Bass Mid Control by E.W.S. schematic  [schematic]

All about modern commercial stompbox circuits from Electro Harmonix over MXR, Boss and Ibanez into the nineties.
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chicago_mike
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Post by chicago_mike »

Sexy!!! :applause:
Skyline FX 2013

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mrtnnaughton
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Post by mrtnnaughton »

I build this based on Ivlark's vero layout and I am having a couple of issues. I do get sound through the effect but when I adjust the boom or volume trim pot , I get a loud whistle/siren noise. If someone could help me out , I would greatly appreciate it. Here are the voltages I am getting with the components;

IC; D1; Q;
1) 3.84 Anode to cathode=-2.17 D=4.62
2) 3.84 Anode to ground= 2.34 G=3.09
3) 3.82 Cathode to ground= 3.08 S=2.33
4) -0
5) 7.6 D2;
6) 3.83 Anode to cathode=0.69
7) 3.83 Anode to ground=8.27
8) 3.36 Cathode to ground=7.56

Once again, Thank You

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mrtnnaughton
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Post by mrtnnaughton »

Sorry the format got all screwed up with my first post....
I build this based on Ivlark's vero layout and I am having a couple of issues. I do get sound through the effect but when I adjust the boom or volume trim pot , I get a loud whistle/siren noise. If someone could help me out , I would greatly appreciate it. Here are the voltages I am getting with the components;
IC;
1)3.84
2)3.84
3)3.82
4) -0
5)7.6
6)3.83
7)3.83
8)3.36

D1;
Anode to cathode=-2.17
Anode to ground= 2.34
Cathode to ground= 3.08

D2;
Anode to cathode=0.69
Anode to ground=8.27
Cathode to ground=7.56

Q1;
D=4.62
G=3.09
S=2.33
Thank you

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mrtnnaughton
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Post by mrtnnaughton »

I read the IC incorrectly;
1-4 are correct
5)3.35
6)3.8
7)3.8
8)7.62

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alexdepaulo
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Post by alexdepaulo »

lietuvis wrote:I redraw pcb if anybody interested (sprint layout 6). The PDF is ready to transfer.
lietuvis, excellent job!
Just a question: Where is the 330uF capacitor that is in the original schematic ???

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phatt
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Post by phatt »

mrtnnaughton wrote:Sorry the format got all screwed up with my first post....
I build this based on Ivlark's vero layout and I am having a couple of issues. I do get sound through the effect but when I adjust the boom or volume trim pot , I get a loud whistle/siren noise. If someone could help me out , I would greatly appreciate it. Here are the voltages I am getting with the components;
IC;
1)3.84
2)3.84
3)3.82
4) -0
5)7.6
6)3.83
7)3.83
8)3.36

D1;
Anode to cathode=-2.17
Anode to ground= 2.34
Cathode to ground= 3.08

D2;
Anode to cathode=0.69
Anode to ground=8.27
Cathode to ground=7.56

Q1;
D=4.62
G=3.09
S=2.33
Thank you
Hi Mate,, Just be aware,,, that vero layout has the input right next to the output and that is an open invitation for feedback problems.
It's wise to layout your in/out on opposite sides of the Board. The circuit may well be right but the above gotcha is a common mistake. :thumbsup
Phil.

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alexdepaulo
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Post by alexdepaulo »

phatt wrote:
mrtnnaughton wrote:Sorry the format got all screwed up with my first post....
I build this based on Ivlark's vero layout and I am having a couple of issues. I do get sound through the effect but when I adjust the boom or volume trim pot , I get a loud whistle/siren noise. If someone could help me out , I would greatly appreciate it. Here are the voltages I am getting with the components;
IC;
1)3.84
2)3.84
3)3.82
4) -0
5)7.6
6)3.83
7)3.83
8)3.36

D1;
Anode to cathode=-2.17
Anode to ground= 2.34
Cathode to ground= 3.08

D2;
Anode to cathode=0.69
Anode to ground=8.27
Cathode to ground=7.56

Q1;
D=4.62
G=3.09
S=2.33
Thank you
Hi Mate,, Just be aware,,, that vero layout has the input right next to the output and that is an open invitation for feedback problems.
It's wise to layout your in/out on opposite sides of the Board. The circuit may well be right but the above gotcha is a common mistake. :thumbsup
Phil.
:scratch: :scratch: :hmmm:
I did not understand that answer! :wink:

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phatt
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Post by phatt »

Hello Alex,
That Whistle noise as you turn up the controls is most likely oscillation. The cause is most likely positive feedback which might be due to a phase issue.
With some circuits the phase of the signal at the output can end up in phase with the input and if the Input is right next door to the output then the circuit can oscillate,,Feedback on itself. Much like when a microphone gets to close to a speaker it squeals like a pig as the input is to close to the output.

With layout wires, Electric fields exist *Outside of the wire* and if the gain is high the circuit can also feedback on itself if input is close to output.
I think the term is *coupled inductance* Better minds here may explain it in more detail. :thumbsup
Phil.

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Post by alexdepaulo »

phatt wrote:Hello Alex,
That Whistle noise as you turn up the controls is most likely oscillation. The cause is most likely positive feedback which might be due to a phase issue.
With some circuits the phase of the signal at the output can end up in phase with the input and if the Input is right next door to the output then the circuit can oscillate,,Feedback on itself. Much like when a microphone gets to close to a speaker it squeals like a pig as the input is to close to the output.

With layout wires, Electric fields exist *Outside of the wire* and if the gain is high the circuit can also feedback on itself if input is close to output.
I think the term is *coupled inductance* Better minds here may explain it in more detail. :thumbsup
Phil.
Ah! Yes! Now I understand.
But is this really? I do not think so much :hmmm: ... but then the best proposal is a totally different PCB layout. :?

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phatt
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Post by phatt »

If you are certain the circuit is correct then I'd try a different layout.
That is why I always bread board circuits before I commit to a build as it allows you to find all the little quirks that might be lurking just waiting to stump you. Nothing worse than spending days perfecting a great PCB only to find one small oversight renders it junk and ends up as land fill. :slap: No medals for guessing HOW I know this,,,winky Phil.

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Post by reddesert »

You could make a very simple modification to move the output further away from the input. The only thing connected to board output is a 330R resistor. Disconnect that 330R resistor from the output row and connect it to the bottom row of the vero board instead (it will have to be a standing resistor). Add another cut in the bottom row to isolate it from the trimpot. Move the output wire from its old location to the bottom row. Now the output and input are separated by several rows.

Of course, you should also check for solder bridges and missed connections.

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Post by jeepe »

phatt wrote: 20 Feb 2017, 11:09 Hi Mate,, Just be aware,,, that vero layout has the input right next to the output and that is an open invitation for feedback problems.
It's wise to layout your in/out on opposite sides of the Board. The circuit may well be right but the above gotcha is a common mistake. :thumbsup
Phil.
hi,
as a matter of fact, it is NOT right next to the output...
and builders have built this exact vero layout with success, and without oscillation
as we can see it here:
https://tagboardeffects.blogspot.com/20 ... ntrol.html

no offense, just for the facts,
and your point still has been taken :)
pedal building, tracing and sharing is such a beautiful freedom movement... If only it could be viewed as a future heritage, but it really is ephemeral, as it seems

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