Tycobrahe - Parapedal  [schematic]

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

Re: Tycobrahe - Parapedal

Postby armdnrdy1 » 03 Jun 2015, 20:25

The original value for C3 is .001µf
The original ParaPedal used MC1458 op amps.
The original diode type for D1 is 1N270.
J1-3 on the layout are wire jumpers (to connect traces)
There is a "work alike" Dual pot available for purchase on ebay
http://www.ebay.com/itm/10K-DUAL-POT-LO ... 23285963a9
You might want to purchase it. It will save you a search for a dual pot with a long shaft. In the auction description, there is a suggestion on how to "hack" a wah gear onto the pot. You will have to find a wah gear online.

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Re: Tycobrahe - Parapedal

Postby JimSalabim » 04 Jun 2015, 00:46

Wow, thanks so much for the quick answer!
I have just ordered this pot:
http://www.ebay.de/itm/251940960110?_tr ... EBIDX%3AIT
I think it should work as well?
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Re: Tycobrahe - Parapedal

Postby armdnrdy1 » 04 Jun 2015, 02:49

Well..the price looks good but the bushing may be too short to fit on the bracket of a wah enclosure.

The Dunlop enclosure I have here....the bracket measures 4.5mm.

The pot that I provided a link for has a much larger bushing. It would work for sure.

I guess you'll find out when it arrives. :wink:

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Re: Tycobrahe - Parapedal

Postby JimSalabim » 04 Jun 2015, 17:21

Alright, I’ll find out in a few days … :-)

Could you have a look at the layouts in the pdf and tell me what the R14 and R15 resistors in the second layout are for (seem to be 1M resistors) and why a different diode (D2) is used? And maybe anybody knows which diode this one would be?

http://www.geofex.com/FX_images/newparapedal.pdf
http://www.geofex.com/FX_images/parapedal.gif

And would you use the second or the third layout?
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Re: Tycobrahe - Parapedal

Postby armdnrdy1 » 04 Jun 2015, 18:12

R14 & 15 are added 1M pull down resistors to reduce switch popping.
The designation "D2" is probably a mistake. It is the same as D1.
It is a reverse polarity protection diode. Note the different polarity orientation from the original layout.
Since it is in line with the power supply, you should use the 1N270 for lower voltage drop.

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Re: Tycobrahe - Parapedal

Postby JimSalabim » 09 Jun 2015, 20:23

My wah case is a bit different than the Dunlop ones. I was able to put in a standard Alpha dual pot (10K).
I also drilled a hole for a LED.
Now I'm waiting for the PCB and the diode to arrive ... :-)
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Re: Tycobrahe - Parapedal

Postby armdnrdy1 » 09 Jun 2015, 21:58

Progress!

A thinner added bracket instead of one that is "built In" to the casting.

What type of enclosure is that? It resembles an "Eleca" but the bracket is a bit different.
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Re: Tycobrahe - Parapedal

Postby JimSalabim » 09 Jun 2015, 22:47

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Re: Tycobrahe - Parapedal

Postby JimSalabim » 12 Jun 2015, 12:39

Just finished. But it doesn’t work:
The bypassed signal is coming through as it should when the pedal is switched off. When I switch it on, only the LED works, but no sound, just hum.
I used the second layout of this PDF:
http://www.geofex.com/FX_images/newparapedal.pdf
and the values of the components listed here: http://www.geofex.com/FX_images/parapedal.gif (second layout)
I wired it with true bypass.
Opamps are MC1458p, the diode is a 1N270 (I also tried a zener ZPD 5,1V, but it doesn’t work either).
Checked all connections with a multimeter. Everything is in the right place, just like in the layout.
Any ideas?
IMG_5450.jpg

IMG_5449.jpg
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Re: Tycobrahe - Parapedal

Postby JimSalabim » 12 Jun 2015, 15:04

… and sometimes not even hum, just nothing.
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Re: Tycobrahe - Parapedal

Postby armdnrdy1 » 12 Jun 2015, 15:19

I don't see anything that stands out in the images.

Do you have a meter?

Start at the beginning. Make sure the board is getting powered properly.
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Re: Tycobrahe - Parapedal

Postby JimSalabim » 12 Jun 2015, 15:50

In this schematic http://www.freestompboxes.org/viewtopic.php?f=19&t=120&start=20#p249614 there is a second diode (D2), whereas in the geofex schematics there is a resistor (R13) instead.
Could this have anything to do with it?
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Re: Tycobrahe - Parapedal

Postby armdnrdy1 » 12 Jun 2015, 16:56

The added resistor provides for a voltage divider to bias the op amp. The zener really wasn't needed.

Take voltage measurements of all of the op amp pins.

The measurements might shed some light on what's going on.
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Re: Tycobrahe - Parapedal

Postby JimSalabim » 12 Jun 2015, 18:18

8.7 V at all opamp pins, except Pin 7 of U2: 8.25 V
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Re: Tycobrahe - Parapedal

Postby JimSalabim » 12 Jun 2015, 18:37

Did I wire the pot correctly? I wired it as follows:
Bildschirmfoto 2015-06-12 um 19.35.42.png
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Re: Tycobrahe - Parapedal

Postby JimSalabim » 12 Jun 2015, 18:40

and sorry, it’ not pin 7, it’s pin 6 that shows 8.25 V. All the others 8.7 V as I sad
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Re: Tycobrahe - Parapedal

Postby armdnrdy1 » 12 Jun 2015, 19:01

You have a major problem!

I can't tell from the images....are you sure you have the op amps in the correct way?

If you are absolutely sure...pull them out of the sockets...and take voltage measurements of the socket pins.

Starting at the top left.

Check the op amp data sheet if you are unsure.
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Re: Tycobrahe - Parapedal

Postby JimSalabim » 12 Jun 2015, 20:04

OK, I think I didn’t measure it correctly. I had one side of the multimeter at the battery and the other one at the pins. The multimeter was set on DC.
How do I measure the voltage correctly? Where to put the black side and where to put the red side? Sorry, never had to do that before …

Here’s a picture where you can see the opamps. And one of the multimeter … :-)
And the data sheet: http://www.ti.com/lit/ds/symlink/mc1458.pdf
IMG_5452.jpg

IMG_5453.jpg
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Re: Tycobrahe - Parapedal

Postby JimSalabim » 12 Jun 2015, 20:42

… and I just noticed this:

Before putting the diode in:
IMG_5454.jpg


after putting the diode in and switching on the pedal:
IMG_5455.jpg


But I still have 7 diodes left :-)
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Re: Tycobrahe - Parapedal

Postby armdnrdy1 » 12 Jun 2015, 20:46

The black lead of the meter goes to ground.

The red lead goes to whatever you are taking a voltage reading of....ie: IC pin.

The meter should be on DC.

Edit: You are measuring the voltage drop of the diode. (.23 volts) Diodes are polarized. They pass current one way.
The diode is fine.
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