Trem ain't tremmin'

RicF · Post by **RicF** » Wed 09/24/03 10:52 pm

I just fired up my first 18 watt build, and it mostly works, still have a few problems with hum/grounding, but no more than expected. It also did have the problem with high-pitched squealing when the normal channel tone control is turned all the way down, but a 100 ohm resistor took care of that.

The trem channel works okay as well, but no trem sounds no matter what the speed and intensity settings. It almost sounds like it's trying to start if I click the footswitch on and off, but never seems to get going. With the intensity all the way up, it just sounds a bit thinner than with the trem switch closed. I'm using all the standard values, and haven't tried any substitutions yet. Any suggestions on where to start debugging would be appreciated.

My first impression is, the amp is LOUD. Through a pair of 12" celestions I couldn't turn it up high enough to get it to distort before I was afraid of waking the neighbors, so I'll have to try again when I can open it up a little more. The normal channel sounded too muddy to me though, even with the tone control cranked. Is this normal? I'm only using a 50uf cathode cap too.

Post by **Plexi** » Wed 09/24/03 11:25 pm

RicF; First ,as always,try a different tube in the trem. which you probably already have done. Then,the best way for us to help,{if you can} is post some pics. In the trem channel, if the trem is not working,look over the wireing,and connections. Mostly a wrong value part,or just left off a wire,to small things like that. Its easy to do.

I'm going to start a thread to ask Gabi,if there is some way for us to have a place for people having problems to upload there pics too,so we can look them over. And as always you can send them to my e-mail,and i'd gladly look them over,to see if there is something theat might help..
plexi@alltel.net

Richie

RicF · Post by **RicF** » Thu 09/25/03 9:08 am

Thanks Richie,

Tonight I'll spend a bit longer debugging and looking over the circuit, if I get nowhere I'll send or post some pics. I've tried two different tubes, I'll pull one from another amp and try it as well. I'm curious, I know different tubes can cause differences the way the trem works, but could the wrong tube make it not start at all? I don't think that's the problem in my case, I'm just trying to educate m'self.

RicF · Post by **RicF** » Thu 09/25/03 9:01 pm

Alright, I spent a little longer working on my amp tonight, and verified that I've tried 3 different types of tube for V2 (JJ, EH, crappy sovtek), and still no trem. I also tried adding some capacitance across my footswitch jack (which is set up so the trem channel is operational when nothing is plugged in). The speed control seems to have no effect, but the intensity lowers the volume a little bit as I increase it.

I took some pictures and posted them in the troubleshooting gallery, hopefully they show things clearly enough. If not let me know and I'll upload more. The amp uses Paul Ruby's excellent turret board, so the layout is a little different than normal. Its also a head layout stuffed into a 6" wide chassis so it's a bit tight. I'm going to go look it over a bit more.

RicF · Post by **RicF** » Thu 09/25/03 9:13 pm

Woops, that should say V3 instead of V2 above. The trem channel tube, not the PI.

Post by **Plexi** » Thu 09/25/03 11:26 pm

Ric, what are the cap values in the trem, they look pretty small in size.
I would replace them with a higher voltage cap, .01

Also might disconect the wire to the jack switch for the trem..and see what that does.

Richie

Post by **zaphod_phil** » Fri 09/26/03 6:50 am

RicF wrote:The normal channel sounded too muddy to me though, even with the tone control cranked. Is this normal? I'm only using a 50uf cathode cap too.

If you go to the Rev 5 Pedal Monkey schematic, which has been updated to include details of Ian's original 18W, you will see that the values of C1 and C18 get swapped. This means that the Normal channel is now coupled to the PI by a .01uF instead of 0.022uF cap. So first try that. You should also make C3 much bigger, as that actually helps to tighten up the low-end response. On the original 18watters, I understand that it was usually 500uF, and I know that Graydon uses this value in all his amps and they certainly don't suffer from a muddy low-end response. If you still felt you wanted to reduce any cap's value after that, it would have to be C11 (50uF). However, you should *not* need to do that, as no one else generally has had to.

Apart from that, if your 12" Celestions are current production (ie re-issue) Greenbacks, they are notorious for having poor low-end definition in open-backed cabs.

bubba2 · Post by **bubba2** » Fri 09/26/03 8:05 am

Couldn't get the the trem on my build to work for days until I discovered a suspect ground on the trem footpedal input.

RicF · Post by **RicF** » Fri 09/26/03 9:38 am

Richie, the caps are .01uf, but they're only 100v I think. I'll have to order some new ones, 500v or 1000v. Hopefully that's it. The trem *almost* starts when right when I hit the footswitch, I hear the volume dip up and down about 3 times before evening out, but the intensity is very low. So I think the footswitch jack is working correctly at least. It sounds great when the trem is switched off, too.

Phil, I did in fact originally have C1 and C18 swapped, but I've since fixed it. I don't think I tried it through my 2x12 (closed back G12H & V30, BTW) cab since I fixed that problem, I'll try it and see what I think. I played through a 1x12" last night and it sounded better. I need to sit down and just play and listen for a while, since all I've done have been short littls sound tests.

Thanks a ton for the help, guys.

Post by **zaphod_phil** » Fri 09/26/03 12:33 pm

Although I haven't tested this myself, generally G12Hs are said to sound better in open-backed cabs. You just can't win sometimes!

Post by **Plexi** » Fri 09/26/03 3:12 pm

Ric: Also check the value of the resistors in the trem circut.ones that attach to the small caps. Its hard to tell the value of those blue resistors from the pic. Hey the troubleshooting pic thing looks like it will help alot.
Richie

RicF · Post by **RicF** » Fri 09/26/03 5:19 pm

Phil:
I've heard the same thing. Maybe someday I'll build them a new open-backed cabinet just to see what the difference is. They sound great as they are though, so I'm not complaining.

Richie:
I'll triple-check the resistors; they're practically impossible to read in real life as well as pictures. Yes, the troubleshooting gallery is a good idea. Thanks again for your help.

RicF · Post by **RicF** » Fri 09/26/03 9:59 pm

The resistors and pots in the trem channel all check out okay as per the schematic, but I looked up the .01 CD caps and they're definately only 100v. When I get a chance I'll try replacing C10 with the closest higher voltage cap I've got until I can get the right ones. I think I've got a some .022s, its worth a shot, and I don't really know what bad things can happen if I keep running it with C10 way over voltage. C9 and C8 should be okay for now, right? I'll post the results when I get a chance to try it.

RicF · Post by **RicF** » Sat 09/27/03 9:33 am

Good news, it's working. I replaced C10 with a 600v .022uf, and the tremolo now starts and runs just fine. It's slow, even with the speed turned all the way up, and pretty choppy even with the intensity turned down, but I'll wait till I get the right caps in there before I worry too much. Thanks again!

Post by **Plexi** » Sat 09/27/03 11:02 am

Ric: Cool. the .022 is good to slow the trem, but put over by the 2.7m side. Radio Shack usually has higher voltage disc caps in .01 if you had one close by. Putting the .022 in the spot next to the 100k and .05 will give a bit more thump. But i know you just wanted to test it,and place it over on the higher voltage side..So i think you'll be ok when you get all the right parts in place..Main thing is its working.then you can fine to if you want to.

Richie

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Trem ain't tremmin'

Trem ain't tremmin'

Re: Muddy Low End Response