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Author Topic: Confusion about Brian Wampler’s modified MXR Distortion Plus  (Read 2315 times)

SurreyNick

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I’m confused.  I want to build Brian Wampler’s modified MXR Distortion Plus but the board layout I have found produced by storyboardist on the Effects Layouts blog (http://effectslayouts.blogspot.co.uk/2015/07/wampler-distortion-plus-mods.html) differs from the schematic I found which is apparently the one produced by Brian Wampler and which appeared in the article in Premier Guitar.  They both claim to be from the same source though.  Are there two different Wampler mods to the MXR?

Both versions (see attached) have distortion, tone and volume pots, plus switches for smooth, bass and compression but the version on the Effects Layouts blog has 9 diodes instead of 8, has 7 resistors instead of 4, and has 9 capacitors instead of 7.  Some of the values are different too.

Am I going mad, and which of these two versions should I build?
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nosaj

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Re: Confusion about Brian Wampler’s modified MXR Distortion Plus
« Reply #1 on: March 09, 2018, 05:07:05 PM »

I'm sure he verified this before putting it in premeir 
heres the link build this one.https://www.premierguitar.com/articles/mxr-distortion-plus-mods-1

nosaj
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galaxiex

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Re: Confusion about Brian Wampler’s modified MXR Distortion Plus
« Reply #2 on: March 09, 2018, 05:11:07 PM »

I’m confused.  I want to build Brian Wampler’s modified MXR Distortion Plus but the board layout I have found produced by storyboardist on the Effects Layouts blog (http://effectslayouts.blogspot.co.uk/2015/07/wampler-distortion-plus-mods.html) differs from the schematic I found which is apparently the one produced by Brian Wampler and which appeared in the article in Premier Guitar.  They both claim to be from the same source though.  Are there two different Wampler mods to the MXR?

Both versions (see attached) have distortion, tone and volume pots, plus switches for smooth, bass and compression but the version on the Effects Layouts blog has 9 diodes instead of 8, has 7 resistors instead of 4, and has 9 capacitors instead of 7.  Some of the values are different too.

Am I going mad, and which of these two versions should I build?

The first schematic does not show the power supply filtering and reverse polarity diode protection.

That would account for some of the differences...

I didn't minutely compare both... try drawing a schematic for the second one and compare then...
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SurreyNick

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Re: Confusion about Brian Wampler’s modified MXR Distortion Plus
« Reply #3 on: March 11, 2018, 09:40:57 AM »

OK I have had a go at drawing the schematic for the Effects Layouts version and this is what I think it looks like.  I have highlighted in pink the additions of the Effects Layouts version.  Is this what Brian Wampler intended?  It looks quite different.

A couple of the component values weren't clear so I have put a ? next to those too.
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galaxiex

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Re: Confusion about Brian Wampler’s modified MXR Distortion Plus
« Reply #4 on: March 11, 2018, 10:52:27 AM »

OK I have had a go at drawing the schematic for the Effects Layouts version and this is what I think it looks like.  I have highlighted in pink the additions of the Effects Layouts version.  Is this what Brian Wampler intended?  It looks quite different.

A couple of the component values weren't clear so I have put a ? next to those too.

The 1M at the input jack is the only difference I see as far as the audio path is concerned.

The other two 1M resistors form a voltage divider to provide the bias voltage for the op-amp.
The two caps are for power supply filtering and the diode is for reverse polarity protection.

Since this is a mod for an existing pedal,
it's possible Brian didn't show those components as part of the mod, because they are already there in the pedal.

The storyboardist Effects Layouts blog seems to assume that you will build the circuit from scratch,
rather than modify an existing pedal.

If that is the case then you definitely need those extra components, with the exception of the 1M at the input.
Further suspect that the 1M at the input was added to increase input impedance. (that's a good thing)
Try it both ways, with and without the input 1M.

Are you building from scratch or modding an existing pedal?
« Last Edit: March 11, 2018, 10:53:58 AM by galaxiex »
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SurreyNick

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Re: Confusion about Brian Wampler’s modified MXR Distortion Plus
« Reply #5 on: March 11, 2018, 12:08:53 PM »

Thanks galaxiex

I'm building from scratch as I want to use this modified MXR Dist + as the pre-amp stage for a battery-powered amp.  My idea is to use a TDA2005 in bridged mode for the amp and drive a single Jensen Chicago 8/20 MOD Speaker (8 inch, 20 watt, 4 ohm) with the whole thing powered by a Ritar RT1250 12v 5.0Ah SLA battery.

Could you suggest what values I should use for the components which I have a ? against (see below)?

On Brian Wampler's modified schematic, off pin 3 is reference to 4.5 something. I can't work out if this should read 4.5v or 4.5uF.  On the Effects Layouts version it is shown as a cap rated at 1uF.

Off pin 7 on the Effects Layouts version is a diode marked D9. Any suggestion what one I should use?

Also off pin 7 on the Effects Layouts version is a cap the value of which looks to be 47uF.  That seems very high.  I've proposed 0.47uF in my drawing but is 47uF reasonable?

The only other question I have, which perhaps you could help with, is for the caps which should be ceramic, poly, electrolytic etc.?

Thanks
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galaxiex

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Re: Confusion about Brian Wampler’s modified MXR Distortion Plus
« Reply #6 on: March 11, 2018, 04:04:42 PM »

Quote
On Brian Wampler's modified schematic, off pin 3 is reference to 4.5 something. I can't work out if this should read 4.5v or 4.5uF.  On the Effects Layouts version it is shown as a cap rated at 1uF.

Reference to 4.5V. This is the bias voltage needed by the op-amp on pin 3.
The cap is to filter that 4.5 volts and 1uf electro should be fine.
Could go higher to 47uf or even 100uf.

Quote
Off pin 7 on the Effects Layouts version is a diode marked D9. Any suggestion what one I should use?

Could leave that diode out.
It is simply for reverse polarity protection in a pedal, in case some doofus uses the wrong polarity supply. (wall wart)
If you want to add it, it won't hurt anything. Could use almost anything silicon. 1N4001 is common.

Quote
Also off pin 7 on the Effects Layouts version is a cap the value of which looks to be 47uF.  That seems very high.  I've proposed 0.47uF in my drawing but is 47uF reasonable?

That cap is for power supply filtering. 47uf electro is fine.
Could use anything from 47uf to 100uf.

None of these things will affect the "sound" of the circuit which is why their values are not critical.

HTH
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SurreyNick

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Re: Confusion about Brian Wampler’s modified MXR Distortion Plus
« Reply #7 on: March 12, 2018, 07:26:44 AM »

Thanks galaxiex.  I think that sorts out the circuit now  :)

Out of interest what would the effect be of pushing 12v through this circuit instead of the 9v specified?  I know the LM741 is optimised for 15v and can take 22v, but would any of the component values need to be changed?

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galaxiex

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Re: Confusion about Brian Wampler’s modified MXR Distortion Plus
« Reply #8 on: March 12, 2018, 07:13:10 PM »

I'm sure 12V would be ok. Probably not sound much different from 9V.
Maybe a little more headroom?

Just make sure the caps are rated for the higher voltage.
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SurreyNick

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Re: Confusion about Brian Wampler’s modified MXR Distortion Plus
« Reply #9 on: March 13, 2018, 02:45:46 PM »

Thanks.

I was thinking of using electrolytics for the caps rated 1uF and 47uF, any suggestion for the others (tantalum, ceramic, polyester, polystyrene etc.)?  I think the original spec called for ceramics, but just wonder if anyone has had good results with something else.  I'll be assembling on a veroboard or perfboard.

I believe 1/2W resistors will suffice, but I think I read somewhere that 1W will give better results.  Is this true?

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galaxiex

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Re: Confusion about Brian Wampler’s modified MXR Distortion Plus
« Reply #10 on: March 13, 2018, 08:35:15 PM »

Yes, electros for the power supply caps.

For the rest, ceramic or plastic film types are fine.

Don't bother with tantalum. They are polarized and often used only in fairly specific applications.

A word of warning...
There are "tone snobs" all over the internet that claim to be able to "hear" the differences in capacitor types,
and that it makes a big difference in the "tone" of your amp, pedal or whatever....

I say BS.
 
Maybe, really big maybe,
that you could hear the difference in caps in a high end full frequency music reproduction system... ie, a home stereo.

This is for guitar, it won't matter a hoot.

Also, I don't know how 1W resistors could give "better results".
Better how? Please define "better".

Millions of pedals, amps, etc have been built with 1/8, 1/4, and 1/2 watt resistors in the audio path.

You only need higher watt resistors (1 watt and above) if the circuit demands require it.

Brush up on ohms law and calculate the current flowing in the circuit to determine if the higher wattage resistor is needed.

Now, resistor types are a different story.
Carbon, carbon film, metal film etc.
The differences?
Noise.
Or I should say, potential noise.

Carbon composition resistors (pretty much obsolete) can potentially cause noise in circuits.
The newer film types are quieter.

But again, it's for guitar, I'm betting it won't make a whit of difference even if you get a hold of some carbon types.

Read here for more on this...

http://www.aikenamps.com/index.php/resistor-types-does-it-matter

Edit; please note that in the above link he is talking about resistors for TUBE amplifiers with high voltages in the range of 250V to 450V or higher.
So some of what he says doesn't really apply to low voltage designs in SS amps.
« Last Edit: March 13, 2018, 08:48:15 PM by galaxiex »
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phatt

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Re: Confusion about Brian Wampler’s modified MXR Distortion Plus
« Reply #11 on: March 14, 2018, 12:36:40 AM »

Some advice that will help;
1/ The circuit you post is not the best design as it's a pedal not really intended as a dedicated preamp, unless you just want distortion all the time with no real tone control.
The circuit is potetually noisy as it has no buffer stage.
Look to the people who knew how to do this and you will come to realize that these botique pedal circuits are actually not well designed.

If you want to understand then a good place to start is here;
http://www.geofex.com/Article_Folders/TStech/tsxtech.htm

8 out of 10 of all these fancy dirt pedal circuits are derivatives of the TS anyway.

With no buffer stage you do get a bit more gain but noise levels go up 10 fold.
There is nothing worse than noisy circuits. :grr
If you want a small battery powered amp then just build a simple preamp and add dirt circuits afterwards.
Just track down some easy small amp circuits,, try Vox pathfinder 10 comes with clean and dirt. :tu: The preamp will work from single supply with some modifications.
Phil.
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SurreyNick

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Re: Confusion about Brian Wampler’s modified MXR Distortion Plus
« Reply #12 on: March 14, 2018, 05:35:49 PM »

Also, I don't know how 1W resistors could give "better results".
Better how? Please define "better".

You only need higher watt resistors (1 watt and above) if the circuit demands require it.
Brush up on ohms law and calculate the current flowing in the circuit to determine if the higher wattage resistor is needed.

I certainly don't need higher watt resistors, by my calculations 1/2W is more than enough.  I don't know what the author meant by 'better' when he suggested a 1W resistor.  It was someone who posted online a variation of the MXR Distortion Plus and all the instructable said was "1/2W is sufficient, but 1W will be better".  No explanation what 'better' means.  I'll stick to 1/2W  ;)

Thanks
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SurreyNick

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Re: Confusion about Brian Wampler’s modified MXR Distortion Plus
« Reply #13 on: March 14, 2018, 05:49:31 PM »

Some advice that will help;
1/ The circuit you post is not the best design as it's a pedal not really intended as a dedicated preamp, unless you just want distortion all the time with no real tone control.

If you want a small battery powered amp then just build a simple preamp and add dirt circuits afterwards.
Just track down some easy small amp circuits,, try Vox pathfinder 10 comes with clean and dirt. :tu: The preamp will work from single supply with some modifications.
Phil.

Thanks for the advice, which I would love to adopt, but I fear modifying the Vox Pathfinder 10 (or similar) to run from a 12v SLA is a bit beyond my expertise.  I'm disappointed to hear my proposed approach is likely to have disappointing results.  I did try and find instructions for a 12v battery-operated amp with decent wattage but had no luck, 6W was about as good as it got and the design of that looked pretty poor.  :(
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phatt

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Re: Confusion about Brian Wampler’s modified MXR Distortion Plus
« Reply #14 on: March 15, 2018, 08:02:36 AM »

Yes getting more than 10 watts from a small amp is not easy but I found this one;

https://circuitsalad.com/2012/08/31/20-watt-battery-powered-guitar-amplifier-circuit/
Schematics shown with and without reverb.

I have no idea if this is worth it but should work ok,,, Jfet's might be a little hard to find.
It is a complete battery amp to run from a car battery or even a drill battery pak.

At least this gives a proper preamp with tone control.
You can still use the TDA2005 if you wish.
TDA2005 at 12 volts will likely deliver around 10 Watts clean in bridge mode.
Phil.


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