Roland JC120 Power Transformer

[rshepard10]

Hey Everyone,
I hope someone can help. I'm looking for a substitute power transformer for a Roland JC-120 (ut) Model amp.
I Added the service manual for the amp to look at if needed

[The Dude]

Your location isn't in your profile. If you update with that info, it makes it easier for us to help you.

So, do you need:
G245713501 TRANSFORMER 100V/117V
or
G245713601 TRANSFORMER 230V/240V

Here's a link to Roland's contact page. You might just get ahold of them.

Contact Us*| Roland U.S.

I also have to ask out of curiosity: Are you sure yours is bad? Transformers are usually last on the list of things that fail.

[rshepard10]

Its actually an interesting story. Mine isn't bad because I don't have one, haha. I'm trying to see if I can build one as a challenge from another audio engineer. I know, I know, its a stupid idea and whatever but I like a challenge. I'm not an electrical engineer or anything but I'm proficient in electronics and mostly fix recording consoles but it sounded like fun to try and I thought I would take up the challenge.

[The Dude]

I Googled the part number. No luck. You might have to call Roland.

[rshepard10]

I followed that link you sent and shot them an email. Lets see if they get back to me. Thanks for the link by the way!

[The Dude]

Looking at the schematic, the PT is a simple primary to single center-tapped secondary. If you could get specs, you could probably find something most anywhere. If you have access to an amp, measure the secondary. Secondary voltages aren't stated at first glance, but the main fuse value is 4A and the filter caps on the main supply are 63V (which will be overrated). You could probably approximate something from that info.

[rshepard10]

That is great information, but I don't really have access to one of these amps. Hopefully someone can read through this that has one and take some measurements for me It would be most appreciated.

[J M Fahey]

Main supply caps are C31-C32 ; 3300uFx63V each.

For 60W into 8 ohms you need a roughly +/- 42V supply, +/-45V top.
So you need a 30+30 to 32+32 VAC transformer.
3 Ampere current capacity would be enough; getting a 4 A one won´t hurt; anything larger will probably be too large, no problem in a home built unit, definitely a problem if replacing a missing original one, you must match available space.

Do you have experience and machinery to wind a power transformer?

Worst case, a hand winder like this one is enough , it just takes longer:


Most suggested on Google search have some kind of gear or pulley arrangement so 1 hand crank turn means, say, 6 bobbin turns; that´s fine for thin wire and thousand turn coils, but for a large transformer buy/kludge a 1:1 one like the one above (which makes construction far easier, even out of plywood) because wire is thick and relatively hard to bend.

[rshepard10]

Hum, okay. With that information what would be a good transformer that I could get that has that spec on it?

I personally have no exsperence winding transformers. although this would be a skill I wish I had. I honestly don't know that much about transformers except for the basic knowledge so I feel like if I tried I would mess it up something wicked and it would end up costing me more then it is worth.

[rshepard10]

experience* -__- too early for work

[DrGonz78]

I am over in Scottsdale AZ here and may have a couple left over transformers that might work in your amp. Not sure exactly at this moment and as I have just moved they are in a box somewhere. Tonight I will dig them out and check to see what I have here.

[rshepard10]

I am over in Scottsdale AZ here and may have a couple left over transformers that might work in your amp. Not sure exactly at this moment and as I have just moved they are in a box somewhere. Tonight I will dig them out and check to see what I have here.

Oh that would be awesome! I don't need anything genuine or super fancy as long as it will work, haha that would be awesome!

[J M Fahey]

Oh, I thought you had said:

I'm trying to see if I can build one

Maybe I have poor reading comprehension skills

[DrGonz78]

So I got this tranny from a Rogue GS-100R. That amp is a 100 watts and the JC120 is obviously 120 watts. I am not so sure this PT would be a good candidate but maybe it could work. Let the brain trust here help with some of that part of it. The cool part about this transformer is it has a bell on it and I think if you can replace the mounting bolts it could possibly be mounted into a JC120. That all depends on the measurements of the PT in relation to the JC120 chassis. I have not measured the voltages yet but the secondary does have a center tap. This transformer also has low voltage secondary taps too, but they won't be used in a JC120. There was a thread on SSguitar.com where RG (very reputable member here too) had posted something about this amp. The only difference is that the amp I took it from was gold instead of silver chassis and of course the bell is not on the other transformer. I think this transformer is from an older late 90's version of that Rogue amp.

https://www.ssguitar.com/index.php?topic=1252.0

[rshepard10]

Oh, I thought you had said:
Maybe I have poor reading comprehension skills

Haha Build the amp, not the components I wish I had that kind of talent

And would the watt difference of the two amps effect it? I don't know that much of the math behind transformers and things like that (so education is always appreciated, so everyone feel free to chime in and give me suggestions and knowledge, haha) But what would a drop in wattage mean in terms of amp "performance", you know what I mean?