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Does a guitar tube preamp still push/pull?
Old 5 days ago
  #1
Gear Maniac
 
camacozie's Avatar
 

Does a guitar tube preamp still push/pull?

Hello,

Is there a push/pull relationship with the preamp tubes like there is with the poweramp section and the speaker? If so, is there wear and tear on the circuit if the load from the preamp is an delivered directly to an AD converter's line in?

I'm considering a guitar tube preamp for the line out ability. After recently purchasing my first tube amp, I am so blown away with the sonic characteristics that I'm having a hard time with any other technology. However, the convenience of the sims and what not do leave something to be desired for those of us with adjoining neighbors - who are big puss'es.

So, I'm considering an all tube guitar preamp with a line out direct to the AD, only to apply an IR later. I get that I am sacrificing some tonally key components in exchange for convenience. But hey, I don't have to marry this thing; I can kill it, or at least "F" it.

Thanks!
Old 5 days ago
  #2

Most tube pre-amps are single-ended. I'm not aware of any guitar amps that use a differential pair on the first stage.

If you want as much of the tube amp "magic" before hitting your A/D, you probably want a silent loadbox.



-tINY

Old 5 days ago
  #3
Lives for gear
 
lame pseudonym's Avatar
 

I once built a phono stage that was kinda push-pull, the tubes were in series. Its frequency response went up to the AM radio band, and I don't know how high it ultimately went because that's as high as my test equipment went.
Old 5 days ago
  #4
Quote:
Originally Posted by lame pseudonym View Post
I once built a phono stage that was kinda push-pull, the tubes were in series. Its frequency response went up to the AM radio band, and I don't know how high it ultimately went because that's as high as my test equipment went.
Tubes in series are not push-pull. Sorry.

As far a "push-pull" preamps are concerned, I don't know of any guitar amps like that. It would take 3 tubes (or two if one is a double tube like a 12AX7). You'd need one for a phase splitter and two for outputs, plus a transformer for combining the outputs of the preamps, minimum.

I don't think you're likely to find that.
Old 5 days ago
  #5
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For a time on some models of Jim Kelley amps the overdrive stage was a 12AX7 twin triode wired actual push-pull (Class AB2 by definition Parallel, impossible in series FWIW) into a small OT about the size of a Fender reverb transformer that terminated in a simple resistive load and provided a scaled down signal that behaved a lot like it's big brothers. It was quite cool but never really caught on... just not enough bang-for-bux.

On the flip side I once experimented on a broken down Showman, replacing the OT and wiring all 4 6L6s in parallel single-ended Class A (sort of a Champ on steroids... roughly 30 watts) to experience if single-ended Class A with enough headroom to actually play clean at stage volume would sound good. It did sound good but it was basically a waste of 3 x 6L6s, which is why the value of single ended is primarily in low cost. It wasn't anywhere near cool enough or even unique enough to warrant all the gear to run like that. Push-Pull, especially Push-Pull Class A, is simply worth it where power is what one is after. There is very little discernible audible difference between single-ended and push-pull properly biased and loaded.
Old 4 days ago
  #6
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Quote:
Originally Posted by John Eppstein View Post
Tubes in series are not push-pull. Sorry.
Far be it from me to pick a fight with a crazy person, but if you've got two tubes connected in series, and you're taking your output from somewhere between them, and when one tube is inhaling the other tube is exhaling, and vice versa, that's defacto push-pull even it if doesn't fit the official description of something completely else.

Having said that, I HATE HATE HATE when people steal perfectly good words for perfectly good things and apply them to something else. The one that enjoys my ire at this moment is "meme". It used to, and had always, had a meaning for a specific, defined social condition. Now it just means the captioned pictures that children think are funny. So what happens to the concept of the original meaning? Does it just disappear? It it now a thought that doesn't exist anymore because it doesn't have a name?

Love ya John.

.
Old 4 days ago
  #7
Gear Maniac
 
camacozie's Avatar
 

Quote:
Originally Posted by lame pseudonym View Post
I HATE HATE HATE when people steal perfectly good words for perfectly good things and apply them to something else. The one that enjoys my ire at this moment is "meme". It used to, and had always, had a meaning for a specific, defined social condition. Now it just means the captioned pictures that children think are funny. So what happens to the concept of the original meaning? Does it just disappear? It it now a thought that doesn't exist anymore because it doesn't have a name?.
You mean like how "producer" used to mean the person that was on the phone all day lining up people/time/materials/services/money/etc, but now just means the person that makes a stupid "beat" in 15 mins using Fruity Loops?


Back to the original post about guitar tube preamps, I think I'm just going to stick with the full blown guitar amps. Having no experience with such standalone preamps (and I know this isn't the scientific method) Youtube seems to only have poor quality examples that just don't sound pleasant. Seems even the "All Tube" guitar preamps are still lacking in the "awesome" category. They all sound harsh, flat, and not much better than a pedal.

Why take the chance? F the neighbors!
Old 4 days ago
  #8
Quote:
Originally Posted by lame pseudonym View Post
Far be it from me to pick a fight with a crazy person, but if you've got two tubes connected in series, and you're taking your output from somewhere between them, and when one tube is inhaling the other tube is exhaling, and vice versa, that's defacto push-pull even it if doesn't fit the official description of something completely else.
Except that's not how push-pull works. The output is not taken "somewhere between" the output tubes. It's taken from the plates of the tubes, which are on the "outside" of the circuit. The connection in the middle (to the power supply) merely provides the power. It doesn't have signal on it.

"In Series" would mean the plate of the 1st tube connected to the grid of the 2nd.
Old 4 days ago
  #9
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I thought that maybe people would interpret it that way but nono, I meant it literally.

Current enters the first tube, comes out the plate, goes through a resistor or two, enters the second tube, goes through that tube's plate, and then on to B+. Signal comes out between the tubes.

I'd call it a totem pole but if I did some rich white college kid would throw rocks at my house
Old 4 days ago
  #10
Quote:
Originally Posted by lame pseudonym View Post
I thought that maybe people would interpret it that way but nono, I meant it literally.

Current enters the first tube, comes out the plate, goes through a resistor or two, enters the second tube, goes through that tube's plate, and then on to B+. Signal comes out between the tubes.

I'd call it a totem pole but if I did some rich white college kid would throw rocks at my house
Can you upload a schematic?

It doesn't appear that you're talking about what I'm talking about.

Or you don't understand how the circuit works.
Old 4 days ago
  #11
Quote:
Originally Posted by lame pseudonym View Post
I thought that maybe people would interpret it that way but nono, I meant it literally.

Current enters the first tube, comes out the plate, goes through a resistor or two, enters the second tube, goes through that tube's plate, and then on to B+. Signal comes out between the tubes.

I'd call it a totem pole but if I did some rich white college kid would throw rocks at my house
Current enters both tubes at the cathode. It's modulated by signal at the grid. The grid signal to the two power tubes is out of polarity (from the phase inverter), so one pushes while the other pulls. Current exits at the plates of both tubes, out of phase.

There are two signals running through the output transformer. One is the DC to power the circuit. One is AC audio output by the tubes. One power tube does not drive the other. They are not in series, they are, actually, in parallel, but are running in opposite polarity to each other, creating the push-pull effect.
Old 4 days ago
  #12
Quote:
Originally Posted by lame pseudonym View Post
Far be it from me to pick a fight with a crazy person, but if you've got two tubes connected in series, and you're taking your output from somewhere between them, and when one tube is inhaling the other tube is exhaling, and vice versa, that's defacto push-pull even it if doesn't fit the official description of something completely else.

Having said that, I HATE HATE HATE when people steal perfectly good words for perfectly good things and apply them to something else. The one that enjoys my ire at this moment is "meme". It used to, and had always, had a meaning for a specific, defined social condition. Now it just means the captioned pictures that children think are funny. So what happens to the concept of the original meaning? Does it just disappear? It it now a thought that doesn't exist anymore because it doesn't have a name?

Love ya John.

.
I thought Richard Dawkins coined meme as a word to describe a unit of cultural transfer/evolution. Good memes spread, bad memes die. Dumb pictures with funny captions spread if they align with the prevailing culture. They are like cultural genes. Just like good genes spread as they are preferable reproduced and bad genes die out. The genes/memes aren't aware of the process. It was a very well observed concept by Dawkins. The meaning hasn't changed as far as I can see.

And anyway.... words are just random sounds that we (society) decide mean something. And when "we" decide they mean something else, they mean something else.
Old 4 days ago
  #13
Quote:
Originally Posted by soldat View Post

And anyway.... words are just random sounds that we (society) decide mean something. And when "we" decide they mean something else, they mean something else.
Words have meaning. The meaning can evolve, but generally NOT in science, where it's important for people to understand their proper meanings.

Else we end up with a "tower of Babel" situation, where nobody can understand each other.

So yes, the meaning of words drift in colloquial speech. Not in science.

So in this case you're incorrect.
Old 4 days ago
  #14
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This is the little cutie that I'm talking about:




If you want to read the whole article that this came from, here:

http://www.valvewizard.co.uk/SRPP_Blencowe.pdf

Eight pages, no waiting. Warm up your slide rule, there are plenty of big scary math here.

You might think that it's just a current source, but there is signal applied to both grids, so maybe not.

.
Old 4 days ago
  #15
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Looks a bit like a Cascode arrangement, but I searched out and read the full article you posted and the author claims it is a genuine push-pull amplifier at least under some conditions. I knew I had seen that schematic for an output transformerless circuit right after cascode was discussed so I checked. The SRPP is in my copy of The Audio Cyclopedia so it appears I owe you an apology and you now have it. I had forgotten about this circuit probably because it never saw wide usage... but nevertheless it did exist and you were correct.
Old 4 days ago
  #16
Lives for gear
 
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Oh, I'm sure that I wasn't explaining it properly.
Old 3 days ago
  #17
Quote:
Originally Posted by lame pseudonym View Post
This is the little cutie that I'm talking about:




If you want to read the whole article that this came from, here:

http://www.valvewizard.co.uk/SRPP_Blencowe.pdf

Eight pages, no waiting. Warm up your slide rule, there are plenty of big scary math here.

You might think that it's just a current source, but there is signal applied to both grids, so maybe not.

.
Very interesting! I'd forgotten about that, probably because it's seldom if ever used for anything.

Every few years somebody comes up with a transformerless tube guitar amp, but so far none of them have ever been successful - I assume there's a reason for that. I'm guessing that this circuit might have something to do with that.

So does that mean that we have to insert the word "conventional" into discussions of amps now?

I also don't see what it has to do with the subject of this thread...?
Old 3 days ago
  #18
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Well John there is the fact that not only has no transformerless tube output circuit ever been used in any guitar gear, I don't think any have gotten past mere laboratory proof-of-concept builds. As for my view, the circuit exists and probably works, but I LIKE Output Transformers, especially for guitar amps, and for more than one reason.
Old 2 days ago
  #19
Quote:
Originally Posted by enorbet2 View Post
Well John there is the fact that not only has no transformerless tube output circuit ever been used in any guitar gear, I don't think any have gotten past mere laboratory proof-of-concept builds. As for my view, the circuit exists and probably works, but I LIKE Output Transformers, especially for guitar amps, and for more than one reason.
I tend to like output transformers in pretty much everything.
Old 2 days ago
  #20
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kingofspain's Avatar
Quote:
Originally Posted by enorbet2 View Post
Well John there is the fact that not only has no transformerless tube output circuit ever been used in any guitar gear, I don't think any have gotten past mere laboratory proof-of-concept builds. As for my view, the circuit exists and probably works, but I LIKE Output Transformers, especially for guitar amps, and for more than one reason.
I think I read somewhere that output-transformer-less (OTL?) circuits are popular for hi-fi headphone amps, whatever one of those is...

If indeed they do exist, we should approach with extreme caution. Suitably armed with pointy sticks, flaming brands and a belly full of righteous suspicion.
Old 2 days ago
  #21
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Quote:
Originally Posted by kingofspain View Post
I think I read somewhere that output-transformer-less (OTL?) circuits are popular for hi-fi headphone amps, whatever one of those is...

If indeed they do exist, we should approach with extreme caution. Suitably armed with pointy sticks, flaming brands and a belly full of righteous suspicion.
:D Granted I haven't worked on vast numbers of tube Hi Fi gear, but I've never seen an OTL headphone circuit and I've owned several pieces featuring Headphone Out jacks. Usually those were just padded down off the main output... no need for an additional stage.

Were you referring to a standalone headphone amp? If so I'd like to see and hear one.
Old 2 days ago
  #22
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Quote:
Originally Posted by enorbet2 View Post
Were you referring to a standalone headphone amp? If so I'd like to see and hear one.
Just having a joke really, based on a dim recollection of something I once read. I'll have a browse through my bookshelves and see if I can turn up the right passage. I'm genuinely curious myself now...

Old 2 days ago
  #23
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zvukofor's Avatar
SRPP and other circuits of this family (there are lot of them!) was used at radio freqs a lot, have not seen any guitar preamp based on this, only a couple of rare tube mic pres.

Some pedals use SRPP with transistors, BTW.
Old 4 hours ago
  #24
Gear Guru
 
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There was a guy called Eric the Viking in Virginia that was selling transformerless guitar amps, a friend of mine bought one. It was "light weight." I never did get to hear it, oh well.
Old 3 hours ago
  #25
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BTW, and just FTR, I'm betting there are lots of commercial sound system installers with repeatedly blown speakers, especially Hi Freq drivers, that dearly wish their amps had the DC isolation of Output Transformers, if they even realized "it is a thing". However those installers likely marvel at why anyone would employ 200 Watt amps on 60 watt compression drivers
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