Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: TakingFrags on January 03, 2011, 11:28:34 am
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Hi all,
I began looking at the 'CleanTone' schematic that was saved in the 'HoffmanSchematics' file available for download (schematic/layout attached). I have been reading quite intensively for two weeks now on tube designs but have not begun building. Therefore, this is new to me!
Does anybody have any experience with this schematic? By looking at the schematic, I am not able to foresee what this amp will sound like. What type of sound can I expect? I also plan to remove the reverb components and effects loop to simplify it.
Also, how many watts is this designed for?
Thank you all for the help!
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Moved this over from the schematics section to get more response.
I believe Tubenit designed this, but I'm not sure it has ever been built.
~~25 watts of Fender-ish brown-type tone is what it looks like to me(?)
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If you have room for another hole and if you can stand an extra pot I would use something like a 500k pot in place of the 220k resistor in the tone stack. Really gives you some nice tonal options. I've also used a pot in place of the 18k resistor. Not quite as useful, but worth it if you ask me. You could try something like 100k.
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Moved this over from the schematics section to get more response.
I believe Tubenit designed this, but I'm not sure it has ever been built.
~~25 watts of Fender-ish brown-type tone is what it looks like to me(?)
Thank you! Hopefully Tubenit will check this thread out and provide some feedback.
If you have room for another hole and if you can stand an extra pot I would use something like a 500k pot in place of the 220k resistor in the tone stack. Really gives you some nice tonal options. I've also used a pot in place of the 18k resistor. Not quite as useful, but worth it if you ask me. You could try something like 100k.
If I replace the 220k resistor with a 500k pot, is that essentially putting in a "Mid' component of the EQ or am I being fooled by the location of the Bass and Treble? Also, what would a pot in place of the 18k resistor do as far as tone?
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Here's what I've been working with. If you haven't already downloaded Duncan's Tonestack Calculator you might want to consider trying it out. Its a lot of fun.
http://www.duncanamps.com/tsc/ (http://www.duncanamps.com/tsc/)
The 500k pot changes the location of the dip when bass and treble are high and the location of the hump when bass and treble are low. The 100k pot I would call a mid because it makes the dip less pronounced. When bass and treble are high increasing the 500k pot cuts the bass and boosts the treble, more or less. The opposite happens when you decrease it. That's the basic sound you get. If bass and treble are low then it does the opposite: turn it up more bass, turn it down more treble. When bass and treble and/or mid is up you don't hear much, but you hear something. I think its great.
The mid seems to reduce insertion loss when its up which can be nice. I've been messing around with this for the past couple of months. Yes, more knobs which can be a drag, but lots more tonal options.
One of the things I'm sure many experimenters have done is build the five knob James on their breadboard.
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I have NEVER built the amp. It was just a DRAFT idea that evolved from someone wanting to build a Chet Atkins type amp. I think WeberVST may have at one time posted the Standel Chet Atkins type amp schematic???
With respect, Tubenit
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Here's what I've been working with. If you haven't already downloaded Duncan's Tonestack Calculator you might want to consider trying it out. Its a lot of fun.
http://www.duncanamps.com/tsc/ (http://www.duncanamps.com/tsc/)
The 500k pot changes the location of the dip when bass and treble are high and the location of the hump when bass and treble are low. The 100k pot I would call a mid because it makes the dip less pronounced. When bass and treble are high increasing the 500k pot cuts the bass and boosts the treble, more or less. The opposite happens when you decrease it. That's the basic sound you get. If bass and treble are low then it does the opposite: turn it up more bass, turn it down more treble. When bass and treble and/or mid is up you don't hear much, but you hear something. I think its great.
The mid seems to reduce insertion loss when its up which can be nice. I've been messing around with this for the past couple of months. Yes, more knobs which can be a drag, but lots more tonal options.
One of the things I'm sure many experimenters have done is build the five knob James on their breadboard.
Thanks for sharing!
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Has anyone ever built one of these? Ive been looking for a new project, a nice clean sounding amplifier with lots of tonal variations.
Ive only got 1 other build under my belt, a 5e3 that was pretty easy.
You think this would be too tough for a second build?
Thanks
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Ive only got 1 other build under my belt, a 5e3 that was pretty easy.
You think this would be too tough for a second build?
If you leave off the reverb, then there's not really much more to it than the 5E3, so I think you could do it
.......the thing is, you'll have to make your own chassis (either have a box box made at a local metal fab shop or use a "blank" hammond box) and drill all the holes & such. Not that big a deal, but you need to be prepared...
Or, you might be able to find a "stock" chassis that would work(?), something with Vol/treble/bass, 2x 9-pin holes & 2x or 3x octal holes.
G
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Id like to leave the reverb on. I have 3 other amps and none of them have reverb. They are all 'bare-bones' amps.
I used a blank chassis for my 5e3 build and punched/drilled all the holes so the chassis part wont be a problem for me.
So the resistors should all be 1/2watt unless noted otherwise correct?
Also on the caps, ( this is a newbie question Im sure ) how do I know what voltage rating a cap should be if it is not listed on the schematic?
Thanks for the help
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So the resistors should all be 1/2watt unless noted otherwise correct?
I'd use 1 w or 2 w resistors in plate positions, 3 w for screens.
Also on the caps, ( this is a newbie question Im sure ) how do I know what voltage rating a cap should be if it is not listed on the schematic?
B+ is 390 V, you should use 450 v caps for coupling. Small signal cathode Cs can be 25 V-rated. The ones in the tone stack aren't critical as the TS is AC-coupled but I' use some quality mica and film caps which happen to be rated at 450 v or 500 v.