Express Low End

[strato17]

Can anyone point me in the direction of the Express low end tweaks? I have a francesca clone I built. While it sounds pretty amazing, the low end is a little lacking. I believe that some of the later express models(kelly?) had some different values. I know there is a thread somewhere, but my search skills are failing me.

Also, it seems that the eq controls do very little if anything to the sound. I suppose this is to be expected/normal?

Thanks!

[JazzGuitarGimp]

Hi,

The only Francesca schemo I was able to find is a version of Kelly that was modified by UR12 to be the same as Francesca. Don't know if you're working from this schematic or not. Here is the link to it:

[http://ampgarage.com/forum/viewtopic.ph ... +schematic]

Based on what I am seeing, I would start by increasing the value of the 0.022uF coupling cap at the grid of V2 (pin 2). If you get all the way up to 0.1uF and you still don't have enough low end, try also increasing the value of both the 0.022uF coupling caps at the grids of the output tubes. These two caps should always be the same value (don't mean to insult you - just don't know if you know this or not).

Cheers,
Lou

[Firestorm]

It's a funny circuit. Lou is right; the filter coupling the third stage attenuates lows; but changing that without throwing the baby out with the bathwater is hard. You need cap values that don't exist. The tonestack is another place to play: it's awfully like the 6G6 Fender stack (bass channel) that throws away all the lows in order to have more gain.

[Reeltarded]

Fixed res might do it for you. .0047 in series with the NFB wire to wherever it is now. You just turn the bass down a notch or two. Thumpy, no mud.

.0022 gets you more low mids and might be mud, but maybe not. Express has a bright face.

[jelle]

In addition to the fixed resonance circuitry that Reeltarded posted, a choke will also give more lows in that circuit. Another avenue to explore... Have fun!

[eazilyled]

Maybe the Ingrid mod where you use parallel caps in C8 (which ends up doubling the value to 0.0044uF) may give you the extra bass?

http://ampgarage.com/forum/viewtopic.php?t=18142
http://ampgarage.com/forum/viewtopic.ph ... a6f560f834
http://ampgarage.com/forum/viewtopic.php?t=18134

I've been meaning to try this myself.

[Reeltarded]

If you like the sound but it just lacks lowend, always try the fixed res first. Everything else changes other things along the way..

You might like those things though.

Uhoh.. let's address the tone controls not doing much when you change settings. Compared to what? Not as much as a BF Fender, and way more than a 70s MV Marshall is what you expect. No?

[Roe]

change the 25uf k cap on the second gainstage to a .68uf

[Tillydog]

...Based on what I am seeing, I would start by increasing the value of the 0.022uF coupling cap at the grid of V2 (pin 2).

Based on my experiences with a 4-4-0 which became an Express, that cap holds the key to the low end (it's C6 on the 'stock schematic').

It's down as 2n0, rather than 2n2. It is powerful medicine, and I think the difference is easily audible. I don't think that it's any coincidence that Expresses have been found with parallelled caps here, because I think that you may well need "cap values that don't exist". I experimented with 1n0 in parallel with various other cap values. I don't recall what I have there now (doesn't really matter!) - maybe 1n0 and 820p ?? You would need to go the other way. 3n2 on the original 4-4-0 schematic (1n0 + 2n2) gave waaaay too much bass for me in Express form. The truth lies somewhere in between!

Andy

[Jackie Treehorn]

Change the phase inverter tail/bias resistor from 10k/470 to 39k/1krespectively. Lots of quality bass with that change even with .002 cap on the third stage.

[Colossal]

Strato,

Some non circuit related things that affect the apparent low end with the Express is the choice of preamp tubes. It is surprising the amount of variation in tone and the individual qualities of low, mid, and high end that each tube can bring. One thing I have kept coming back to get a little more beef to the Express sound is using a balanced, high gain 12AX7 in the PI position. Anything less, just seems a bit colder, not worse, but just lacks the added warmth I can tell the power tubes being pushed just slightly harder bring (I am using a PPIMV too), it makes a difference. So I keep coming back to a hotter 12AX7 there. Although I really like the gain and overall sound of the JJ Gold Pin 12AX7 there, I am a bit at odds with it because there is a hard roundness to the edge which I don't really care for.

Pickups make a significant difference to my ear. The amp is a chameleon. I have experimented with a a lot of value changes in the circuit in a lot of positions (just so I could truly understand it and test all these ideas out) and I keep coming back to the stock values; it's quite amazing. One thing I will say is that I do have a Presonance control, Cut, and PPIMV in an Express circuit and they work very, very well together and give the amp a lot of flexibility to truly dial in the power amp response. However, I should say that I very much prefer the sound of an Express when the grid leak values are <220k (Gain at 1 o'clock). It has an absolutely awesome slightly more modern sounding crunch when the the PI is a bit loaded but that's just my thing.

All I mean in blathering on about all this is that (if you haven't already) try a few tube change outs. I'm using 3 different 12AX7s presently to get a tone that does it for me. I really got a much smoother and deeper sound after some tube rolling.

If that doesn't do it for you, bump C8 up and consider Roe's suggestion of tightening up the stage to 0.68uF since you will be pushing more low end through to V2a making the coupling cap larger. You want to keep any added low end tight, not letting it get mushy and woofy.

Finally, as a lot of guys have said, technique really plays into it with these amps. I now play very light gauge strings to get a very fat sound and I concentrate on being very delicate and letting the amp do the work. It's a constant work in progress. When my technique is on, the sound is very elastic with a lot of low end, just magical. Treble in = treble out so pickups make a difference too! Check your pickup height.

EDIT.

p.s. what transformers did you use for your Francesca clone? Also, my EQ seems to be quite sensitive. Maybe a wiring issue or a pot taper issue?

[Colossal]

Change the phase inverter tail/bias resistor from 10k/470 to 39k/1krespectively. Lots of quality bass with that change even with .002 cap on the third stage.

JT,

How do you find the fizz associated with 1k/39k and do you run the gain up but attenuate? Reason I ask is that I've tried:

1k/39k
820R/22k
470R/22k
470R/12k

and of course the stock values of 470R/10k.

I use a PPIMV at a max of about 10am to 12noon-ish to get the crunch I like (as well as some volume control) so those PI values will interact with those preferred PPIMV settings. I really liked 470R/12k. That seemed perfect. I gave the Dumbly 820R/22k a try and while I like it in some high gain amps, it did not work for me in the Express circuit. I did love 1k/39k in the Liverpool with an Express tonestack. Monstrous sound.

[strato17]

Thanks for all the help everyone! Will definitely be looking into some of these.

Strato,

Some non circuit related things that affect the apparent low end with the Express is the choice of preamp tubes. It is surprising the amount of variation in tone and the individual qualities of low, mid, and high end that each tube can bring. One thing I have kept coming back to get a little more beef to the Express sound is using a balanced, high gain 12AX7 in the PI position. Anything less, just seems a bit colder, not worse, but just lacks the added warmth I can tell the power tubes being pushed just slightly harder bring (I am using a PPIMV too), it makes a difference. So I keep coming back to a hotter 12AX7 there. Although I really like the gain and overall sound of the JJ Gold Pin 12AX7 there, I am a bit at odds with it because there is a hard roundness to the edge which I don't really care for.

Pickups make a significant difference to my ear. The amp is a chameleon. I have experimented with a a lot of value changes in the circuit in a lot of positions (just so I could truly understand it and test all these ideas out) and I keep coming back to the stock values; it's quite amazing. One thing I will say is that I do have a Presonance control, Cut, and PPIMV in an Express circuit and they work very, very well together and give the amp a lot of flexibility to truly dial in the power amp response. However, I should say that I very much prefer the sound of an Express when the grid leak values are <220k (Gain at 1 o'clock). It has an absolutely awesome slightly more modern sounding crunch when the the PI is a bit loaded but that's just my thing.

All I mean in blathering on about all this is that (if you haven't already) try a few tube change outs. I'm using 3 different 12AX7s presently to get a tone that does it for me. I really got a much smoother and deeper sound after some tube rolling.

If that doesn't do it for you, bump C8 up and consider Roe's suggestion of tightening up the stage to 0.68uF since you will be pushing more low end through to V2a making the coupling cap larger. You want to keep any added low end tight, not letting it get mushy and woofy.

Finally, as a lot of guys have said, technique really plays into it with these amps. I now play very light gauge strings to get a very fat sound and I concentrate on being very delicate and letting the amp do the work. It's a constant work in progress. When my technique is on, the sound is very elastic with a lot of low end, just magical. Treble in = treble out so pickups make a difference too! Check your pickup height.

EDIT.

p.s. what transformers did you use for your Francesca clone? Also, my EQ seems to be quite sensitive. Maybe a wiring issue or a pot taper issue?

I have a NOS Mullard 12AX7 in V1, V2 is a NOS Brimar, V3 is a balanced triode LPS. NOS Siemens EL34's. Maybe the Brimar is causing some unwanted low attenuation?

As for transformers, I have the Toneslut tranny's in this one.

[leadfootdriver]

You can just run a set of JJ KT77's. They have a ton of lowend.

[strato17]

Small Update:

I did the Ingrid mods, except for the parallel caps. I don't have a ceramic cap of that value, just another .0022 like that one that is already there. Perhaps it won't have the same effect as the ceramic on would?

The amp has definitely smoothed out with the additions of the two resistors on pin 2 and 7 of V1. I'm liking the sound. I still might try the parallel cap when I get a chance.

I went ahead and rechecked voltages which I had everything opened up. Does everything seem ok? Wall voltage is at 113, not 120.