Single or dual differential? - Page 7

john curl · 15th November 2003, 07:10 PM

You are close, hitsware. This design concept is about 30 years old, as it was first used in the JC-2. Now, how can we improve it?

Bricolo · 15th November 2003, 08:32 PM

by adding current sources?

hitsware · 15th November 2003, 10:19 PM

Quote:

Originally posted by john curl
You are close, hitsware. This design concept is about 30 years old, as it was first used in the JC-2. Now, how can we improve it?

I know it can be unstable. In at times unpridictable ways. Also at times it will blow the P channel output (using Hitachis). Perhaps it blows the outputs by pulling the gate too low and burning the input zener so gate resistors may solve that. The whole thing may be better implemented with bipolars (putting the - input devices on the heatsinks for thermal compensation. AND carefull selection of the outputs (rugged enough to withstand the SOA problems this type output scheme (common emitter(source)) seems to engender.........mike

jam · 15th November 2003, 10:54 PM

Mr.Curl,

What if we replace the resistors on the tails of the differential with adjustable current sources, we would be then able to adjust bias and dc offset at the same time.
My question , how the bias stability of such a circuit would be?

Regards,
Jam

john curl · 15th November 2003, 10:55 PM

First, think about removing ALL the current sources and just using 1 resistor between the source pairs on the input. Second, this is actually a very stable design, because it has almost no gain, but 1/2A Hitachi devices can be problematic, because they are not well matched in this situation. The P channel looks like a triode, but the N channel looks like a pentode. Too much 2'nd harmonic. How do we fix this?

jam · 15th November 2003, 11:04 PM

Cascode the output pair?

john curl · 15th November 2003, 11:06 PM

Yep, makes a world of difference, in this case. This is essentially the 2'nd stage for my Vendetta Research phono preamp.

fdegrove · 15th November 2003, 11:10 PM

Hi,

Quote:

Cascode the output pair?

Good thinking, that would change the harmonic spectrum reducing the second harmonic.

Oops... I just see you had a reply already.

Cheers,

jam · 15th November 2003, 11:16 PM

Mr. Curl,

If you were to update the JC-3, would this be the topology you would use? It would be fairly simple to add a Vbe multiplier and outputs to the circuit.

If this is is correct would you choose bipolars (with drivers) or mosfets for the outputs, and would you still use the inverting configuration?

Regards,
Jam

jam · 15th November 2003, 11:24 PM

Frank,

Trolling the solid state section again? .......................

You will soon be joining us.

Regards,
Jam

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Discrete Dual Differential DAC?	dantwomey	Digital Source	18	5th March 2011 07:24 AM
single-ended to differential?	gentlevoice	Digital Line Level	16	17th December 2008 07:18 AM
Single Differential Non-feedback	lumanauw	Solid State	3	5th September 2004 03:29 AM
Differential to single ended...	Bas Horneman	Tubes / Valves	21	2nd April 2003 03:05 PM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read


	Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving

15th November 2003, 07:10 PM	#61
john curl diyAudio Member Join Date: Jul 2003 Location: berkeley ca	You are close, hitsware. This design concept is about 30 years old, as it was first used in the JC-2. Now, how can we improve it?

15th November 2003, 08:32 PM	#62
Bricolo diyAudio Member Join Date: Nov 2002 Location: Grenoble, FR	by adding current sources?

15th November 2003, 10:54 PM	#64
jam diyAudio Member Join Date: May 2001 Location: Charlotte,NC,USA	Mr.Curl, What if we replace the resistors on the tails of the differential with adjustable current sources, we would be then able to adjust bias and dc offset at the same time. My question , how the bias stability of such a circuit would be? Regards, Jam

15th November 2003, 10:55 PM	#65
john curl diyAudio Member Join Date: Jul 2003 Location: berkeley ca	First, think about removing ALL the current sources and just using 1 resistor between the source pairs on the input. Second, this is actually a very stable design, because it has almost no gain, but 1/2A Hitachi devices can be problematic, because they are not well matched in this situation. The P channel looks like a triode, but the N channel looks like a pentode. Too much 2'nd harmonic. How do we fix this?

15th November 2003, 11:04 PM	#66
jam diyAudio Member Join Date: May 2001 Location: Charlotte,NC,USA	Cascode the output pair?

15th November 2003, 11:06 PM	#67
john curl diyAudio Member Join Date: Jul 2003 Location: berkeley ca	Yep, makes a world of difference, in this case. This is essentially the 2'nd stage for my Vendetta Research phono preamp.

15th November 2003, 11:16 PM	#69
jam diyAudio Member Join Date: May 2001 Location: Charlotte,NC,USA	Mr. Curl, If you were to update the JC-3, would this be the topology you would use? It would be fairly simple to add a Vbe multiplier and outputs to the circuit. If this is is correct would you choose bipolars (with drivers) or mosfets for the outputs, and would you still use the inverting configuration? Regards, Jam

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)