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Phase splitter types

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Wavebourn

Wavebourn

Member
Joined 2006
wavebourn.com
For lead guitar if you want a classical overdrive you should go with what Fender did in last amps. IMHO.

One more option (it is one of my secrets) is to use a LTP - type class A output stage where the input tube is connected as triode, an opposite tube is connected as pentode with grounded grid. Very sweet sound, very musical overdrive. Try it. No need for an additional phase splitter.
 
Yvesm

Yvesm

Member
Joined 2004
dissident-audio.com
Wavebourn said:

. . .
One more option (it is one of my secrets) is to use a LTP - type class A output stage where the input tube is connected as triode, an opposite tube is connected as pentode with grounded grid. Very sweet sound, very musical overdrive. Try it. No need for an additional phase splitter.
Click to expand...

Looks like a perfect CCS feeding the other primary half :)
A better way to use an OPT than inserting an air gap ! for sure !

For "true" PI, pentodes LTP are seldomly used in audio although they give vy good results and sometimes void the use of an additional stage gain.
Use medium current/hi Gm types like 6BX6, 6EJ7 with starved g2 ... one of my secrets :cool:

Yves.
 
M

m6tt

Member
Joined 2007
If you are short on gain, use a cathodyne with directly coupled voltage amp, this uses one tube and provides good drive for fairly sensitive output tubes (EL84 etc.)

If you are short on drive or max voltage swing, use a LTP/Schmidt with low-Rp triodes with high current, this uses one tube but provides less gain than option 1. This is better for big tubes like 6L6, KT88...

you may still want additional grid drivers, cathode followers or mosfets after the PI if you have the space/power supply for these, they will help prevent blocking distortion.

Also, balance in guitar amps is not always that important, since you probably want a mix of odd and even harmonics. Otherwise the sound will be a bit sterile for anything but Jazz/Classical guitar.
 
B

bigwill

Member
Joined 2004
In my amp which found experimental use for guitar (had too much gain), I found that an LTP with a CCS in the tail can sound great when driving PP triode mode EL34s into clipping, very nice tone indeed. Probably its lack of tone and distortion and letting the outputs do their thing, actually
 
M

m6tt

Member
Joined 2007
Sorry Wavebourn, I was not specific enough. I was referring more to the non-clipping state of the amp. Mismatched power tubes and/or imperfect phase splitters often sound very much more "tube colored" than if they were precision. That is often a benefit in some guitar sounds. The overdriven/clipped sounds of even a perfect tube PI are going to be square wave "clarinet" sound. That too is part of a good guitar sound, and I didn't mean to imply balancing the drive would somehow prevent the amp from getting a good overdrive/grind!
 
K

kenpeter

Member
Joined 2007
Wavebourn said:
For lead guitar if you want a classical overdrive you should go with what Fender did in last amps. IMHO.

One more option (it is one of my secrets) is to use a LTP - type class A output stage where the input tube is connected as triode, an opposite tube is connected as pentode with grounded grid. Very sweet sound, very musical overdrive. Try it. No need for an additional phase splitter.
Click to expand...

A secret about your secret:

Barely matters which grid choosen to ground, Triode or Pentode...
You can drive into either grid, or both in differential. All the same.
Driving into the Pentode's grid might involve less Milller...

I prefer twin constant current sources, bridged with a large cap.
Both imbalanced branches then auto bias equally.
 
Merlinb

Merlinb

Member
Joined 2006
lulu.com/spotlight/valve_wizard
slideman82 said:
I would like to know about phase splitters, which are quite linear, which not. I know there is the LTP, cathodyne type, etc..
The point is I want to build a guitar amp, and probably whithout cloning a popular one. Sure I'm gonna use sweep tubes as output.

Thanks!
Click to expand...

For a guitar amp the inherent linearity is largely irrelevant. What matters is how the PI overdrives, and how it responds to overdriving the power stage.
The LTP is almost universally used because of its high output swing, high sensitivity (it is easy to overdrive) and fairly consistent operation when overdriving the power valves.

The cathodyne is not so easy to overdrive, and strange things can happen when it overdrives the power valves, but these effects can be fixed.
 
ray_moth

ray_moth

Ex-Moderator
Joined 2004
Re: Re: Phase splitter types

Ty_Bower said:


There's a lot of helpful info here, in a format which I found easy to understand.
http://www.freewebs.com/valvewizard/index.html
Click to expand...

I agree, that's a great site for helping people understand what's going on, and not just for phase splitters. IMHO, it must be one of the best online resources around for audio design, especially because it's so clearly explained with lots of practical examples. I would recommend it to anyone struggling to come to terms with audio amp design.

We just have to remember (as the author often reminds us) that it's primarily intended for guitar amps; however, that in no way detracts from the usefulness of the articles (except, perhaps, in the case of power supply design).
 
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