MXR 1970 6 band EQ

[tcio]

I have been building boosters, buffers, etc in an attempt to duplicate the tone I get out of an old 1970s MXR 6 band EQ with no success. I have yet to find any schematics for anything that sounds like it. I am still working on Mr. EQ and went over the circuit 3 - 4 times now to make sure that everything is right. It still won't work so I'm throwing in the towel on that one and going on a search for the schematics for the MXR 6 band EQ, preferably the 1970s model. I know they used different parts than in the newer models as the 1970s model has some serious kick to them and the newer models do not have but perhaps the shematics are close. If anyone out there knows where I can find these schematics or knows of a DIY pedal that sounds similar to the MXR EQ 1970s model please let me know. I have been searching on and off for almost a year now. Thanks all

[miqbal]

Is it MXR 1970 a solid-state EQ with gyrators? What do you mean by "tonal differences" between this EQ" and "that EQ"? If "tonal differences" means different in its "fixed frequency", I think you can tweak its gyrators to suite your preference.

[Mark Hammer]

The old MXR 6-band had the interesting property of aiming for more gain than was appropriate.  I don't suppose I should treat the legending on the chassis as "truth", but it did say +/-18db instead of the more common +/-12 or 15db.  When I had one of those some 30 years ago, I used to use it a an overdrive.

[tcio]

Thanks guys for your responses.

Yes. That is totally correct. I use this for a slight overdrive/boost. It really pushes an amp nicely, even solid state amps and gives it a nice crunchy tone. The frequencies are the same as on the newer model but the sound and tone are much more ferocious which is great if you are not looking for a clean EQ but more of an extra edge. This thing blows away every booster I have ever tried in regards to tone and bite IMO.

My guess is that the components are different in the older ones. I don't know what the newer ones have in them but mine (the 1970 model) has some really old color coded caps and two different kinds of chips. Three TLO22CPs and one CA1458E RCA730. I use mine to drive my pedals into sheer overdrive or with all of my other pedals off just to drive my tube amp (running tube amp clean) for a nice light distortion/overdrive tone.

It is the core of my whole sound and I am always wondering what I would do if it croaked on me. I have repaired mine and installed a 3PDT switch in it, then later an LED. When I got it off from Ebay it was barely held together. Who knows, it may last forever but I like to have a backup seeing these are older pedals and you just never really know when it could go as it is a vital component to my setup. I could always pay $45 to $75 on Ebay for a backup but I would much rather build one that way I can have a backup indefinitely!

[tcio]

Oops! Wanted to add a pic. It was a total piece of junk when I bought it (paid about $19 total - Yes!) and it didn't even work but it was only some old corroded battery terminal wires so I replaced them first thing. Although it still looks like crap it is one of the best pedals I have ever owned in my life and I have tried just about everything out there on the market. Again, I use this pedal to juice other devices up (.e.g. Overdrives/distortion pedals, and amps) otherwise as a standalone pedal it may not be anything to write home about.

[George Giblet]

Do a forum search I think the schematic for the one of the old MXR 6-bands was released already.

It's a straight forward circuit.

[soulsonic]

Is the new black one they're selling with the footswitch the same as the old blue one?
I remember that old blue one was good as a booster. It seemed to always be kinda distorted, even if you were playing clean.

[tcio]

Is the new black one they're selling with the footswitch the same as the old blue one?
I remember that old blue one was good as a booster. It seemed to always be kinda distorted, even if you were playing clean.

The new ones (M-109) which are black with a foot switch are not really the same although I believe they were basically meant to replace the older models. They definitely do not sound the same. I personally am not fond of the newer MXR EQs. They have a weird frequency that filters my tone that I just cannot seem to get rid of. Kind of like the Boss Metal Zone issue many people complain about. Some people don't notice these things or perhaps they just sound good to them with their gear. My favorite EQ pedal for clean is the DOD FX40B.  I have built 4 EQs in the past week and couldn't get one of them to work. Three of them didn't show the voltage in the schematics so I just tried the usual 9v with no luck. Finally I tried Mr. EQ but I can't for the life of me get any sound to come out. I was getting a complex as I am relatively new at building pedals so I went on to something else and it worked the very first time I plugged it in. Not sure what I'm doing wrong but I'll go back to it later and hopefully get it to work.

I was hoping to swap some components and see if I can get it to sound like the old MXR EQ pedal. Although I am new at this I love building my own pedals and doubt if I'll ever by another one again. Thats how I ended up doing this. I could not get the sound that I really wanted out of any pedal I tried out. Ive tried everything from a Sansamp GT-2 to a modded Keely Tube Screamer. It took me about 6 months of tinkering around to find my sound. I even gave up one time as it was just too intimidating I wasn't getting anywhere but aster spending another $200 or so on more pedals again with no success (which were even modded) I knew I had no choice but to build my own as there was nothing else out there to try out LOL!

I am so happy now that I stuck it out and endured through all of the frustration and failures as long as I did. It certainly paid off. I absolutely love my pedals and not just because I made them.......They literally scream!

[miqbal]

Yeah.....I can't find any schematic either, even for the new version one. The only thing I got is a paid schematic from schematicconnection. Not sure whether it is a new or an old version of schematic.

[tcio]

I saw that one. It is the new one (M-109). I don't think the old one was ever called M-109 but don't quote me on that. I may have to break down and pay for that if I can't get Mr EQ going. I'm thinking the schematics are similar if not the same. Probably just different types of components. I don't know if these new MXR EQs have metal film caps but I know the old ones do. Also I don't know if there are any chips in the newer ones and if there are, if they are different chips than the older ones have in them. Hey, if anybody out there has an M-109 open it up and let us know lOl!

[soulsonic]

Grrrrr.... I have one of those old blue ones somewhere!!!! If I could only find it, I could trace it easy.

[tcio]

I just wanted to let everyone know in case anyone else was looking. After receiving some help on this forum I was directed to an alternatve for the MXR 6 band EQ if you are only using it as a mid boost. The Anderton FreqBooster works just fantasic!

[Mark Hammer]

I just wanted to let everyone know in case anyone else was looking. After receiving some help on this forum I was directed to an alternatve for the MXR 6 band EQ if you are only using it as a mid boost. The Anderton FreqBooster works just fantasic!

+1

Note that you can easily and painlessly cascade boost stages with the Freq Booster.  Stick a 3-position toggle for frequency-selection in each of 3 stages and you've got a lot of flexibility there for little cost and a small footprint.

[tcio]

Note that you can easily and painlessly cascade boost stages with the Freq Booster.  Stick a 3-position toggle for frequency-selection in each of 3 stages and you've got a lot of flexibility there for little cost and a small footprint.

FANTASTIC! Thanks Mark

[dellamorte]

any luck getting a schematic or a pic to trace?

[tcio]

any luck getting a schematic or a pic to trace?

No. In fact, although the Anderton FB worked really well (even better) with one of my pedals it didn't do so hot with the other and I still cannot get that sound out of it (or even close) as I get out of the MXR 6 band. I would like to build something with the same components minus all of the bands seeing I mainly only use the 3 mid frequencies and only notched up slightly. One of the chips I cannot find anywhere though (CA1458E RCA730). I can find CA1458E but nothing with the  RCA730.

I am about to construct something with the other chip it uses (TL022CP). Seeing it uses three of them and only one CA1458E RCA730, I am hoping I can get in the ball park. I'm just deciding whether to build an EQ or booster.

[George Giblet]

This was put up ages ago,

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

PS: I suspect the overdriven sound is largely to do with overdriving the '1458 opamps and the filtering effect of the pre-emphasis (around R4 and C2) and de-emphasis network (R8, R9, C4).

For an overdrive you might be able to build a circuit which contains only top part of the circuit U2 then connect one 50k pot with a cap and resistor to ground.  Basically the way the 3.2kHz band is wired but with a smaller resistor say 470 ohm and a larger cap say 4u7 to start.  Make the cap smaller to knock off some bass, make the resistor smaller to get more gain.

(The hotcake uses a form of pre-emphasis/de-emphasis)

[George Giblet]

Here's a circuit that reasonably approximates the behaviour of the MXR 6-band EQ when all the bands are boosted equally.  The circuit is set-up as a booster so that the full counter-clockwise position boost pot positoins is like the centre position of the EQ - that gives you better control instead of wasting half the pot rotation for the unused cut region.  The use of the 5k pot (which is actually like a 10k when you consider the  boost only design) better models the behaviour of the original over the span of the pot wiper.

The network 15k + 1.8n network mimimcs the slight roll-off of the original, you can complete remove this or experiment with values yourself:

http://www.geocities.com/george_giblet/effects/eq6_approx.jpg

[jakehop]

Yes, George is right. I have two of these. They came without footswitch and DC-jack. Awesome little effects!

Jake

[tcio]

Fantastic! I searched high and low even for the M109 and only found one download for $15. I wasn't sure how close it was to the original as they certainly do not sound the same so I wouldn't pay for it.

Although the M109 for some reason does not respond or sound anything like these old blue 6 band EQs this may be enough to go on. I was thinking that because some of the values (Caps, resistors) were different, that could cause the older ones to break up more but the tone is still not the same. I tried the newer ones and they added a color to my tone that I didn't like and just couldn't get rid of no matter how much I tweaked the sliders.

Thanks for this info! I will post my personal results. This may just be the answer I have been looking for (for 2 years now!).