Friday, 10 November 2017

EHX "Booster" pedal family

I've recently been exploring some of Electro-harmonix early pedals... The LPB-1, the Screaming Bird & the Mole. They are really simple circuits & fall into the family of Boosters - all using a transistor for amplification.
The component values determine if the circuit boost all frequencies, bass or treble.

The LPB-1 boosts all frequencies, cutting nothing out.
R1 & R2 can be 430K & 43K respectively.
The transistor is a 2N5088 on my vintage example but you could also use a 2N5133 or BC239
if building your own.
 The Screaming Bird boosts treble.

The LPB-1 and the Screaming bird pretty much are the same circuit apart from
two capacitors (C1 & C2). The first part of the circuit (C1 & R2) work like a high pass filter.
Increasing the value of C1 should let in more bass. If you decrease it, more treble should appear.
With 0.1uF, most of the input signal goes through. In the case of the screaming bird, EHX have indeed reduced C1 to introduce more treble.

The Mole has a slightly different design even though one can see a family resemblance to the LPB-1.

EHX added two caps (C3 & C4) and again changed the value of C1 & C2 (the coupling caps).
R2 & C3 form a passive Low Pass RC (Resistor-Cap) filter .
R3 & C4 do the same. We have two LP filters ... before & after amplification.

+ Electro harmonix time line
+ My LPB-1

Wednesday, 8 November 2017

Linear Power Booster 1 - Electro-Harmonix

This is the "pedal" that started it all for Electro-harmonix.
Note the chicken head knob.
This pedal boosts input signals making the output stand out more. Most of the examples I've seen have a jack at the amp output allowing you to plug this directly into your guitar amp.  You could just sit this one on the floor or use it earlier in your signal chain, between effect pedals rather than at the end. I'm guessing this is from around 1969 to 1971 ??? The pot markings are obscured with solder making this difficult to date.

I've read this sold for about $20USD in 1970 which in today's money (2017) equals $128USD
What a shock. No PCB.

Good Old Eddie

The schematic is uber basic.
Just 4 resistors, 2 caps , a transistor and a pot.


R2 = 1M
R3 = 100K
R4 = 10K
R5 = 390R
R6 = A100K (volume pot)

C1 = 100nF/0.1uF
C2 = 100nF/0.1uF

Transistor 2N5088

It's interesting that C2 is ceramic & C1 a polyester.
I think they are just coupling caps to pass the wanted audio (AC) signals, while blocking any DC.

The first part of the circuit (C1 & R3) works a bit like a high pass filter.
Increasing the value of C1 should let in more bass. If you decrease it, more treble should appear.
With 0.1uF, most of the input signal goes through.

R2 & R2 forms a voltage divider. It determines the bias at the base of the transistor
The ratio between R4 (collector resistor) and R3 (emitter resistor) controls the gain of the transistor.

The trannie is a 2N5088. Its a NPN. They are cheap as chips on Ebay.

It's a nice little amplifier circuit. Could easily be used in a modular synth

Moog Mother Drums

A great little synth. Versatile.
Trying to use it as a drum .,... a bit lofi. I can see why more than one would be very handy.

A post shared by jono (@dj_jondent) on

I'm using the CVs from the Kb output to modulate the mix between VCO and noise .
The lower the CV's octave the deeper the sounding is the note.
Higher octaves trigger more noise and brighter sounds.

The ARP 2500 clocks the Moog mother 32 perfectly.

A post shared by jono (@dj_jondent) on

Thursday, 2 November 2017

EHX Black Russian Big Muff

I think this Electro-harmonic Big Muff dates from around 2004.
Power was from a 9V battery only. A red LED light shows when the circuit is on.
Note the  “chicken head” style knobs 
.....and the lack of an AC power adaptor jack. 
Notice also that there are only 4 screws .. therefore it's most likely a second edition V8.
The 1st edition had 6 screws.
 Versions 7-8 only run on 9V DC power. The V8 was the last Big Muff ever made in Russia.
For some first editions and all second edition V8s,  the words "MADE IN RUSSIA" on the back panel was moved under the input jack.

 The resistors all look to be metal film.

The V8's used 547C transistors, and all second editions had a true bypass switch, which this has.

+ mods to Russian Big Muffs

Monday, 30 October 2017

MXR Stereo Chorus - M205

 The MXR dates from around 1983. Its very heavy.

 It's a great sounding pedal

The era of BBD based delays & chorus appears to have just been very short . Between 1976 and 1983 ?
So this comes from the very end. It appears that pedal companies all released digital  based delays in the 1980s killing the demand for the BBDs.

Uses a Reticon SAD4096.... super long delays.
 The SAD4096 is super rare. It's a general purpose 4096 bucket (2048-sample) n-channel BBD. It's useful where a long delay is required. (2ms to 250msec). The delay is controlled by the clock frequency.

The RC4558 is a texas Instruments General purpose dual Op amp.
The MCI458p is also an op amp
The SCL4013 is of course a CMOS logic chip. Dual flop flop.
The CD4013 provides an excellent clock source with their Q and -Q outputs.

Saturday, 28 October 2017

The Clifford Pier - Singapore

Located at the first floor of The Fullerton Hotel Singapore this beautiful and historic building is well worth a visit.
Built in 1933, it was a landing point for immigrants and a ferry terminal to the southern Islands like Kusu & St. Johns. It was the melting pot for the interaction of different races and cultures.

In the early days, the car park surrounding the entrance was transformed into a hawker centre. It was the meeting point for musicians, night owls, and lovebirds. Today it's still a meeting place but it's been transformed into a something very stylish.

Click here for more travel postcards

Thursday, 26 October 2017

MXR Time delay

Picked this up on Ebay.
I am addicted to Reticon bucket brigade chips. So couldn't pass this one up.

Heavy, and built like a tank.
This one dates from around 1981 to 83.
M206/Series 2000
Serial No. 206-001729

The seller described it thus:
"This is a supremely luscious vintage analog delay. Thick, decadent delay repeats you could cut with a butter knife. Forget that Panasonic/Matsushita malarkey: Reticon did it right."  Yes !!!!

Reticon SAD4096 bucket-brigade delay chip with in'n'out running through a NE571 compander. It's socketed as are the op-amps (MCI458p)

....SCL4013BE ... CMOS chip ,,, its a dual D-type flip flop

 Built with love in beautiful Rochester

Buchla Easel - Portabellabz bob expander.

These are my build notes for the Bucha easel BOB by Portabellabz.
You can find the docs here .
It's quite a neat little unit. And it's expandable.

The two ICs are a TL071 op amp and a CD 4093. The TL071 is I think used to invert the EG.... the second left output jack.  The 4093 is I think used for converting gates to triggers ???... for the pulser trigger out ???

The trimmer sets the voltage level of the pulse trigger out. ... If using eurorack the voltage level of the pulse out can be reduced to 5V

Papz has left a section on the right blank to add your own circuit.
I'm putting in a square wave LFO/audio oscillator which you can find in the build notes.
I first tested this on some bread board.

Used just one 741 op amp, one capacitor (220nf) & 7 resistors.
The uber basic circuit is here
It's about as simple a circuit as you can get. An op-amp with positive and negative feedbacks.
The inverting input is connected to a RC (resistor capacitor) network. The non-inverting input is connected to a voltage divider.
It's classified as a astable multivibrator which has two states, neither of which are stable. It is constantly switching between these two states with the time spent in each state controlled by the charging or discharging of the capacitor through a resistor. The op-amp works as an analogue comparator... comparing the voltages at its two inputs.
The full schematic is here:

 Yup. It works both as a modulation oscillator and a audio oscillator.

Now to build it into the board.

So the the connections from left to right are:
- sequencer pulse in
- envelope inverted out / envelope trigger out (switchable)
- pulser pulse in
- pulser trig out (the internal short pulse occuring at the end of its cycle, not the ramp on yellow bananas)
- MO modulation switch CV
- LPG1 mode switch CV
- LPG2 mode switch CV
- LPG2 signal routing switch CV
- extra oscillator - switchable between LFO & Audio.