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Have you tried the TBV mod?
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Post subject: Tbv mod for HRDX, continued
Posted: Sun Mar 03, 2019 10:52 am
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The original title didn't describe the mod.
I've updated the original posts to include links to pics.

This is about a series of mods to improve the sound of a Hot Rod Deluxe, original and reissue. It is especially useful for players who can't crank it up past 2 or 3. These will not be found anywhere else. I have developed them in secret, until now.
It all started in 2007 when Rich asked me to modify his HRDX into something like an old Fender BF. He had a Mesa for high gain and this was sittin around not being used.
So I channeled Leo and removed one tube stage and seven resistors in the signal path to compensate. It was ten jumpers and sounded pretty good. Later, it got 270k plate resistors to bump up the gain a bit. It was a rats nest of wires, but the beginnings of the TBV mod.
Over the next ten years, I fiddled with different ideas and perfected the mod. It keeps the tube stage and stock gain, but reroutes the signal path. It addresses the muddiness at low volume settings on the Hot Rod and improves definition throughout all volumes.
You can appreciate the improvement by comparing the Hot Rod signal path to the BF/SF topology. A BF Fender input goes to the preamp and then the tone control, then the volume control. The HRDX sends the signal to the volume controls before the tone controls. If the volume is turned down, the capacitors in the tone stack get very little signal compared with the BF/SF tone stack.
So I move two parts, cut one trace and add a jumper to reroute the HRDX signal path into the tone before volume or TBV, configuration. There were two approaches I used. The grid swap method and the plate swap method. I settled on plate swap mostly for ease of mod.
I developed this mod for Blues Deluxe and Blues Jr as they have the same layout. I will be posting each of these separately. Each has their own iteration of the Tone Before Volume mod.
You have to pull the board away from the chassis. If you don't know how to do that safely, stop reading and forward this to your qualified tech.
1 Remove R8 100k and R41 10 k
2 Cut trace at V1 pin2 on the main board to R1/R2
3 install jumper from R1/R2 to R41 +Pin7 of V1
4 install 10k resistor from R41 to R8 +Pin2 of V2
5 Install 100k resistor from R8 to pin2 of V1
Image I'm working on getting the pics up.
You can use the old resistors, but new one with long leads work better. Once its done and tested, anchor the mod to the board with silicone for vibration control. Https://forums.fender.com/viewtopic.php?f=13&t=109897
I'm posting a new topic to leave BillM and put in a poll here.
Let me know how it worked.


Last edited by TimsAudio on Mon Mar 04, 2019 1:11 pm, edited 1 time in total.

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Post subject: Re: Tbv mod for HRDX, continued
Posted: Sun Mar 03, 2019 1:44 pm
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Joined: Fri Feb 05, 2010 4:31 am
Posts: 14045
Location: Province de Québec, Canada
TimAudio write ;
" You have to pull the board away from the chassis. If you don't know how to do that safely, stop reading and forward this to your qualified tech."

Good advise Tim

:lol:

It's a big headache this amp for a newbie who could damage the amp


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