Search found 173 matches

by FourT6and2
Sat Nov 26, 2022 5:35 pm
Forum: Technical Discussion
Topic: Bogner Helios: RF Radio Noise
Replies: 8
Views: 911

Re: Bogner Helios: RF Radio Noise

I tried various grid stopper values and settled on 5K7. The lower I went, the more the original sound/feel of the amp returned (good thing). 33K affected the amp's sound too much. RF and radio noise came back at 1K2. 2K7 was better, but still a slight bit of radio when amp is cranked. So I went up t...
by FourT6and2
Sat Nov 26, 2022 12:26 am
Forum: Technical Discussion
Topic: Bogner Helios: RF Radio Noise
Replies: 8
Views: 911

Re: Bogner Helios: RF Radio Noise

I decided to just install a grid stopper and pretend like there's no grounding issue lol. 27K. That did the trick. Dead quiet. But yeah... it did affect the sound/feel of the amp. Kinda surprised because the math says with a 27K grid stopper, low pass filter has a cut-off of -3dB at about 25kHz, whi...
by FourT6and2
Fri Nov 25, 2022 4:44 pm
Forum: Technical Discussion
Topic: Bogner Helios: RF Radio Noise
Replies: 8
Views: 911

Re: Bogner Helios: RF Radio Noise

That's what I was getting at, but I didn't want to make an assumption on the basis of something I can't see. I think I'd want to ground the shield, too. As for the lack of a grid stopper, I think you know that it is typically the 68K or 33K mounted at the jack. Assuming it's not there, I'd want to ...
by FourT6and2
Thu Nov 24, 2022 8:43 pm
Forum: Technical Discussion
Topic: Bogner Helios: RF Radio Noise
Replies: 8
Views: 911

Re: Bogner Helios: RF Radio Noise

in the first picture, the one where the black wire on the terminal strip is labeled "not grounded," where does that black wire go at the other end? Where does the other wire (pin 2 of the socket) go? Maybe you said, but I can't get it from what you wrote. That's the input grid of the first stage. T...
by FourT6and2
Thu Nov 24, 2022 5:42 pm
Forum: Technical Discussion
Topic: Bogner Helios: RF Radio Noise
Replies: 8
Views: 911

Bogner Helios: RF Radio Noise

I recently got a Bogner Helios 50. I like it. But there's a good bit of RF/radio noise. The amp is really two different amps in one. "Plex" input and "Hot" input are two different "amps". Not the traditional hi/lo jacks. Plex input bypasses V1. Plex input = no noise. Hot input = tons of noise: hum, ...
by FourT6and2
Thu Nov 10, 2022 3:47 am
Forum: Technical Discussion
Topic: Questions/Build Log: Soldano SLO 100 Clone
Replies: 44
Views: 6719

Re: Questions/Build Log: Soldano SLO 100 Clone

I used O'Netics in my SLO Clone and they were 100% quiet. Just a thought... did you sand off the powder coating of the chassis at all the necessary places? All of the pot mounting holes, some of the switches, jacks, ground point connections, etc. It could be a grounding issue if you did not. Also, t...
by FourT6and2
Thu Nov 03, 2022 3:56 pm
Forum: Technical Discussion
Topic: Presence Circuit and Shunt Resistor
Replies: 13
Views: 875

Re: Presence Circuit and Shunt Resistor

How are those all wired up? Cap in series or parallel?
by FourT6and2
Thu Nov 03, 2022 12:17 am
Forum: Technical Discussion
Topic: Presence Circuit and Shunt Resistor
Replies: 13
Views: 875

Re: Presence Circuit and Shunt Resistor

I discussed the argument in another forum. I hope to be ok to link it here to give some more points of discussion here, otherwise please moderators remove the link: http://www.slocloneforums.com/viewtopic.php?f=24&t=14225 Thanks, I saw that. I'm having trouble visualizing which plots go with which ...
by FourT6and2
Tue Nov 01, 2022 4:22 am
Forum: Technical Discussion
Topic: Presence Circuit and Shunt Resistor
Replies: 13
Views: 875

Re: Presence Circuit and Shunt Resistor

Actually, wait... as you said, it would reduce NFB too
by FourT6and2
Tue Nov 01, 2022 12:32 am
Forum: Technical Discussion
Topic: Presence Circuit and Shunt Resistor
Replies: 13
Views: 875

Re: Presence Circuit and Shunt Resistor

Alright thanks!

Seems like a weird choice then. Just stick with Arrangement 1 with 5K pot and you get the same result, but with more range if you want to dial it in?

But maybe the builder chose to do that to prevent the end user from making amp too bright and complaining.
by FourT6and2
Tue Nov 01, 2022 12:08 am
Forum: Technical Discussion
Topic: Presence Circuit and Shunt Resistor
Replies: 13
Views: 875

Re: Presence Circuit and Shunt Resistor

#3 reduces the amount of feedback, and thus the amount of Presence when the pot is dimed. It increases the closed loop gain. The pot will still be scratchy. You could get some of the Presence back by changing to the 16 Ohm tap. Ok so essentially, it's simply reducing the overall range of the presen...
by FourT6and2
Mon Oct 31, 2022 11:00 pm
Forum: Technical Discussion
Topic: Presence Circuit and Shunt Resistor
Replies: 13
Views: 875

Presence Circuit and Shunt Resistor

I'd like to discuss the pros/cons and theory behind each of these three presence circuits. Amp is a 50-watt JCM800. But focusing just on presence. I'm asking because I'm familiar with Arrangement 1 and 2. In #1, the 5K presence pot acts as the end of the PI tail. In #2, a 25K pot is used and the pre...
by FourT6and2
Tue Aug 06, 2019 12:01 am
Forum: Marshall Discussion
Topic: Amp Build: JCM800 2204 HG Jose
Replies: 33
Views: 9864

Re: Amp Build: JCM800 2204 HG Jose

lovetone wrote: Tue Jul 30, 2019 5:53 am wow thats a great build, well done.

Can you point me in the direction of the schematic with your mods?

Cheers
It's in the Rig Talk tech section somewhere.
by FourT6and2
Sun Jan 27, 2019 2:30 am
Forum: Marshall Discussion
Topic: Dual bias adjustment and effects on grid leak/PI load?
Replies: 3
Views: 819

Re: Dual bias adjustment and effects on grid leak/PI load?

Also, the grid leaks form a filter with the PI couplers. So as you change the grid leak value, you need to also change the cap value if you want to keep the same cutoff frequency as the stock 220K/0.022uF combo. There's a calculator online at ampbooks.
by FourT6and2
Mon Jan 14, 2019 4:37 am
Forum: Marshall Discussion
Topic: Amp Build: JCM800 2204 HG Jose
Replies: 33
Views: 9864

Re: Amp Build: JCM800 2204 HG Jose

Ceriatone is offering this as a kit now haha. I suppose it was inevitable.