Deluxe Tweed-Style Preamp Mod - Master Volume

[Jason A]

Hi,

New to the forum and I hope this type of question hasn't been answered a hundred times before. I've been searching past posts and haven't found anything. I have an early 70's Deluxe Reverb amp. I modified the normal channel per the Super Deluxe: Tweed-style Preamp mod in Aspen Pitman's Tube Amp Book. I already loved the sound of this amp and love the new sound that I'm getting out of the previously unused Normal channel.

My question concerns the new Master Volume control that I added as part of the tweed-style mod. (Both the treble and bass tone controls are swapped for 1M pots that become the new tone and master volume control.) When the master volume is dimed the amp sounds great, but as soon as I try to adjust the master down, it sounds like I just threw a blanket over the amp... I lose all my high frequencies. It essentially makes the master volume useless, as I lose all the 'crunch' and treble.

Is there anything I can do to modify the master volume so that I don't lose all the treble? Or is this just indicative of master volumes (I haven't yet owned another amp that has had a master). I triple checked all my wiring and connections, but does it sound like maybe I missed something while doing the mod?

Thanks for any and all help,
Jason

[Bruce / Mission Amps]

Draw up a little schematic of what you have done.
Assuming you have not added an additional preamp section, or are trying to run the normal channel back into the vibrato channel for two extra gain stages, a dual gang MV after the Phase Inverter is the only way to really get the standard black face Fender preamp to work as a mild to moderately heavy distortion MV preamp.
I've done many many mild to wild mods on black face and silver face amps and, around here am known as the Fender go to guy.... trust me on this, move the MV to after the Phase Inverter and use a dual gang 500K to 1M pot.

[Jason A]

Thanks Bruce,

I'll send you a sketch or scan of the changes I made tomorrow.

Jason

[rf7]

I've done that Tweed mod and the Master Volume interacts with the tone control, that's your problem. Adding the Master Volume also cuts the volume down out of that channel, compared to the other channel. I ended up changing the tone control to a treble boost control to try and counteract that issue. Bruce's suggestions may work out better for you, I thought that Tweed mod was not the greatest idea out there, as you may have discovered.

[jbever]

Hi Bruce, Jerry here in Alaska. Your 5E3 that I built is still my favorite!

I have a late 70's Vibrolux blackfaced that I was wanting to do a tweed mod on the normal channel. Do you have a layout for the mod that a person could buy?

Thanks and hope all is well,
Jerry

[Bruce / Mission Amps]

Hi Bruce, Jerry here in Alaska. Your 5E3 that I built is still my favorite!

I have a late 70's Vibrolux blackfaced that I was wanting to do a tweed mod on the normal channel. Do you have a layout for the mod that a person could buy?

Thanks and hope all is well,
Jerry

No Jerry, I don't sell anything like that.
Things are better... pretty tough last 30 days though and I have the "move" about 95% done but I'm still waiting for the phone system to come back on line.... they say maybe Friday here. I just don't understand why it is so hard to have a phone number ported over to a new location.

If you want to make your amp sound a little more small bore tweedy at high power/volume, use a 1m audio pot with a push pull DPDT switch on it in place of the 1m volume pot.
Use half the DPDT switch to dump about one third to half the raw signal from the plate (use a .1uF cap to isolate the B+) to ground and the other half to bypass about 80% of the tone stack with .0022uF to .015uF coupling cap around the stock tone stack's 250pF treble cap.
I know it sounds like an odd mod but try it with different value caps and resistor divider on the attenuating side of the DPDT until it turns your crank. After this you won't really care if it sounds just like a tweed amp or not...
you'll be trying to figure out how to switch it with a remote pedal.

[jbever]

Bruce, thanks for the info. I'll see if I can get my arms around this and try it. Phones ... don't even get me started. They can't port easily because you're most likely switching carriers and they're just so accomodating when you do this! ... See you got me started! Hope things get back to normal for you and you get a chance to enjoy your holidays. Did I mention I love my Mission 5E3 tweed amp!! Take care,
Jerry

[Bruce / Mission Amps]

Bruce, thanks for the info. I'll see if I can get my arms around this and try it. Phones ... don't even get me started. They can't port easily because you're most likely switching carriers and they're just so accomodating when you do this! ...
Jerry

Yes exactly... I want to move from them to my VOIP Comcast line which is FREE!!!...The Qwest folks now tell me they will not release my current number but it will be available at the end of June, 2008! A**holes every one of them.
My secondary line still works fine... 303-593-1665
that probably will be the new Mission Amps phone number for a long while.
**********************************************
I had Qwest come out today and install a third line using the 303-423-4103 number.
I'm still going to cancel this as soon as I notice people are using the new 303-593-1665 number.
Sick of these Qwest crooks anyhow

[Jason A]

Draw up a little schematic of what you have done.
Assuming you have not added an additional preamp section, or are trying to run the normal channel back into the vibrato channel for two extra gain stages, a dual gang MV after the Phase Inverter is the only way to really get the standard black face Fender preamp to work as a mild to moderately heavy distortion MV preamp.
I've done many many mild to wild mods on black face and silver face amps and, around here am known as the Fender go to guy.... trust me on this, move the MV to after the Phase Inverter and use a dual gang 500K to 1M pot.

Bruce,

After having reviewed the layout of the mod that I did, would your suggestion above, concerning the dual gang MV still be the way to go?
Thanks,
Jason

[Bruce / Mission Amps]

Bruce,

After having reviewed the layout of the mod that I did, would your suggestion above, concerning the dual gang MV still be the way to go?
Thanks,
Jason

If you have no other preamp gain stages then yes, because it allows the gain stage mixer in front of the driver to be run full out all the time and then the PI will also be over driven with the standard volume control while you turn the MV pots down to keep the power tubes from being hit with too high of signal swing.
If you do this dual gang MV mod I'd also reduce the bass response a bit with smaller cathode bypass caps (2.2uF to 4.7uF).

[JoeM]

If you want to make your amp sound a little more small bore tweedy at high power/volume, use a 1m audio pot with a push pull DPDT switch on it in place of the 1m volume pot.
Use half the DPDT switch to dump about one third to half the raw signal from the plate (use a .1uF cap to isolate the B+) to ground and the other half to bypass about 80% of the tone stack with .0022uF to .015uF coupling cap around the stock tone stack's 250pF treble cap.

Bruce,

When you say "the raw signal from the plate", are you referring to the first stage (that drives the tone stack) or the second stage? (sorry for my confusion)

[Bruce / Mission Amps]

Bruce,

When you say "the raw signal from the plate", are you referring to the first stage (that drives the tone stack) or the second stage? (sorry for my confusion)

Yes, right off the plate.... as it goes to the treble cap and the 100K slope resistor.
That is where I put the new, secondary DC blocking capacitor on it's way to the DPDT switch.

[JoeM]

OK, that clarifies it for me, thanks Bruce.

[Jason A]

I've done that Tweed mod and the Master Volume interacts with the tone control, that's your problem. Adding the Master Volume also cuts the volume down out of that channel, compared to the other channel. I ended up changing the tone control to a treble boost control to try and counteract that issue. Bruce's suggestions may work out better for you, I thought that Tweed mod was not the greatest idea out there, as you may have discovered.

I don't have the problem you mention with the volume being cut down compared to the other channel. In fact, it's louder across the board if I set each channels volume to the same level... and the modified channel has a lot more gain (that's with the Master Volume all the way up). The only complaint I have with it is when turning the MV down. Thanks for the info, though.