Q.A. Rice, Guitar Note Expander, Electronics Today International, April 1981 🇦🇺

Post by **modman** » 26 Jun 2022, 14:49

PDF:

1979-4 Guitar Expander - Electronics Today International.pdf: (112.34 KiB) Downloaded 163 times

: 1979-4 Guitar Expander - Electronics Today International 4.jpg (61.52 KiB) Viewed 3664 times

uncleboko · Post by **uncleboko** » 26 Jun 2022, 16:08

Why post these cheapo circuits from ETI, which at best were crap at the time???

Post by **modman** » 26 Jun 2022, 19:41

So everybody can see they are crap with their own eyes and need not obsess about it?
But you probably have a point.

CheapPedalCollector · Post by **CheapPedalCollector** » 26 Jun 2022, 21:34

There are sometimes interesting ideas that may not be executed well, that can be expanded on. Other times they are just bad and fun novelties. You can bet some booteeker is building them and selling them as the next magik boolet though.

Manfred · Post by **Manfred** » 26 Jun 2022, 23:21

This post reminds me that I have this pedal slumbering in the depths of my collection, a reason to wake it up and get it running.
I am putting it in the queue for refurbishment.

cspar · Post by **cspar** » 27 Jun 2022, 05:52

I'm grateful that you post old magazine articles Modman. Thank you.
:worship:

CheapPedalCollector wrote: ↑26 Jun 2022, 21:34 There are sometimes interesting ideas that may not be executed well, that can be expanded on.

I've had a lot of fun and learned a lot while breadboarding old diy circuits regardless of if I ended up building them or not.

This one is pretty interesting. I don't remember ever seeing a compressor or an expander with a similar cmos topology.

Lani · Post by **Lani** » 27 Jun 2022, 09:57

cspar wrote: ↑27 Jun 2022, 05:52 I'm grateful that you post old magazine articles Modman. Thank you.

I agree, keep em coming. Thanks Modman!!

deltafred · Post by **deltafred** » 28 Jun 2022, 16:48

uncleboko wrote: ↑26 Jun 2022, 16:08 Why post these cheapo circuits from ETI, which at best were crap at the time???

Yes they were crap at the time and they haven't improved with age but it is nice to see them again.

At that time I was in a job where half the time we were insanely busy, the rest we sitting around with virtually nothing to do. Our boss said that in case anyone important walked into the lab we should be always be looking busy and would fund small projects out of the department budget.

Most of the pedals that I built out of the Elektor, ETI, Practical Electronics, and Practical Wireless were so underwhelming that they never got boxed up and were immediately stripped for parts.

I did use a digital echo for quite some time that sounded like a ring modulator above the 12th fret because the sample frequency was not fast enough. Our rhythm guitarist used a treble booster for a while (I couldn't tell if it was on or bypassed but he seemed to like it so who was I to argue).

Manfred · Post by **Manfred** » 30 Jun 2022, 16:13

I bought the used pedal in March 2018 and started to make the PCB clone for it, still missing the component values I will put in.
I forgot about it, first now through this topic I remembered.

Manfred · Post by **Manfred** » 21 Jul 2022, 22:45

Here the finished PCB clone.
Next I will reassemble the pedal and make some measurements.

Ready-to-Print PDF-files:

ETI Guitar Note Expander Components Side.pdf: (24.35 KiB) Downloaded 66 times

ETI Guitar Note Expander Solder Side.pdf: (5.29 KiB) Downloaded 79 times

SprintLayout6.0 file:

ETI Guitar Note Expander Layout.zip: (26.01 KiB) Downloaded 54 times

mictester · Post by **mictester** » 27 Jul 2022, 02:39

deltafred wrote: ↑28 Jun 2022, 16:48
uncleboko wrote: ↑26 Jun 2022, 16:08 Why post these cheapo circuits from ETI, which at best were crap at the time???
Yes they were crap at the time and they haven't improved with age but it is nice to see them again.

There are several errors in the published circuit. My take on this circuit did away with the rotary switch, and had two options - compression or smoothly distorted compression (with remarkably little intermodulation distortion). The levels of the two modes were quite wildly different, so I had a switched compensation circuit, using a preset to equalise the levels. The CMOS IC used is somewhat vulnerable to static, so I built a buffering input interface....

When I built it, I expected it to be the usual let-down - a slightly unusual circuit, but nothing special....

It actually sounds great! What a surprise!

I'll see if I can find my modified version of this circuit, and I'll post it here.

mictester · Post by **mictester** » 30 May 2023, 00:00

Just stumbled across this thread. I remember the author of the article above - Quentin Rice worked in the same place as me at the time! My take on the circuit (which really wasn't all Quentin's work) was a simplified version without the rotary switch, but with two DPDT footswitches: Effect / Bypass and Compression / Overdrive. My prototype (which is around here somewhere) was built into a small diecast box, and had an internal jumper for single coil / humbucker. It sounded really good, and was recorded many times. I've built a few dozen of them over the years:

: Overdriving_Compressor_Sch.png (7.81 KiB) Viewed 739 times

The only further modification I'd do these days is to use a relay or even a 3-pole double throw footswitch for mode change to allow two "effect" controls to be selected too, allowing a better range of control in the two modes, and add a proper buffer stage to both the input and the output to isolate the CMOS from the outside world.

It's cheap enough to build, and it sounds pretty good.

Manfred · Post by **Manfred** » 30 May 2023, 10:33

Interesting story!
Is the second MOS fet also a BS170?

cspar · Post by **cspar** » 30 May 2023, 10:59

Manfred wrote: ↑30 May 2023, 10:33 Is the second MOS fet also a BS170?

Looks to be the Q1 portion of the 4007ube. Mictester would know for sure though.

Manfred · Post by **Manfred** » 31 May 2023, 07:00

cspar wrote: ↑30 May 2023, 10:59
Manfred wrote: ↑30 May 2023, 10:33 Is the second MOS fet also a BS170?
Looks to be the Q1 portion of the 4007ube. Mictester would know for sure though.

You're right, if I had looked closely I could have seen that from the pin labels.

mictester · Post by **mictester** » 02 Jun 2023, 01:22

The finished versions of this circuit I've built lately have had additional transistor buffers on the way in and the way out. The 4007 is quite a sensitive beast, and easily killed by large voltage spikes. The transistor buffers ("emitter followers") completely eliminate the problems at very little cost. The buffers do not change the "sound" of the circuit at all. I'll sketch the additional bits later today and post them here.