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-   -   Converting a Threshold S300 to SA/3? (http://www.diyaudio.com/forums/pass-labs/205291-converting-threshold-s300-sa-3-a.html)

Redwingnine 25th January 2012 08:30 PM

Converting a Threshold S300 to SA/3?
 
I would like to be able to convert a Threshold S300 to a SA3. From looking at the manuals, it looks like the amps are very similar.

Was looking for input as to if this is possibe? The speakers I'm using seem to work fine with a SA/3 I tried out on them (loves the high current).

Thanks for any help.

seng 26th January 2012 02:56 AM

Converting a Threshold S300 to SA/3?
 
1 Attachment(s)
I just convert my SA3 to S300 , if you want convert S300 to SA3, it only need to changed the supply voltage from +- 62 V to +- 34V (the original transformer had this wiring) and adjust the VR5K to the proper bias for the out put transistors (totat 2.2A for each channel).

analog_sa 26th January 2012 06:10 AM

Don't think all S300 transformers have this option though.

Redwingnine 26th January 2012 09:59 PM

Thanks much for the feedback. My S300s are optical bias types, so the trasformers should support this.

Curious as to why you converted to S300? Do you need the extra voltage for your speakers? I have found that the Class A output to sound better overall with my speakers.

seng 27th January 2012 07:11 AM

Converting a Threshold S300 to SA/3?
 
3 Attachment(s)
Yes, class A is better, so I had Threshold SA3 & T100, but SA3 can converted to S300 to drive my Dynaudio Speakers.
Besides,please replaced the 4pcs rail fuse to 8A after you converted to SA3.

Redwingnine 5th February 2012 12:32 PM

3 Attachment(s)
Completed the conversion of the first of two S300 to SA/3. Also changed out the emitter resistors.

The bias was a bit tricky, but it did stay at the new setting after a couple of tries.

I continue to be amazed at just how different (and better) tha amp sounds runnig in class A. It seems that most speakers are quite happy with 50 watts in class A. The speakers seem to have more bass heft running class A, and the reduced distortion is audible, no question.

This is one my favorite amps from Nelson. It just sounds like music.

Zen Mod 5th February 2012 12:48 PM

just be sure that that Graetz cooling plate on top of caps isn't too hot

everything above hand temp is too much for caps

relocate Graetz on back plate , if needed

Redwingnine 5th February 2012 03:48 PM

Quote:

Originally Posted by Zen Mod (Post 2892761)
just be sure that that Graetz cooling plate on top of caps isn't too hot

everything above hand temp is too much for caps

relocate Graetz on back plate , if needed


The chassis, plate, and internel layout of the S300 and SA/3 iis identical, so no worries there.

Class A is definately the way to go if the speakes support it. :cool:

PKI 5th February 2012 11:19 PM

and can S200 be converted in to class A amp SA/something? Thanks.

Redwingnine 6th February 2012 02:36 AM

Quote:

Originally Posted by PKI (Post 2893531)
and can S200 be converted in to class A amp SA/something? Thanks.


The short answer is, no, do not think so. The trnsformer in S200 is only 400VA, and I am not sure what other rails are on it.

You could check with Jon S. ay Vintage Amp Repair to ask.


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