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Projects => IC-based Overdrive => Topic started by: Mastergammler on April 04, 2012, 06:58:52 AM

Title: DOD 308 replica
Post by: Mastergammler on April 04, 2012, 06:58:52 AM
Hi guys,

I've build a DOD 308 replica, based on this manual.

http://diy.musikding.de/index.php/der-308.html
(308schalt.pdf is the electronic schematic)

The overdrive works fine, but the distortion is to heavy to me.
Is there a way to alleviate the distortion by putting in another resistor or something else?



PS: Sorry, that my english is not perfect  ;)
Title: Re: DOD 308 replica
Post by: Steve Mavronis on April 04, 2012, 07:12:00 AM
Not sure what you're going for. If you used all the same part values it should sound just like the stock 308 does. I have an original DOD YJM308 Overdrive that I changed a couple part values to make it "gray spec" from 1979.... mainly change the IC to a 1458 (dual 741), remove the feedback cap, and change the input cap. It sounds identical to the gray 250 clone that I made with the 741 IC. Here is my guide for the conversion but if you want it to be a true 308 clone matching its part specs, leave it be.

(http://home.comcast.net/~snmavronis/yjm308gray.jpg)
Source: http://sites.google.com/site/snmavronis/NeoClassicFX/mods-and-repairs
Title: Re: DOD 308 replica
Post by: Mastergammler on April 04, 2012, 07:52:21 AM
http://www.musikding.de/product_info.php/info/p347_MC1458P.html

or

http://www.musikding.de/product_info.php/info/p348_uA741CN.html

Is one of these the right IC?
Title: Re: DOD 308 replica
Post by: Steve Mavronis on April 04, 2012, 08:12:08 AM
Both of those have different pinouts so be careful. Remember the 1458 is a dual 741 inside. I'm confused because the schematic diagram you linked shows the layout of the 308 with the 25pf feedback cap. Your linked PCB parts list shows a 741 but the original 308 has a 4558 which has the same pinout as a 1458. So there is a mismatch here. If your clone is already using the 741 then you don't need the 25pf feedback cap at all and remove that cap. The was put in to tame the high end of the 4558 and is not needed with the 741, or a 1458. Maybe that is the cause of your problem.
Title: Re: DOD 308 replica
Post by: Mastergammler on April 04, 2012, 08:54:56 AM
Jea you're right.
It uses already the uA741
And C2 is also unused.
In 308bomde.pdf you see the parts of this clone.

If i remove the 25pf feedback cap, the drive should be lower?




 
Title: Re: DOD 308 replica
Post by: Steve Mavronis on April 04, 2012, 09:09:25 AM
I don't know if the distortion would be less or not without that, or affect the tone, but if you're using the 741 then the 25pf cap doesn't belong. Remember overdrive and distortion are really the same thing. It's all in the marketing of a product. The 250/308 family of overdrives is actually based heavily on the MXR Distortion+ (as was the original bud box Ross Distortion) so that should tell you something. The circuit is the same, but the part values makes the tone slightly different sounding.

Also noticed your diodes are different too. The 250 and 308 just used two 1N4148 diodes. Using the other diode too probably does affect the flavor of distortion.
Title: Re: DOD 308 replica
Post by: Mastergammler on April 04, 2012, 01:45:14 PM
Thanks for the help, but i wantet to know if i can easily reduce the distortion.
The Distortion is controlled by a adjustable resitor.
So i thougt, if you put another resistor in or if you leave a resitor out, that could change the strength of the distortion.
Or isn't it that easy?
Title: Re: DOD 308 replica
Post by: Steve Mavronis on April 04, 2012, 02:40:45 PM
Well, the type of diodes used will affect the resulting distortion sound. See this topic: http://www.diystompboxes.com/smfforum/index.php?topic=79986.0

Here's a topics discusiing the 4.7K gain resistor effect on the circuit: http://www.diystompboxes.com/smfforum/index.php?topic=20253.0

Title: Re: DOD 308 replica
Post by: Renegadrian on April 30, 2012, 10:00:25 PM
I'd say try a couple of red leds as diodes - you'll get a cleaner sound, with more "air" and volume and less compressed and distorted sound. I love 308 with leds!!!
Title: Re: DOD 308 replica
Post by: Steve Mavronis on May 01, 2012, 08:14:47 AM
Try different color LED combinations too affecting clipping. Some colors have different forward voltage characteristics depending on the wavelength of light:

LED Color Chart (http://www.oksolar.com/led/led_color_chart.htm)