Sarno Earth Drive

General documentation, gut shot, schematic links, ongoing circuit tracing, deep thoughts ... all about boutique stompboxes.
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sugarinthegourd
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Post by RnFR »

moved to REQUESTS FOLDER.
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sugarinthegourd
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Post by sugarinthegourd »

Here's a pic of the back of the board. 3 board-mounted pots, maybe an IC in the center. Looks like fairly low parts count. YATS?

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Post by caspercody »

Any updates on this?

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roseblood11
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Post by roseblood11 »

Two IC's - maybe a TS with opamp buffers, aka vintage Maxon OD-808?

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Post by aegert »

Bump to poster.. any pics of the front

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Post by Kitrae »

I did not photograph the other side when I reviewed it, but I can tell you is is TS based.
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Post by Cub »

Thanks, Kit ! I half expected it to be TS based. Brad Sarno did well on this one.
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Post by ozzy666 »

Any update on this?

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Post by GratefulEight »

I might know someone that took some gut shots of an EarthDrive they bought years ago...this same person might have done a full trace after getting pissed off that the diodes were gooped and the IC sanded. I was able to find the pictures and some of the parts values for now.

I do know the IC was eventually determined to be a 4558; the sanded one was put in a test circuit and had voltages measured at the various pins under several sets of conditions that matched pretty much exactly with a labeled 4558.

Image Image Image Image Image Image Image Image Image Image Image Image Image Image Image Image Image Image

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Post by GratefulEight »

Also found one of the back:

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And the schem from that trace I mentioned:

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Post by Manfred »

I redrew the circuit diagram, so you can see the circuit structure better.
My guess for the IC are TL072 or CA3240 and for the germanium diodes 1N34A.
Sarno Earth Drive.jpg
Last edited by Manfred on 19 Sep 2022, 09:50, edited 1 time in total.

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Post by GratefulEight »

Manfred wrote: 19 Sep 2022, 00:00 I redrew the circuit diagram, so you can see the circuit structure better.
My guess for the IC are TL072 or CA3240 and for the germanium diodes 1N34A.
Sarno Earth Drive.jpg
I know a TL072 was tested and didn't measure in the same ballpark as the mystery IC; not sure about the CA3240. Also not sure about the exact testing methodology, whether it was a reliable way to make an informed guess, or anything else about that part really.

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Post by GratefulEight »

The Ge diode (clear DO-7 with 2 black stripes--see picture) that survived de-goop measured Vf = 0.644V, with a test current of 4.294mA on a Peak DCA55 tester; a standard DMM said 0.241V on diode test mode. Not sure why the discrepancy...leakage? Low DMM battery? :scratch:

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Post by mauman »

Your DMM probably uses around 1mA for testing diodes, while the Peak used 4.29 mA. Diode forward voltage drop varies with current, and makes a curve that increases with increasing current. A reading of 241 mV @ 1 mA and 644 mV @ 4.3 mA would be in the normal range for Ge diodes.

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Post by Intripped »

@Manfred
1N4001 diode not correctly oriented
C3 is 100pf in GE's schem

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Post by Manfred »

Intripped wrote: 19 Sep 2022, 09:37 @Manfred
1N4001 diode not correctly oriented
C3 is 100pf in GE's schem
Thanks, I fixed the wiring diagram in the post above.

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Post by Manfred »

GratefulEight wrote: 19 Sep 2022, 02:40 The Ge diode (clear DO-7 with 2 black stripes--see picture) that survived de-goop measured Vf = 0.644V, with a test current of 4.294mA on a Peak DCA55 tester; a standard DMM said 0.241V on diode test mode. Not sure why the discrepancy...leakage? Low DMM battery? :scratch:

Image
I got a bunch of 1N60P Germanium diodes that look the same as the diode on your snapshot, also the readings are in the same range.
Reading: Vf=0,736V at 5,00mA
1N60P Germanium.jpg
PN Junction 1N60P Germanium.jpg
Clipping Diodes Sarno Earth Drive.jpg
Last edited by Manfred on 19 Sep 2022, 15:51, edited 5 times in total.

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Post by Nocentelli »

So essentially Paul Cochrane's Timmy, minus the bass pot but with half ge diodes?
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Post by Manfred »

Nocentelli wrote: 19 Sep 2022, 11:52 So essentially Paul Cochrane's Timmy, minus the bass pot but with half ge diodes?
In fact the same circuit structure, then what's the point of gooping components. :?: :o
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