Eko - Multitone  [schematic]

Discussion regarding early stompbox technology: 1960-1975 Please keep discussion focused and contribute what info you have...
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Bononoob
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Post by Bononoob »

I traded and repaired a Eko Multitone a while back. Apparently it's the firt multi-effect ever.
It has Wah (called Strepitoso in italian), Treble/Bass Booster, Distortion and Repeat (percussion tremolo).
So I traced the 4 different circuits, you can find attached the schematics and some pics.
FS33805 are npn BJT with 1:C 2:B 3:E pinout. I tested one and hfe was 216. BC208 is apparently an equivalent and if i'm not mistaken 2n3904 could do the job.
4JD5E44 is a UJT (maybe equivalent to 2n2646 ?)
I hope I got it right the first time, but if you find anything weird on one of the circuits, point it out and I'll check the board
Attachments
StrepitosoSch.png
TBBSch.png
DistortionSch.png
RepeatSch.png
IMG_20190515_023908.jpg
IMG_20190515_023830.jpg
IMG_20190515_013014.jpg
IMG_20190515_023716.jpg

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rockola
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Post by rockola »

Bononoob wrote: It has Wah (called Strepitoso in italian)
Eko gear has the best labels. I have an Eko Duke combo where the power switch is labeled SI/NO, inputs INGRESSI, and the tone controls ALTI and MEDI-BASSI :D

Ben N
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Post by Ben N »

rockola wrote:
Bononoob wrote: It has Wah (called Strepitoso in italian)
Eko gear has the best labels. I have an Eko Duke combo where the power switch is labeled SI/NO, inputs INGRESSI, and the tone controls ALTI and MEDI-BASSI :D
I have GOT to use this.

nightraven
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Post by nightraven »

The first? It seems unusual for an Italian effects manufacturer to come up with something original...
Does this thing predate the Selmer Fuzz/wah/repeat? (c. 1969)

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Dirk_Hendrik
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Post by Dirk_Hendrik »

nightraven wrote:The first? It seems unusual for an Italian effects manufacturer to come up with something original...
Does this thing predate the Selmer Fuzz/wah/repeat? (c. 1969)
Careful here. Italy had a very respectable industry of electronic musical instruments in the 70's and eigthies. Especially in the synthesizer arena they did cool stuff. Think brands like Crumar and Siel. Siel was taken over by Roland for production capacitywhen they lost the battle against the DX7 (and they weren't the only one) later which resulted in some very characteristic Siel design work showing up in Roland equipment.

Which means that it's not that hard to imagine some original effects technology can originate from Italy. Or perhaps be more known under another non-italian brandname.
Sorry. Plain out of planes.

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idy
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Post by idy »

Is that booster schematic right? very unusual...?

Manfred
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Post by Manfred »

idy wrote:Is that booster schematic right? very unusual...?
I cannot recognize any circuit principle.
Thought to myself, who knows and ran a circuit simulation, but the circuit was not working.
I think the circuit needs a review.

Bononoob
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Post by Bononoob »

Manfred wrote:
idy wrote:Is that booster schematic right? very unusual...?
I cannot recognize any circuit principle.
Thought to myself, who knows and ran a circuit simulation, but the circuit was not working.
I think the circuit needs a review.
Oops looks like I swapped Input and Output. It makes sense if you read it the other way right ?
I corrected it, and ran it through a circuit simulation. You tell me if it still looks wrong (it's a weird boost anyway, lot of treble very quickly).
Thanks for the heads up
Attachments
TBBSch.png

Manfred
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Post by Manfred »

The EKO booster circuit very similar to the VOX V8401 booster circuit.
I run the simulaton, using a BC183BP transistor that is a good replacement for the FS33805 transistor.
There is no significant gain, but a gain less then one namely from 0.14 to 0.91 depend on the potentiometer setting.
Thereby the input voltage was 50 Millivolts @ 1kHz.
Following the VOX booster circuity a changed the resitor values of the base voltage divider
form 22k to 220k and from 68k to 680k.
The circuit work now and have a gain form 1.4 to 8.6.
VOX_V8401toEKO_Treble-Bass_Booster.jpg

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