Bass Boost CMoy Problems - Page 2

Well, technically R5 isn't in parallel with R4. However, looking at how bass boost is implemented in a PPA, it would appear that you might want to jumper R5 (not really necessary to remove if it is a low value <100 ohms, up to you) and put the bass boost in series with R4, between R4 and the output. Not sure if this will work any better or not, but I guess its wortha shot.

Okay, so I also built a cmoy amp with bass boost according to the advice on the other thread that xluben posted at, and i put in r7/c7 in parallel in the place where r5 is on the original cmoy schematic. its on a home etched pcb laid out in eagle, and works perfectly except when bass boost is on. when i close the switch and it shorts r7 and c7 turning off bass boost it works great, but when i open the switch all i can hear is massive staticy distortion. i'm using .068uf caps and 24k resistors for the bass boost portion of the circuit. i'm not sure how it should be put in the circuit, but how i've got it is clearly wrong. i guess i'll try putting it in series with r4.

I think when I was advising xluben a couple of years ago, I didn't really understand bass boost, so may have given him bad advice in one of the threads. At any rate, I would try putting the bass boost circuit in series with R4, and the load, not in parallel with R5, per the following schematic. This appears to be how the other poster in that thread got it working from his markup.

thanks i will definitely try that tomorrow. before i found the other thread i had been looking everywhere for a schematic to see how to put in the bass boost. i'm attempting to learn to use eagle, etch pcbs and get into headphone amps all at once so your advice is greatly appreciated.

Yes, xluben made a mistake. Connect the parallel capacitor and 24k resistor in series with resistor R4. This creates a low pass filter inside the feedback loop at 6 dB/octave. Pars' schematic is correct. I assume you obtained those capacitor and resistor values from my site. Let me know if you need help.


Edit: Since Pars says he still doesn't understand, here's a mathematical explanation.

The ideal gain of a non-inverting opamp configuration, using the cMoy component naming conventions is:

Two key points:

-For AC circuit analysis, the impedance of a capacitor is modeled as: 1/(jwC), where w = 2*pi*frequency

-Two impedances in parallel = (Z1)(Z2)/(Z1 + Z2)

Therefore, using xluben's naming convention, the resulting theoretical gain is:

That equation isn't exactly easy to read, so here it is plotted (in dB):



As you can see, bass frequencies are boosted.

--JDS

I already understand how these work (but hadn't really thought about it 2 years ago). Thanks for the equation(s) though.

base on the scheme above, i followed that scheme and make my own drawing:

Left
http://i355.photobucket.com/albums/r445/jmwreck/1-2.jpg
Right
http://i355.photobucket.com/albums/r445/jmwreck/2-2.jpg

now the problem is, i dont know why it doesnt make any changes when i turn it on/off.

questions are:

1. is the original schematic (1st image) correct for bass boost?
2. are my own schemes (2nd & 3rd image) correct?
3. did i burn or damaged my "bass boost" resistor and cap?
4. it is still working perfectly right now, even with the bass boost switch is on/off, its just that it doesnt make any changes when i select it.  if it was damaged (#3), does the amp still work?
5. as you can see, the values in the original bass boost circuit, especially the cap is different from the one i did?  I know the fact that the higher its values, the lesser it cuts off the low frequency.  but at least i can hear difference because of it, am i correct?

thanks :D

Edited by jmwreck - 9/24/11 at 4:13am

bump

I'd like to see the whole circuit before commenting, do you have a picture

 

cheers

ok, this is what i followed: HERE

 

then I have created mine with THIS

dont mind the pads you see on the mid bottom part, those were just to jump to the power and ground circuit

 

Edited by jmwreck - 9/24/11 at 7:46am

That will work, I use a higher value resistor say 33-39K but the principles the same, experiment with the values useing AMB's bass boost calculator

 

http://www.amb.org/audio/mmm/

 

cheers

YUP, I know it will but it doesn't affect the sound in my case, I have tried using different headphones and putting the toggle to switch the input caps from different values, still no effect :D

If its not affecting the sound I'd double check your wiring, its easy to make a mistake and keep missing it :-)

 

good luck

yup, maybe on my next build, but now, im quite satisfied, it really has a lot of bass, I have tried it on my friends stock Iphones pads, the bass is drowning the entire sound and ask me if there is any way to decrease it.  but in my headphones, I have been using the philips 250 and sony ex50, the overall mix was great. so I guess it all depends on the headphones used for now -- on this build.