70's Grey 250 PCB 22K Resistor/Diodes Touching?

[Steve Mavronis]

I had mapped out the following graphic to see what connects to what on the old 70's grey DOD 250 Overdrive circuit board by studying all the photos I could find. Look at the highlighted area below next to the arrow:



I'm questioning myself as to if that connection really exists between the 22K resistor and the diodes. On the circuit board photos the gap is really close (if there is one) and I had thought they were touching so I showed them as connected in my graphic. The only trace side photo that I found has this area hidden by the level pot in the way.

Now I'm not so sure comparing what I see to well known schematics and tracing this out. Plus to confuse me further some of the paired in series resistor/capacitor parts order is reversed from what the schematics show.

Are there any grey "250" experts here who can help me clarify if that 22K resistor pad is touching the diode pad, or not touching it at all?

[JKowalski]

No, it is not connected, because that would mean the output of the effect is Vref and that's obviously wrong.

[Steve Mavronis]

Does it matter the order of a resistor and capacitor in a schematic if they are adjacent in series with each other? It just looks wierd compared to the actual PCB with the way the signal path from IC pin 6 makes it's way to the polarized 4.7uF cap and to the diodes and back around to the level pot output is like playing a game of twister!

Thanks for your answer, that's what I was seeing reading the schematics and cross-referencing the pcb graphic I made. In this other photo there are dark rings around the pads below the diodes which I guess indicates a separation:

[Steve Mavronis]

Sorry to nag anyone on this but looking at the PCB layout, doesn't it appear that the signal leaving the op amp pin 6 and going through the 10K resistor and 4.7uF cap joins the line going to the level pot output "after" the diodes and .001uF cap (in a different order or sequence) instead of before it like all schematics show? Maybe it doesn't really matter if it all adds up anyway but please educate me.

[anchovie]

The diode pair, the .001uF capacitor and the volume pot are all in parallel between signal and ground with nothing between then to isolate their operation, therefore they perform their functions simultaneously. A good way to visualize it is if you soldered the cap onto the pot itself, it doesn't matter if you put it on the front or the back of the lugs!

[Magnus]

Hello together,
some time ago I did exactly the same thing - re-engineering the gray DOD 250-version,
here is my layout, I will post the PCB-File later, I have to extract it first...

Click on images to see bigger ones  

This layout is verified, I have built it:



And here is my DOD-Clone:



...a comparison between original and cloned pcb:



...a large pcb-shot:



...and finally the gutshot:



The last thing I will change is the IC, I will get some original LM741CN next time 


Greetings from Germany
Magnus

[Magnus]

sorry double-post, please delete this message

[FisTheGoon]

Hi.I have done this pedal using 77 Grey DOD Overdrive 250 on Vero. Layout by Ulysses.
The problem is the reverse log 500k.
Then i stumble upon this http://music-electronics-forum.com/t3084/
Mark Hammer stated"My advice? Unless you plan on using gain factors less than x2, use a linear OR log 50k pot and be done with it. Alternatively, along with the 50k pot, change the 2k7 resistor to 3k3, change the 56k feedback resistor to 68k, replace the 10k output terminating resistor with a 10 log volume pot, and you will be able to nail ANY preset level from less than unity up to x26, with no sacrifice in tonal quality or bandwidth. Plus, with the added versatility of the output level pot, you'll have far more precision than the original permitted. Keep in mind that 70's pedals tended to opt for fewer knobs/switches, so the requirements of the pots they did use were sometimes outlandishly specific because of that."
I just wanna know if somebody have done this mod? Please shed me some light.

To Steve Mavronis ,I'm SORRY if i hijack your thread.I post this as the discussion is bout DOD 250.

[Steve Mavronis]

No don't worry. Please write any info relating to the 250. I like your clone by the way. I was (and even might one day) make an exact looking clone like yours inside and out. By the way check out my other thread called Neo-Classic Gray Overdrive which is my 250 clone attempt but using my own PCB layout design. Feel free to post and comments or suggestions there too.

[Magnus]

Hello together,
I don't know why but I can not edit my message above (I'm already logged in),
so here is the layout which should be in my message above...

...and the pcb-file for etching of course 



PCB:
http://forum.musikding.de/cpg/albums/userpics/17258/DOD_OVERDRIVE_PREAMP_250_%28gray_version%29-PCB.pdf


Greetings from Germany
Magnus

[angusruiz93]

I had mapped out the following graphic to see what connects to what on the old 70's grey DOD 250 Overdrive circuit board by studying all the photos I could find. Look at the highlighted area below next to the arrow:



I'm questioning myself as to if that connection really exists between the 22K resistor and the diodes. On the circuit board photos the gap is really close (if there is one) and I had thought they were touching so I showed them as connected in my graphic. The only trace side photo that I found has this area hidden by the level pot in the way.

Now I'm not so sure comparing what I see to well known schematics and tracing this out. Plus to confuse me further some of the paired in series resistor/capacitor parts order is reversed from what the schematics show.

Are there any grey "250" experts here who can help me clarify if that 22K resistor pad is touching the diode pad, or not touching it at all?

hola como andan? permiso