Counterpoint SA7 modification.. shottky diodes.. thoughts?

[240z4u]

I have a recently aquired counterpoint SA7 that I am fixing up. It has some leaky caps etc.. that I am swapping.

I read on altivista.com that one of the mods is swapping in high speed diodes for the stockers in the main power supply.

I just happen to have four shottky diodes in my posession that will work just fine. Is this a worthwhile mod? I know its a lower end preamp but I am attempting to squeeze as much good sound out of it as I can.

Anyone else have any suggestions for modding? I am going to do the wool felt trick and I dampened most of the chassis with dynamat already.

Thanks! - Evan

I hear these puppies run hot, so I will likely build an entire mesh top for it to keep things cool(er).

 

[kenpeter]

High voltage Schotkeys? I ususally see that type only on the low
voltage end of a switcher.... Unless you got something special?
I mean, they do make em to 200V, but its not a common item.

What you need is simply "Fast Recovery", probably Hexfreds...
Schotkey is extremely fast , no doubt. But if yours won't stand
the required reverse voltage, can't use it.

 

[240z4u]

Thanks for the headsup, they are at home and I have not had a chance to take a look at the voltage ratings lately. I can't remember what they are.

I will have to order some parts anyway here soon, so maybe Ill just grab something that I am sure will work.

Thanks - Evan

 

[audiopro]

I just finished doing one for a customer. Turned out quite well.
I used Hexfred diodes on the HV and ultrafast for the filament.
If you've got the board out, one thing to do is change the filter cap that is before the regulator. That one tends to fail.
If you're really into modding the power supply, get rid of the wimpy power transformer that's internal. I mounted a custom made toroid externally in a seperate enclosure. Still uses the front panel power switch though.

 

[240z4u]

Thanks Dan, I ordered replacements for all of the electrolytics. Mine are corroded at the ends and definitely need replacement.

I had considered at least moving the power supply outboard, but I want to see how this thing sounds in stock-ish form before I go too crazy. Ill want to build an umbilical etc.. if I do that.

In its current state, its definitely not right. If left on long enough, the resistors between the board and power supply start smoking .
I am not sure what the cause is but I figured replacing the visibly damaged caps was a good start.

I still have the original counterpoint tubes (not installed right now) and was wondering if anyone knew the actual maker of them.

Thanks guys, I have heard good AND bad things bout' this preamp and am prepared for disappointment honestly.

Evan

 

[analog_sa]

Hi Evan

Once i owned an SA-7. Not too bad but a bit bright and thin though quite detailed. An oversized PS may help but if you build a nice PS why not build an entire pre? It's really easy to beat the SA7.

My experience with the Cree Shottkys hasn't been very positive. Waited and waited for a miraculous break-in but it never happened. If anything they will exacerbate the thin, bright character of the preamp.

My advice: fix it, listen to it, sell it and build something nice.

 

[240z4u]

I picked up this SA7 for cheap and am going to dump a few dollars into it to get it back to 100% I always like the opportunity to try something different.

I agree I can probabally build something better, but I am SUPER slow when it comes to DIY stuff because I am such a noob. I have been working on a 12b4 preamp for months now on and off.

Thanks alot fellas, Ill just get this one back up to 100% without spending too much money on it.

Evan

 

[Lowrider]

There are Cree Schottky diodes up to 1200 Volts, I use them, and they did improve the sound a bit...

http://www.cree.com/products/power_docs2.asp

 

[240z4u]

http://www.cree.com/products/pdf/CSD01060.M.pdf

I have four of these, I am leaving town to go to my mothers house today.

Evan

 

[durkla18]

If anything it will be a learning experience. Let us know about those diodes and how they sound!
Andy

 

[240z4u]

I plan on fixing the preamp so it doesn't smoke and replacing electrolytics. Ill live with it for a bit then swap diodes to see if I can tell.

Evan

 

[poynton]

The best mod to make to a SA-7, is to replace the horrible input switch arrangement.

The phono stage is permanently in circuit !

I replaced the switch with a 3-way on-on-on .


Andy

 

[durkla18]

Hexfred diodes?

HFA04TB60PBF-ND DIODE HEXFRED 600V 4A TO220AC from Digikey

they have a 28ns reverse recovery time. Is this good for a tube amp power supply? And are rated for 600V and 4A.

The reason why I ask is because I would like to replace my UF4700 full wave diode bridge with four of these.

What does everyone think? Or, should I use a combo?

Thanks,

Andy

 

[durkla18]

K16 diode bridge?

I ordered the hexfreds, some Schottky diodes and some UF4700's so I will let everyone know how/which combination works the best for the diode bridge on the K16.
Andy

 

[Lowrider]

I use 1200V 6A for plate and 600V 4A for Bias, the original plate supply diodes where rated 1000V...

 

[durkla18]

Thank you for your response. I originally had a one piece diode bridge in my K16 amp from S5. I believe it was rated at 1amp, so I'm guessing that 4 amp will be OK to use.

Kind Regards,

Andy

 

[240z4u]

Wow, not sure how this thread took off without me noticing.

I replaced the electrolytics tonight and promptly broke off two of the transformer wires on the board. I see where they go but am not sure which one is which...

The white wire with black stripe and plain black wire. One goes twoard the outside of the board and one to the inside. It broke off at the board so repair is no huge problem.

That board/supply arrangement sure makes it a hassle to work on!

Evan