SR45 amplifier

[Matts]

I've been enjoying my system for the some years, haven't been soldering or posting- hi to everyone!  I bought one of the original SR45 kits with the intention of picking up a pair of the PT-2's, but it looks like I've missed that boat, and the later group buy.  Is there another current substitute for it?  I also have the iron to build 45 direct-coupled amps that I haven't got around to, with the PGP 8.1's.  Maybe I could make that an SR-45 instead?  I also have some of the Exemplar Audio driver regulation boards, but no directions for them.

Is the new SR-45 project going to be a complete amp, or an add-on board for the regulation?

[denti alligator]

Maybe in the Spring I can do the comparison, or maybe Sail Doctor can take his 45 paramounts over to Clark's place and compare to the sr-45s over there.

That would be great!

[Paul Birkeland]

If we can get Sail Doctor to bring his 45 Paramounts over to Clark's, I can bring my SR-45's with Paramount output iron along for comparison.

[debk]

Wish I can e there
Love to hear the SR45 with Clark's Uni speakers

Deb

[Paul Joppa]

...
Is the new SR-45 project going to be a complete amp, or an add-on board for the regulation?

I'm just back from a 6-week vacation, and will probably be ordering parts for building the prototype new SR-45 amp in the next week or so - I already have the chassis plates on hand.

It's a complete amp.

The problems I have with the older design are mostly that it gets too hot - the heat sinking is inadequate and there were no cooling vents in the original chassis plate. In addition, I have always felt that the hum and fluctuations from unregulated AC filaments and heaters is inconsistent with the sonic potential of the high-voltage circuit. So the new design has much larger heat sinks, a large vent, and an actual cooling airflow design, plus regulated filament voltages, high-voltage delay, and a relay to protect the output transformer from magnetization by turn-on transients. It's more of a no-holds-barred design philosophy than I have used in other products.

[johnsonad]

Welcome back Paul!

[Matts]

Paul, very cool that you're doing an "all-out" design!  You're such a master at getting the most out of the "thriftier" designs, and I'm sure this will be something special.  Your mention of heat reminds me of all the items used by gamers on their motherboards. I'm thumbless and too old for games, but I bought a motherboard from the wall at Fry's some years ago because it had copper radiators and copper tubing that work on a convection method.  The salesman kept telling me I didn't need it for my computer use, but I couldn't pass up the hot-rod looks.  Maybe some shiny cooling tubes that look like the old street-rod headers would look cool coming out the sides, or some coming out of the top that look like velocity stacks?   I'm sure yours will be more elegant than that!

[debk]

Some mods to my SR45's:

A larger heat sink thanks to fellow Bottlehead forum member Jim R.
Replaced the electrolytic capacitors in the power supply with film capacitors.  Still not sure how I made every thing fit


(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi284.photobucket.com%2Falbums%2Fll38%2Fdebk3141%2F25c5c09b-a7fb-4286-a06b-420645b4a52d.jpg&hash=6f35077773d13c707e378831cd04f8f4a71ef018)

Debra

[xcortes]

Cathode bypass still electrolitic?.

[debk]

Yes not sure how I would fit anything else there

Debra

[debk]

So if I were to parallel a small film capacitor with the 100uf cathode bypass what value would you use?
Is 1% or the bypass cap or 1uf too low?  There really is not much room for a largish capacitor.

Deb

[Jim R.]

Hi Deb,

I'd eeven try 0.1uF as a bypass., but have you tried the amp with no cathode bypass cap at all?

What does the manual call for here -- I don't have mine handy -- it may be that a smaller cap than the specified value could be used. I know my amp has no cathode bypass at all but it was configured as a tweeter amp and as soon as my new speakers get here I plan to experiment with some different values and types here.

Glad the heatsinks got to you ok.

-- Jim

[Grainger49]

Like Jim says, try some.  Just get out the jumpers and see if you like the sound. 

Since it is the cathode it sees lower voltage.  So a 100V cap is fine.

BTW, is this a Paramour or Paramour II chassis?  It is getting full.

[johnsonad]

It's been my understanding (and I may be wrong) that the cathode bypass cap, switching from electrolytic to film, will have a larger effect on the sound vs. a PS cap in a Parafeed design.


The cathode bypass cap is not a high voltage rating but finding a large valued cap in a lower voltage is a little painful. I'm using the new Panasonic EZPE series in my next project. They are cheap and look to be a little smaller than those.

[Grainger49]

Aaron,

The power supply and cathode bypass cap are both in the signal path.  But those cathode bypass caps are large values.  Harder to find a good substitute.

To Deb and Aaron.  Look at the last post in this thread.  I am upgrading everything except the power supply caps.  They are already 47uF@650V PP/Oil caps.

http://www.bottlehead.com/smf/index.php/topic,3303.new.html#new