value of gain pot on DOD overdrive

[feddozz]

Hi all
this is mi first post.
I am planning to build a DOD Overdrive. I am following a different schematic because I want to use veroboard. I can post the link here if you want.
The gain pot is 500k ohm. My question is can i replace it with a 470k ohm. specifically can I use this?
http://spiratronics.com/16mm-potentiometer-linear-470k.html
Thanks

[Joe]

I think the original uses a reverse-log taper. The 470K linear part will work just fine, but might have a more abrupt difference between lower/higher gain levels. Probably not a huge deal. Are you building a DOD-250? (It's one of my favorites..)

[Mark Hammer]

470k = 500k

You'll find that really anything above 100k doesn't really make much of a difference.

[feddozz]

Thanks for the quick reply.
Yes, I am making a DOD 250. Great sound!
I live in the UK, can someone suggest a good supplier for compoents? The only 500k pots I found cost about 3-4 british pound. is this the right price? The 470k in the link above costs far less.

[feddozz]

Hi
I have a couple more questions.
I cannot find a 27pF ceramic disc capacitor in my supplier catalog. Could I use a 22pF and a 4.7pF capacotors of the same type in parallel instead?

[Cozybuilder]

Yes, you could parallel the two values you indicated, or Small Bear carries 27pF ceramic caps, and it looks like they have more than 4200 in stock:

http://smallbear-electronics.mybigcommerce.com/xicon-ceramic-4-7-pf-to-33-pf/

[antonis]

Of course you can do it but a 4p7 cap is a marginally small value for use on a IC feedback loop (values lower than 10pF are not recomended..)

If you use 22pF instead of 27pF you'll raise the cut-off frequency from slightly lower than 6kHz to slightly higher than 7kHz..

IMHO, you'll practically not notice any difference.. 

There are also many (old) schematics in which this cap is 25pF or is totally ommited... 

[smallbearelec]

can someone suggest a good supplier for compoents?

If you can find up to four ounces of things you want from my shop (usually not difficult):

http://smallbear-electronics.mybigcommerce.com/

postal service shipping for the bag is about $9.00 U.S. If you want a European source, Banzai and Musikding in Germany are both good.

[feddozz]

Hi all,
Thanks again for the prompt replies.
I have another question about capacitors. I read about their voltage rating and that it should always be above the operating voltage, and that's reasonble.

I am trying to follow this page http://www.guitars-of-love.com/DOD_OD-250.html
Has anyone tried it? Does it sound good?

It suggests a 4.7uF/10-35V electrolytic, could I use a 4.7uF 50V electr instead?
Also, could I use 100V 1nF MKT instead of 63V 1nF MKT?
Does the change in voltage make much difference?

@smallbear, thanks for the info.

Thanks

[Gargaman]

I got this one on my breadboard now.
Have you ever think about breadboarding it? It's a good way for prevent frustration after putting it into the vero and then onto a enclosure.
I'm sure 4.7uF 50v will work because that's what I got in my circuit.
I believe that 100V for the 1nF (or any higher voltage than the operating one, as you have read), will work too, but you may want to wait for the old cats here to clarify this for you. 
I have seen this schematic and it has two little things different from others that I know:
The gain potentiometer is 500kC (reverse logarithmic).
The IC has different pinouts, I guess. Does your schematic source tells you what IC to use?
Take a look at this and compare for getting more into this rocker.
http://www.generalguitargadgets.com/pdf/ggg_dist_250_sc.pdf
Good luck!

[SuzukiScottie]

Yes you can use higher voltage rated caps. But they are usually physically larger and that can offer challenges when fitting them into a design you might be following.

Worrying about space isn't usually a consideration on a breadboard though, so you can try out lots of things to see how they affect a circuit. Then figure out how to get all into a pedal.

[feddozz]

Guerrilla, are you saying that i would get more from the ggg schematic?
the IC from my schematic is 4558 or TL062
Which schematic did you breadboard? Do you have an image of the breadboard layout?

thanks

[bluebunny]

I live in the UK, can someone suggest a good supplier for compoents? The only 500k pots I found cost about 3-4 british pound. is this the right price? The 470k in the link above costs far less.

Try Bitsbox or Tayda (look out for the regular discount coupons in the Members Only sub-forum for the latter).

[Gargaman]

You'll get more (knowledge) by comparing many different scheamitcs of this project as you can.
Here a few:




Those above calls for a 741 IC. The 4558 and TL062 are dual opamp. The 741 is a single opamp. Although you can you use a dual in place of a single (as if you were only using half of the IC), the connections would be different. Maybe your schematic tells you that, I don't know.
I don't have a image of the layout on breadboard. All I have is a draft I did before breadboarding.
There it is:

You might feel free to draw your on.

[Gargaman]

I am following a different schematic because I want to use veroboard.

I understand now.
The link you posted got the job done. A breadboard layout for a further vero soldering.
Follow this one and see if it works.
I would need more knowledge and time to take a closer look and see if it works with the dual amps, so I won't dare.

When I breadboard I don't think about an arrangement that will become a layout (I guess vero users do that). I just connect the parts to see how it goes and after that I draw an layout for a printed board.

Am I being sufficiently clear? (English is not my native language)
This is a vero layout with a 741 that may help you:

[feddozz]

All,
thanks for the replies. I am back on this project now and I am settled on this version.
You can see the powr supply goes through D1 and thena 22k resistor, another 22k res and then to ground.
I mistakenly ordered only one 22k res. I have a bunch of 10k resistors. Could I replace the second 22k, the one that goes to ground, with a couple of 10k resistors in series?
Thanks

[Cozybuilder]

Those two 22K resistors are used to divide the voltage in half to provide Vref for the op-amp. You can replace both of them with 10K resistors.

[feddozz]

Those two 22K resistors are used to divide the voltage in half to provide Vref for the op-amp. You can replace both of them with 10K resistors.

thanks for that, I proceded by using a couple of 10k resistor. Does it make no difference at all if the two resistors are 2x22k or 2x10k? I understand the pronciple behind the voltage divider, but is the current going to change and does it make a difference?

On Another note, I finally I got to build the dod 250 board. I am currently populating the box and there is room for more components. I thought I would fit in a bazz fuss. If possible, I would like to use the same foot switch for both and switch between the two with a toggle switch.

I do not see any advantage in using them together, but I never tried so I am open to advice. I guess it's matter of preference as for everything.

I am planning to switch the power supply and th einput with a DPDT toggle switch. Both ground and board output would be always connected.

Is this ok?

I posted a schematic, sorry if the quality is not great. Let me know if it is not clear

Thanks
f

[duck_arse]

the opamp draws such little current (sometimes known as SFA) that those resistor values don't make much difference, as long as they are equal, in this inst. the dist + uses 1M//1M and 1M in the same configuration. any values, 10k~100k will be 'fine'.

and I think you need to add another switch pole for the two circuit outputs, they won't play nice connected together. these circuits draw such little current, they would be easier to connect both to the suppy all the time (via an R//C power filter each), instead of switching the supply in/out.

[bluebunny]

^ what the duck says.  Turning power on and off when you switch FX is not a good habit to get into.

Edit: ...and if you're gonna tie anything together, make it the inputs (rather than the outputs).