Questions about some mods to my Hot Rod Deville

[AlNewman]

Hi folks,

First time posting here, I've been creeping the forums for the last while soaking up all the info I can.  Everybody here seems very helpful and knowledgeable, with minimal BS, it's refreshing to see that these days on the interwebs.

https://el34world.com/charts/Schematics/files/Fender/Fender_hotrod_deville.pdf

I'd really like to make some improvements to my Deville, I have a few things in mind, but I'd like to bounce some ideas around and see what kind of feedback I can get and what other ideas are out there.  Like most people, I love the clean channel, it is the 410 with Jensen p10r speakers, and absolutely sings without the extra drive stage.  Unfortunately, it has that bee in a tin can sound, the channels and especially the boost really don't work well together volume and tone wise, and I'd like make everything a little more synchronous.

So here's what I have in mind...

I'd like to do the twin stack conversion.  Pretty straightforward, bridge the wiper on the mids pot, but I'm not really sure what the 220k r105 really does in this circuit?  I'm pretty sure I'm going to snip it out, but I'm kinda curious what purpose it serves.

I think I'm going to change the value of the V1A bypass cap to a 22uf from a 47uf.  This amp seems to get some really nasty low end distortion when it's pushed, I'm hoping this helps that some, although I can't really experiment in circuit.

C23 V1A drive channel coupler from 1.5nf-0.22uf.  Was able to test this, really fattened up the tone.
I might raise the value of R52 to match R9 just so there is a little more room on the drive knob before it gets too saturated.

I'm going to change the value of C8 cathode bypass on V2A from 1uf to 22uf, and jumper R23, so it's always on rather than have it pass through the more drive switch.  The amp will break up a bit sooner on the clean channel, and there also won't be such a huge increase between the drive and more drive.  This seems to push the bottom end a little too hard, so I'll also lower C2 coupler from .047 to .022.  I can't really test that coupling cap in circuit, but I have a bass eq pedal, and was able to sort of dial out the harsh frequencies.  I'll likely also increase R22 to 130k so it matches R18...Although, maybe a bit of a treble boost isn't a bad Idea on the drive channel?  I'd like to keep the eqs pretty close.

That's kind of where I'm at as far as things I'm fairly certain of, but I do have some questions as well...

Would you reccomend removing the treble bleed circuits at C3 and C11? C3 I kind of understandalthough it is a pretty large value on that 1 meg resistor in the clean channel, but the one that bridges the master volume doesn't make any sense to me.  Seems like it would change frequency response as the volume changes.  As well as the coupling cap, for that matter.  Maybe somebody could explain that?  Any suggestions on possible changes if neccessary?

Also there seems like a lot of loops to ground that I don't really understand in the drive channel, like what is the purpose of R42 and R19?

Anyhow, so far that's about all I could come up with.  I'd love to hear any more suggestions or experiences with this amp, so I can make a game plan before I open it up. 

Thanks for reading.

[sluckey]

Sounds like you already have a plan. Heat up the iron and have some fun. Let us know how it goes.

[AlNewman]

I hope so!  Maybe it'll work out 1st try....  I did some work on my blues junior and it turned out really good, but I had to open it up twice to do some final tweaks.  Kinda sucks with the pcb, but keeps me outta trouble, I guess.

[dude]

Try one mod at a time, play, add another if you can… circuit boards can be challenging. 

[AlNewman]

Easier said then done, initially all I was going to do was the tone stack, and I figured....well....since I'm going to have it apart anyways....
I'm still trying different things before I pull the board off, and getting some good results.  Might be a while yet before I'm done chasing rabbits down holes.

[pdf64]

R105 limits the max bass setting. Kinda equivalent to using a 100k pot with a 30% taper.

[AlNewman]

R105 limits the max bass setting. Kinda equivalent to using a 100k pot with a 30% taper.

Ok.  When I jumped it, it pretty much removed all bass in the signal.  I put another 220k in parallel, and it didn't really change the tone much...  I wonder what it will do after I ground the mids pot?  Just wondering if I should leave it in or not...? 

[pdf64]

… When I jumped it, it pretty much removed all bass in the signal. 

That’s because shorting the bass and mid pots effectively sets them to 0.

I put another 220k in parallel, and it didn't really change the tone much...

It just limits the max bass available a little.

  I wonder what it will do after I ground the mids pot?  Just wondering if I should leave it in or not...?

Have a play with http://www.guitarscience.net/tsc/fender.htm#RIN=38k&R1=100k&RT=250k&RB=250k&RM=10k&RL=1M&C1=250p&C2=100n&C3=47n&RB_pot=LogA&RM_pot=Linear&RT_pot=LogA
Compare the mid pot of the ‘treble-mid-bass TMB’ and ‘Bassman 5F6-A’ options in the Fender tab.

[AlNewman]

Thanks, pdf64!

I did realize later the mistake I made grounding out the signal.  Lol.  Luckily before I started tearing things apart.  That looks like a great link, it'll be bookmarked for sure.  I left that resistor in place for now.

I did most of what I mentioned, just tweaked some of the values, and changed up switching on the bright channel, and the cathode bypass which is driven from there.  Turned it more into a mid boost, and made it so it also stays engaged with the drive channel.  It sounds really good now, not harsh at all, but I think I can still shape it a little more.  The drive channel turned out amazing, and works well with the clean, so I don't need to change the eq when I switch  channels.  The more drive is more better, still needs a bit of a tweak, but at least it's usable now. 

I'm going to play it for a few days, figure out what else I'd like out of it.  I ordered a few things, when they get here I'll pull it apart again and finish it off for good till the next time.  Lol. 

[AlNewman]

Hi again, and merry Christmas.

So I've been making progress on my amp, and it's getting the tones that I want, but I started having issues with blocking distortion when I changed the tone stack.  It was the only thing I changed in the clean channel, so I'm guessing I changed the load on V1b, which created my problem.

I bridged the mid pot to ground, removed r105, and changed the mid cap to .033 uf.

I traced the signal and found issues at V1b, so i reduced the cathode bypass cap in V1a to 1uf, and reduced R9 before the volume pot to 180k, and increased the grid stopper R41 to 82k.  This solved my problem up to the plate of V2a, where I have some blocking distortion still, though not nearly as much, it starts lightly at about halfway on the volume.

So I'm wondering if I could get some advice on the best way to solve this problem at this point?  Would setting the bias differently have an effect, or mainly just increasing the grid stop resistor?

Also, I'd like to allow more swing in my drive channel pot, so I'm thinking of maybe increasing the cathode resistor and changing the bias in v2b so it breaks up at higher volumes?  Or is there something different I can do at the voltage divider to clean it up a bit? 

[JPK]

I'd experiment with larger grid stopper resistors. I had a blocking distortion issue on a recent build and the amp tech that helped me with it used 220k. Mine also only occurred at half volume and higher on clean channel. He said he tried a 320k but noticed signal loss putting it on a temp switch. Not the same amp but solution might apply.

[AlNewman]

Thanks JPK.  Actually 220k worked just about perfect.  I also played with the grid leak as well, so I got rid of almost all of the bad mojo.  I might play with the impedence at the jack a bit to try to filter the rest out.  It sounds fricken awesome, mission accomplished.

[bbmade]

I went down this rabbit hole a while back and found the book “How to Hot Rod Your Fender Amp” by Jeffrey Falla to be a solid source of information.

You might be well ahead of the game and not need it but, it helped me transform a Hot Rod Deluxe.

I was trying to make the overdrive less harsh and more pleasant.  To me, you can get the mild overdrive sounding “better” or the highest gain sounding “better” but not both.

Cleans on those are decent to my ear and then book helped get it a little better.

Enjoy the rabbit hole!

[AlNewman]

I went down this rabbit hole a while back and found the book “How to Hot Rod Your Fender Amp” by Jeffrey Falla to be a solid source of information.

You might be well ahead of the game and not need it but, it helped me transform a Hot Rod Deluxe.

I was trying to make the overdrive less harsh and more pleasant.  To me, you can get the mild overdrive sounding “better” or the highest gain sounding “better” but not both.

Cleans on those are decent to my ear and then book helped get it a little better.

Enjoy the rabbit hole!

There are certainly plenty of options with their circuit, lots of handy switching and definitely enough tubes.  I think the 400v plate voltage makes things a little tricky to piece it all together, but i did manage to get a nice clean channel to full volume.  It starts to break up at 12 oclock or so, so definitely high enough to start pushing the output if I ever turn it up that high without a volume pot in the effects loop.

I'm really happy with both gain stages, I have good travel on the pot, so I can get some nice low gain up to about 3 on the dial, and then by noon, it gets pretty hairy.  Full gain is still more than enough.  More drive is actually pretty cool now too, I removed the bypass cap on v1a, so it only operates the second bypass cap, and then lowered the value of the cap to make more of a treble/solo boost with the more drive switch engaged.  And it's still a subdued enough gain that it can be more of a vintage sound at lower volumes, but when it's cranked up it's a really nice full distortion, especially with the bright switch (mid boost) engaged.  It has really nice response and versatility now.  I'm super happy.

I may record some sound bytes and post them, but I'm not too technically savvy or well equipped.

[AlNewman]

So I have a video with a demo here:

Sorry about the poor playing, I just wanted to display some of the different options available in one take.

These are the modifications I made:

Bridge middle pot to ground.
Clip R105
Change R12 slope resistor to 100k from 130k
Change C6 mid cap to .033uf from .022uf

Change C1 cathode bypass to 1uf from 47uf
Change C4 cathode bypass to .68 from .068
Remove C8 cathode bypass cap v2a
Change C10 cathode bypass to .47uf from 22uf
Bypass R102
Add 1000pf cap between the ground leg of C1 and the downstream leg of R25
Remove C11

Change C23 to .022 from .0015
Change C10 to .022 from .047
Change R9 to 180k from 220k

Change R41 to 220k from 10k
Change R8 to 220k from 100k
Change R20 to 220k from 100k
Bridge C3 with 330k resistor
Bypass R27

Future considerations:

Reduce or remove value of C3 if possible
Slightly increase value of C1 to 2.2 or 5 uf if possible