a push/pull tube o.d. for the summer...

[samhay]

This is (I think) what I have on the beadboard.
The valve biasing needs refinement and I think it would benefit from some filtering.

[Johan]

Cool. Conceptually a little different from mine as you use the tube as preamp/pi and i run mine to mimic a tiny tube poweramp...But it looks cool too

[Johan]

As always, things are likely to change along the way, but this is what I'm planning of boxing up. 
For breadboarding or convenient open stage at the local wateringhole. One of those "10 year" lithium smoke detector batteries would probably last three or four hours. But in the long run a quality wallwart like 1spot is the way to go
Changes are resistor and cap values, drive pot configuration. Added tone pot and added pp/se control.
J

[samhay]

Cool. Conceptually a little different from mine as you use the tube as preamp/pi and i run mine to mimic a tiny tube poweramp...But it looks cool too

Thanks. Your right about the concept. Almost (well at a a big stretch) a Fender vs Marshall thing.

Your new schematic looks good. Will have to try the tone control.
If I understand correctly, you have unequal loading on the valves - 200k on the valve feeding the non-inverting op-amp, and only 100k on the other. This may cause enough imbalance that you don't get good cancelling of even order harmonics.

[Johan]

..Oh. .I'm not bright enough to answer that. .You're right about the difference in impedance. I just listen and look the signal path through with an oscilloscope. It didn't look any different one plate from the other and in the regular high voltage operation we know that a typical gainstage such as in a Fender can drive a tonestack which is lower z than the plate resistor. ..i guess we have to wait for one of the gurus for a definitive answer on that one. But it works and sounds good so I'm happy. .
J

[samhay]

If it sounds good and looks symmetrical on the scope, then I guess it doesn't matter. Ultimately, the output op-amp is going to act a little differently from a power tube anyway.

[Bill Mountain]

I think Samhay's and Johan's designs are very different.

Johan's is clipping tubes in an Class AB-ish fashion and the Samhay's is just clipping a phase splitter.

Are they supposed to sound similar?  Are they supposed to sound different?

[Bill Mountain]

If it sounds good and looks symmetrical on the scope, then I guess it doesn't matter. Ultimately, the output op-amp is going to act a little differently from a power tube anyway.

Isn't the opamp sort of acting like an output transformer here?

[Johan]

That was the idea. Having the opamp do the summing and impedance change that a transformer would do in a big tube amp. The tube stages on 9 volt can probably only deliver around 1 volt ac so the output opamp set at unity gain never clips.
If you have one, using a transformer would Of course be ideal. But sourcing one for this type of application could prove both difficult and  expensive.
J

[Johan]

But ultimately is about sound, so now there are two new tube od's to explore. .

[samhay]

But ultimately is about sound, so now there are two new tube od's to explore. .

Indeed, but the schematic I posted is supposed to be a work in progress - it works, but needs work. I will start a new thread once it is ready to fly.

I think Samhay's and Johan's designs are very different.

Johan's is clipping tubes in an Class AB-ish fashion and the Samhay's is just clipping a phase splitter.

Are they supposed to sound similar?  Are they supposed to sound different?

The similarity is the use of the output op-amp to combine two out-of-phase signals that have been through a valve run at low voltage.

My idea was to do the phase inversion with the valve, which is why I first tried a cathodyne. Note that it is only a cathodyne when the cathode bypass capacitor is out of circuit. With the 'Class pot CCW, it is just two gain stages in series.
A LTP can also do the phase inversion, and i am trying to get this to work at 9v too. Will post progress.

[Bill Mountain]

But ultimately is about sound, so now there are two new tube od's to explore. .

Indeed, but the schematic I posted is supposed to be a work in progress - it works, but needs work. I will start a new thread once it is ready to fly.

I think Samhay's and Johan's designs are very different.

Johan's is clipping tubes in an Class AB-ish fashion and the Samhay's is just clipping a phase splitter.

Are they supposed to sound similar?  Are they supposed to sound different?

The similarity is the use of the output op-amp to combine two out-of-phase signals that have been through a valve run at low voltage.

My idea was to do the phase inversion with the valve, which is why I first tried a cathodyne. Note that it is only a cathodyne when the cathode bypass capacitor is out of circuit. With the 'Class pot CCW, it is just two gain stages in series.
A LTP can also do the phase inversion, and i am trying to get this to work at 9v too. Will post progress.

But what's the point of the phase inversion and then combining them if there is no overdriven component in between?

I hope I'm not coming off as rude.  This stuff is a little over my head and I am genuinely interested in what is being discussed here.

[Lurco]

Crossover distortion?

[Johan]

I could never get LTP or self split (basicly the same thing) to work at low voltages. I'm sure it can be done but some kind of trickery is probably needed. That's why i chose a transistor Cathodyne pi. An inverting opamp solution would work too. But again, the simplicity of a single transistor and two resistors lured me in. .
If Samhay get it to work it opens up a world of new possible 9 volt tube designs. ..Very exciting. .

[Johan]

Ok. Here is a little change again. .a rebias of the transistor making it smoother. . I'm really happy with what I've got on my bench now...

http://www.aronnelson.com/DIYFiles/up/ppdriver_rev1.2.mp3

[deadastronaut]

they both sound cool, but my ear likes the original better..

the second one sounds a bit more warm fuzz like as you turn up the vol rather than a bitey , jangly, drive sound......just my ears and 2p..

cool stuff guys..

[samhay]

Cool - you've tried them both on the breadboard then?
If that's the case, did you play with the 'Class' control on mine? It changes the character quite a lot.

Edit - Never mind, just spied Johan's second clip. I assume this is what you are referring to.

Johan - the overdriven sound from the second clip sounds better to my ears, but it sounds just a pinch gated at lower volumes.

[samhay]

But what's the point of the phase inversion and then combining them if there is no overdriven component in between?

I hope I'm not coming off as rude.  This stuff is a little over my head and I am genuinely interested in what is being discussed here.

No Bill, that's a good question. At the moment, I am still at the tinkering stage, so I not sure if there is any real point other than that it is a fun little engineering challenge.
However, you could add a second valve and drive another gain stage with each of the cathodyne's outputs. This way you would get some pretty significant overdrive before mixing the signals back together.

I could never get LTP or self split (basicly the same thing) to work at low voltages. I'm sure it can be done but some kind of trickery is probably needed. That's why i chose a transistor Cathodyne pi. An inverting opamp solution would work too. But again, the simplicity of a single transistor and two resistors lured me in. .
If Samhay get it to work it opens up a world of new possible 9 volt tube designs. ..Very exciting. .

It's tricky as there isn't much room to get the valves biased - hopefully Merlin will stop by at some point and offer some sage advice.

Ok. Here is a little change again. .a rebias of the transistor making it smoother. . I'm really happy with what I've got on my bench now...

This is a cool idea. You knock the input to the PI down to keep it from freaking out and re-bias it for more headroom at the same time.

[Johan]

Thanks
The is a little more gain from the first stage now. Compare the schematic in original post with the last one.  So if it's fuzzier, you can always turn down the drive. What I'm particular happy with is how it cleans up just like a good amp and not with that lingering buzz that always seem to come with stompbox distortions.  I tried to capture that in both clips. I hope it got through. ..i recorded this with the tone on full but i think the tone cap should be 10x bigger than drawn, or it might be too suptle...

[deadastronaut]

Edit - Never mind, just spied Johan's second clip. I assume this is what you are referring to.

yep, ive, never messed with valves yet! total noob on that, ..but this looks/sounds like it would be a cool intro to them for me anyway..(rather than the usual fet stuff)

sounds really cool..i'll get a couple of 12au7's to play with..