Master Volume for Hoffman 5e3 based on Sluckey's

[waldner]

I am trying to add a master volume to my 5e3 and came across this method from Sluckey so I tried to apply it to the Hoffman 5e3 layout.  Can anyone tell me if this will work?  Also, if you turn the master all the way up is it essentially gone, or could you use a no load 1 Meg pot to be back to stock?

The first pic is my attempt to draw it into the Hoffman layout, which is based upon Sluckey's layout in the 2nd pic.

Thanks

[sluckey]

That won't work. In fact, it's dangerous and will likely burn up some components.

[Fresh_Start]

This is a bit off topic, but here's a post from Bruce Collins at Mission Amps disparaging the very idea of a master volume in a Tweed Deluxe:

http://archive.ampage.org/threads/4/gamt/237026/master_vol_mod_for_5e3-2.html

What's so funny is that I was searching for a schematic of the master volume kit Bruce sells now!

Here are two different approaches to a master volume for this circuit.  One is pre-phase inverter and the other is post-PI.

http://robrobinette.com/5e3_Modifications.htm#Add_Master_Volume

Ahhh, here's the drawing I was looking for - right here:
http://el34world.com/Forum/index.php?action=dlattach;topic=10243.0;attach=19862


Note that this is for a long-tailed pair phase inverter, not a cathodyne like the 5E3.

A long time ago, Geezer worked out an idea for master volume of a cathode biased amp which manipulated the power tube cathode RC filter(s). Sorry but I can't find that right now.

Cheers,

Chip

[waldner]

I figured it wouldn't be that easy.

Has anyone ever done a layout for master volume with the Hoffman 5e3? Or can anyone?

[MadMax]

If this is so you can overdrive the tubes but keep the amp at bedroom level volume, I've been really pleased with putting an L-pad attenuator between the amp and the speaker. You don't get the effects of pushing the speaker hard, but its still got sweet tube drive at moderate levels.

-MadMax- 

[kagliostro]

If you mean Master Volume (and not PPIMV)



May be this version with the MV pot connected to ground at the capacitor is better



---

Revise it

K

[mresistor]

I second using an attenuator rather than MV. I use one for getting a little grind out of my Princeton Reverb, and I like it a lot. Weber mini mass.

[TIMBO]

Hi guys, I'm a bit keen on this topic as I have a similar PI in the old amp I'm doing up.

[darryl]

Hi guys, I'm a bit keen on this topic as I have a similar PI in the old amp I'm doing up.

The circuit modification below should work. This mod places the master volume inside the negative feedback loop, but that is a limitation of most retro-fitted master volumes.

You may also need a grid stopper resistor on pin 2 of the phase inverter - anywhere from 47k to 470k would work fine, as there is no Miller capacitance in a cathodyne phase inverter.

[waldner]

Sounds like an attenuator may be a better sounding and easier solution.  Now I'm looking at getting something like a weber MASS or mini MASS.  Plus then I can use it with other amps. 

[Fresh_Start]

Hi guys, I'm a bit keen on this topic as I have a similar PI in the old amp I'm doing up.

The circuit modification below should work. This mod places the master volume inside the negative feedback loop, but that is a limitation of most retro-fitted master volumes.

You may also need a grid stopper resistor on pin 2 of the phase inverter - anywhere from 47k to 470k would work fine, as there is no Miller capacitance in a cathodyne phase inverter.

Respectfully, I think that this modification stays closer to the original circuit for TIMBO.  Modify treble bleed capacitor to taste.  A larger grid stopper moves you further away from the stock circuit when the MV is full up.

Cheers,

Chip

[waldner]

Well I found a deal on a used Weber Mini Mass and it works quite well.  You loose a little of the magic, but not a ton.  The best results come from bringing back some of the lost treble with the +3 or +6 switch and keeping the volume on the higher side.

Which gets me to my next stupid question:  I'd like to put a negative feedback loop in to my Hoffman 5e3 with a switch to be able to make it go away.  I know that you are taking a wire from the output transformer where it connects to the speaker output tip, but where do you run that to and what resistor value might be a good starting point to try.

It would be great if someone could point it out on Doug's layout.

Thanks again.

[sluckey]

This will add the NFB circuit from the Princeton Reverb. If the amp squeals or makes nasty sounds you will have to reverse the OT plate leads.

[waldner]

Thanks man.  Just to make sure I've got it from the schematic I've drawn it into the layout minus the switch.  Is this correct?

[sluckey]

No, that's not right.

You will need to unsolder that 22/50v cap and 1.5k resistor from the bottom terminal. Stand these two components up. Now solder a 47Ω in the terminal that you just removed the cap/resistor. Stand this resistor up also. Now solder all three of the free ends of the 22µF, 1.5k, and 47Ω together, leaving them standing up like a teepee. Finally, solder a 2.7k to the top of the teepee and solder a wire to the dangling end of the 2.7k. Connect the other end of this wire to the tip of the speaker jack.

There's a much neater way to do this if you can add two turrets to the board.

[waldner]

Ok, .... I'm getting it-- I think. 

Is this more like it?

[sluckey]

That's it.

[waldner]

Cool.   I should have seen that the turret that the 22uf and 1.5k connect to on the original layout at the bottom of the board are ground because they are tied to the dashed blue wire (under circuit board) which is tied to ground at the input jacks.  Sorry, just trying to learn by thinking out loud here. 

So to make this switchable, the schematic shows a basic spst switch on the 2.7k resistor, but wouldn't that leave the 47 ohm resistor still in the circuit?  What is the best way do a switch?

[sluckey]

Do it like I drew it. Don't worry about the 47Ω.

[morton]

Hate to bring back a year old post, but i'd been looking for a nfb mod for the 5e3 and came across this one. Installed in a standard 5e3 build with the 2.7k on a switch. Doesn't seem to have much effect, wondered if there was an alternate modification or maybe a resistor change would help?

Thanks,
Gary

[mayburyds]

This worked for me -


https://robrobinette.com/5e3_Modifications.htm#Switched_Negative_Feedback


Cheers.

[kagliostro]

..... maybe a resistor change would help?

if you have all the connection on the right place but you have not enough NFB you can try to lower the resistor value

as a try you can put there a 4.7K pot (instead of the 2.7k resistor) connected as a rehostat and turn it till you are satisfied

then measure it and put a correspondent resistor on the circuit in substitution of the pot or use a trimmer, set it and forget

Franco