overtone wrote:
I have to ask, because I have no experience with the JTM45, but isn't the ghost note issue due to the low filtering chosen for the power supply in that amp? Why would the shape of cap make a difference?
Best, tony
It doesn't have to do with the shape per se, but probably with the physical proximity of several caps in one "box", and maybe their common grounding.
I can't give you a scientific answer without digging out some litterature, though. Someone else can surely give you a more informed answer.
I only brought it up because can caps were talked about like an advantage with the JTM45.
BTW, this amp shouldn't be louder than the Bassman since it's basically the sampe amp, should it? (@jelle)
Lynxtrap wrote:BTW, this amp shouldn't be louder than the Bassman since it's basically the sampe amp, should it?
No, it's a completely different amp. It's upside-down and uses KT66's
- 'Peavey, quit stealing my designs' - Mike Soldano
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overtone wrote:
I have to ask, because I have no experience with the JTM45, but isn't the ghost note issue due to the low filtering chosen for the power supply in that amp? Why would the shape of cap make a difference?
Best, tony
It doesn't have to do with the shape per se, but probably with the physical proximity of several caps in one "box", and maybe their common grounding.
I can't give you a scientific answer without digging out some litterature, though. Someone else can surely give you a more informed answer.
I only brought it up because can caps were talked about like an advantage with the JTM45.
BTW, this amp shouldn't be louder than the Bassman since it's basically the sampe amp, should it? (@jelle)
The physical size of an electrolytic capacitor does play a role in determining the ESR. Stated another way, e-caps of similar size tend to have a similar ESR. It isn't often discussed but the ESR does play a part in the feel of an amp. Since we tend to use caps that are about the same size in all of our amps (can caps included) we don't notice it so much but people do complain when we use something radically different. People gripe about the microFarad sized film caps being to "quick" for example. The ESR of these new large film caps is so good that they can deal with the hard transients like they are nothing. Can caps I think are about as good quality-wise as your standard electrolytic radial or axial part, they are just made to fit a smaller form factor.
As far as how this plays into ghosting, I don't think it's the caps or the caps alone that causes this. Old electrolytic caps have a really high ESR (bad) and can't effectively do their filtering job because the ripple current that's supposed to be swallowed by the cap is turning back into voltage when it sees a high resistance. When the caps go bad, they become less effective at filtering the rectified voltage and also allows each stage to "couple" into one another. The e-caps are called decoupling caps because they literally decouple the different circuits in an amp from each other. The preamp stages aren't so picky because they don't draw a lot of current but the power amp stages tend to have multiple stages of filtering not just to reject noise but to prevent the B+ voltages from being tugged all over the place when you start playing. If you don't filter the high voltage enough then the peaks and valleys that appear on the B+ voltage (supposed to be a pure DC) start getting into the preamp and causing all sorts of problems..
LeftyStrat wrote:
No, it's a completely different amp. It's upside-down and uses KT66's
But it only goes to 10, the old Fenders went up to 12.
I found where I had recently read about can caps. It was in Kevin O'Connor's TUT3. What he says, in short, is "multi-section caps destroy ground integrity".
His opinion is that they contribute to ghosting in "plexis".
Of course, he also says that caps nowadays are "small and cheap", which is a good thing
My friend received his Mojotone parts today. Out of the blue, he asked me about using a resistor instead of a choke. I have no idea how this will affect the amp's performance.
The New Steve H wrote:My friend received his Mojotone parts today. Out of the blue, he asked me about using a resistor instead of a choke. I have no idea how this will affect the amp's performance.
Is there any point in doing this?
Steve
Not to blow you off, but if you google "choke verses resistor" or "JTM 45 choke verses resistor", you'll get lot's of hits to digest at your leisure. IMHO, build the JTM45 as is and then season to taste. A good place to start would be to sustitute in 3, 7 or 10H choke. I like the 3H myself.
TM
Last edited by ToneMerc on Tue Jan 24, 2012 1:37 am, edited 1 time in total.
Softer in the low end...trying to imagine that. This guy likes a harder sound than the Bassman I made, so I don't think he wants anything softer. I'll look for older threads. Thanks.
Lower the cathode cap on the input. Dump the rectifier. Increase filtering. Switch to 33k slope resistor and 500pf treble cap. Switch out KT66's for EL34's or E34L's.
The New Steve H wrote:Softer in the low end...trying to imagine that. This guy likes a harder sound than the Bassman I made, so I don't think he wants anything softer. I'll look for older threads. Thanks.
Lefty and TM are totally right, Steve.
Stay with the choke (3h here). I have a 50 with the lowest ever filtering, it has no ghosting at all. It is at the edge of loose stool cranked though. Like electronic ExLax. Shake your money maker til it makes change for that dollar. If I didn't have an aggressive attack it might be a little flubby. Dark guitars stay at home on this one. I use the open lowend to effect.
Lefty, you have issues with authority. lol
@ Lynx, these amps are louder than Bassman amps if you have the right setup, by half again. Way more forward.
Signatures have a 255 character limit that I could abuse, but I am not Cecil B. DeMille.
