It's possible to increase the cut/boost of a MXR 10 bands EQ?

[gigimarga]

Hello,

I'm a big fan of EQs and I've just bought a MXR 10 bands EQ. Before it i had a Danelectro 7 bands EQ and i liked it very much, but it isn't true bypass.

Before i've bought I saw that Danelectro has +/- 15dB on each frequency and MXR only 12dB, but i thought that it's not a big difference...but i did a big mistake: it's a big difference (mainly i heard this at 1kHz, because i used to scoop it very hard)!!!

So, my question is: how cand i increase the +/-12dB cut/boost of MXR to 15dB or, even better, +/-20dB?

Another problem is that I have no schematic of it.

Thx a lot all!

[earthtonesaudio]

If all the internal components can handle it, my first suggestion would be a higher supply voltage.

[George Giblet]

The bandwidth of the bands can make a big difference to the perceived boost, wider bandwidth = more perceived change.

[gigimarga]

@earthtonesaudio: The power supply is at 18V...not enough?

@George Giblet:
The bandwiths of MXR: 31.25 Hz, 62.5 Hz, 125 Hz, 250 Hz, 500 Hz, 1 kHz, 2 kHz, 4 kHz, 8 kHz, 16 kHz
The bandwiths of Danelectro: 100 Hz, 200 Hz, 400 Hz, 800 Hz, 1.6 kHz, 3.2 kHz, 6.4kHz

I think that Danelectro's bandwidths are more useful for guitar as the MXR's 

Anyway, how can i calculate the cut/boost of an eq?

Thx a lot all!!

[George Giblet]

The frequencies you gave are the *centre* frequencies.

The bandwidth is how wide the boost or cut is around that frequency.  See the right hand picture of:

http://mobile.jlaudio.com/pdfs/Parametric_Equalizer.pdf

A wide bandwidth (also called low Q) means the equalizer affects a wide spread of frequencies around the centre frequency.  Because you are affecting more of the spectrum it appears to change the sound more for the same (peak) boost than a lower bandwidth (also called high Q).

Technically a 1 octave graphic equalizer should have the bandwidths chosen such that bands next to each other in the "correct" way.  However many eqs, particularly guitar types have widely varying bandwidths between units.  (They also have varying bandwidths at different boost/cut positions).   For a 1/3rd octave equalizer "correct" requires a narrower bandwidth than a 1 octave because the centre frequencies are closer together. There's a few papers on the rane site about equalizers:

http://www.rane.com/note101.html

[gigimarga]

Thx a lot George!
I will study as soon as possible...

[gigimarga]

 

[gigimarga]

 

[vondran]

I find increasing the gain slider on the MXR 10-band effects the amount of cut/boost for each band.  You really have to play with gain, volume out, and each slider to find the right mix.  You may also want to ask Kevin at ToneJam.  He briefly offerred a mod to the MXR 10-band.

[gigimarga]

@vondran: thx for your answer...i want to increase the depth of the cut/boost from +/-12dB to 20dB.

[George Giblet]

There's a few ways to mod the unit:
-  One involves a complete redesign reconsidering the Q's of each stage etc. 
   The mod would require a considerable number of part's changes.
-  another is a simple "hack" which will give you more boost/cut without considering any consequences.
   this is quite a simple mod.

However, without a schematic and parts layout I can't give you precise instructions. All I can do is tell you how to go about it.

Here's the circuit circuit for the MXR 6-band:

http://www.geocities.com/george_giblet/effects/mxr_eq6_v10.png

I suspect the 10-band has a similar structure but all the band components will be different (I think the 470R's are the same on the 10-band)

Here's the steps:
- Find the two tracks that connect all the band boost/cut pots together. 
- On the "cut" end of the pot follow the track and see if you can find the equivalent to R6 on the 6-band schematic.  It might be 10k it might be 22k (I don't know).
- On the "boost" end of the pot follow the track and see if you can find the equivalent to R7 on the 6-band schematic.  Again it might be 10k it might be 22k (I don't know).

For +/-20dB: Increase the value of these two resistors by a factor of about 3.
For +/-18dB: Increase the value of these two resistors by a factor of about 2.3.
For +/-15dB: Increase the value of these two resistors by a factor of about 1.6.

I'd be going for the lowest boost you can handle since this will minimize the change in tone.  For what it's worth I wouldn't go all the way to 20dB perhaps only say 18dB.

[gigimarga]

Woooooooow...thx a lot George!!!

That's what i'm looking for...i will try as soon as possible and i will post the results.

Thx again!

[George Giblet]

I've found some PCB pics and I've started to trace the circuit out but there's few areas which aren't clear on the pics.  I think the two resistors in question are 2.4kohm.  I think they are located each side of the last IC.

I've simulated the circuit with spice and the first thing I found is you have to increase the 2.4kohm resistor a bit more than my educated guess values.   If you use 10k's it will give you around +/-18dB.

One thing that concerns me a little is I can see two ceramic caps on the board.  One of these appears to connect across one of the 2.4k resistors.  By increasing the 2.4k resistors to 10k this may cause some roll-off of high frequencies.  Can you read the value of the ceramic caps?

[gigimarga]

Thx a lot George!
I will read the values of the ceramic caps later because i must to go to work now 
Do you want some pics from the inside?

[George Giblet]

I've drawn a schematic with a few part values missing:

http://www.geocities.com/george_giblet/effects/mxr_eq10_v10.png

The parts to change are R5 and R6.  (Which are similar in function to R6 and R7 on the 6 band schematic in the previous posts.)

Here's the parts I can't see:

http://www.geocities.com/george_giblet/effects/mxr_eq10_parts1.jpg

As far as the mod goes the effects of C4 needs to be checked.  If you are lucky C1 and C4 might not even be on your board.

If you want to check the missing parts: C1, C4, R2, R3, R8, it's up to you.  It's pretty easy for me to add the values to the schematic and at least then the schematic is complete.

[gigimarga]

Big big trouble!!!
The box has some strange screws (called nimbus here...i don't know if in English is the same thing)...i have a set of 8-10 nimbus but no one fit in (i think they have a non-standard dimension).

I soon as i will remove the screws i will post the values that you want.

Thx a lot again!

[George Giblet]

Good luck getting the screws out!

[cheezit]

@earthtonesaudio: The power supply is at 18V...not enough?

@George Giblet:
The bandwiths of MXR: 31.25 Hz, 62.5 Hz, 125 Hz, 250 Hz, 500 Hz, 1 kHz, 2 kHz, 4 kHz, 8 kHz, 16 kHz
The bandwiths of Danelectro: 100 Hz, 200 Hz, 400 Hz, 800 Hz, 1.6 kHz, 3.2 kHz, 6.4kHz

I think that Danelectro's bandwidths are more useful for guitar as the MXR's 

Anyway, how can i calculate the cut/boost of an eq?

Thx a lot all!!

I agree, there are some particular spots that are very useful for guitar, like 3kHz, and others that aren't, like anything above 8kHz (except maybe for hiss reduction).  Both units are centered on octaves (note the frequency doubling) but it's *where* the centers are that matters.  Check the analysis of the Harmonic Converger (google for it) to see some useful curves that apply well to distortion tones.

Be aware, though, that extreme ends of boost/cut are also introducing heavy phase distortion.  If you like the sound, go for it, but you may notice that it sounds unnatural in a mix or has a hard time cutting through a live drummer.