Roland JC120 Power Transformer

[DrGonz78]

I have a PT for a Crate GT1200 amp. I need to locate that one but it's somewhere in packed up land. Good thing about that one is that it belongs on a 120 watt amp. Will let you know when I find it.

But what would a drop in wattage mean in terms of amp "performance", you know what I mean?

Well for one it would mean less headroom.

[rshepard10]

So correct Amperage but what does that mean for operating voltage of the amp?

And oh okay so if you lower the wattage of the transformer, it will in turn drop the headroom and that's what can cause an amp to start to distort at higher levels?

[DrGonz78]

So correct Amperage but what does that mean for operating voltage of the amp?

And oh okay so if you lower the wattage of the transformer, it will in turn drop the headroom and that's what can cause an amp to start to distort at higher levels?

Yes lowering the secondary voltage will be less headroom before clipping point of the amp. Also, I need to confirm what the secondary voltages are on the power transformers too. Once I find it, I have good hopes on the Crate PT since it is for another 120 watt amp.

[J M Fahey]

The Rogue transformer is probably 30+30VAC and the proper size, so it will work.

Besides , actual power will be practically the same.

[rshepard10]

What do you mean the actual power will practically be the same?
The wattage difference between the two amps wouldn't be that big of a problem?

[DrGonz78]

What do you mean the actual power will practically be the same?
The wattage difference between the two amps wouldn't be that big of a problem?

Yeah not much difference between 100 and 120 watt. I was thinking the same thought while trying to pick through my leftover transformers. Honestly as I remember it I think this Rogue PT is more hefty in feel of iron than the Crate one. BTW working all weekend but at some point in the next day or so I will check the voltages to confirm.

Edit: Trying to get the bolts out of the Rogue PT might prove difficult. The Crate one might be easier to mount. Are you just installing this into a JC120 chassis or are you building that whole thing as part of your project?

[rshepard10]

Okay okay I think I understand, they are close enough to call it good.
And Thank you so much, you are the best. All of you guys have been a really big help! I appreciate it.

[J M Fahey]

100W and 120W ar practically the same, inaudible difference.

To boot we do not know the exact winding data, not even the real specs of the original Roland transformer so even one with exact same voltage (which we ignore anyway) will not have the exact same power because it will not react exactly the same under load.

So splitting hairs is useless; here we have a practical problem, we provide a practical answer which will so the job properly and end with a happy customer.

You want the exact same performance as the original one?
EASY: just pay through the nose for an original Roland one and call it a day.

[rshepard10]

Haha I'm not that picky xD haha I can live with the practical solution

[rshepard10]

Edit: Trying to get the bolts out of the Rogue PT might prove difficult. The Crate one might be easier to mount. Are you just installing this into a JC120 chassis or are you building that whole thing as part of your project?

I am building the whole thing from scratch so I can custom fit any size.

[J M Fahey]

Cool.
Then the Rogue transformer will do fine.

One small nag: what will you do about PCBs?

If drawing your own, you have a huge job ahead; if cloning the original ones, you still have a huge job ahead , only somewhat reduced, and maybe youŽll find it hard to find some parts; same value but with different footprint which wonŽt match original PCB artwork.

It is an excellent but complex amplifier.

You also need to solve the "mechanical" side: chassis, front and back panels, heatsinks, etc.

It might pay to buy a Crate/Marshall/Fender "Stereo Chorus" model for relatively low price (definitely not for peanuts, unless hopelessly broken) , gut it and mount your own electronics.

Definitely a complex project.

[DrGonz78]

If I was going to build such an amp clone of a Jc120 I would simplify the amp design as much as possible. For example, the distortion channel would get removed from the project on day 1. Just such an awful sounding distortion it would not be worth the effort to even build it. I personally would ditch the effect send/return and anything I could to do to simplify the build. I would focus on a preamp section and the stereo output sections, plus how to make the chorus/reverb effect board.

[rshepard10]

Cool.
Then the Rogue transformer will do fine.

One small nag: what will you do about PCBs?

If drawing your own, you have a huge job ahead; if cloning the original ones, you still have a huge job ahead , only somewhat reduced, and maybe youŽll find it hard to find some parts; same value but with different footprint which wonŽt match original PCB artwork.

It is an excellent but complex amplifier.

I was gonna use the original PCB layouts and make small "Daughter Boards" to use if the new parts didn't fit in the original locations with small jumpers between the two.

If I was going to build such an amp clone of a Jc120 I would simplify the amp design as much as possible. For example, the distortion channel would get removed from the project on day 1. Just such an awful sounding distortion it would not be worth the effort to even build it. I personally would ditch the effect send/return and anything I could to do to simplify the build. I would focus on a preamp section and the stereo output sections, plus how to make the chorus/reverb effect board.

That is a very great idea I didn't even think about! Awesome Thanks!