Express in single ended format?

[geoffrod]

Is it posible to create the express feel in a single ended format?
or because of the lack of a PI does it loose something???
I understand that getting a single ended amp to be an express is not going to happen, but surely the touch sensitivity and response can be somewhat replicated???
cheers
Geoff

BTW, this is a great forum with loads of great info.

[Cliff Schecht]

You'll want to create a fourth stage before the power stage that matches the gain of one of the PI tubes, otherwise you'll lose some of the gain in the circuit. I think doubling the 470 Ohm cathode resistor and maybe scaling a few other parts accordingly would do the trick but you'll lose the sound of the power stage, that is you'll be getting a lot of third order harmonics and not a lot of second order unless you can figure out a way to make the power stage clip asymmetrically.

[dartanion]

My Absinthe is an Express style preamp, retains the PI, and uses a parallel single ended output section. It can be done, but it's a different beast altogether. Way more aggressive and raunchy and still quite loud.

Retaining the whole PI was done to ensure that the characteristics of the PI remained in the amp.

However, you can emulate the gain from the PI using a single gain stage as Cliff mentioned.

[geoffrod]

My Absinthe is an Express style preamp, retains the PI, and uses a parallel single ended output section. It can be done, but it's a different beast altogether. Way more aggressive and raunchy and still quite loud.

Retaining the whole PI was done to ensure that the characteristics of the PI remained in the amp.

However, you can emulate the gain from the PI using a single gain stage as Cliff mentioned.

Firstly, thanks for the reply,
is there any reference material to your build ? and sound clips might be nice too.

cheers
geoff

[dartanion]

My Absinthe is an Express style preamp, retains the PI, and uses a parallel single ended output section. It can be done, but it's a different beast altogether. Way more aggressive and raunchy and still quite loud.

Retaining the whole PI was done to ensure that the characteristics of the PI remained in the amp.

However, you can emulate the gain from the PI using a single gain stage as Cliff mentioned.

Firstly, thanks for the reply,
is there any reference material to your build ? and sound clips might be nice too.

cheers
geoff

Hey Geoff,

Here's a video of an Absinthe from this past summer:

http://www.youtube.com/watch?v=7T3itawwRe0

It's not the greatest recording, but it gives you an idea. This guy wasn't hit it very hard with his tele, more so trying to keep it on the edge of break-up. I will be doing a bunch of video this weekend during the Austin Amp Show that will have better audio quality.

There is no reference material for the build as it is part of my production amp line. The idea is simple though. You feed the output section from only one side of the PI. You may have to use a heater elevation circuit to reduce hum, but it's otherwise pretty straight forward.

[geoffrod]

My Absinthe is an Express style preamp, retains the PI, and uses a parallel single ended output section. It can be done, but it's a different beast altogether. Way more aggressive and raunchy and still quite loud.

Retaining the whole PI was done to ensure that the characteristics of the PI remained in the amp.

However, you can emulate the gain from the PI using a single gain stage as Cliff mentioned.

Firstly, thanks for the reply,
is there any reference material to your build ? and sound clips might be nice too.



cheers
geoff

Hey Geoff,

Here's a video of an Absinthe from this past summer:

http://www.youtube.com/watch?v=7T3itawwRe0

It's not the greatest recording, but it gives you an idea. This guy wasn't hit it very hard with his tele, more so trying to keep it on the edge of break-up. I will be doing a bunch of video this weekend during the Austin Amp Show that will have better audio quality.

There is no reference material for the build as it is part of my production amp line. The idea is simple though. You feed the output section from only one side of the PI. You may have to use a heater elevation circuit to reduce hum, but it's otherwise pretty straight forward.

Dartanion,
thanks again for the reply, i have since read a few post and worked out it is one of your production amps, sorry for being rude thru my ignorance.
edit due to dohness

I took an interesting angle on SE that was suggested by a few well know ampoholics. I wanted to retain the Wreck mojo, so I retained the PI and feed the SE output section from one side of the PI. It's pretty cool and sounds great. It really isn't much different than the SE/PP control in theory.

so in this quote of yours from the DLM thread, i am taking it you are talking about putting 1 leg of the phase inverter into the SE power section,
so the SE power section can be a single tube, it doesn't have to be a paralleled power section? and will this produce the asymmetrical clipping and consequent harmonics that are desired???

sorry if these questions are basic or silly, i am just interested to learn.

thanks
Geoff

[geoffrod]

You'll want to create a fourth stage before the power stage that matches the gain of one of the PI tubes, otherwise you'll lose some of the gain in the circuit. I think doubling the 470 Ohm cathode resistor and maybe scaling a few other parts accordingly would do the trick but you'll lose the sound of the power stage, that is you'll be getting a lot of third order harmonics and not a lot of second order unless you can figure out a way to make the power stage clip asymmetrically.

Cliff,
Please forgive my ignorance, but is what you are saying possible, the asymmetrical clipping i mean??

what would i achieve by just puting the preamp section of the express infront of a 6v6 se power section? anything that resembles the feel or sound of an express??

[dartanion]

It doesn't have to be parallel tubes, so one tube will work fine.

Look up the Derailment for a simple wreck se amp. That would be a good place to start.

[geoffrod]

Not sure what this is
the pic say SExpress
pre-amp looks like it

[KellyBass]

I'm intrigued by this schematic as well. It looks completely do-able to me...but I'm sorta new at this.

[geoffrod]

I'm intrigued by this schematic as well. It looks completely do-able to me...but I'm sorta new at this.

hey KellyBass,
yeah i am a bit of a novice myself, one thing that puzzles me about this schematic is the power tube Bias setup???? Where is it???

maybe the abreviation means it is assumed? i am not sure, maybe someone else could chime in.

i also found these ones.

cheers
Geoff

[paulster]

one thing that puzzles me about this schematic is the power tube Bias setup???? Where is it???

See that 470R resistor on the power tube cathode? That's it.

It's cathode biased in this particular setup rather than fixed bias like you'd use in the push-pull Express.

[Cliff Schecht]

You'll want to create a fourth stage before the power stage that matches the gain of one of the PI tubes, otherwise you'll lose some of the gain in the circuit. I think doubling the 470 Ohm cathode resistor and maybe scaling a few other parts accordingly would do the trick but you'll lose the sound of the power stage, that is you'll be getting a lot of third order harmonics and not a lot of second order unless you can figure out a way to make the power stage clip asymmetrically.

Cliff,
Please forgive my ignorance, but is what you are saying possible, the asymmetrical clipping i mean??

what would i achieve by just puting the preamp section of the express infront of a 6v6 se power section? anything that resembles the feel or sound of an express??

The easiest way to achieve asymmetrical clipping is to use diodes, but this isn't what I was implying. I was stating that you can bias a stage in such a way that it doesn't swing around a center point but has a certain amount of offset that would cause one half of the wave to clip before the other. This will give you asymmetric clipping and if done right will give you a nice mixture of even and odd harmonics. You could use a bias circuit on the grid to achieve this or perhaps play around with the cathode/plate resistors a bit. I've never tried this mind you, it was just a thought .

[geoffrod]

one thing that puzzles me about this schematic is the power tube Bias setup???? Where is it???

See that 470R resistor on the power tube cathode? That's it.

It's cathode biased in this particular setup rather than fixed bias like you'd use in the push-pull Express.

sorry paulster,
i have not been very clear.
i was talking about the first schematic i posted, the one that KellyBass refered to.
bad referencing on my behalf.

the one you are refering to is what i am used to seeing.

[paulster]

Ah, I didn't look at that one.

That schematic doesn't show the power supply at all so you need to use a bias circuit just like a regular Express and then and inject it in via the 220K resistor R25 to get the negative voltage on the power tube grid.