Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: kagliostro on October 27, 2025, 10:25:34 am
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I recently discovered this amp, the Two Rock 35
it has a preamp that rensamble some of the Dumble preamp functions but has a unique feature, at the input it has a selector to perform the Pickup Loading
I never seen this feature in other amps and was intrigued about it
It really seems a Boutique Amp feature and I think that in studio it will give it's best allowing very different guitar pickup to perform at they's best
I did a search and seems that 60% of people that use that amp are satisfied using that feature, the other or don't are in feel with the spec or ignore absolutely what it does
What do you think about ? Which is your opinion ?
A friend told me that as the impedence will be less than 1M (689K) it will be detrimental to sound, resulting in high frequencies loss
I'm not so sure about and, more, if instead of use a 5 way Rotary Switch a 6 way rotary switch is used with a 311K (330K || 5.6M = 311625.75ohm) in the sixth position it will be the same to have a 1M at the input (the near allways present value)
Newly .... which is your opinion ?
Many Thanks
Franco
p.s.: May be the schematic is missing something, on the BackPlate the control has 5 positions, not 4 as in the schematic
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Looks like unnecessary complication. A 1M pot with the signal input to the wiper will accomplish something similar without the headaches of switching and wiring multiple resistors.
And what it's accomplishing seems counterproductive.
Paying $5,000 for a slick amp only to choke the signal off at the input is a strange concept to me.
Plus it'll be very interactive with pickup type, cable length/properties, and if you're using any buffered pedals, then the impedance relationship they're aiming for gets disturbed.
In short, I don't like it. But if you are going to do it, then just use a pot.
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I like those amps very much -- most of my recent builds have been very similar with Dumble inspired tone stacks.
BUT, I've never used nor included that feature in my builds. Theoretically it should be of benefit in the right circumstance -- impedance matching is important as we all know. For me as a hack guitarist, I probably would not use it. Betcha someone with better hands and younger ears would find it useful, though.
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Thanks for your replies and for sharing your thoughts.
The counterpart of using a pot is you can't have a precise and quick repeat of the setting (assuming you have find tha position in wich the pickup of your guitar performs better)
Plus it'll be very interactive with pickup type, cable length/properties .....
And, yes, the purpose is exactly that, adapt different situations, obviously interactively
If a guitarist is of the 3 pots and no more, I can understand, but there are also people who like to have controls to fine tune the response (unlucky I'm not a guitarist or player)
Franco
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@ stratomaster
I did a search and seems you are right
There are versions of the amp that has no marks on the PickUp Loading Control and this is actually a clue that a potentiometer may have been used in place of a rotary switch (with an in serie a resistors ti avoid zero value), the model is the Two Rock 35 Studio Pro
(https://i.imgur.com/ltHa8Sh.png)
(https://i.imgur.com/Fg5nhDE.jpeg)
(https://i.imgur.com/tCSeWBw.jpeg)
Franco
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Besides Two Rock are there any builders that provide adjustable grid leak for matching guitar pickups?
This is the first time I have seen it.
If it is a worthwhile consideration why don't more builders use it? or more gimmick
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Seems to me this might be an adjustable version if the Fender hi / lo inputs???
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Don’t really see what it accomplishes above and beyond the guitars own ‘pickup loading’ vol pot.
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If it is a worthwhile consideration why don't more builders use it?
This is a thing I wondered about too
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Seems it worth the effort only if you are building a clone, not someting to add to other projects
Franco
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I can't envision what the pickup loading control does that can't already be achieved using the instrument's tone control?
Until the tone control's resistance is set really low (typically lower than required to achieve Clapton's 'woman' tone), I suspect most of what it does to the tone is due to varying pickup loading.
http://buildyourguitar.com/resources/lemme/