Surround Decoder - Subtract amplifier

mod_evil · 8th July 2006, 01:24 PM

Hi Friends.

How I can make a subtract amplifier with tubes? I'm talking to a friend to make a surround sound decoder from stereo. But I'm not like to do this with op-amps. I like to do with tubes.

I haven't idea to how make this. But I think I need a negative input and a postive input.

I'm not talking about pre-amplifier, amplifiers or anymore. I'm talking to all to make a surround decoder for stereo sound!

In OP-AMPS this is very simple:

Page: http://sound.westhost.com/project18.htm

But, the problem to make it with tubes is HOW I MAKE A SUBTRACT AMPLIFIER WITH TUBES?

This is the frist problem...

Best Regards,
Felipe Navarro

Eli Duttman · 8th July 2006, 02:12 PM

Felipe,

Opamps were made with tubes before they were made with SS. The key element for building an opamp is the differential gain block at its I/P. The long tailed pair and Schmitt phase splitter circuits are variations on the differential amp theme. Look here.

Differential amps work best when a current sink is in the "tail". We used FETs for the CCS in "El Cheapo", but a pentode, like the 6AU6, is fine.

The 5965 is very linear and has good section to section balance. With its mu of 44, it also provides a fair amount of gain. IMO, 5965 based differential gain blocks are a good place to start your surround sound project.

mod_evil · 8th July 2006, 02:20 PM

Eli,

Thanks for your reply.

With phase splinters or diferencial amplifiers only will amplifier the sound.

I need a subtract amplifier.

I'm stay reading this page: http://www.tubecad.com/march2000/page13.html and I think i need something similiar.

The subtract amplifier diminish the differeces of the channels and make the surround sound.

Are you undestanding me?

Best Regards,
Felipe Navarro

Eli Duttman · 8th July 2006, 03:18 PM

Felipe,

When used as a phase splitter, the non-inverting I/P is either grounded or used for the application of NFB. For your surround project, you connect a channel to the inverting I/P and the 2nd channel to the non-inverting I/P. 2 out of phase signals are produced. Those signals are the difference between the 2 channels and that's exactly what you are looking for.

Edit: typos fixed

mod_evil · 8th July 2006, 03:27 PM

Hi Eli,

Can you draw this? Because I'm not undestanding how are you speaking

Can you?

Please.

Best Regards,
Felipe Navarro

poobah · 8th July 2006, 03:27 PM

Felipe,

The second schematic in your link is correct and is also the "the long tailed pair" that Eli is talking about.

poobah · 8th July 2006, 03:51 PM

Here.

You must use caps to remove DC levels... and you must adjust your resistors for a gain of 1.

mod_evil · 8th July 2006, 04:03 PM

Hi Poobah and Friends.

I have simulated this processor on the circuit maker and I have a senoidal very very distorced.

But...

Without the V5, with 35v simetrical rails, I haven't distortion on the senoidal.

What they think about it?

poobah · 8th July 2006, 04:04 PM

Like this...

JoshK · 8th July 2006, 04:06 PM

Great idea! Muito bem!

However, I am not much of a fan of 5.1. I have heard an alternative to typical SS, known as ambiophonics (google search and you'll find a website named as such and tons of info) which in my mind sounded the most realistic that I have ever heard from non-live playback. A friend of mine modded a JVC pre DD SS decoder to do this type of SS, but he still has it.

Then there is the SpreadSpectrum version of taking stereo to trinaural. I think that could be done like this as well. Anyway, good luck with your project and keep us up on the progress.

Josh

8th July 2006, 01:24 PM	#1
mod_evil diyAudio Member Join Date: Dec 2004 Location: Rio	Surround Decoder - Subtract amplifier Hi Friends. How I can make a subtract amplifier with tubes? I'm talking to a friend to make a surround sound decoder from stereo. But I'm not like to do this with op-amps. I like to do with tubes. I haven't idea to how make this. But I think I need a negative input and a postive input. I'm not talking about pre-amplifier, amplifiers or anymore. I'm talking to all to make a surround decoder for stereo sound! In OP-AMPS this is very simple: Page: http://sound.westhost.com/project18.htm But, the problem to make it with tubes is HOW I MAKE A SUBTRACT AMPLIFIER WITH TUBES? This is the frist problem... Best Regards, Felipe Navarro __________________ Brazilian Tube Amp Builder.

8th July 2006, 02:12 PM	#2
Eli Duttman diyAudio Member Join Date: Apr 2004 Location: Plainsboro, NJ	Felipe, Opamps were made with tubes before they were made with SS. The key element for building an opamp is the differential gain block at its I/P. The long tailed pair and Schmitt phase splitter circuits are variations on the differential amp theme. Look here. Differential amps work best when a current sink is in the "tail". We used FETs for the CCS in "El Cheapo", but a pentode, like the 6AU6, is fine. The 5965 is very linear and has good section to section balance. With its mu of 44, it also provides a fair amount of gain. IMO, 5965 based differential gain blocks are a good place to start your surround sound project. __________________ Eli D.

8th July 2006, 02:20 PM	#3
mod_evil diyAudio Member Join Date: Dec 2004 Location: Rio	Eli, Thanks for your reply. With phase splinters or diferencial amplifiers only will amplifier the sound. I need a subtract amplifier. I'm stay reading this page: http://www.tubecad.com/march2000/page13.html and I think i need something similiar. The subtract amplifier diminish the differeces of the channels and make the surround sound. Are you undestanding me? Best Regards, Felipe Navarro __________________ Brazilian Tube Amp Builder.

8th July 2006, 03:18 PM	#4
Eli Duttman diyAudio Member Join Date: Apr 2004 Location: Plainsboro, NJ	Felipe, When used as a phase splitter, the non-inverting I/P is either grounded or used for the application of NFB. For your surround project, you connect a channel to the inverting I/P and the 2nd channel to the non-inverting I/P. 2 out of phase signals are produced. Those signals are the difference between the 2 channels and that's exactly what you are looking for. Edit: typos fixed __________________ Eli D.

8th July 2006, 03:27 PM	#5
mod_evil diyAudio Member Join Date: Dec 2004 Location: Rio	Hi Eli, Can you draw this? Because I'm not undestanding how are you speaking Can you? Please. Best Regards, Felipe Navarro __________________ Brazilian Tube Amp Builder.

8th July 2006, 03:27 PM	#6
poobah diyAudio Member Join Date: Nov 2005	Felipe, The second schematic in your link is correct and is also the "the long tailed pair" that Eli is talking about.

8th July 2006, 04:06 PM	#10
JoshK diyAudio Member Join Date: May 2004 Location: Toronto, ON	Great idea! Muito bem! However, I am not much of a fan of 5.1. I have heard an alternative to typical SS, known as ambiophonics (google search and you'll find a website named as such and tons of info) which in my mind sounded the most realistic that I have ever heard from non-live playback. A friend of mine modded a JVC pre DD SS decoder to do this type of SS, but he still has it. Then there is the SpreadSpectrum version of taking stereo to trinaural. I think that could be done like this as well. Anyway, good luck with your project and keep us up on the progress. Josh

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