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The Valve Wizard
What is this cascode pre-amp design? What does it do/sound like?
have you read this?
The Valve Wizard
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.
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 itOriginally Posted by daz
(*Courtesy Jamie Tyson)
Building a better world (one tube amp at a time)
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
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.
The ever-popular Firefly also has a cascode:
AX84.com - The Cooperative Tube Guitar Amp Project
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?
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.
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.
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.
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
This happened in Ca. I live in Ca. I can tell you that things like this are the norm here. Criminals have more rights in Ca then law biding people do. what do you expect from a state that allows all the illegals that we can fit here to live happily ever after w/o being deported and paying taxes and allowing them to use our medical care. Everything here is a$$ backwards. If my family and friends weren't all here i'd be long gone. I didn't want to say anything because i knew it would set me off, and as you can see i was right.
Sorry, guys, I got so tied up in whining about my stolen gear, I forgot to post you a cascode schematic! It's an old one from 1999, but things haven't changed much since then, tube-wise.This one's a bit different, in that it has cathode degeneration on the top and bottom tubes (self-biased). You can change the ratio of the two cathode resistors to modify the symmetry of the clipping characteristics. Here you go:
Last edited by raiken; 02-19-2010 at 10:40 AM.
That is not a cascode it is an SRPP, which does not have the high gain or low input capacitance of a cascode (bascially it's not much different from a regular gain stage, nothing pentode-y about it). Not sure what the clipping characteristics are like, but I doubt they look much like a cascode.
I think the added gain of a cascode input driving a typical plexi style preamp would be very interesting. Probably similar to a JCM800 preamp with the added gain stage, but I don't know that a cascode provides higher level of gain vs two cascaded triode's. One advantage appears to be a simpler layout. If they approximate the sound of pentodes another advantage could be enhanced harmonics and fuller bandwidth.
Born, raised and lived in Ca. for 37 years myself.
Not exactly... IMHO. But Ca. is VERY liberal over all. But these seemingly a$$ backward laws DO have some consideration. If the pawn shop owner DID come across an item that he thought was legit, or bought it from someone he thought was legit, then... Well, at some point the stuff has to move into general circulation again. Otherwise someone else who paid market price is going to feel like it was stolen from them too.
And as far as the illegals go... Tax leniency and free medical via the state is available to all the white trash in Ca. too. It's not there specifically to benefit the illegals, it's there to benefit the free loaders. Not that that's much better. And the practice of looking the other way regarding illegal labor is a trmendous benefit to the construction and agricultural industries in Ca. Having worked in Ca. as a painting contractor for most of my life I can tell you that for certain. I never had an illegal worker on my crew, But I do know how the game is played. The same practice is fast filtering into surrounding states and up the coast too. I don't agree with it and never supported it in my business. But believe me when I say that Ca. needs the agricultural workers. That is, if you ever want a tomato on your hamburger or a salad again. You just can't get gringos to pick produce or do other nasty farm work for a wage that makes farming possible. Ca. looks the other way to avoid further damage to the economy. In this one respect the illegals are actually helping, not hurting.
I feel the same way. Oh wait, I did move, about three and a half years ago. And let me tell you first hand, you're going to find fault with every states policies somewhere.
Try to see the good in the system. Think of all those homeless, smelly bums that decorate all Ca's down town areas. Or the giant state supplanted hospitals full of pregnant minorities, victms of gang violence and homeless detoxing addicts.
Sorry for the off topic.
Chuck
Last edited by Chuck H; 02-20-2010 at 07:23 AM.
What does SRPP stand for?
"Created at the end of 1950s and designed by Japanese designer"
Oops! I think the Japanese might be being optimistic there, since the SRPP was already patented in 1940! espacenet — Bibliographic data
You can't believe everything you read on the net!
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