Plain AB763 vs. AA1164 with loop advice

[ViperDoc]

I want to build another Princeton, but with more power and an effects loop to allow for later time/space effect injection . I have a box of Metro loops, but the traditional spot for that is in-between the treble and volume pots which, in a blackface circuit, is right after the first gain stage and tone stack.

1) Is that a problem?

2) I’d likely delete the trem and possibly the onboard reverb and go full pedal platform. How different would the AB763 be from the AA1164?

Thanks as always.

[Reeltarded]

Ya know, the loop wants to be the last thing before the PI.. I am forever unsure about the Metro loop in many situations. It is a decent piece of engineering that on the one hand is/can hard to setup without destruction (and the results vary) but it might work great.

I am primarily a big amp guy, but if I had to pick a really fantastic little amp, the 80s PRII is insanely good. Maybe there are ideas in there for you?

Defeat the reverb on a Fender amp? Why own one!?? heh

[pdf64]

I can’t perceive the rationale for adding an fx loop to amps with rather linear, low gain preamps?
Surely their ‘reason for being’ is to be placed after overdrive preamps?
Putting one immediately prior to the cathodyne of an AA1164 would be inside its global NFB loop. I think that the NFB ratio is pretty low, so even with a complete flip of signal polarity, that may not cause problems per se, but nonetheless, it doesn’t seem a good idea.

[ViperDoc]

Ya know, the loop wants to be the last thing before the PI.. I am forever unsure about the Metro loop in many situations. It is a decent piece of engineering that on the one hand is/can hard to setup without destruction (and the results vary) but it might work great.

I am primarily a big amp guy, but if I had to pick a really fantastic little amp, the 80s PRII is insanely good. Maybe there are ideas in there for you?

Defeat the reverb on a Fender amp? Why own one!?? heh

I know, sacrilege. I don't use a ton of effects, but I do prefer time and space after the preamp if I can get it. The Princeton/DR Reverb mix point makes a loop difficult to place, although I have seen a few examples where the onboard reverb is mixed into the other leg of an LTPI. So there's that, which was mainly why I wondered if a loop was even possible with a Princeton. I don't want reverb first in the chain.

I just put a Metro loop in my 18-watt superlite and it sounds great, although it took a bit of adjustment and it does seem to take a *very very small bit* of high end. Maybe that's enough to make it a bad idea, maybe not.

[ViperDoc]

I can’t perceive the rationale for adding an fx loop to amps with rather linear, low gain preamps?
Surely their ‘reason for being’ is to be placed after overdrive preamps?
Putting one immediately prior to the cathodyne of an AA1164 would be inside its global NFB loop. I think that the NFB ratio is pretty low, so even with a complete flip of signal polarity, that may not cause problems per se, but nonetheless, it doesn’t seem a good idea.

Exactly, and yes, I'm looking for a way to allow for better front-end overdrive without feeding delay into the front end. I was also interested because Two Rock seems to have it figured out, as well as Howard Dumble, although I don't have any experience with his circuits. I recall he uses a "preamp out" into a rack impedance matcher/effects loop and then back into the power section.

[didit]

... if I had to pick a really fantastic little amp, the 80s PRII is insanely good. Maybe there are ideas in there for you?

Defeat the reverb on a Fender amp? Why own one!?? heh

An '80s PR II essential bones are single channel AB763 DR derived with various tweaks. Not had patience to fully follow all the details in that "lead" circuit. Fiddling with it's basic formula seems cool. Ridding it of reverb and then adding a loop is a tight rope, with knots.

Best .. Ian

[pdf64]

I can’t perceive the rationale for adding an fx loop to amps with rather linear, low gain preamps?
Surely their ‘reason for being’ is to be placed after overdrive preamps?
Putting one immediately prior to the cathodyne of an AA1164 would be inside its global NFB loop. I think that the NFB ratio is pretty low, so even with a complete flip of signal polarity, that may not cause problems per se, but nonetheless, it doesn’t seem a good idea.

Exactly, and yes, I'm looking for a way to allow for better front-end overdrive without feeding delay into the front end. I was also interested because Two Rock seems to have it figured out, as well as Howard Dumble, although I don't have any experience with his circuits. I recall he uses a "preamp out" into a rack impedance matcher/effects loop and then back into the power section.

In the absence of adding further cascading preamp stages and a master volume, how do you envisage achieving 'front end overdrive' in a PR AA1164? Look at the typical signal VAC (in the ovals) on the RI schematic https://el34world.com/charts/Schematics ... e/Loop.pdf
Please provide further info about the Two Rock and Dumble models you're thinking of.
Note that as it has a 250k pot feeding its 'send' jack, the Dumblator / Dumble Loop should not be considered to have a low impedance send circuit https://el34world.com/charts/Schematics ... e/Loop.pdf
Hence it should not be thought of as being intended as a 'transparent' loop, rather it may best be thought of as an effect in itself. Its bright switch should provide a strong indication of that.

[ViperDoc]

In the absence of adding further cascading preamp stages and a master volume, how do you envisage achieving 'front end overdrive' in a PR AA1164?

Right. In the rare event I can crank the volume, then. But mostly with overdrive pedals. It is much easier--and perhaps the only sane option--to run delay post overdrive into the input.

Please provide further info about the Two Rock and Dumble models you're thinking of.

How reliable are the Ceriatone files? I can only usually find clone schematics.

Note that as it has a 250k pot feeding its 'send' jack, the Dumblator / Dumble Loop should not be considered to have a low impedance send circuit https://el34world.com/charts/Schematics ... e/Loop.pdf
Hence it should not be thought of as being intended as a 'transparent' loop, rather it may best be thought of as an effect in itself. Its bright switch should provide a strong indication of that.

Very good point. Thanks for all of the above.

[pdf64]

In the absence of adding further cascading preamp stages and a master volume, how do you envisage achieving 'front end overdrive' in a PR AA1164?

Right. In the rare event I can crank the volume, then...

Consider that even with the volume cranked, the PRRI schematic shows that there will be very little gain between the input jack and the 2nd stage grid.
For almost any non-master volume amp, cranking the volume will result in the output valve grid being (as signal level rises from 0VAC) the earliest point of clipping in the signal chain, and for that amp, the depth and degree of clipping will be most intense there too.
With BF / SF reverb preamps, the next point to clip is typically the reverb driver valve's grid. Then the 3rd stage grid, and then the 2nd stage grid.
So even with a transparent fx inserted at the output of the 2nd stage, the degree of overdrive there is likely to be a small fraction of that at the 6V6 grids.

Please provide further info about the Two Rock and Dumble models you're thinking of.

How reliable are the Ceriatone files? I can only usually find clone schematics.

Sorry but I've no idea
My suspicion is that if an amp has a (transparent) fx loop but has low preamp gain and no master vol, then the loop is there purely as a vanity feature, to assuage the marketing dept / the users who will not accept an amp that doesn't have an fx loop.
Kinda akin to a standby switch; they're included because it's less mither to do so than to omit it and then spend forever explaining why it's pointless, to potential customers who flat out will not buy an amp without one.
Crudely put, the probable scenario may be characterised as 'more features = more sales and less time wasted', regardless of how pointless some of those features might be.

[ViperDoc]

All very good, I'd like to study up on the gain stage order in those other amps before deciding how seriously to pursue this issue. I've got a Deluxe Reverb, Super Reverb and a Tweed Super in the lineup before this. Likely the Tweed Super next...and no, I won't be putting a loop in that one.

[Reeltarded]

how about make the amp you want and a resistive load with a line out.. I like effects after everything and its easy to eat a sub 50w amp with 5 parts minus the wire lol

If you are going to build amps in the future, making a dead-load that can eat 400w with impedance switching can be a good idea, and a simple line level out with a level knob means you can drive effects after amp and playback through anything with audio inputs..

the audio inputs might be the hardest thing these days.. do not ask me about USB3 pinout i will bluetooth you to the moon and wifi mountains into the sea

[ViperDoc]

how about make the amp you want and a resistive load with a line out.. I like effects after everything and its easy to eat a sub 50w amp with 5 parts minus the wire lol

Tell me more...

[Reeltarded]

I edited while thinking about it read the last message again..

my big rig is three 50-100 watt amps on Palmer 04 rack loads and XLR out to a mixer with inserts for the effects and amps are channelized into a 2200w power amp with a pair or a quad of 4x12s.. you can do it without the mixer and just insert effects between the load and the power.

You need

a big resistor

one pot

one cap

a small resistor

a box to mount it

two jacks

a small length of wire

[ViperDoc]

That sounds divine. The other guitarist in my band would love that, I’m sure...

“What do you mean you can’t hear the drummer???? WHAAATTT???!!!! Who’s talking to me???!!!!”

[Reeltarded]

it is an effective way to maintain control and it even sounds like the radio at a volume you can drown out by thinking or breathing