# Bass Boost CMoy Problems



## xluben

I built a CMoy with Bass Boost based on this layout:







 I wired up the I/O jacks with no pot, no switch for bass boost, OPA2132, .047uF for C7, 100K for R7, and a gain of 2. Last night I wired it up with one 9V and after about 30 seconds of being hooked up the C1 cap for the left channel was very hot. I unhooked the battery and tried fixing any suspect soldering. I hooked the battery back up and it didn't get hot (I didn't think), and then tried listening to some music. There was sound out of both channels but it was VERY scratchy and not very loud.

 I gave up on it for the night and this morning I decided to try hooking up two 9V's in series, because I thought it sounded kind of like when my batteries were dying in my other CMoy's. I did this and within a few seconds of having the batteries hooked up the C1 cap for the left channel made a popping noise and it looked like something was bubbling out of the end of it.

 I should be getting a digital multimeter soon, and then hopefully I can try to figure out what the problem is myself, but until then I was wondering if there was anything obviously wrong that anyone could notice.

 Thanks.


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## xluben

I also removed one emty line on the protoboard you can see it marked in this pic:





 I just shifted everything up. Could this cause a problem? I never knew why that open line was there, or if it needed to be there.

 Here's some actual pics of my work:



 



 In the first pic I marked a couple of jumpers that I put underneath. I didn't do a very good job soldering them, and I thought that was my problem last night, but I'm not really sure.


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## skyskraper

firstly a few of your joints look like they could be cold, try reflowing them so that you get universal coverage of each pad. secondly there looks like there could be a short near the yellow box on the right and in a couple of other places around the board. check on those, clean the board of flux. also the the resistor near the left leg of the green cap on the right looks like it could be shorting out on to the cap, same with its mirror image resistor on the left, but to either the jumper sticking out from the bottom of the board or to one of the pins of the dip socket.


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## Mod_Evil

Check the voltages in the virtual ground. My frist Cmoy have destructed 2 OPA2132 because the voltages with the virtual ground aren't stables.

 Use A TLE2426 for make the virtual ground.

 Thanks in Advance,
 Felipe Navarro


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## xluben

OK, now here's what I've done:

 - Flux on whole board and reflowed all joints
 - Added in switch as shown in diagram
 - Removed damaged C1 capacitor (left channel)

 Then I hooked up one 9V and tested it out. (Is it bad to test this amp when it doesn't have any C1 capacitor installed?) With the bass boost swithc 'off' I get what I would think is normal amped sound out of the right channel. The left channel is slightly quieter than the right, but I assumed this was due to the missing C1. When I switch the bass boost on everything gets all scratchy again.

 I thought that maybe this was due to my choice of R7 (100K -> 20dB) being too much bass boost for my headphones to handle so I switched the R7 (in the right channel) to a 10K resistor for 6dB of boost. This still causes similar amounts of distortion.

 For my C7 I am using Polyester-Film Capacitors. Is this OK or should I switch to Metalized-Film? Would that be enough to cause my distortion?


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## xluben

I'm going to get some 0.1uF Metalized-Film Capacitors to use as C7 and also a replacement C1. I'm hoping the noise in the bass boost circuit is due to the fact that the caps I used were Polyester-Film, and that the Metalized-Film caps will fix my problem.


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## Pars

It would appear from your pics that you may have both C1s in backwards (wrong polarity). If it is wired up per the diagram (Tangent's), with the + battery lead coming in on the left side and negative on right side, they should be:

 + -
 C1 C1
 - +

 Stuff bubbling out of electrolytics is a pretty good indication that they are in backwards 
	

	
	
		
		

		
		
	


	




 Take a really close look at Tangent's tutorial and the board layout. Then look at the black negative stripe on your caps.


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## xluben

OK, that was a stupid mistake. I switched the caps to right direction and hoped that would fix my amp, but it didn't.

 Right now I have one working side (right) and one side that works, but is quieter (left). When I switch on the bass boost both sides are mostly static.


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## Pars

It's always alot easier to narrow down and fix one thing at a time. Get the basic amp working first, then go on to the bass boost.

 Go over the bottom side of the board with a magnifying glass or other magnification (I don't care how young you are, even my 15 yr old without glasses and perfect vision misses stuff until I make him use one
	

	
	
		
		

		
		
	


	




 ). Take an xacto knife and run it between any pads that look like them might be bridged or anything. Clean the flux off the board... rubbing alcohol and a toothbrush work good for this, 99% is the best (little water content), but the normal 70% will work fine for this.

 Pull the opamp from the socket, and with a meter (DMM) ohm out from virtual ground to each of the socket pins while looking at the schematic. Make sure that things make sense according to the schematic, i.e., if you have a 1K resistor running to (virtual) ground, that you are seeing 1K ohms. If you are seeing something that doesn't make sense, figure out why and fix it. Or ask about it. If you are seeing any really low readings (<10 ohms), you have a bridge or a short. Also ohm out adjacent pins on the socket looking for shorts.


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## xluben

Thanks for all the suggestions!

 I think you're onto something with the vision thing. I decided to turn on my desk lamp as well as my ceiling lamp and it seems I can't tell the difference between red/orange/brown on a resistor!

 For R4 (which should be 10K) I had a 1K (right channel) and a 100K (left channel). I think I must have just zoned out when picking my resistors. If I had a multimeter I would have matched my resistors and this never would have happened.

 Anyways, after a lot of desoldering and resoldering now I have a working CMoy with a gain of 2 and OPA2132. I am using two 9V's in series (I haven't even gotten to trying to put in my DC jack). 

 For the bass boost circuit I have a 0.1uF cap (lowest, Hz, bass boost) and a 15K resistor. I'm a little unclear as to whether 10K or 100K does more bass boosting. I was assuming that 10K would give less bass, but now that I think about it, does 100K give the least bass boost? 

 With the 15K resistor in place I get A LOT of distortion. Right now I'm running the amp out of my iPod's headphone out so I can control the volume. With the 15K resistor I hear distortion unless the iPod is at about 25% or less. With 100K resistors I don't hear the distortion until about 50%. But with either I don't hear any bass boost even when the volume is low enough that there is no distortion.

 So, my question is what do I do next?

 - Change the bass boost cap to 0.047uF?
 - Change the bass boost resistor to 100K?
 - Add in the pot and see if that will help?

 Using these cap/resistor values what configuration would give me the least bass boost (I just want it to work!):

 - 0.1uF/0.047uF cap 
 - 10Kohm/100Kohm resistor

 Thank you


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## xluben

Just want to make sure that I'm having problems with the bass boost off, so here's a quick drawing of how I have my switch hooked up:






 That drawing shows the direction of the switch in what I assume is bass boost off (this is how the switch is when my amp works). It is a DPDT Micromini Toggle Switch from Radioshack, and the A,B,C,D labels are shown on the picture in the original post of this thread.


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## xluben

Bump

 I'm getting really tired of de-soldering and soldering different cap/resistor combinations, and I'm out of ideas with what I currently have. I think my new enclosure should arrive in a week or so, and I'd like to figure this out before then.

 Is there something wrong with my layout? Or with the components I'm using?

 Thanks for any help!


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## Pars

Well, the only thing that comes to mind is that you have the bass boost essentially in the R5 position (inside the feedback loop). The first two CMoys I built used R5s and I screwed up and put 470 ohm resistors in instead of 47 ohms. The result was massive distortion. So I guess I'm not really certain if bass boost will work as you have it configured. How is it wired in in a Pimeta for example (although with buffers in a Pimeta that may not be an apples-apples comparison).


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## leftshoe

Clean the flux off of the board. When I built my cmoy it kept having weird problems, like voltages beging wrong, huge DC offset, static, etc. 
 All the problems went away after cleaning the flux off of the board.


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## xluben

Quote:


  Originally Posted by *Pars* 
_Well, the only thing that comes to mind is that you have the bass boost essentially in the R5 position (inside the feedback loop). The first two CMoys I built used R5s and I screwed up and put 470 ohm resistors in instead of 47 ohms. The result was massive distortion. So I guess I'm not really certain if bass boost will work as you have it configured. How is it wired in in a Pimeta for example (although with buffers in a Pimeta that may not be an apples-apples comparison)._

 

From my original post (http://www6.head-fi.org/forums/showthread.php?t=151722) I thought that putting the bass boost circuit in place of the R5 would be correct. Now that I look at the schematic for a PPA it seems that the bass boost circuit should be in series with R4 which is in parallel with R5. I think that may be my problem.

 Once I realized I may have set up my bass boost circuit incorrectly I thought that cutting one of the pads of the proto board to make the bass boost circuit in series with R4 would fix my problem. I cut it with my new Dremel only to plug in my headphones and get no sound at all. I then realized that this also cut one pin (from each channel) of the op-amp out of the circuit, thus causing my to get no sound.

 I think I may be able to just add a jumper and get bass boost to work, but I'm gonna have to think about it a little bit more. Hopefully I can figure it out before my enclosure gets here. If I can get it to work I think I'll just re-do the layout (using a little bit more space) and make sure to get it right.


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## Pars

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.


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## xluben

Quote:


  Originally Posted by *Pars* 
_ 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._

 

That's exactly what I was thinking of doing (except for jumpering the R5, which seems like a good idea). I think I may just start over with a few more lines of proto board and add a 12V linear regulator for wall power.


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## Hivoltage

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.


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## Pars

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.


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## Hivoltage

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.


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## blackinches

Quote:


  Originally Posted by *Hivoltage* /img/forum/go_quote.gif 
_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._

 

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:

  Quote:


 Av = 1 + R4/R3 
 

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:

  Quote:


 Abb = 1 + [R4 + (R7*(1/(j*w*C7)))/(R7 + (1/(j*w*C7)))]/R3 
 

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







 As you can see, bass frequencies are boosted.

 --JDS


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## Pars

Quote:


  Originally Posted by *blackinches* /img/forum/go_quote.gif 
_Edit: Since Pars says he still doesn't understand, here's a mathematical explanation._

 

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


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## jmwreck

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


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## jmwreck

bump


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## Fred_fred2004

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


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## jmwreck

Quote: 





fred_fred2004 said:


> 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


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## Fred_fred2004

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


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## jmwreck

Quote: 





fred_fred2004 said:


> 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


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## Fred_fred2004

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


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## jmwreck

Quote: 





fred_fred2004 said:


> 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.


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