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DIYstompboxes.com  |  DIY Stompboxes  |  Building your own stompbox  |  How to figure something out on my own? 0 Members and 1 Guest are viewing this topic. « previous next »
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Author Topic: How to figure something out on my own?  (Read 469 times)
Seven64
Posts: 482


How to figure something out on my own?
« on: March 16, 2012, 09:32:30 PM »

Should i just try and see if it works, or if im wrong?  I am trying to figure out how to change the gain in my hm2 heavy metal.  i want alot more.

http://www.hobby-hour.com/electronics/s/hm2-heavy-metal.php

there is the schematic.  i was thinking just replacing r42 with a 22k, so that it could in theory have about twice as much.  is this right or wrong?

what should i do so that i don't have to ask questions like this anymore?
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CynicalMan
Posts: 1613


Alex L. - Canada


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Re: How to figure something out on my own?
« Reply #1 on: March 16, 2012, 09:59:26 PM »

If you want more distortion that will work. The only other thing I would change is C22. You should increase it by the same factor that you decrease R42. So if you halve R42 to 22k, you should double C22 to 0.1u, or if you make R42 4.7k, C22 should be 1u. The reason for this is that the capacitor makes the op amp act as a high pass filter. With lower frequencies its impedance is high, which reduces the gain of the op amp stage. The cutoff frequency of this filter is 1/(2*pi*R42*C22), which is 72Hz with the original values. If you halve R42, you double the frequency to 154Hz, which will reduce bass. So to keep the cutoff frequency at 72Hz, you need to double C22.

If you want to know this stuff without asking, you really need to know the theory. The best ways to learn that is to read about it and ask lots of questions. So keep asking questions until you feel you don't need to anymore. It's still worth it to simulate, breadboard, and build your ideas to get a more empirical understanding of how they sound, and you should do a lot of this too so that you can apply theoretical knowledge to practical applications.
« Last Edit: March 16, 2012, 10:11:55 PM by CynicalMan » Logged

R.G.
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Posts: 16199


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Re: How to figure something out on my own?
« Reply #2 on: March 16, 2012, 10:01:29 PM »

Should i just try and see if it works, or if im wrong?  I am trying to figure out how to change the gain in my hm2 heavy metal.  i want alot more.
there is the schematic.  i was thinking just replacing r42 with a 22k, so that it could in theory have about twice as much.  is this right or wrong?
That will increase the gain of that one stage.

There are other places to increase the electronic gain, not what most guitarists mean by "gain". You could also double (or more) R20, and increase gain in other places before the distortion stage. You could could convert IC1B to inverting gain, which would reduce the amount of undistorted signal mixed with the distorted signal, so it would sound more distorted, even if the gain is actually a tiny bit lower. You could increase the AC gain of Q6 and/or Q7 by splitting the resistor between collector and base in about half, then putting a suitably-sized capacitor to ground to remove the feedback that reduces the gain of these stages a bit.

Quote
what should i do so that i don't have to ask questions like this anymore?
Big job. Pretty much you have to go learn how to estimate and change the gain of many types of transistor and opamp/feedback amplifier circuits and be familiar with what the impedances before and after them do to the gain. It takes a lot of time. Some of it's just memory - this transistor stage has this gain and changing *this* by this much increases/decreases it and also does this...

A circuit simulator is a big help in testing out ideas and getting the experience needed to reduce the math to an instinctive feel.

Big job.

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R.G.

Every single NASA manned mission starting with the Gemini series has carried a roll of duck tape.
Yes, really. Look it up.
Seven64
Posts: 482


Re: How to figure something out on my own?
« Reply #3 on: March 16, 2012, 10:16:08 PM »

you guys are awesome.  i love how you always help out people like me.  I go back and forth with this pedal.  it sounds good for what it is, but it deff needs a few tweaks.  i am adding a mids control to open up the dynamics a little more.  it also just doesnt have enough "gain" for my taste.  maxed out it sounds like a weak slayer sound.  i want that sound around 50%. 


thanks guys.
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