pre amp blender

[Andy Le Blanc]

A happy mistake, I rigged a blend pot before an old fashioned volume and tone controls.
Its just a 1M log that swings between a cathode bias and a zero bias stage.
More like blending between "normal" and "brilliant" channels.

But you can hear the color changes between the two dissimilarly biased stages.

I figured I'd post the notion, it feels very usable, nothing new... but very easy
It expands tone options without obsessing about circuit values,
And without the losses of a TMB tone stack.

[marcoloco961]

A happy mistake, I rigged a blend pot before an old fashioned volume and tone controls.
Its just a 1M log that swings between a cathode bias and a zero bias stage.
More like blending between "normal" and "brilliant" channels.

But you can hear the color changes between the two dissimilarly biased stages.

I figured I'd post the notion, it feels very usable, nothing new... but very easy
It expands tone options without obsessing about circuit values,
And without the losses of a TMB tone stack.

Andy, would you mind drawing a quick schematic to illustrate? It sounds interesting, but I am having a hard time understanding exactly what you did.

[Andy Le Blanc]

It'll be a few days until I can post a scheme...

In short it simply a 1M pot between two coupling caps with the wiper as the
output to the top of a vol pot, both pre stages are in phase but the THD of either
is very apparent as you pan between the two, Its like the blend pot on an old fender verb.

Very simple, I was surprised at how effective it seems, one stage is cathode biased
and the other is the old zero bias or grid leak, with the cathode at ground potential
with a cap and large meg value resistor on the grid, old style.

[echuta13]

Not sure if this is similar, but this thread comes to mind: http://music-electronics-forum.com/t19358/ (seems to be in the same vein at least).

[Andy Le Blanc]

Similar, I tried those, not as responsive as I hoped . It really is just like
an old fender add on reverb, the mixer at the output... model "6G15"
simple , just hadn't tried it as a pre amp mixer...

[Richie]

Dana built an amp called the switchblade, and it had a preamp blend control. Kind of like your stereo balance. Or maybe think of how working volume controls on a LP with switch in center position..

One side was was a octal pentode, and the other was a 12AX7 I think if i remember it went into a single ended 35watt OT . You could use either, or bring in whichever channel you wanted or both. you could blend them together. Might be some clips on here of it somewhere.

[John_P_WI]

The first I saw something like this was back in '93 when I built John McIntyre's bluesmaker. The "pre amp" balance worked well.

Good sounding amp with a few tweaks and if you had a large enough room to open it up.

Of course today the popular MV's and VVR / power scaling would go a long way to making more useable.

John

[Drumslinger]

Andy,

Sounds interesting. I'll have to give it a try.

[Andy Le Blanc]

I hadn't seen Dana's rig, lol... but it sounds the same.
Its nice to utilize both sides of a twin triode, voice one bright, one dark.
Try two different gain stages, two tube types etc... on one knob.
One of the Standel schematics that looked authentic had one side of a 12ax7
on its own gain pot before the amps volume knob, get a fractional gain
control out of the pre. As long as everything is in phase its pretty simple.

[Andy Le Blanc]

Here's a quik scheme of what I rigged, pretty easy to dress P-P as well.
The input on the cathode biased stage is dress like the input of an old Ampeg.
The instrument sees a high impedance

[marcoloco961]

Here's a quik scheme of what I rigged, pretty easy to dress P-P as well.
The input on the cathode biased stage is dress like the input of an old Ampeg.
The instrument sees a high impedance

Thanks Andy, It helps me to see it on paper. That looks very interesting and I think I will give it a go on one of the future builds. Might be a nice addition for someone who plays several different model guitars in one evening.

[marcoloco961]

Here's a quik scheme of what I rigged, pretty easy to dress P-P as well.
The input on the cathode biased stage is dress like the input of an old Ampeg.
The instrument sees a high impedance

Thanks Andy, It helps me to see it on paper. That looks very interesting and I think I will give it a go on one of the future builds. Might be a nice addition for someone who plays several different model guitars in one evening.

[marcoloco961]

sorry double.

[Andy Le Blanc]

I tried several other blend approaches in the process. That one, for what
ever reason seemed the most effective. If you invest a little time into swapping
around the cap values and types you should be able to find an agreeable
tone blend. The pot. values and tapers can be to taste etc....
It did seem important that the two circuit types, whatever they are, need to
play well together. I landed upon the Ampeg dress with the input cap of the
leak bias, as opposed to the fender input dress, the high input impedance
helped both. The fender dress at the input jacks is too far away from the
socket pin for good P-P dress and lack of a grid stopper at the pin doesn't help either.