Here are some YJM308 PCB pics:

[Steve Mavronis]

That explains it, that resistor is R8, which has to be changed to 10k from 100k.  The carbon comp is just an AnalogMan thing, he always seems to use carbon comps in his mods, it has nothing to do with what was in the originals.  It just stood out in the pic, as it was the only carbon comp there.

Interesting about the carbon resistor mod, but on my stock YJM308 and the large PCB picture in my last post R8 is still a 10K value with 5% tolerance - brown-black-orange-gold. I'm not sure where that forum post that I found and quoted got that 100K info. Maybe it's a typo on his part?

[Brymus]

Well that throws my idea out the window ...
I thought it was the feedback loop resistor.

Zombie even explained that a post above 
I should wear my glasses when reading, DUH

That is the place likely to have the highest voltage swing signal wise though. AFAIK (could be wrong)
So I guess, why not, a 10K isnt as likely to have as much noise as a 1M.

[Brymus]

Thanks Brymus, I can't express how grateful I am for everything =)

Hey I am very glad to help  :
Its nice to pay forward the generosity I have recieved in the DIY circle,especially here.

[zombiwoof]

That explains it, that resistor is R8, which has to be changed to 10k from 100k.  The carbon comp is just an AnalogMan thing, he always seems to use carbon comps in his mods, it has nothing to do with what was in the originals.  It just stood out in the pic, as it was the only carbon comp there.

Interesting about the carbon resistor mod, but on my stock YJM308 and the large PCB picture in my last post R8 is still a 10K value with 5% tolerance - brown-black-orange-gold. I'm not sure where that forum post that I found and quoted got that 100K info. Maybe it's a typo on his part?

If the stock R8 value for the 308 is already 10k, then I don't know what the explanation is for the carbon comp in the picture.  Of course, we don't know if that is something that AnalogMan did or not, the owner of the pedal could have done it himself.  I'll have to check my 308 and see what it has there.

Al

[Steve Mavronis]

I'm trying to update my model year comparision table of parts used in the 250 and searched through my collection of gut shots for an example of a 1977 gray. It is supposed to not have the 470K (yellow-violet-yellow-gold) bias resistor value coming off pin 3 of the 741 op amp. Instead it should be 510K (green-brown-yellow-gold). I found these images of the same unit that has either a 510K or 570K bias resistor, depending on the "brown or violet" color shift of the image. But the pot date code says this gray is at least from the 15th week of 1978:





Does anyone have a clear PCB image from a 1977 model gray that I can read the resistor color codes of, so I can update my table? I can't read perf board or vero layouts to tell what connects to what. Even some PCB layouts of a 1977 model include modifications so I can't take anything but the real thing as reliable.

Here is a resistor color code calculator webpage to make life easy:

http://www.hobby-hour.com/electronics/resistorcalculator.php

[Renegadrian]

The first thing I noticed between a YJM308 and a gray 250 when playing through it is tone. The YJM308 sounds more like a treble booster whereas a gray 250 has more midrange tone. The YJM308 is very noisey at higher gain levels. My clone 250 is not as noisey. 

The input cap makes all the difference (and the IC, but not so much to my ears...) - I made a grey one with an input cap switch - that is very useful!!!

hear some samples!!!
Gain at min.
Gain at max.

The same licks with the original 308
Gain at min.
Gain at max.

Anyway, I'd like to post this pic of my layout...

[Steve Mavronis]

The input cap makes all the difference (and the IC, but not so much to my ears...) - I made a grey one with an input cap switch - that is very useful!!!

hear some samples!!!

Thank you very much for the samples comparisons! What input cap values are you using?

[Renegadrian]

The input cap makes all the difference (and the IC, but not so much to my ears...) - I made a grey one with an input cap switch - that is very useful!!!

hear some samples!!!

Thank you very much for the samples comparisons! What input cap values are you using?

Basically it's a grey that uses the same BOM you listed above, so C3 (input cap) has .01uF and .001uF on a dpdt.

[Brymus]

@ Adrian ,Nice,what amp and guitar are you using ? so people know for comparison purposes.

In the samples with the input cap on a switch.
Are you switching PUs ? I hear four different sounds.
Its amazing how much a difference the input cap can make,not just treble wise but mid and total loudness wise as well.
I am undecided,    But I think I like the fuller sound better,it would definetly cut through a mix better if that were a deciding factor.
I think after hearing your examples I would need at least 3 settings,maybe .001 , (.0033/.0047/.0068) not sure on the middle one , and .01

And Yeah thanks for posting that Adrian,thats a good idea and good to have for this thread.
Some more soundclips might be helpful to people trying to decide if they should build the pedal or not ?