More Bass for C Moy: Boost, other OP?
Feb 27, 2006 at 11:33 PM Thread Starter Post #1 of 17

Vul Kuolun

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Hi,

i just finished building my first C Moy, but i would like to have it a bit of a warmer, bassier sound. To be precise, i would like to have a whole of a lot warmer/ bassier sound.

First, what would be the bassiest, smoothest OP you could recommend? Right now, i´m using a 2132 and i find it to thin with my DT 880; I know, these should have an hell of an amp, but i´d like to try if i can get this working;

Second, I couldn find exact information about a bass boost for the C Moy; I can´t believe, this isn´t a popular feature? Of what i found in the depths of this forum, there should be the posibility to put a C and R in paralell to the feedback circuit; could somebody give me some details please?
 
Feb 28, 2006 at 12:16 AM Post #2 of 17

ericj

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It may not make sense to artificially 'boost' the bass if you have not configured your cmoy to be able to deliver it.

If you used the standard cmoy parts list with a .1uf capacitor on the input, your first step should be to upgrade that to .22, .33, or .47uf - that way you have bass to boost. And it may turn out to be enough.

I don't think different opamps seriously exhibit that much difference in bass characteristics. The 2132 should certainly be one of the bassier chips, if any of them. As far as the opamp choice, it comes down to how much power it can sink when swinging that close to a rail - a deep bass note is almost DC.

The 2132 should be fine. I wouldn't change it at this point, but if you end up ordering from digikey anyway, some people like the 2227, and some people say the 2107 has 'tighter' bass which i think is really just the lesser current output ability of the 2107 showing itself.

Speaking of current capability, some people think it helps to upgrade the power caps to 470 or 1000uf, and there is arguably some logic in that. You may have to go down in power rating to fit that into your existing build.

The virtual ground topology of the cmoy design effectively places the power caps in series across the rails. When caps are combined in series, the voltage rating increases additively while the capacitance is divided proportionally.

Thus, two identical 220uf 35v caps in series, assuming they aren't leaky, form the equivalent of a 110uf 70v capacitor.

Since you know your layout works, then there is little chance that you will put the whole power supply voltage across one capacitor.

Assuming a power supply of no more than 24v, it would be perfectly reasonable for you to use two 16v capacitors in series in your cmoy, if you have to go that far down in voltage rating to fit in the capacitance you desire.

As for the actual bass-boost circuit, searching these forums for 'bass boost cmoy' should be enlightening. But you may not need it if you do everything else first.
 
Feb 28, 2006 at 5:12 AM Post #4 of 17

Vul Kuolun

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I already tried increasin the Input Caps (0,47uF)as well as the power caps (470uF), wich i think didn´t make a real differene.
Right now, i´m thinking about adding a railsplitter to the circuit, but as i know the 880 could seriously benefit from a little bass boost, i´d like to add a boost circuit anyway.

The search for "bass boost cmoy" didn´t show any useful stuff; i was hoping for some schematic, which i couldn´t find.

Thank you for the hint with 2227.

Anybody else?
 
Feb 28, 2006 at 5:39 AM Post #6 of 17

ericj

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Quote:

Originally Posted by Vul Kuolun
The search for "bass boost cmoy" didn´t show any useful stuff; i was hoping for some schematic, which i couldn´t find.


I thought this schematic was pretty obvious:

cmoyBB2.png


fwiw .1uf is a reasonable value for that cap.

The bass-boost calculators at tangent's site, amb's site, etc, would be valid for this - taking into consideration different part numbering.
 
Feb 28, 2006 at 5:51 AM Post #7 of 17

xluben

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Yep, I tried the Bass Boost CMoy. That schematic should be right. You can get more info on Tangent's site (not under CMoy's though). I believe I wired up a CMoy correctly according to that schematic, but for some reason turning on the bass boost just resulted in a mumble jumble of not good sounding music. It worked fine with the switch off, so it was definitely something wrong with the bass boost loop. I don't have much free time right now, so I've kind of given up on the project, but someday I hope to try and figure out what I did wrong and fix it.
 
Feb 28, 2006 at 5:56 AM Post #8 of 17

amb

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If your cmoy is running on a single 9V battery, be aware that a bass boost circuit (which can cause as much as 5x to 10x more gain at low frequencies) may lead to clipping. It's much less of a problem if your amp runs on two 9V batteries in series, or has a wall-powered 18V+ power supply.
 
Feb 28, 2006 at 3:00 PM Post #9 of 17

Vul Kuolun

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@ ericj: Hell, maybe i was blind, dumb, or the server is playing tricks on me; i found that thread, but would you believe me that the schematic wasn´t there? Probably not, so i just say thank you very much.

I´m already using to batteries, so that should´t be a problem;

The other question is, if its usefull when xluben already failed using the circuit.
 
Feb 28, 2006 at 11:49 PM Post #10 of 17

Vul Kuolun

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Works (fine); Thanks guys.

Maybe 10K is still quite a strong boost. For just a tad more bass/ warmth, 5 K maybe more suitable.
 
Mar 1, 2006 at 12:57 AM Post #11 of 17

MisterX

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Quote:

Originally Posted by Vul Kuolun
Works (fine); Thanks guys.

Maybe 10K is still quite a strong boost. For just a tad more bass/ warmth, 5 K maybe more suitable.




What size capacitor did you use?
 
Mar 1, 2006 at 10:16 AM Post #12 of 17

Vul Kuolun

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I used a 0,1 ug MKP Cap;

Of course, variing the sizes will be interesting too.

The bossted bass sounds a tad slow, so i asume theres quite much deep bass in it; as decreasing the size of the cap will reduce upper bass relative to lower bass, i don´t expect it to be too interesting. Anyway, i will try as soon as i can get other caps.
I think a little less bass than with 10k R will be just fine for me (and the DT 880).
 
Mar 1, 2006 at 2:35 PM Post #13 of 17

xluben

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You got it to work!!!!! Now, I'm pissed. J/K, but now I want to fix mine. Is there any way you could post a layout of your board or hi-res pics of the top and bottom of it? This is what I layed out:

http://img477.imageshack.us/img477/9...tcmoyii3ml.jpg

(purposely made it so you would have to click the link, so there wouldn't be a huge pic in the thread)

But the bass boost doesn't work at all, it totally garbles the sound.

Did you use a 0.1 uF cap (you wrote 0,1 ug)? I thought smaller caps meant a higher frequency bass boost, but now I can't find the link on tangent's site which explains what changes in R and C (in the bass boost circuit) do.
 
Mar 1, 2006 at 5:24 PM Post #14 of 17

tomb

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Now that you've introduced a cap and another resistor (and a switch terminal) in series between R4 and the Opamp output, the position of the final Opamp output connection has changed. The "l.out" and "r.out" must be moved. If I interpret things correctly, your headphone output connections must be on the same pad as the "switch 'B/A'" and the R7 pin toward the center of the board.

At least, that's my guess.
 
Mar 1, 2006 at 6:33 PM Post #15 of 17

xluben

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What you said makes total sense. I don't know what I was thinking before. I tried doing what you said by piggy-backing the output wires inot the same holes as the A/B wires of the switch, and this seems to bypass the whole bass boost circuit (I think). CMoy sounds fine, but I switch the Bass Boost on and off and I don't hear anything different. I put in 100K resistors (max bass boost) just to make sure it wasn't my ears, but there's definitely no change with bass boost on or off.
 

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