Dual Simple SE's in Push Pull w Differential Input - diyAudio
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Old 4th August 2010, 09:51 PM   #1
Anchan is offline Anchan  United States
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Default Dual Simple SE's in Push Pull w Differential Input

My dac has a balanced output, and I have been recently messing around lately building balanced linestages.
My first one is the zen balanced line stage, by Mr. Pass:
http://www.passdiy.com/pdf/balzenpre.pdf

I plan on building some variations, and possibly a tube version after that.

My question is, if I already have a line stage with inverted outputs capable of around a 50Vpp swing, can I just plug the outputs right into the Simple PP circuit as seen in the attached, thereby bypassing the phase splitter?
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Old 5th August 2010, 07:51 PM   #2
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Assuming that your line stage could actually deliver the needed drive level with a reasonable amount of distortion, the method you describe should work, but I have not actually tried it. Most pentode P-P amps require some negative feedback to control the output impedance, and there would be no way to connect it with your proposed circuit. The amp could be operated in triode mode where it might be possible to operate without feedback, but the power output will be lower.

There is another possible solution, which I have done. The Simple SE board could be operated in P-P mode with your proposed drive system. Only normal drive levels are required. Use the two out of phase signals from your balanced line stage to drive each channel, and connect one P-P opt to the board with the red lead on B+ and a plate lead to the plate of each channel. In class A triode mode you can get 12 to 20 watts depending on tubes and load impedance. The "normal" 6600 ohm OPT nets about 35 watts leaving class A only on signal peaks. Again there is no provision for global negative feedback, but I have not found it necessary if you stick with triode mode operation. Of course two boards would be needed for a stereo amp.
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Old 5th August 2010, 08:22 PM   #3
Anchan is offline Anchan  United States
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Quote:
Originally Posted by tubelab.com View Post
Assuming that your line stage could actually deliver the needed drive level with a reasonable amount of distortion, the method you describe should work, but I have not actually tried it. Most pentode P-P amps require some negative feedback to control the output impedance, and there would be no way to connect it with your proposed circuit. The amp could be operated in triode mode where it might be possible to operate without feedback, but the power output will be lower.

There is another possible solution, which I have done. The Simple SE board could be operated in P-P mode with your proposed drive system. Only normal drive levels are required. Use the two out of phase signals from your balanced line stage to drive each channel, and connect one P-P opt to the board with the red lead on B+ and a plate lead to the plate of each channel. In class A triode mode you can get 12 to 20 watts depending on tubes and load impedance. The "normal" 6600 ohm OPT nets about 35 watts leaving class A only on signal peaks. Again there is no provision for global negative feedback, but I have not found it necessary if you stick with triode mode operation. Of course two boards would be needed for a stereo amp.
Ok. So if I use the 2 board SE solution, I could use the same OPT as you have spec'd on your site for a single SE, and only 1 OPT per channel, correct?
I understand I would need 2 boards.

Of course, I could leave well enough alone and use what looks like an awesome PP kit.

I am just wondering what a PP amp sounds like without the phase inverter stage- if it is somehow cleaner. What leads me to this question is that I have a really cool original Dynaco ST-35. It sounds great, but what bothers me about it is, with complex music, things get a little blurry, and there seems to be some phase issues. When I look at the schematic, the output stage is so damn simple, that I think something must be getting confused in the input stage. I am thinking the simpler the input stage, perhaps the better the phase information will be preserved. But my assessment maybe nonsense.

It seems like most decent DACs these days have balanced outs, yet most amps have single ended inputs. Seems like it might be nice to use balanced since I have them

Anyway, I love your site, and will be ordering something from you soon. Keep it up!
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Old 5th August 2010, 08:30 PM   #4
Anchan is offline Anchan  United States
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If I use your simple PP in triode mode, how many watts might you expect? And how about for pentode?

Thanks
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Old 5th August 2010, 09:33 PM   #5
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George:

please check your email / forum PM
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Old 6th August 2010, 01:27 AM   #6
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...or one could use a line transformer. See this post. Though, I do like the idea of using two Simple-SE boards to form a differential input Push-Pull amp...

~Tom
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Old 6th August 2010, 03:14 AM   #7
Anchan is offline Anchan  United States
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Originally Posted by tomchr View Post
...or one could use a line transformer. See this post. Though, I do like the idea of using two Simple-SE boards to form a differential input Push-Pull amp...

~Tom
Tom, thanks for the link to that thread. There are so many threads on this site, even searching pretty hard its easy to miss. So what did you decide in the end? Did you go transformer input w your 300B?

Anyway, I am considering going with the dual simple SE route, but maybe I am making too big a deal out of using a differential input. Maybe its not that big a deal, and I go with the simple PP... I'll have to think on it a bit.
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Old 6th August 2010, 03:22 AM   #8
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Quote:
Originally Posted by Anchan View Post
What leads me to this question is that I have a really cool original Dynaco ST-35. It sounds great, but what bothers me about it is, with complex music, things get a little blurry, and there seems to be some phase issues.

I'll bet you that it's clipping, coupled with poor overload recovery.
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Old 8th August 2010, 01:04 AM   #9
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Quote:
If I use your simple PP in triode mode, how many watts might you expect? And how about for pentode?
The power output depends on which tubes you use and what voltage you run them at. With good tubes (I use JJ's) and about 350 volts I get 8 watts in triode and 17 watts in pentode.

Quote:
I could use the same OPT as you have spec'd on your site for a single SE, and only 1 OPT per channel, correct?
NO! You are essentially making a P-P amp, therefore you need to use a P-P transformer.

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George: please check your email / forum PM
I know you (and a dozen others) have been trying to contact me. The place where I work has instituted a new policy that does not permit "any activity that supports a personal business" from company property which includes the phone, computer and internet connection. This makes it rather difficult to answer anything related to selling boards or components since I have been there for 10 to 12 hours per day almost every day. I had 2 days off in July. I should get to yours tonight or tomorrow.
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Old 8th August 2010, 01:20 AM   #10
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Smile Pentod push pull without phase inverter

Hi

I have worked on all sorts of tube amps, including Hammond and other organ amps, from the 1930's on up.

A lot of Hammond amps have no phase inverter.

The organ preamp drives a line out transformer, that gives a balanced out through the big cable to the Leslie amp. There are about seven different Leslie or external speaker amps all the way up to four #45 tubes in PP parallel

By having all the gain and drive levels worked out, you can balance everything so the amp never goes into distortation.

Also, a number of these amps run the input through a 12au7/6sn7 balanced stage, with the cathodes hooked together. I think they take a feed off the speaker out, sometimes this is balanced, and apply Neg feedback to the 12au7/6sny grids, or, if split cathodes, the cathodes.

So you could keep your speaker outs balanced, or use the 4 and 16 ohm taps and balance Neg back to the buffer stages.

You could also use a line in trans, and if there was another winding, drive it with speaker out. You would have to find a transformer with 3 windings, but very smooth sound that way.

Using a balanced input buffer to drive the pentodes, easier, just drive the cathodes from the 4 and 16 ohm taps in Negative

gEorge
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