Transformer for Deluxe Electric Mistress

[mark.carline]

I have just picked up an old Deluxe Electric Mistress from ebay but the unit hummmmms alot and unpon further investigation I discovered at some point that somebody has replaced the transformer inside the unit (it also looks unsheilded). Is anyone here able to give me the specifications of the transformer that was used and maybe also recommended a replacement ?

Many Thanks

Mark

EDIT: By the way I am in the UK so need a 240v supply. I am also tempted to use a Toroidal Mains Transformers - due to the "Very low magnetic leakage field - ideal for audio, video and measuring techniques". I have found on here but not sure about the rating, anyone know:

http://www.maplin.co.uk/module.aspx?...36677&doy=15m8

EDIT2: I have also discovered that (I THINK!) it uses an 18v transformer so I managed to find an 18v Toroidal from farnell as per:

http://uk.farnell.com/jsp/search/bro...equestid=35829

Problem I have is that there are 3 to choose from and i am not sure what the rating is for the EM:
3.2VA:
http://uk.farnell.com/9531467/electr...comp-mcfm32-18
5VA:
http://uk.farnell.com/9531548/electr...comp-mcfm50-18
7VA:
http://uk.farnell.com/9531610/electr...comp-mcfm70-18

I have also discovered that RS do these also:

1.6VA:
http://uk.rs-online.com/web/search/s...duct&R=2786807

3.2VA:
http://uk.rs-online.com/web/search/s...duct&R=2786891

7VA:
http://uk.rs-online.com/web/search/s...duct&R=2787002

[cjlectronics]

I may have a 240vac transformer for an original electric mistress. Years ago, a local music store bought a few EH pedals that were wired for 240vac. I replaced all of the transformers with 110vac transformers and I even found transformers that were an exact FFF.

Shoot me an email at cjlectronics at yahoo dot com. I'll make you a good deal.

CJ

[mark.carline]

many thanks for your help but i think this unit will be going back to the seller and i'm getting a full refund.

I might get another used one anyway and to be honest from what I have read i wouldnt be too keen to replace it with exactly the same type as it looks like they did suffer from noise/humm.

I would be interested to know what the spec is and if anyone has used these newer torroid type transformers as (i guess) they would be ideal in a non shielded environment

mark

[Mark Hammer]

Alternatively, you might consider keeping the transformer completely out of the pedal and adpting it for use with an AC wallwart. That is, the regulation of the power is still done on board, as per usual, but the pedal gets fed an AC voltage by an adaptor that simply steps down the mains supply from 220 or 110 to 12vac or whatever. Companeis do this all the time. EHX simply decided to avoid the hassle of answering queries about "correct" adaptors by sticking the transformer and power cord on the pedal itself .

[mark.carline]

ok thanks - I have noticed that alot of high end high-fi kit and high end pedal power supplies boast that they use a "Toroidal" transformer. I guess when combined with the very low leakage magnetic fields that they (dont) produce they make an excellent choice for pedal / guitar pickup environments.

I am now very keen to know if many people here have used them in their projects or thought about replacing tranformers for this type.

[Mark Hammer]

The qualities of toroidals that you describe are indeed excellent for small packages where the transformer can't be spatially isolated from the more hum-sensitive parts of the circuit. Trouble is that toroidals are not as readily available and they also don't come in a form that provides easy mounting to a PCB or chassis. In most instances, they're basically "wire bagels" and the user/builder has to figure out how they're going to mount the sucker.

[mark.carline]

I checked and the EM uses a 7815 voltage regulator as per this image on GGG :

http://www.generalguitargadgets.com/...ms/dmistsc.gif

And according to this post:

http://archive.ampage.org/threads/1/...istress-1.html

somebody on there mentions:

The EM *probably* wants +/-15v. A +/-22v transformer, after rectification, will provide MUCH more than that, so the EM will probably have some voltage regulation to bring that "too big" supply voltage down to size, and smooth it out.

Not sure what the circuit is, but the rule of thumb for standard 3-pin regulator chips (7809, 7812, 7815, etc) is that you should feed them at least 2 volts more than you want out of them.

Just thought I would mention it incase anyone else was wanting to replace theirs.

EDIT: - I just received an email from EH about the spec of the transformer and they said:

I do not have the exact specs on the transformer, but according to the schematic I have in our archives, it should be about 40 volts center-tapped at 100 ma. It is possible that the original transformer was not shielded. If you get about 20 to 25 volts at the input of the regulator chip, I would suspect that the transformer is OK and would look in the direction of of dried out filter caps or a bad ground connection.

[Liam]

What a weird and small world. Here I am looking for transformer specs for a Deluxe Electric Mistress that failed during PAT testing last week (grrrrrr!), and I find myself redirected to an "Ampage" question I asked 8 1/2 years ago. IIRC 15-0-15 worked fine in the reissue I had at the time, 22-0-22 was for the 1979 Mistress that has just blown the trans on me!

Liam