EH Ramhead Big Muff repair
Since I became obsessed with this great old sustain pedal some of you may have heard of called a Big Muff, I get a few sent to me for repairs now. I got to know this circuit inside out by making my own versions of most of the different types it has been released in. I'm now getting requests from all over the world to repair old ones, which is kind of nuts for me as I still look at pedal building (and repairing) as a hobby.
As I had a Friday afternoon with a little spare time (ie: sick of working on guitars) I thought I'd get into a couple of these Big Muff repairs.
This old seventies "Ramhead" era Big Muff came from down south and sounded a little worse for wear. It had been repaired several times over the years and was intermittently making noise, it just wasn't the right noise.
The first thing to do was check the obvious. These old EH pedals weren't particularly well made in terms of reliability (and consistency) and a lot of old Big Muffs have been repaired and moded over the years to keep them on the road. This one was no exception.
This had all the "usual suspects" when it came to repairs/issues. Wires changed everywhere. One original pot. Battery switch broken. Just the usual wear and tear for a pedal of this age and use.
The first thing I did was pull up the board and check for components that may have been badly/incorrectly installed ? Most of the board components were original with the exception of a cap that had been replaced.
The one original pot dates it at 1976 and the board components are close to one of my previously traced out circuits for this era Muff except this one used 2N5088 transistors where the other ones used 2N2222's. The 5088's are generally higher gain and I'm not a fan of them in the Ramhead circuit.
Because this wasn't a "museum piece" pedal and has been and will be used, I wasn't too concerned with originality for collectability. I replaced the pots and the switch as both were faulty. The switch was almost definitely the cause of the "intermittently making noise" and all the pots had track issues and were noisy even after cleaning.
With the jacks, pots, the switch and the wiring re-done, it was time to make some noise !!!
OK, we're going to have to go much deeper. I started measuring values against what they "should" be. Now when I say "should be" there are no hard and fast rules for EH values. This period EH Big Muff is terribly inconsistent for component values and I have personally traced out (and seen online ?) over 30 different "Ram head" BM circuits.
I usually keep a record of any BM I work on and this one had some amazing value differences. After going through colour codes on resistors and then measuring values (both in and out of the circuit depending on where the resistor is) there was some crazy stuff going on. The most out of wack values were a couple of 470K's (colour code and common value) was measuring close to 130K. Nearly half the board values were up to 25% out (ie 100K to 86K).
After some work I had signal to the third transistor and then things were going bad. I replaced this transistor with an equivalent (gain, and values is the key to a BM tone, NOT transistor type) and it sprung into life.
After more work I had a sound like a ......... Ramhead. There it was. What a glorious sound.
With a new quality battery switch in place it was time to start comparing "tones". My Ramhead is based on my favorite version I've heard so far. It has lower gain transistors than this one, which I personally prefer, but there's no "rule" to how a Big Muff should sound.
This original version has more volume and gain (no surprises) and has a "splutter" when driven hard. It looses a little of that clarity I like, but still has more than say a version 3 or Russian. It has heaps of bottom end and sounds like a "Ramhead"
I installed true bypass switching but not an AC adaptor because I didn't want to start drilling holes into the enclosure and it now has the switch for turning the battery off when not being used. Some new knobs and we're away.