freestompboxes.org

bajaman wrote:well here you go
resolution is 600 dpi
email me if you want higher res
cheers
bajaman

EMG DG20 combined SPC and EXG board.png

Any chance for a through-hole version of this?

In the meanwhile, I've redrawn the scheme in Eagle...
If there's a hero which draws a tiny through-hole PCB, is welcome!

Hello.

Anyone made this work?

I made spc control but something is wrong, I get only clean signal when pot is all the way up, exactly the same as bypassed.
I used substitute opamp - tl072 and ne5532, I found it can be substituted with those, could this be problem?

nope

rockstrana wrote:Hello.

Anyone made this work?

I made spc control but something is wrong, I get only clean signal when pot is all the way up, exactly the same as bypassed.
I used substitute opamp - tl072 and ne5532, I found it can be substituted with those, could this be problem?

Does your build affect the sound at other points in the pot rotation or does it always sound like it is bypassed no matter the position of the pot? These circuits are designed so that when they are turned down to minimum, the signal sounds the same as bypassed (because there is no on/off switch for them when used in a guitar). You may have your wires to the pot backwards if turning clockwise decreases the affected signal.

gilmour_pugliese wrote:In the meanwhile, I've redrawn the scheme in Eagle...
If there's a hero which draws a tiny through-hole PCB, is welcome!

something like this?
its 31x40,single face,no links,space for cubic Panasonic caps.

CHEEZOR wrote:

rockstrana wrote:Hello.

Anyone made this work?

I made spc control but something is wrong, I get only clean signal when pot is all the way up, exactly the same as bypassed.
I used substitute opamp - tl072 and ne5532, I found it can be substituted with those, could this be problem?

Does your build affect the sound at other points in the pot rotation or does it always sound like it is bypassed no matter the position of the pot? These circuits are designed so that when they are turned down to minimum, the signal sounds the same as bypassed (because there is no on/off switch for them when used in a guitar). You may have your wires to the pot backwards if turning clockwise decreases the affected signal.

It is possible I wired it backwards, but when turned it cuts volume, there is no any boost.

alexradium wrote:something like this?
its 31x40,single face,no links,space for cubic Panasonic caps.

Yes, just like that. Thanks!

rockstrana wrote:It is possible I wired it backwards, but when turned it cuts volume, there is no any boost.

Its been a while since I have heard one these things, but I'm pretty sure there is supposed to be at least a slight boost... :S If you have some nice close up pics of your wiring I would post them to the troubleshooting section and see if someone can help you out.

Bajaman,
in your first post you said that the SPC puts a 10db boost at 600hz. But on the EMG website, it says "6db boost around 1300hz" ?!

My 10 year old SPC has a peak around 600Hz, so let's forget the statement about that 1.3kHz peak. I read that on the website of the german seller thomann.de, and it's most probably wrong.

But the picture of the SPC shows two more parts, that are not in the schematic: A capacitor and a diode or transistor, both close to the power supply wire. What are these for? Filtering or polarity protection?

roseblood11 wrote:But the picture of the SPC shows two more parts, that are not in the schematic: A capacitor and a diode or transistor, both close to the power supply wire. What are these for? Filtering or polarity protection?

They are present on the schematic - upper right corner. You're right - their purpose is filtering and polarity protection. Look at the bajaman's PCB, they are the same as EMG's.
There's one difference - 1k resistor is missing.

Vero layout, small changes to the circuit for use with pasie pickups. I used a OPA2134, because the higher current draw doesn't matter for me, as I will add a true bypass pushbutton switch for the mid boost. Could be replaced with LF442, TL062, TLC2272 ...

Is the circuit still the same in this version?

He puts the EXG before the SPC in the signal chain - with the input resistors shown on the schematics in this thread, this wouldn`t work with passive pickups...

According EMG INSTALLATION INFORMATION :

The EXG has buffered inputs and can be used with passive pickups.

Hi Folks
Only just seen this thread. I'm building the combined SPC and EXG and have a question.
On the 'Bass Boost' op amp is the feedback resistor (in parallel wth 2n2) 4.99 or 499 ?
Thanks for any help.

On the 'Bass Boost' op amp is the feedback resistor (in parallel wth 2n2) 4.99 or 499 ?

499k makes a lot more sense based on the relative values of Bass and Treble boost.

4.99k would make the bass circuit fairly benign. Even 49.9k would only produce a small amount of bass lift.

george giblet wrote:

On the 'Bass Boost' op amp is the feedback resistor (in parallel wth 2n2) 4.99 or 499 ?

499k makes a lot more sense based on the relative values of Bass and Treble boost.

4.99k would make the bass circuit fairly benign. Even 49.9k would only produce a small amount of bass lift.

Thanks. I went for 470k which seems ok.

Awesome work by bajaman and other contributors BTW. Price for both EMG SPC and EXG in the uk is around £120.

I'm still not sure, which opamp is best for the SPC midboost with input buffer.

- OPA2134 and LM833 produce distortion/oscillation. There is some positive feedback in the circuit, which might cause this.

- 1458/4558. Better, but current draw is a bit high for use inside the guitar.

- LF442. Best sound and low current draw, but it wants to see a higher voltage. The circuit stops working, when the battery is still above 7V.

So, which is the best opamp for this circuit?

I don't want to treat my super-duper Warmoth body with a router to install a second battery...

For the LF442:

You can change the 1N914 diode on the power to a lower drop Schottky (choose a type with a low drop as they aren't always the same) to get a little less drop. You can save 0.6V drop by removing the series diode altogether and instead using a *reverse* 1N4004 etc. *across* the power rails for protection. Read-up on parallel protection, this is fine to battery stuff like inboard preamps.

If you have an oscilloscope you can tweak the voltage dividers on each of the opamps so swing stays symmetrical at lower battery voltages. That's usually done by raising the value of one of the divider resistors to the next available value, either the one to +v or one to -v depending on which rail starts to clip first. You will need to tweak all the dividers; highly likely they will all need to be adjusted by the same amount.

For the oscillating opamps. You might try moving the cap across to the power rails to the opamp side of the diode instead of the battery side. I haven't tried to retrace the PCB so I'm not sure what the original was. Whatever the case moving that cap to the opamp side can only help reduce oscillations. If that's not enough you can sometimes add small caps across the feedback resistors of the opamps. It would help if you knew what part of the circuit was oscillating.

Guys, how do I make the EXG to be a linear booster (without a frequency peak)? I don't even need a potentiometer (I have a push-pull bypass), if I close the contacts under 100k, I will get a line graph? how to make a linear characteristic? I like this device because it has very little noise and low consumption, but I wanted to convert it to gain without an equalizer. Please tell me, thank you.