Home › Forums › Help/Technical Questions › 70s Deluxe Electric Mistress – Removing Transformer
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July 28, 2011 at 2:35 pm #81801alex192Participant
Hi guys,
I’ve just bought a late 70s EH Deluxe Electric Mistress, but it is a 110v version with the internal transformer and American plug (I have not received it yet so couldn’t say if it is a 2 or 3 prong plug).
I want to get it working on UK voltage. If my understanding is correct, the input on the circuit is 24v, so would it be feasible to remove the transformer, wire in a DC jack and use one of these:
http://www.banzaimusic.com/EH-24V-DC-UK-100mA.html
to power the pedal?
Cheers!
July 28, 2011 at 3:35 pm #103151The EH ManModeratorYes, it would work. It’s actually a better idea since in the future you can sell it and the buyer just gets a new wall wart if needed.
You’ll be able to tell if it’s really a vintage unit when you open it up. The vintage unit model # starts with EH and the reissue starts with EC.
July 28, 2011 at 3:44 pm #103004alex192ParticipantThanks for the info (This forum is great, BTW)
Just looked at the serial number on one of the pics and it looks to read EH5150 D. Any more info that could be had from that serial number?
Cheers!
July 28, 2011 at 5:22 pm #103002The EH ManModeratorQuote:Thanks for the info (This forum is great, BTW)Just looked at the serial number on one of the pics and it looks to read EH5150 D. Any more info that could be had from that serial number?
Cheers!
Not really, other than it’s a vintage unit.
August 8, 2011 at 5:28 pm #104919alex192ParticipantJust had a look at the unit today. It’s a 2 prong plug and looks to all be in original condition, apart from the knobs. Am I correct in thinking if I want to wire up a 2.5 mm jack to the unit all I need to do is run the ground (negative) wire from the jack to where the single green wire connects from the transformer to the board, and wire the positive wire from the jack to where the two brown wires from the transformer connect to the board? Would there be any benefit using two wires as it is at the moment, or would one be sufficient?
Also, does the transformer output 24v ac or dc? I think I read somewhere that the transformer outputs 24 vac and it is rectified to 18(?) vdc on the board. Would it matter if the jack to the board is being fed 24 vdc and then this is being fed through the rectifier stage on the board? Would this stage need to be bypassed or does it not matter? Sorry, I have not had too detailed a look at the circuit layout yet.
Thanks in advance.
August 8, 2011 at 6:00 pm #104909The EH ManModeratorQuote:Just had a look at the unit today. It’s a 2 prong plug and looks to all be in original condition, apart from the knobs. Am I correct in thinking if I want to wire up a 2.5 mm jack to the unit all I need to do is run the ground (negative) wire from the jack to where the single green wire connects from the transformer to the board, and wire the positive wire from the jack to where the two brown wires from the transformer connect to the board? Would there be any benefit using two wires as it is at the moment, or would one be sufficient?Also, does the transformer output 24v ac or dc? I think I read somewhere that the transformer outputs 24 vac and it is rectified to 18(?) vdc on the board. Would it matter if the jack to the board is being fed 24 vdc and then this is being fed through the rectifier stage on the board? Would this stage need to be bypassed or does it not matter? Sorry, I have not had too detailed a look at the circuit layout yet.
Thanks in advance.
You’ll need to either find the voltage regulator on the board and run the + into it or you could run it through one diode first then to the regulator. This would give you some polarity protection and drop a little bit of voltage. The – can go where the green wire of the transformer is.
The transformer puts out AC which is rectified to DC by a couple of diodes, then fed into the regulator.August 8, 2011 at 11:02 pm #104860alex192ParticipantThanks for the info. I have found the voltage regulator (7815) so all I need to do is run the positive wire into it and the ground to where the green wire connects at the moment?
Am I correct in thinking that the regulator outputs 15v? I will be using the 24v EH transformer at the top of the page. If I were to use, say, an 18 v output from a pedal power or something similar, would it work fine? I am interested as to why EH sell a 24v adapter when the pedal runs 15v (and the reissue 12v??). What is the need for this headroom? I’m just a little curious.
Cheers!
August 8, 2011 at 11:25 pm #104861The EH ManModeratorYes, the regulator puts out +15vdc. 18vdc would also work fine. They use the 24vdc adapter because some other pedals need the higher voltage and it makes for less models to keep in stock.
August 22, 2011 at 10:00 pm #115692alex192ParticipantGreat, got it working on UK voltage with the method described above. The colour knob was not operating properly (it would feedback uncontrolably on full) so I tweaked the trim pot a little. I think I’m going to get hold of a signal generator and sort out the rest of the trim pots using a long method I found on the internet.
Just another quick question. I’m rewiring it as true bypass (don’t always do this to pedals, but this is one pedal that does colour the tone a little in bypass mode). What is the purpose of the resistors R1, R18 and R19 in these two schematics:
Code:Can I just leave these out when I rewire the switch?
Thanks
[Edit, pics were far too big to post]
August 23, 2011 at 8:14 pm #115669alex192ParticipantActually, scrap that idea. I am now considering building a true bypass box (well, the circuit) and housing it inside the DEM.
Can you see any problems with this?
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