Morley - Power Wah Fuzz  [schematic]

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Morley - Power Wah Fuzz  [schematic]

Postby Noth » 04 Jul 2018, 21:49

I did purchase a non-working Morley PWF stompbox from the 70'.
The seller told me the Fuzz part wasn't working anymore.
This post is a work in progress of my attempt to revive it.

IMG_20180630_115415.jpg


Power
First things first : This pedal is 110 VAC powered, I'm in Europe and we're using 220V.
At the same time, I don't like having 220V at my feet with high powered vintage cables on my pedalboard.

If we take a look at the schematics : http://doktorsewage.com/wp-content/uploads/2011/06/pwfes.pdf (found on http://doktorsewage.com/mondo-morley-me ... -wah-fuzz/ ) we can see that from the 110VAC 4 tensions are generated from the converted 28VAC:

- +60VDC (Wah Q2 collector)
- +7VDC (Fuzz)
- +20VDC (Wah Q5 collector)
- +25VDC (bulb power)

I did purchase a 220VAc to 28VDC adapter and then:

- drop the original 110V transformer
- drop CR1, CR2, C4 and C5
- connect the 28VDC + to R5 and R7
- connect the 28VDC - to the ground

IMG_20180630_132155.jpg


After power up, bingo ! The light bulb did properly turned on.

I then decided to check tensions and then realized my mistake: How this circuit is supposed to upgrade my 28 VDC to 60V ?
Open question : Actually from the original 28VAC there is no diode bridge to convert it to DC, so are CR1, CR2, C4 and C5 acting as some kind of charge pump ?

Anyway I found the following tensions after my circuit upgrade:

- 60VDC : 25VDC
- 7VDC : 2,6VDC
- 20VDC : 8,7VDC
- 25VDC : 20VDC

So .. I'm quite far from what is expected, nevertheless I checked the PWF and surprise : The Volume effect (Wah and Fuzz off) is working just perfectly fine, The Wah effect works quite well too and the Fuzz is extremely light depending if the wah effect is turned on or not (from light to extremely light).

I guess that the Fuzz has some dead transistor or capacitor and the general low tensions have some impact on the circuit "stability"..
I'm thinking about setting up a complete power section based on the 28VDC external power supply and a batch of LM317 to generate expected tensions (and let use 28V for the expected 60V, I'll see that later.).

To be continued... !
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Re: Morley PWF - Ressurection

Postby Manfred » 05 Jul 2018, 01:14

As far as I can see, the 60VDC are not used in the rest of the circuit.
The operating voltage of the bulb and the LED-circuit is 28VDC
Here is my suggestion:
PWF_PSU_MOD.jpg

Maybe R5 and R6 need some adjustment.
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pinkjimiphoton (22 Jul 2018, 01:16)
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Re: Morley PWF - Ressurection

Postby Noth » 05 Jul 2018, 05:21

Hi Manfred, thanks for your suggestion I'll test this tonight !
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Re: Morley - Power Wah Fuzz

Postby Noth » 06 Jul 2018, 18:58

So, I did follow Mandfred's instructions and replaced R5 and R6 by 1K:

- 60VDC : 24,1VDC
- 7VDC : 7VDC
- 20VDC : 20,7VDC
- 25VDC : 20VDC

The Volume still works great, the Wha has more dynamics and the Fuzz effect is back !
That's it, it was quite simple after all (and thanks again Manfred for the R5/R6 adjustment suggestions) !


So as a recap, in order to power up a Morley PWF with a 28V DC adapter:
    - drop the original 110V transformer
    - drop CR1, CR2, C4 and C5
    - connect the 28VDC + to R5 and R7 (a red wire jumper is used here)
    - connect the 28VDC - to the ground
    - replace R5 and R6 by 1k resistors

IMG_20180706_195438.jpg


The purple wire is -, black wire on the 28VDC connector is + (sorry for that, I just didn't wat to touch to the original switch).
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