Okay amp gurus, what is a 'discrete' method of design..

[Ranbat]

and does it involve more than swapping transistors for tubes? The reason I ask is, Alamo had two versions of the 2525. One all transistor and the other tube. Word is, they had the same circuit, with one having tubes in the circuit and the other transistors. I have come across this term for other amps as well, specifically Peavey. So, is this done? Or is it an urban legend from guys that don't know any better?

[justinhedrick]

and does it involve more than swapping transistors for tubes? The reason I ask is, Alamo had two versions of the 2525. One all transistor and the other tube. Word is, they had the same circuit, with one having tubes in the circuit and the other transistors. I have come across this term for other amps as well, specifically Peavey. So, is this done? Or is it an urban legend from guys that don't know any better?

I think that in laymen's terms, it means that they use OP amps.

From what little knowledge I have about amp circuits, it would be pretty difficult to have "the same circuit".

but Nick or Hemi will chime in with a much better/correct explanation.

[dunwichamps]

im not entirely sure what your asking about. Do you mean converting a tube circuit into a SS circuit. The most analogous SS device in terms of basic electrical operation is the JFET. Tubes are a normally on device where at 0V they will be flowing current similarly to JFETs which also are normally on. So there are several examples of converting basic preamp circuits from tube to jfet. In terms of power amps I am not so up to snuff on SS power amps so I dont have much to say

[Mr. Foxen]

I've generally taken it to mean actual individual components making a circuit rather than having an integrated circuit on a chip that does a bunch of stuff. I think it has become like 'handwired', 'point to point' and 'pcb boards' in the lexicon of marketing with no clue what you are actually saying or relating it to the actual product.

[dunwichamps]

in general Oli is right, the word discrete means individual components which form a circuit rather than a single IC which does all or the majority of your functions.

[Ranbat]

I'm talking converting them back and forth. Allegedly, during early solid state development, they were using the same amp designs and just swapping in transistors where the tubes were. In the case of Alamo, they lost their tube supplier, but kept making the same models and just used transistors in place of the tubes. Sorry, I'm not real knowledgeable here. I'm just trying sort out if the SS Alamos could be converted back to tube.

[Ranbat]

So there are several examples of converting basic preamp circuits from tube to jfet. In terms of power amps I am not so up to snuff on SS power amps so I dont have much to say

In the mid-70s, Alamo switched from a tube preamp to solid state preamp. So, perhaps this is what they did. I'll search for some schematics of the tube and solid state models to compare.

[dunwichamps]

I'm talking converting them back and forth. Allegedly, during early solid state development, they were using the same amp designs and just swapping in transistors where the tubes were. In the case of Alamo, they lost their tube supplier, but kept making the same models and just used transistors in place of the tubes. Sorry, I'm not real knowledgeable here. I'm just trying sort out if the SS Alamos could be converted back to tube.

yes this sounds like JFET substitution in a tube circuit. But if the circuit design could be relaxed a little BJTs or FETs also could be used but their biasing schemes are different. BJTs are biased with a base current and FETS need a VGS that is positive unlike a JFET which needs a VGS which is negative (again not a absolute rule but generally true)

[moose23]

Presumably in this case it's a marketing ploy to say they used transistors instead of integrated circuit because you know individual transistors sound better than transistor arrays on an IC. It's similar to Trace Elliot and Marshall having Mosfet on their amps rather than just saying it's solid state. Whether they actually sound any better or different is up for debate.

Interestingly these guys list Transistor Arrays as discrete components:

http://www.needasample.com/dw/components/discrete-devices.html

[Ranbat]

It wasn't a term used by the company themselves. I've come across it at other forums where oddball amps seem popular if not actually preferred over 'name' amps. It was suggested that these amps could be more easily converted to tube than ones featuring an integrated circuit.

[dunwichamps]

possibly converted, depends on the supplies. A lot of SS stuff runs on bipolar supplies where as more tube designs that are popular use uni-polar supplies

[Pissy]

Could you use it in a sentence to degree that you've seen it?

In my line of work, discrete is used to refer to specific bits of data and PLC logic so for example I might have a conversation with someone who says: "I need this discrete to go 'true' in order for the goddamn rocket to take off, you sun-the-bitch!!"


Now, if someone asked me if my amp was tube or discrete, I might think it was weird that they put it that way, but would generally take that to mean they are asking me if my amp is tube or solid state.

If under the subgenre of solid state, someone were to ask me if my solid state and was analog or discrete, my first thought would go to more of a traditional amp vs. a modeling amp sort of scenario.

If someone were to describe an amp design as being discreet I would expect to open it up and find processor chips inside the thing, whose primary function would be to process 1's and 0's.

Did I miss the point of the question?

[moose23]

Could you use it in a sentence to degree that you've seen it?

In my line of work, discrete is used to refer to specific bits of data and PLC logic so for example I might have a conversation with someone who says: "I need this discrete to go 'true' in order for the goddamn rocket to take off, you sun-the-bitch!!"


Now, if someone asked me if my amp was tube or discrete, I might think it was weird that they put it that way, but would generally take that to mean they are asking me if my amp is tube or solid state.

If under the subgenre of solid state, someone were to ask me if my solid state and was analog or discrete, my first thought would go to more of a traditional amp vs. a modeling amp sort of scenario.

If someone were to describe an amp design as being discreet I would expect to open it up and find processor chips inside the thing, whose primary function would be to process 1's and 0's.

Did I miss the point of the question?

Dunno if you missed the point but I've always thought discrete closer to analogue even though I know you can do digital with single transistors it'd be more common that digital would be non discrete using complex processor ICs. A tube and a transistor are active discrete components where a processor IC is not.

[Pissy]

Ok. I think I'm thinking of the logic world rather than the component world.

[RacerX]

I'm thinking I'm glad I own tube amps & don't have to worry about this shizzle.

[moose23]

Ok. I think I'm thinking of the logic world rather than the component world.

I thought that might be the case. What you wrote reads familiar from college a fair few years ago.

I'm thinking I'm glad I own tube amps & don't have to worry about this shizzle.

Tube is discrete. 

[RacerX]

Ok. I think I'm thinking of the logic world rather than the component world.

I thought that might be the case. What you wrote reads familiar from college a fair few years ago.

I'm thinking I'm glad I own tube amps & don't have to worry about this shizzle.

Tube is discrete. 

No speakee english.

[Ranbat]

On the specific model in question, the tube version uses 12AU6, 50C5 and 35W4 tubes. I'm on the hunt for both schematics.

[SoupKitchen]

Hmm, sounds like your standard series-string amp design. If you're going to go to the trouble to mount sockets, change circuits, etc. I'd just go ahead and swap in a Champ circuit or similar small single-ended circuit. Much safer, as series-string amps don't use power transformers and ground directly to the chassis. Or if you want to keep it true to the original circuit, you should add an isolation transformer. Please. Otherwise these amps are electrocution waiting to happen. As far as a schematic goes, it is probably similar to many student- or basic-level amps from the '60s. Silvertone 1449 (amp-in-case) comes to mind. Again, and I can't stress this enough, IF YOU INSIST ON BUILDING A TUBE AMP USING 12AU6/50C5/35W4 OR SIMILAR TUBES, PLEASE USE AN ISOLATION TRANSFORMER!

[Ranbat]

Hmm, sounds like your standard series-string amp design. If you're going to go to the trouble to mount sockets, change circuits, etc. I'd just go ahead and swap in a Champ circuit or similar small single-ended circuit. Much safer, as series-string amps don't use power transformers and ground directly to the chassis. Or if you want to keep it true to the original circuit, you should add an isolation transformer. Please. Otherwise these amps are electrocution waiting to happen. As far as a schematic goes, it is probably similar to many student- or basic-level amps from the '60s. Silvertone 1449 (amp-in-case) comes to mind. Again, and I can't stress this enough, IF YOU INSIST ON BUILDING A TUBE AMP USING 12AU6/50C5/35W4 OR SIMILAR TUBES, PLEASE USE AN ISOLATION TRANSFORMER!

Um, yeah, "live chassis" has been mentioned with the tube version of these amps. I don't plan on doing anything myself. If I decide to do any converting, it'll be done by my local tech.

[dogfood]

Don't even look at it!!!  RUN FOR YOUR LIFE!! 

(sorry, it's the drunk electrician in me)

[jibberish]

To address the initial question: "what is a 'discrete' method of design.."

discrete vs integrated. the whole thing started with integrated power amp chips to cheat on space requirements like for car stereos which made sense.  Then of course these integrated circuits went into anything small and cheap, or just mfrs cheating like in a receiver.

SO, an important marketing  technique was used to maintain the difference between the amps still using discrete transistors etc vs the integrated amp chips. Of course, as time went on, the integrated chips were refined more and more and actually spec'd well vs discrete components. Today it is far less of an issue than in the early days when integrated amps really were worse than the discrete circuits could be.

obviously the money saved is huge using IC's, but some things still can benefit from carefully matched sets of discrete components.

a tube amp like the kind you guys build are all discrete, unless maybe you cheat in some DC regulation chips or rectifier. this however, has zilch to do with the audio path, and you could still legitimately call your amp discrete wrt the audio path.


it has nothing to do with tubes vs transistors(both discrete)

[jibberish]

btw, an OP AMP (operational amplifier) is an integrated chip made of w/e 100 discrete transistor/capacitor/resistor/? all formed on a single die and black-boxed up so you only have to deal with 2 inputs, an output and power whilst looking at the spec sheet for the performance values.

this is obviously not a discrete component and the use of one in a circuit would nullify any claims that it was a discrete circuit.

[jibberish]

?Is something catastrophic going to happen now?  when have all of us agreed on something?

heh

[Mr. Foxen]

this is obviously not a discrete component and the use of one in a circuit would nullify any claims that it was a discrete circuit.

Having SS rectifier doesn't stop amps claiming to be all tube, or amps made on anything other than green PCB claiming to be 'point to point'. Pretty much have to learn to tell by looking because anything other than pro audio type spec sheets are full of BS.