AO-44 echo amp input question.

[Toxophilite]

I'm making a little echo amp in an A0-44
By echo amp I mean an amp I run the wet signal from my space into
I also like to have a little dry in the echo amp too to retain the 'size of the sound even when the echo is turned off
I take this 'dry signal from a lineout on my main dry amp
I'll include a schematic of my main dry amp (which at one point was a deluxe build and now is a vibrolux)
For the purposes of this question I'm only posting this to show where the lineout signal will come from


So I need two channels on my AO-44


I already have a fender AB763 style input and tone stack in the AO-44, it sounds good. I use this for the echo signal


I found that by taking the lineout signal from the main dry amp and running it into a 1/4 jack, into a 1 meg pot, then  a one of two 220k mixing resistors (the other resistor is on the echo channel right into the PI of the A0-44) I get a good level with the dry signal. It's good with the 1 meg pot maxed but it's good to be able to adjust it down if necessary.


So I have these two channels going into the AO-44 mixed together with two 220K resistors right at the PI


My question is:


Does the lineout signal coming from the dry amp (schematic) need anything on the 1/4" input of the AO-44, like a guitar input jack? for eg" fender 1 meg to ground and 34-68 k resistor


I guess the volume pot maxed is like a 1 meg to ground already

by the by these AO-44 amps are LOUD!! whew! very cool

[sluckey]

Show us a schematic. The schematic you posted looks nothing like the schematic for an AO-44.

[Toxophilite]

Okay
Maybe I wasn't clear. The schematic isn't of an A0-44.
It's of the amp I'll be taking a line out of to go into the PI of the AO-44


It's there to show the type of signal that I was putting into the AO-44 PI via a 1 meg pot and a 220k mixing resistor


i don't have time to redraw an AO-44 schematic this eve. I will make a diagram of what I'm doing.


All I'm looking to find out if if i need to do anything with the input on the AO-44 that accepts the lineout signal from the main dry amp.
As I said the schematic I posted shows the type of line out signal I will be sending to the AO-44

[sluckey]

I know what you want to do but it's not clear "where" you want to tap into the AO-44. V2 is the PI and you must use a coupling cap to connect to V2 pin 1 (grid). V1 is a gain stage just prior to the PI. You could connect the mixing resistors directly to V1 pin 1 (grid). And don't forget about Q1 gain stage.

I'm pretty familiar with the AO-44, but you mentioned it is modified and it's unclear to me exactly what you have done to it. So I would need to see some kind of drawing of your 'modified" AO-44 to really be specific. So, be more specific or make a drawing so I know exactly what you mean to do. What you call PI and what I call PI may not be the same.

[Toxophilite]

Fair enough

I got the unit working satisfactorily with my fumbling along
But I will try to do a schematic over the weekend regardless

With the AO-44 the PI and power amp were left as is, no modifications.  Much like your Peewee
I added another 9 pin socket, wired it up like an AB763 preamp tub and made a deluxe style tone stack . ( bass, treble, mid resistor to ground)
So the preamp is pure AB763 and then it connects to pin 1 of V1 via a .02 ceramic cap
(Which I mistakenly thought was part of the PI. Looking at the Ao-44 schematic it makes more sense now, thanks!)




Now, I have two 220k 'mixing' resistors attached to pin 1 of V1 and the .02 cap from the AB763 preamp is attached to one of them


The other 220k resistor goes to the wiper of a 1 meg pot
the top of which is hooked to tip of a 1/4 jack input jack via another .02 cap
(I'm not sure why i put a cap in there, it just seemed right, likely unnecessary,)
the bottom of the pot is of course grounded.


That's what I'm plugging my 'direct out' from my dry amp  into

it's actually working quite well

I will make a schematic too
I realize it's confusing to describe these things and my electronic vocabulary and understanding is patchy at best.

Apologies for an frustration caused

[sluckey]

No frustration. Now it's perfectly clear how you did this. I would have done it your way too.

In all fairness, since the cathodyne phase inverter only has a gain of one (actually a little bit less than one), many people consider that gain stage to be part of the phase inverter. I usually do too. But in this case, I wanted to be sure about exactly where you would be connecting the mix resistors since you must use a cap to connect to the grid of V2, since there is a healthy dc bias voltage present due to the bootstrap bias circuit. That bias voltage would be upset unless you provide a blocking capacitor. V1 grid operates with zero volts on the grid so it's fine to not use a blocking cap there.

So, what is the source for your 'echo' signal?

[Toxophilite]

Wow Thanks for the schematic!
I should've been cut and pasting


Echo is coming straight from the echo output of my Roland RE-150 Space echo


(It has separate outputs for direct and echo. Using both outputs separates the dry and wet signals , using just the direct combines them)


Generally I go straight from the Roland into an amp


I've had different variations of amps for 'echo' amps
Originally I used half of a practice PA


Always, the lineout from my amp(which I've copied from my super into my other amps) has always been a much hotter signal than the signal from the echo unit.
In this instance it works out well because I don't need extra preamp stage, though I did initially try mixing the two signals
at the stage of the 12AX7 immediately following the tones stack but that was too much.


Quite amazing how much volume this tiny amp has on tap.


A side question;
Would it be detrimental (as in too much B+) to give this unit a SS rectifier?
As usual, I'm not looking to overdrive it.

[Toxophilite]

Here it is in all it's tuny rough glory. Still have a few cosmetic things to do (like the rest of the mounting screws )


Built inside a little test speaker cabinet I made for fun ..that was built inside a vintage reel to reel case using a bit of old organ baffle for the ..baffle
Rough little thing but it has charm and sounds nice to.
Just running a little fender eminence 10" 30 watt speaker which is a nice sounding
Not tonnes of bottom out of the tiny cab but for this purpose that's okay
Cab is open on one side.
I'll probably adding a parallel output jack for plugging in one of my tiny leslies as an extension speaker for extra syrupy goodness

14" x 14" x 7" weights 13.2 lbs


If I wanted to use a SS rectifier (as I'm not looking for 'sag' compression or any of that stuff) should I add anything by way of filter caps or dropping resistors or can I just use put in the diodes on the underside of teh rectifier socket?