Theshold S500II

mike m · 15th January 2003, 09:21 PM

Purchasing this amp. Wondering what mods is there for it and can it be turned into a mono amp?

GRollins · 15th January 2003, 10:00 PM

Mods? How crazy do you want to get? Add caps to the power supply? Swap transistors in the front end? Rebuild it as an X? (Don't take me up on that last one. I've got too many projects on my plate already.)
The amp can be bridged by inverting the input to one channel and using the positive outputs <i>only</i>. Leave the negative outputs alone. The power will be x4 until you exceed the available current; it's a good idea to stick with 8 ohm loads so that this dosn't happen too quickly.
I've got two of the original S-500s. They make good low frequency amps. The mids and highs are a little cloudy, but still match or exceed a number of the units on the market today. Ditto for imaging and detail retrieval.

Grey

Nelson Pass · 16th January 2003, 04:29 AM

I have a nice fix for that: new front end and higher bias.
I believe I've already posted the last (never to be produced)
front end for the Stasis series, delivered as I walked out
the door.

If you can't find the reference, let me know and I'll repost it.
It was remarkable for being totally DC coupled with almost no
drift at all and was improved in every respect over its
predecessors.

mike m · 16th January 2003, 08:14 AM

I cannot find the modification please repost > Thank You.

Nelson Pass · 20th January 2003, 09:43 PM

www.passlabs.com/temp/thr_fe90.tif

mike m · 21st January 2003, 11:28 PM

Quote:

Originally posted by Nelson Pass
www.passlabs.com/temp/thr_fe90.tif

I cannot open that file can anyone help!

planet10 · 22nd January 2003, 12:06 AM

Quote:

Originally posted by mike m
I cannot open that file can anyone help!

Nelson Pass · 22nd January 2003, 04:37 AM

Yep, I was walking out the door about then, and this would
be the last piece of schematic I left, along with my white
paper "IGBT's: Threat or Menace"

Yeah, I know, I really amuse myself with that kind of humor.

I believe this schematic made it into some updates, but not
production. Its primary virtue was that there was almost
no thermal drift, as all the temperature coefficients of each
component were carefully measured and calculated and the
circuit was designed to null the PN junction drift throughout.

macka · 22nd January 2003, 05:23 AM

April 17 1990.

Thats a while go now, quite a few millcentons (Vulcan calander)

"IGBT's: Threat or Menace"

So what was the paper pointing out, or did you build a better mouse trap?

Ian

Nelson Pass · 22nd January 2003, 05:40 PM

The paper discussed the difficulties of matching the
devices due to their dual device nature and the
inability to bias the mosfet part of the part at a
greater current than the Base current of the Bipolar
part. In an ordinary circuit, the driver is biased at
higher than the draw of the following part, which
improves the linearity and speed.

15th January 2003, 09:21 PM	#1
mike m diyAudio Member Join Date: Nov 2002 Location: nevada	Theshold S500II Purchasing this amp. Wondering what mods is there for it and can it be turned into a mono amp?

16th January 2003, 08:14 AM	#4
mike m diyAudio Member Join Date: Nov 2002 Location: nevada	S500II I cannot find the modification please repost > Thank You.

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15th January 2003, 10:00 PM	#2
GRollins diyAudio Member Join Date: Feb 2001 Location: Columbia, SC	Mods? How crazy do you want to get? Add caps to the power supply? Swap transistors in the front end? Rebuild it as an X? (Don't take me up on that last one. I've got too many projects on my plate already.) The amp can be bridged by inverting the input to one channel and using the positive outputs <i>only</i>. Leave the negative outputs alone. The power will be x4 until you exceed the available current; it's a good idea to stick with 8 ohm loads so that this dosn't happen too quickly. I've got two of the original S-500s. They make good low frequency amps. The mids and highs are a little cloudy, but still match or exceed a number of the units on the market today. Ditto for imaging and detail retrieval. Grey

16th January 2003, 04:29 AM	#3
Nelson Pass The one and only Join Date: Mar 2001	I have a nice fix for that: new front end and higher bias. I believe I've already posted the last (never to be produced) front end for the Stasis series, delivered as I walked out the door. If you can't find the reference, let me know and I'll repost it. It was remarkable for being totally DC coupled with almost no drift at all and was improved in every respect over its predecessors.

20th January 2003, 09:43 PM	#5
Nelson Pass The one and only Join Date: Mar 2001	www.passlabs.com/temp/thr_fe90.tif

22nd January 2003, 04:37 AM	#8
Nelson Pass The one and only Join Date: Mar 2001	Yep, I was walking out the door about then, and this would be the last piece of schematic I left, along with my white paper "IGBT's: Threat or Menace" Yeah, I know, I really amuse myself with that kind of humor. I believe this schematic made it into some updates, but not production. Its primary virtue was that there was almost no thermal drift, as all the temperature coefficients of each component were carefully measured and calculated and the circuit was designed to null the PN junction drift throughout.

22nd January 2003, 05:23 AM	#9
macka diyAudio Member Join Date: Dec 2001 Location: Australia	April 17 1990. Thats a while go now, quite a few millcentons (Vulcan calander) "IGBT's: Threat or Menace" So what was the paper pointing out, or did you build a better mouse trap? Ian

22nd January 2003, 05:40 PM	#10
Nelson Pass The one and only Join Date: Mar 2001	The paper discussed the difficulties of matching the devices due to their dual device nature and the inability to bias the mosfet part of the part at a greater current than the Base current of the Bipolar part. In an ordinary circuit, the driver is biased at higher than the draw of the following part, which improves the linearity and speed.

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