Welcome to Solid State Guitar Amp Forum | DIY Guitar Amplifiers. Please login or sign up.

October 05, 2022, 05:50:31 AM

Login with username, password and session length

Recent Posts

 

Help reading schematic (vintage Roland amp)

Started by Voidoid, April 04, 2022, 11:22:45 AM

Previous topic - Next topic

Voidoid

Hi!

I'm a newbie both to the forum and DIY electronics. I hope this type of thing is alright to ask - if not, let me know!

I'm trying to DIY some stuff related to a Roland Super Cube 100 from the '80s. I'm stuck figuring out the FX loop (or rather "Stack jacks") on this amp. With my present knowledge the schematic is a bit above my head. If someone could help me figure this out it would help out a great deal.

I found the service manual online as a pdf on another forum (in post #12): https://music-electronics-forum.com/forum/schematic-requests/51330-roland-super-cube-100-schematic
It wasn't the easiest thing to come by! It has a schematic on page 4 of the manual, with the stack jacks in the upper right corner (top of JK-2 board).

The user manual (separate document) talks briefly about parallell wiring. This pair of jacks is really intended to string several Super Cubes together (hence "Stack jacks" moniker). The Pre Out/Main In secondary labelling sure suggests it, but is this even usable as an FX loop? I got a noticable volume boost plugging in that way compared to just going to the top panel. I'd reeeally like to know how it works.


g1

The signal routes through R46 to the power amp whether the jacks are in use or not.
It won't function as a loop.  You can use them as either a pre-out, or a power amp in, but not both functions at the same time.

Voidoid

Quote from: g1 on April 04, 2022, 01:57:11 PMThe signal routes through R46 to the power amp whether the jacks are in use or not.
It won't function as a loop.  You can use them as either a pre-out, or a power amp in, but not both functions at the same time.

Thank you, that is a huge help! A bit of a letdown as far as my DIY plans are concerned, but such is life :)

Enzo

Just a quick look, seems to me a little reroute of R46 and we could easily convert those jacks to the more common FX loop configuration.   Yes/No?

Voidoid

Quote from: Enzo on April 04, 2022, 09:58:59 PMJust a quick look, seems to me a little reroute of R46 and we could easily convert those jacks to the more common FX loop configuration.   Yes/No?

I'd be curious to know. I'm a little hesitant to modify the amp as I rather like it. Still, could up its versatility.

It's rather limited as a channel switching channel amp as-is because of a rather large volume jump between the channels. Bit of a shame, because the drive is quite usable along with the really nice clean.

My thought was to wire up a combo pot-in-a-box passive volume and channel selector for Drive/Clean on the same switch. Put the passive volume in the FX loop and have it bypassed when clean is selected. Would also be nice to put a delay post-gain.

Boosting into the clean channel with my Soul Preacher was usable on a more compressed setting but didn't seem ideal. Got some distortion with an uncompressed signal (only tested at bedroom levels).

Enzo

Maybe a little experimentation in the R9, R16, R5 area might even up your levels.