Roland JC120 Too Bright

[cejay825]

Just got my first JC120 (UT) and I play a Telecaster (vintage fralins).....the treble is over bearing. I can almost adjust the treble pot to my liking but I hit a certain point and it falls off too much. The amp is playing and functioning properly but its too bright. What can I mod in CH2 to tame it some....C4, C16, C8 ?.....or is there somewhere else I should look. speaking of C8, what is 0p exactly.

[Dave H]

I'd try removing C6.
0p probably means zero picofarad i.e. it's not fitted.

[cejay825]

I thought removing it also....but isn't it negative feedback?? Meaning go higher to cancel out ? I could be wrong

[Dave H]

I thought removing it also....but isn't it negative feedback?

Are you looking at the C6 connected to the top of the Vol pot VR1? That's just a bright cap so it's OK to remove it. It adds brightness through R6 even when the bright switch (SW1) is open.

[cejay825]

Are you looking at the C6 connected to the top of the Vol pot VR1? That's just a bright cap so it's OK to remove it. It adds brightness through R6 even when the bright switch (SW1) is open.

I was looking at C4 and C8 as NFB....maybe not. I was curious as to whether C6 signal could make it through R6...it being 1M. Interesting I can definitely do without C6

[Richard]

Does your JC-120 have the aluminum dome speakers? A speaker swap may make you happy. It seems like the amp is pretty far off from what you like, as far as the treble response, and that more than a minor change could help. I would start with C16. Download Duncan's tone stack calculator and input your values into the Fender Style tone stack, then you can see what tweaks will do to the sound. If you can record your amp and play with an eq to see which frequencies are offensive and which you like.

[Leo_Gnardo]

If fiddling with capacitors doesn't do it for you, consider a change of speakers. Those tin-dome original Rolands sound like nails on a chalkboard, skreeeeeeek! With a Tele, you should be able to cut thru steel like a hi power laser.

[drewl]

Never understood why anyone liked these amps ever, they always sounded shrill and too bright to me.

As suggested try altering the tone stack.

[Leo_Gnardo]

Never understood why anyone liked these amps ever, they always sounded shrill and too bright to me.

As suggested try altering the tone stack.

You could try that too. Richard in Sactown & I had the same idea at the same time, speakers. I got Carlos Alomar to get ElectroVoice in his. Weighed like Twins after that.

[cejay825]

I've considered speakers....but only if I can't solve it with some circuit tweaks. I don't have the silver domes....I have, what appears to be a smaller paper cone. I do know this, I've seen several schematics with different value caps, in these locations...crazy. I'll try the tweaks and report back. If not....maybe some Eminence Red Whites and Blues ??

[Leo_Gnardo]

I've considered speakers....<snip> - - - - maybe some Eminence Red Whites and Blues ??

Even the cheapest Emi Legends not too darn bad. I prefer Emi's Texas Heat, not a whole lot more $$, fat mellow tone with enough top end to carry the message but never make your ears cringe. Just finished outfitting a Twin Reverb with these plus a half-inch oak ply back, covers most of the area with a 3x5 access hole for the cable & pedals. Lots more low end & even sounded very fine today with a Gibson Ripper bass.

[Richard]

When you have the treble pot almost to your liking is it at the low or high end of the range? What is the difference between what your amp gives you and what you want to hear? Sometimes too bright is the shiny jangly stuff at 2K and above, sometimes it's that 1.5K spike in your ear.

[Dave H]

I was looking at C4 and C8 as NFB....maybe not. I was curious as to whether C6 signal could make it through R6...it being 1M. Interesting I can definitely do without C6

Yes, C4 and C8 are NFB.

C6 puts R6 in parallel with the top section of the vol pot at high frequency which could be making it too bright but not as bright as using the bright switch. Ouch!

[cejay825]

Well, problem solved ! Removed C6 from the bright switch circuit. I don't know how much of that signal could have made it through the 1M resistor (R6)..but anway, don't need it. Changed treble tone stack cap C16 from ceramic to silver mica. Replaced C4 with silver mica and raised it to 47p. Bingo ! still nice and sparkly without the ear split. Thanks Everyone !!

[cejay825]

One more thing....with these amps....is the volume supposed to drop off a tad when chorus is engaged ? Oh and no I don't have the silver dome speakers....my factory speakers are a smallish paper dome....don't know whats up with that