I'll try a speaker lead swap test. By the schematic, isn't the chorus being injected into the ("Power Amp R") right channel ?

Quote from: mexicanyella on March 10, 2016, 11:19:10 PM
Cejay, I don't intend the following to sound critical or like I'm doubting your ears...I am asking out of curiosity, and what I want to know applies to both this thread and the one about the JC120.

I'm curious about the point at which you decide to open the amp up and modify it, including what direction you want to modify it in. In your first post on this thread, you say that the main problem with these amps is the caps in them, which might mean more to someone with more electronics experience than me. But I'd like to know what you objected to that you couldn't address with different knob positions, or a pedal or two.

I do kind of like some of those non-DSP Fender SS combos (in particular, I like how they seem to stay pretty clean and bright, but be housed in kind of cheap-ass cabinetry, with speakers that seem to give it up early...so you can get a sort of amp-meltdown-chaos effect from them without using a lot of fizzy preamp gain. One of my favorite lap steel tones ever achieved came from a borrowed cranked Princeton Chorus, on a friend's recording). Anyway, in my case, I always felt able to tame overall brightness sufficiently by just adjusting the EQ differently than I would on my own amp. So I wonder what you experience upon plugging into the thing and deciding "I can't get it to do what I want without opening it up and replacing some __________________." Can't get rid of enough highs? Mid control not adjusting a center frequency you like? Something about the character of the hot channels dirt tone you thought you could improve on with circuit mods? That kind of thing is what I'd be interested to know, both here and in the JC thread.

Thanks

Wow, thats a deep question....I'll try to answer it but some of the content will be subjective.....which is one of my first answers. EVERYTHING tone wise is subjective, everyone is different, everyone has different tastes, everyone hears things differently.

QuoteI'm curious about the point at which you decide to open the amp up and modify it, including what direction you want to modify it in.

My guitar tastes are set in stone.....telecasters with vintage single coils....thats all I like, thats all I play. I use no pedals....guitar/cord/amp...with the exception of when I need overdrive, I use a Visual Sound Open Road (the only OD pedal I'll ever use). The buffer in this pedal is sheer magic, just having a Visual Sound pedal between the guitar and amp is an amazing difference. Once again, my ears, some people I've been around say they can definitely tell....others say "I think so". Thats a whole other thread though....no, I don't sell these pedals or have any affiliation. So, I don't adjust my guitar, I adjust my amp or amps.....is this crazy, yeah but its what I do. That being said, every amp offers something different (circuit wise).....when amps are made for mass marketing, manufactures try to find a happy medium for all styles of music and guitars. Some guitars will sound better with certain amps.....this is where the rise of boutique amps come in.......amps built for certain styles, sound and guitars.....but that is a whole other thread. Anyway getting back, i know the type of tone and reaction I want to hear and a few tweaks will usually get it done and sometimes not....I don't mind the time it takes to do this.

Quoteyou say that the main problem with these amps is the caps in them

Here's a BIG subjective subject. The cap debate has been going on for years. There are two teams, 1. caps are caps 2. Different caps, different sound. It is "generally" agree upon though, that Polypropylene and Polyester have different sounds.....again thats a whole other thread. IMO electronics vary quite a bit over time.....in both their life cycle and manufacturing. Lets look at the amp in question, IMO in 25 years cap construction techniques, materials use and manufacturing processes have changed, not to mention cheap construction vs quality construction......does any of this matter ? I think so BUT there are others who will say no....its subjective and I don't wish to argue it...it doesn't end well. I will say though, I've changed caps in several audio devices and I can most times hear the difference....once again IMO.

QuoteBut I'd like to know what you objected to that you couldn't address with different knob positions

QuoteI always felt able to tame overall brightness sufficiently by just adjusting the EQ differently

QuoteCan't get rid of enough highs? Mid control not adjusting a center frequency you like?

Tone Stacks are limited to how they are built.....changing the parameters of the components changes the reaction and frequency, greatly. I will never be able to tell you in words what I want to hear and whats in my head....lol maybe I've gone off the deep end....maybe I'm too picky.....people just hear things differently.

QuoteSomething about the character of the hot channels dirt tone you thought you could improve on with circuit mods?

I only deal with the clean channels

Bottom line, I'm just sharing my experiences. Everything I've said here is purely my opinion. Here's something, there are amps that I liked as is and didn't feel the need to change, they are:

Holland Brentwood
Fender Cyber Twin
Vox AD100VT
Peavey Bandit 65
Traynor YCV40

Sorry for the long response....did I answer it?

Got the amp sounding great BUT this chorus thing is driving me crazy. With the chorus off it sounds just like it should but when the chorus is engaged, the right speaker/channel (looking at the front of the amp) has a volume drop....I would say in the order of around 25-30%. I'm assuming this is the dry signal channel because you can plainly hear the chorus effect in the left channel. The chorus works and sounds great but theres the slight volume drop. Is this normal ? This would be a great hindrance when playing live.....

Quote from: J M Fahey on March 10, 2016, 07:44:24 AM

.....By the way, I stated this and other doubts in another Forum where this exact same post appeared and met an angry response from the OP.

Oh well.

That wasn't anger.....you told me what I changed would make "no difference" and/or couldn't see how and as far as my ears could tell, it did.....but speaking of anger, just before that post I saw you lambaste a guy for wanting to repair/mod his 60's era amp, which there was a problem, that he did repair.

Anyway, getting back to amps.....yes both of you are correct, I stated the wrong type, they were the yellow axial ceramics not Tantalum.

Hey Enzo, any ideas on the chorus issue I posted in the other thread ? "Roland JC120 Too Bright"

Quote from: J M Fahey on March 04, 2016, 08:04:50 PM

QuoteI measured the new parts, dead on.....all of the old parts and they were dead on, no drift at all....BUT....a big BUT, the originals were the cheapest kind out there.

If new parts were dead on value and old parts too were dead on, to boot had not drifted after all these years, I fail to see *what*  could have caused any sound change at all.

As of price, how do you know?

Just curious.

Well, you also weren't sitting in front of it before and after....so your comment, in my particular case is based on "your" theory. Now if you are saying that parts are parts, then maybe my ears are different than yours. I saw you on another post...do you come around just to contradict people or what

Well said galaxiex......do what you want to do

Quote from: g1 on March 04, 2016, 12:26:50 PM
  It's always nice to know the type of caps you used for replacement.
But even more than that, what everyone is always curious about, and no one ever reports:
what was the capacitance measurement (and ESR) of the old parts, and of the new parts you replaced them with? 

I measured the new parts, dead on.....all of the old parts and they were dead on, no drift at all....BUT....a big BUT, the originals were the cheapest kind out there. You know, the small little chicklet size, that you can actually see the foil wrap through the sub standard coating they were dipped in. So, ESR ? I wouldn't even know where to begin with those cheapies but the replacements, I'm almost certain are better. They were this type....not the actual ones but like this.

ok update for anyone curious, this amp responds VERY well to upgraded components....which I suppose any would. So I've taken the CH2 preamp pcb out and replaced all 5 of the .068uf coupling caps, and the lone 47uf electrolytic cap. This really brought the amp together and was a great improvement. I'm not going to bother with the distortion section of the signal....I'll never use it. Next, replace the components of the effects pcb (reverb and Chorus). If anyone is interested here are the caps used. Vishay MKT469 PN: BFC246921683 for the .068uf and Nichicon FS for the 47uf.

(Preface: I use single coil Teles.)  Just thought I'd throw this out there for anybody who likes the Fender Ultra/Ultimate (non DSP) Chorus amps. I did this purely as an experiment but the results were phenomenal. Is it overboard...probably, just buy another amp...probably but if you have some time and willing to spend $50 on the amp, it really pays off. The biggest problem with these amps is the fact that they have cheap electrolytic and Tantalum caps in the signal path, with these removed it is an amazing transformation. Its a simple task but time consuming. All Tantalum caps that were changed were replaced with silver mica. The other polyester caps were merely upgraded. Attached schematic....Red circles indicate upgraded to mica or polyester caps, capacitance size is determining factor, all pico's are mica. BLUE circles indicate an electrolytic cap changed to non polar polyester cap. The yellow square (C6) was changed from 1000pf to 250pf, this one mod was a tremendous difference.

Quote from: gbono on March 02, 2016, 11:58:18 PM
Do me a flavor and play an ES335/L5/ES175 through your mod and see what it sounds like. Were the ceramic caps X5R dielectric? Are you saying the mica dielectric improved the sound?

I would gladly play one through it if I had one. I'm would assume they were XR5's....I don't see them using XR7's......if size is an indication of temperature range....these were really small...about 3mm across. YES ! the silver mica's greatly improved the sound....I could tell instantly. However, I did replace the bass and mid tone stack caps with CDE polyester 150's but I did this BEFORE the ceramic caps and it made little change. It went from a ratty top end to much smoother....just as you would think a mica would do. JC120 is one of the easiest ss amp I've ever worked on.....the lay out is excellent. Every aspect of the amp has it's own individual pcb....and simple to pull out. CH1, CH2, effects, Ins/outs/effect loop and power section. Nothing double or triple stacked....that's why the amp is so large.....unstacked pcb layout. I'm in the process of removing all of the ceramics, in favor of micas....I'm also replacing all of the .068uf coupling caps with a higher grade and replacing all of the small electrolytic that are in the signal path with Nichicon FS series caps (audio grade). This may have an adverse effect of too sterile....at which point I'll backup. I did this same thing to my Fender Ultra Chorus but eliminated several of the small electrolytic caps for non polar polyester caps and......It.sounds.amazing!! The biggest hindrance of that amp is the 1000pf volume pot bypass cap.

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 !!

yeah, I looked at it on the TSC.....but I like the sound of the amp....minus the extended highs. Thats why i'm trying to avoid the tone stack. I'm going to start with the others and setup a clip in/out rig. Wasn't sure which direction to move, up/down, but since they are NFB, now I do. Thanks for the info !!

Just got my first JC120 (UT) and I play 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 geez its 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.

just picked up a red knob power chorus, everything sounds great except th chorus doesn't work. Took the chassis out to find that the rate pot has been changed out.when turning the chorus on you can hear what sounds like a tone change but no chorus effect and an intermittent static,interference and popping. really bummed out, what should i check for.