Please explain cascode

[Groover]

What is this cascode pre-amp design? What does it do/sound like?

[pontiacpete]

have you read this?

The Valve Wizard

[Groover]

No I had not, thanks for the link. I don't understand all of the theoretical terminology but I get the general idea, which is what I was after.

[daz]

Anyone know where i can find a schematic of an amp that uses this design ?

[tubeswell]

Anyone know where i can find a schematic of an amp that uses this design ?

I think I found this* on Dumble Forum or Hoffman Forum - can't remember which - struck me as interesting at the time. Curious to try it

(*Courtesy Jamie Tyson)

[raiken]

Anyone know where i can find a schematic of an amp that uses this design ?

My Europa amplifier used a 12AT7 self-biased cascode for the first-stage.

Unfortunately, the prototype, along with all my other booth gear (about 16 grand worth of stuff, including several irreplaceable prototype amps and personal items), got stolen at the NAMM show several years back, so I never released it as a production amplifier.

By the way, all the gear finally showed up at a pawn shop in California a few months back. I sent the police out there, and they said that California law says that if the pawn shop owner has stolen gear for more than 3 years, he owns it and can sell it for anything he wants, and I can't do a damned thing about it, except that I have a right to buy it back from him at whatever price he decides to sell it to me for. Nice, huh?

Also, I gave some cascode designs to the 65 Amps guys, and I think they used them in one of their models, but I don't remember which one.

Randall Aiken

[daz]

I think I found this* on Dumble Forum or Hoffman Forum - can't remember which - struck me as interesting at the time. Curious to try it

(*Courtesy Jamie Tyson)

Thanks, i have a sort of experimental amp who's preamp i've been changing completely several time to see what i can come up with, and i'm going to cascode it. Gotta see what this is all about because it sounds interesting and may have potential as a high gain pre that doesn't require 1/2 a lifetime to get right.

[Merlinb]

The ever-popular Firefly also has a cascode:
AX84.com - The Cooperative Tube Guitar Amp Project

[hasserl]

I've played one of these that was built into a 5E3 chassis/cab and it sounded great, I really enjoyed it. Quite versatile too, except I thought the Master Volume was pretty useless, with it turned down the amp ust lost all the majic; an attenuator works much better for getting the volume down than an MV, with this circuit. Great sound though.

https://taweber.powweb.com/store/smokeII_schem.jpg

[daz]

I've played one of these that was built into a 5E3 chassis/cab and it sounded great, I really enjoyed it. Quite versatile too, except I thought the Master Volume was pretty useless, with it turned down the amp ust lost all the majic; an attenuator works much better for getting the volume down than an MV, with this circuit. Great sound though.

https://taweber.powweb.com/store/smokeII_schem.jpg

I like that schematic best because it's pretty similar to what i have and i can just copy the front end. Let me ask you this....I know you didn't like the master, but when played at home levels did that preamp generate much distortion? How much....like a pv classic 30 or JCM 800 master volume? Less?

[hasserl]

There really is no preamp distortion, but there probably is a bit from the PI, mostly from the power tubes. Both of those amps will generate more preamp distortion because they both have multiple stages of gain. The overall distortion from the SJII is probably on par with them, but IMO it's a more enjoyable distortion, less buzzy in nature, and more controllable with the guitar volume.

[daz]

But i thought the purpose of cascode was high gain? Why even use it if there is no preamp drive?

[hasserl]

But i thought the purpose of cascode was high gain? Why even use it if there is no preamp drive?

It is high gain, but it's not driving another stage, so there's nothing to distort, unless the cascode itself distorts, but I don't think it does with just the guitar input driving it. The next thing inline is the PI, so yes, the cascode does probably drive the PI into clipping. But I just played the amp, I didn't scope it.

Why use it is to provide a high level of drive to the PI, and from there drive the piss out of the EL84's? Are you familiar with 18watt Marshall style amps? Have you played one? This is like an 18watt on steroids.

[daz]

I see. So i wonder if it has any value in generating preamp distortion with a stage or two after it that make it advantageous over regular cascaded stages.

[Chuck H]

By the way, all the gear finally showed up at a pawn shop in California a few months back. I sent the police out there, and they said that California law says that if the pawn shop owner has stolen gear for more than 3 years, he owns it and can sell it for anything he wants, and I can't do a damned thing about it, except that I have a right to buy it back from him at whatever price he decides to sell it to me for. Nice, huh?

I got all steamed just reading this... What if you could show evidence to suggest that the guy knew the equipement was hot and intentionally tucked it away for three years to take advantage of the statute? Like find out where he got it (they do keep records) and see if he buys other things from that guy and seems to always hold them for three years.

Chuck