Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Ed_Chambley on July 03, 2012, 12:52:51 pm
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Anyone know how or have a schematic for this mod. I searched and came up with nothing.
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Try a 1M pot between the 6k8 resistor (that's in the tone stack) and the ground return.
Or if you want just a simple 'raw' switch, put the switch between the 6k8 and the ground instead (and if you want to cure the switch popping, put a 1M+ resistor across the switch)
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And here's a schematic. I just used a 250K pot.
http://home.comcast.net/~seluckey/amps/rocky/rocky.pdf (http://home.comcast.net/~seluckey/amps/rocky/rocky.pdf)
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You just got tag teamed, son!
(http://violinonline.ru/img/2e/2e4/John_Morrison_and_Kofi_Kingston_vs_The_Miz_and_Dolph.jpg)
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Honestly, even 250K pot seems like overkill to me. I guess it depends on how RAW you want it to get, but a 25K Mid pot (audio taper) works fine for me. Playing with Duncan's Tone Stack Calculator, going up to 50K gets the frequency response fairly flat and boosts mids significantly. The other thing about a really big Mid pot or resistor is that the Treble and Bass controls become fairly useless.
If you want to maximize gain but still keep a tone control of some kind, you might try LooseChange's "Tweed" switch instead: http://www.el34world.com/Forum/index.php?topic=7862.msg69917#msg69917 (http://www.el34world.com/Forum/index.php?topic=7862.msg69917#msg69917) (schematic in Reply #16).
Just a different take on the topic. Allen's "Raw" switch has been popular for a long time AFAICT.
Cheers and happy Independence Day!
Chip
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Schematic attached
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I ended up installing a 10kl with a 2k2 resistor from lug 3 to ground. Mid pot switchable to a variable resistor. The resistor is mounted to be adjusted by a small flathead through the chassis. I can adjust as if I had a 10kl mid pot or switch to the resistor which has a swing of 0-220k. Pretty much covered it. I have a Switchable NFB so the amp will go from clean to downright nasty with no volume change. I did end up trying 2 MV's. Dual 1meg and the LarMar MV. The amp has no master volume. Does not need it as it sounds much better without it. Still all that is left is adding a switchable dwell in in the cabinet it goes.
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What does RAW do?
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What does RAW do?
Boosts midrange frequencies and reduces insertion loss from tone stack. IOW more gain plus mids.
Chip
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It makes the amp bypass some of the tonestack. In this instance, I can use a middle control on a Princeton reverb as it did not have one. The more you increase the mid the less the effect you will get from the tone stack. Makes for a raw sound. Sort of like getting the amp nasty sounding from the start. I guess the best way to say it is it is more Marshall Plexi sounding, but you don't have to crank it up. The higher you go with the resistance the less effect the the tonestack has. Think of it like having a booster in front of the amp. Sort of pushes the preamp section. Sounds really good in Fender blackface amps.
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And here's a schematic. I just used a 250K pot.
http://home.comcast.net/~seluckey/amps/rocky/rocky.pdf (http://home.comcast.net/~seluckey/amps/rocky/rocky.pdf)
What would you call the type of tone stack on page 4.?
Thank You
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That's a standard Fender BF tone stack, with no mid controll. Mids are set with the 6.8K R at the bottom of the tone stack.
But he added the raw controll, set at 0 it's the standard tone stack, as you turn the 250K pot up, you increase mids and the bass, treb controlls have a harder and harder throwing away signal to ground because your increasing the R that the tone stack is standing on.
Brad :icon_biggrin:
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My mistake, sorry, I was actually looking at Page 3.
Thanks
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It' says in the foot notes on page 4, it's a James tone stack.
Brad :icon_biggrin:
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It' says in the foot notes on page 4, it's a James tone stack.
Brad :icon_biggrin:
Yes it does. I was just looking at that.
sluckey sure does an excellent job with all his info and drawings.
I wonder what his (or anybodies) opinion of that tone stack is. Obviously he removed it. Guess I will do a search to see what you guys have said about it in the past.....james baxandall.
Thanks for your help.
I Appreciate It
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sluckey sure does an excellent job with all his info and drawings.
Yep.
Brad :icon_biggrin:
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JRindt, I've tried the James stack and really liked it. I wish now I had used it on this one instead of the 1-knob-job, but I was wanting to see how simple I could keep it. I'm also pretty sure I don't have the ear that Tubenit and some of these other guys do, (too many years on open tractors) so it might be I'm missing some of the nuances that a mid pot gives you. But I liked it much better than the FMV stack. 1 less hole, 1 less pot to wire, and still plenty of tonal options, just MHO.
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I wonder what his (or anybodies) opinion of that tone stack is. Obviously he removed it.
I removed that particular tonestack because it was designed for hi-fi record playback and would need to be changed (including the pots) to work well with a guitar. It was a RockOla juke box. I chose the Fender tonestack because I just wanted to see what an AB763 with 6SL7s would sound like.
The only guitar friendly James tonestack I ever owned was in my old Ampeg Gemini II. Bought it new and wish I still had it. It did not get the shrill highs that a Fender amp could, but I sure loved the sound. (Right now I'm remembering Tall Cool Woman in a Black Dress.) I'm not sure why I haven't built another Ampeg/James TS. Probably should.
Tubenit has built several amps with a James TS. And his stuff sounds very good.
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That's a great song.
Brad :icon_biggrin:
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Hi guy's, Had a couple of goes at building an amp with the ECL84s (mini bassman and solow watt) and found that both types of TS had very little effect (maybe it may have been the builder) but third time lucky built the BTO with James TS and hit the jackpot and found it easy to tweak to taste. The only change from the original in the BTO was the treble cap i changed from 680p to 250p, this worked very well.Thanks