So I have this pile of Tone Control and pre amp boards. Purchased from the market.
The objective was to test them all. And hoefully learning something.
My gut feeling is that in many cases the trim pot values used are wrong. I found the orignal schematic for one of the boards. And I noticed that the orignal schematic used a 50K trim pot. But the board I had was using 100K.
In another example. 50K trim pot was used when original design was for 10K.
Is there some quick way to figure out if a wrong trim pot was used in a particular circuit. i.e. setting a bass trim pot to center position should make it sound like no bass is being added or subtracted.
Or by looking at the resistor values used with the opamp. I can predict if the trim pot value is too low or too high.
Or if I need to read up and study on this. How do I approach the subject.
The objective was to test them all. And hoefully learning something.
My gut feeling is that in many cases the trim pot values used are wrong. I found the orignal schematic for one of the boards. And I noticed that the orignal schematic used a 50K trim pot. But the board I had was using 100K.
In another example. 50K trim pot was used when original design was for 10K.
Is there some quick way to figure out if a wrong trim pot was used in a particular circuit. i.e. setting a bass trim pot to center position should make it sound like no bass is being added or subtracted.
Or by looking at the resistor values used with the opamp. I can predict if the trim pot value is too low or too high.
Or if I need to read up and study on this. How do I approach the subject.
So basically entering it up in a simulator is the fastest and best route for somebody starting out. Was hoping for some kinda rule of thumb to see if they even got it ballpark right.
Once you have grasped the theory then you can calculate the values of fixed resistors and fitting a trim pot does exactly as described, it trims.
If a design calls for a pre set pot, that is different and will allow for a larger margin of adjustment.
If a design calls for a pre set pot, that is different and will allow for a larger margin of adjustment.
I knew there was a rule of thumb I was looking for. Esp when I know they have not used the same trim pot as the orignal design. i.e. og was 50k they used. 100k.
The rule of thumb I was looking for below.
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Some constructors may have difficulties finding 100k dual linear pots. If this applies to you, then a different value can be used. For example, if you can get 50k dual pots, just double the tone control capacitor values (Cx01 and Cx02), and halve the resistor values (Rx05 - Rx19). This will maintain the same performance. The same basic principle applied for any pot value, with the lower limit being 10k - any less will cause excessive opamp loading (caps are ×10, resistors divided by 10).
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Source
https://sound-au.com/project97.htm
The rule of thumb I was looking for below.
------
Some constructors may have difficulties finding 100k dual linear pots. If this applies to you, then a different value can be used. For example, if you can get 50k dual pots, just double the tone control capacitor values (Cx01 and Cx02), and halve the resistor values (Rx05 - Rx19). This will maintain the same performance. The same basic principle applied for any pot value, with the lower limit being 10k - any less will cause excessive opamp loading (caps are ×10, resistors divided by 10).
-------
Source
https://sound-au.com/project97.htm
Ok still need help. In this circuit diagram he has used 50K trim pots.
If I was to use 100 K trimpots in the same circuit VR1 to VR5. what caps and resistors would I need to change ?. A simple red circle would do.
And by what factor. If this doubt is clarified I can start entering up various ideas in the simulator and see the results.
If I was to use 100 K trimpots in the same circuit VR1 to VR5. what caps and resistors would I need to change ?. A simple red circle would do.
And by what factor. If this doubt is clarified I can start entering up various ideas in the simulator and see the results.
There's at least 22 parts that depend on those pots. Don't expect anybody to do all your mark-up. My fingers got tired. See the trend?
When in doubt, pick up two BOSS GE-7 pedal equalizers. They get no respect but are very useful tools.
When in doubt, pick up two BOSS GE-7 pedal equalizers. They get no respect but are very useful tools.
Fiar enough I just needed a pointer. You saved me a few hours of reading and a lot of head scratching. For which I am much obliged.
My next question.
Having decided to start building sections of my own tone control board. Im not happy with the 3 controls and would rather build a 5 or a 10 setup.
So my plan is to experiment on a bread board where I dial in each control and its frequency. And maybe play with the Q or the width. So the bands dont land up mixing into each others areas too much. I have a 100 Mhz dual channel scope, a function generator.
My doubt is how do I verify what I have built is hitting the right frequency the math says it should.
Here are my options based on what I have read and what others have told me.
1. Use a freq sweep thru the circuit and then look at the scope in FFT mode.
2. Use Pink or white noise and look at the scope in regular a/c mode. Or FFT mode.
3. Any other way to verify the circuit is doing what it should. Using a scope.
Ideall I want to see the Q width and the Freq point at which the signal is being boosted or cut. This way I confirm each section as I build it. When all the sections are built I join them together and chk.
I plan to build two types first one which uses op amps and another which just uses inductors, caps and resistors. Based on which works better or sounds better I build the rest using the same way. This was inspired by the Cello Sound Palette thread. Id like to use the same frequencies it does. A variable Q would be nice but maybe for ver 2. For now just want to learn how to get accurate tone control and tune my existing purchased tone control boards i.e. Most of the boards I have the mids are not mids. They are either more like high or low. I need to learn how to move the existing freq bands around. And control their width.
Im also ok with using both methods i.e. for freq where the inductor would be too large / costly I use op amp and for others I use inductors, caps and resistors only.
I have most of the boards I already own entered up in the simulator. This is a steep learning curve. And Ive started this journey just a few months back.
This place and its members is an amazing resource. For the hobbyist and DIY crowd. And its obvious I have a lot of reading and study to do. As this is a new domain of knowledge for me. My day job is designing and building engines.
Ps: Thanks for the tip.
https://www.hobby-hour.com/electronics/s/ge7-equalizer.php
My next question.
Having decided to start building sections of my own tone control board. Im not happy with the 3 controls and would rather build a 5 or a 10 setup.
So my plan is to experiment on a bread board where I dial in each control and its frequency. And maybe play with the Q or the width. So the bands dont land up mixing into each others areas too much. I have a 100 Mhz dual channel scope, a function generator.
My doubt is how do I verify what I have built is hitting the right frequency the math says it should.
Here are my options based on what I have read and what others have told me.
1. Use a freq sweep thru the circuit and then look at the scope in FFT mode.
2. Use Pink or white noise and look at the scope in regular a/c mode. Or FFT mode.
3. Any other way to verify the circuit is doing what it should. Using a scope.
Ideall I want to see the Q width and the Freq point at which the signal is being boosted or cut. This way I confirm each section as I build it. When all the sections are built I join them together and chk.
I plan to build two types first one which uses op amps and another which just uses inductors, caps and resistors. Based on which works better or sounds better I build the rest using the same way. This was inspired by the Cello Sound Palette thread. Id like to use the same frequencies it does. A variable Q would be nice but maybe for ver 2. For now just want to learn how to get accurate tone control and tune my existing purchased tone control boards i.e. Most of the boards I have the mids are not mids. They are either more like high or low. I need to learn how to move the existing freq bands around. And control their width.
Im also ok with using both methods i.e. for freq where the inductor would be too large / costly I use op amp and for others I use inductors, caps and resistors only.
I have most of the boards I already own entered up in the simulator. This is a steep learning curve. And Ive started this journey just a few months back.
This place and its members is an amazing resource. For the hobbyist and DIY crowd. And its obvious I have a lot of reading and study to do. As this is a new domain of knowledge for me. My day job is designing and building engines.
Ps: Thanks for the tip.
https://www.hobby-hour.com/electronics/s/ge7-equalizer.php
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So I have come up with this idea. For testing.
I will have 5 knobs or 10.
Each knob has 4 caps and 4 resistors. Double gang knob. So 2 caps and 2 resistors per channel.
Each knob is designed to work with a specific freq.
So knob 1 = 2000Hz.
Knob 2= 4000Hz
Knob 3- 8000 Hz
And so on.
Each circuit is tested in the simulator and then on the scope.
This will let me confirm I have the right Trim Pot value. And its doing what it should.
I will add the schematic for this knob in a bit. I also need to confirm that they behave as they should when chained together.
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So what I learned. Its more a rule of thumb and I love rules of thumb. Some expert may well come along and shoot this one down. But what I did find is that in most tone control boards. Changing / increasing the Trim pots value increased the range over which it had control i.e. in the simulator or on the test bench if I put in a 22K trim pot I find the gain / reduction is 3 DB.
When I change it to 47K the gain goes up to +-6 DB. And when using a 100K trim pot. The the gain / reduction goes up to +- 15 DB. The knee point of the freq remains more or less the same.
When I change it to 47K the gain goes up to +-6 DB. And when using a 100K trim pot. The the gain / reduction goes up to +- 15 DB. The knee point of the freq remains more or less the same.
