balanced tube preamp - Page 3

jam · 4th December 2001, 01:21 PM

Allen,

What are your thoughts of using a simple Zener after the current source (low current circuits)?
I own both your excellent books and I am waiting for your tube amp. cookbook. Do you know when that will be published?

Jam

Hedlund · 4th December 2001, 01:52 PM

>>What you have used is not a shunt regulator - it is a series regulator, but as you say - it does not have any NFB.<<

If you read my post again I wrote shunt regulated Mosfet which I still think it is. Should we say remi ?

>>I have tried many series regulators, with and without NFB - but found that a shunt reg fed from a current source always sounded better - even when using a lot of NFB. My experience across 25 years.<<

OK, I had just the opposite experience.

>>I'm sending you a PDF of such a current sourced shunt reg - this is not my design but it shows you the concept. It is VERY complex and this is not good IMO. <<

Thank you. I will take a closer look at it.

>>I prefer the SuperReg current sourced shunt reg topology because:

1/ It's bi-directional - accepting current reflected back from the load as well as supplying current.

2/ It maintains VERY precise powersupply line currents in the ground and B+ wiring - minimising crosstalk and general confusion. <<

Agreed, but what about the sonic signature of the regulating OP-amp which will be overlayed in the current domain.
About a year ago I used a very similar circuit and never got satisfied with it. Sounded just like a all Audio Research preamps that uses their solid state regulator.
Too front up sounstage and harsh upper mid and treble.

Janne

jam · 4th December 2001, 02:08 PM

Janne,

Could you post your schematic. You bring up a good question about the effect of the op-amp, I suspect the op-amp greatly affects the sonics of the regulator.

Jam

Hedlund · 4th December 2001, 02:32 PM

Jam,

I think it would be a better idea to start a new thread on power supply for tube preamps to let more builders ventilate their ideas and knowledge.
I'm sorry this thread have turned out to be a argument between me and Allen Wright. Undoubtly we have were different ideas about how to build a power supply.

I'm leaving. Thanks and goodbye.

Janne

Allen Wright · 5th December 2001, 04:26 PM

Jam,
You asked me:

>>>What are your thoughts of using a simple Zener after the current source (low current circuits)? <<<

It's an easy and quick solution, it's a true shunt reg and has very wide bandwidth - but has a rather high output impedance (OPZ). Zeners by themselves can also be quite noisy - especially the higher voltage ones you might use (say 47V) to advoid needing 30 or more of the quieter 6.2 or 6.8V ones.

But it's very hard to kill the noise with a capacitor as the zener's OPZ is low enough to need a really huge cap to make any difference to the noise - bringing in many other problems...

>>>I own both your excellent books and I am waiting for your tube amp. cookbook. Do you know when that will be published?<<<

The TubePoweramp CookBook will be published only when I have really special designs in all (common) amp formats. So far I have this in P-P, differential, and hybrid - but need some time to research/optimise tube OTL and a killer (if possible) SE.

Sorry, I dunno when this will be...

Allen (VSE)

Luke · 20th October 2008, 08:53 AM

Hi,

ive built this pre and Im having some trouble getting it going. At this stage I have not passed a signal through it but its connected to an amplifier and a test speaker.

It hums really badly, especially bad if its at the begining of the pot or end of the pot. The pot is a noble 50K pot.

The voltages are all fine and I have triple checked all the wiring.

Any ideas?

Just thought I would add, this is my first tube preamp.

Luke · 20th October 2008, 10:30 AM

theres a couple of other points I'm not sure about.

1. I use an umbilicle psu with 80v 12V and Gnd. This ok?

2. The input and output cables are not shielded.

3. I use a tag strip as the star ground point, it has a copper wire along it and mounts to a cast alloy case in two points. Should one point not be grounded, ie one insulated?

4. The transformer I had for the 6922 filaments is 12v. I used a 7812 and raised the ground with a diode to give 12.6 v. I then connected 2 tubes heaters in series with a 1k resistor across each tubes heater. One of my heaters is not grounded should this matter? I cant see why this would cause a problem.

Bandersnatch · 20th October 2008, 09:15 PM

hey-Hey!!!,
I have built a PP linestage. It uses the Russian 6C45 in LTP/diff amp with a cascode CCS in the tail. The plate load is a 20k:600/150 from the Chicago Super Range, the BO-2. It will deliver a Watt into 600 or 150 Ohms and the circuit will back it up. The 10k load presented to each triode yeilds a 5 or 6 to 1 ratio v. its plate Z, so for the balanced 600R output, I'm getting about 100R output Z. On the 150R connection, it is more like 30 Ohms. With drive like that I can put the linestage and source next door( or at least across the room )and not have to worry about losses. The amps I've built are all PP and rigged with the excellent Neutrik XLR input jacks.

So far the OPT's have been remarkably inexpensive on ebay. I have two in service and one spare to unwind and make more at some point. According to the specs both primary and secondary have balanced capacitance to ground and the winding DCR is quite well matched ( around 280 R per half primary ). If there's any interest in a pair of these, let me know as I'd like a second set; we'll start the reproduction process straight away...

cheers,
Douglas

Luke · 18th March 2010, 07:40 AM

Does any one know if its ok to use this as a headphone amp?

hidnplayr · 18th March 2010, 09:50 AM

I'm about to build this circuit, does anyone have any comments for me before I start building it?

I'm not sure about how much current i should let flow through the SN7's.

20th October 2008, 09:15 PM	#28
Bandersnatch diyAudio Member Join Date: Jul 2003 Location: Ann Arbor, MI	hey-Hey!!!, I have built a PP linestage. It uses the Russian 6C45 in LTP/diff amp with a cascode CCS in the tail. The plate load is a 20k:600/150 from the Chicago Super Range, the BO-2. It will deliver a Watt into 600 or 150 Ohms and the circuit will back it up. The 10k load presented to each triode yeilds a 5 or 6 to 1 ratio v. its plate Z, so for the balanced 600R output, I'm getting about 100R output Z. On the 150R connection, it is more like 30 Ohms. With drive like that I can put the linestage and source next door( or at least across the room )and not have to worry about losses. The amps I've built are all PP and rigged with the excellent Neutrik XLR input jacks. So far the OPT's have been remarkably inexpensive on ebay. I have two in service and one spare to unwind and make more at some point. According to the specs both primary and secondary have balanced capacitance to ground and the winding DCR is quite well matched ( around 280 R per half primary ). If there's any interest in a pair of these, let me know as I'd like a second set; we'll start the reproduction process straight away... cheers, Douglas __________________ the Tnuctipun will return

18th March 2010, 07:40 AM	#29
Luke diyAudio Member Join Date: Sep 2001 Location: Wellington NZ	Does any one know if its ok to use this as a headphone amp? __________________ If you give a man a fish he will eat for a day. But if you teach a man to fish he will buy an ugly hat. And if you talk about fish to a starving man then you are a consultant. Dilbert

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4th December 2001, 01:21 PM	#21
jam diyAudio Member Join Date: May 2001 Location: Charlotte,NC,USA	Allen, What are your thoughts of using a simple Zener after the current source (low current circuits)? I own both your excellent books and I am waiting for your tube amp. cookbook. Do you know when that will be published? Jam

4th December 2001, 01:52 PM	#22
Hedlund diyAudio Member Join Date: Oct 2001 Location: Alvesta, Sweden	>>What you have used is not a shunt regulator - it is a series regulator, but as you say - it does not have any NFB.<< If you read my post again I wrote shunt regulated Mosfet which I still think it is. Should we say remi ? >>I have tried many series regulators, with and without NFB - but found that a shunt reg fed from a current source always sounded better - even when using a lot of NFB. My experience across 25 years.<< OK, I had just the opposite experience. >>I'm sending you a PDF of such a current sourced shunt reg - this is not my design but it shows you the concept. It is VERY complex and this is not good IMO. << Thank you. I will take a closer look at it. >>I prefer the SuperReg current sourced shunt reg topology because: 1/ It's bi-directional - accepting current reflected back from the load as well as supplying current. 2/ It maintains VERY precise powersupply line currents in the ground and B+ wiring - minimising crosstalk and general confusion. << Agreed, but what about the sonic signature of the regulating OP-amp which will be overlayed in the current domain. About a year ago I used a very similar circuit and never got satisfied with it. Sounded just like a all Audio Research preamps that uses their solid state regulator. Too front up sounstage and harsh upper mid and treble. Janne

4th December 2001, 02:08 PM	#23
jam diyAudio Member Join Date: May 2001 Location: Charlotte,NC,USA	Janne, Could you post your schematic. You bring up a good question about the effect of the op-amp, I suspect the op-amp greatly affects the sonics of the regulator. Jam

4th December 2001, 02:32 PM	#24
Hedlund diyAudio Member Join Date: Oct 2001 Location: Alvesta, Sweden	Jam, I think it would be a better idea to start a new thread on power supply for tube preamps to let more builders ventilate their ideas and knowledge. I'm sorry this thread have turned out to be a argument between me and Allen Wright. Undoubtly we have were different ideas about how to build a power supply. I'm leaving. Thanks and goodbye. Janne

5th December 2001, 04:26 PM	#25
Allen Wright R.I.P. Join Date: Dec 2001 Location: Schaffhausen Switzerland	Jam, You asked me: >>>What are your thoughts of using a simple Zener after the current source (low current circuits)? <<< It's an easy and quick solution, it's a true shunt reg and has very wide bandwidth - but has a rather high output impedance (OPZ). Zeners by themselves can also be quite noisy - especially the higher voltage ones you might use (say 47V) to advoid needing 30 or more of the quieter 6.2 or 6.8V ones. But it's very hard to kill the noise with a capacitor as the zener's OPZ is low enough to need a really huge cap to make any difference to the noise - bringing in many other problems... >>>I own both your excellent books and I am waiting for your tube amp. cookbook. Do you know when that will be published?<<< The TubePoweramp CookBook will be published only when I have really special designs in all (common) amp formats. So far I have this in P-P, differential, and hybrid - but need some time to research/optimise tube OTL and a killer (if possible) SE. Sorry, I dunno when this will be... Allen (VSE)

20th October 2008, 08:53 AM	#26
Luke diyAudio Member Join Date: Sep 2001 Location: Wellington NZ	Hi, ive built this pre and Im having some trouble getting it going. At this stage I have not passed a signal through it but its connected to an amplifier and a test speaker. It hums really badly, especially bad if its at the begining of the pot or end of the pot. The pot is a noble 50K pot. The voltages are all fine and I have triple checked all the wiring. Any ideas? Just thought I would add, this is my first tube preamp.

20th October 2008, 10:30 AM	#27
Luke diyAudio Member Join Date: Sep 2001 Location: Wellington NZ	theres a couple of other points I'm not sure about. 1. I use an umbilicle psu with 80v 12V and Gnd. This ok? 2. The input and output cables are not shielded. 3. I use a tag strip as the star ground point, it has a copper wire along it and mounts to a cast alloy case in two points. Should one point not be grounded, ie one insulated? 4. The transformer I had for the 6922 filaments is 12v. I used a 7812 and raised the ground with a diode to give 12.6 v. I then connected 2 tubes heaters in series with a 1k resistor across each tubes heater. One of my heaters is not grounded should this matter? I cant see why this would cause a problem.

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