eXStata DIY Electrostatic Amp for Intermediate DIYers

[pabbi1]

What I find so amazing is that when you actually hear all the microdetail, it really changes your opinion of musicians, not just in what they can do musically, but the attention to detail, and how complete the canvas can be. Or, other long held favorites tend to rather wilt in how flat and rushed the effort is compared to someone with the studio time (budget) to really get something right. Well, or just tacking crap on to make something sound more robust without any other real purpose.

Oasis tends to be in my first group, and early AC/DC tends to be in my latter, but, it's hard to kill that 1961 Les Paul (that looks like a SG) or Malcolm's Gretsch.

Yeah, it would be nice to hear more impressions, as this really is a small club, and not that difficult a build.

 

[BoilermakerFan]

Quote:

Originally Posted by pabbi1 /img/forum/go_quote.gif What I find so amazing is that when you actually hear all the microdetail, it really changes your opinion of musicians, not just in what they can do musically, but the attention to detail, and how complete the canvas can be. Or, other long held favorites tend to rather wilt in how flat and rushed the effort is compared to someone with the studio time (budget) to really get something right. Well, or just tacking crap on to make something sound more robust without any other real purpose. Oasis tends to be in my first group, and early AC/DC tends to be in my latter, but, it's hard to kill that 1961 Les Paul (that looks like a SG) or Malcolm's Gretsch. Yeah, it would be nice to hear more impressions, as this really is a small club, and not that difficult a build.

Time has not been my friend as of late and one of the suppliers I need to order from took forever to confirm an order and I'm not sure when it's going to show up...

But once I can start building, there will be two more eXstatas reporting in, one will be my SS and the Hybrid goes to a member who will post his own experiences.


If we have a PS transformer that has the heater windings, is there any reason why it can't be used for a SS amp? I'm assuming it can be used without damage as long as the leads do not short out, correct?

 

[pabbi1]

Quote:

Originally Posted by BoilermakerFan /img/forum/go_quote.gif If we have a PS transformer that has the heater windings, is there any reason why it can't be used for a SS amp? I'm assuming it can be used without damage as long as the leads do not short out, correct?

Yes, that is my experience, though mine is normally that the heater windings are 6.3v and 5v, where the 5v just gets clipped, or tied off, with the liquid electrical tape applied to the ends.

 

[macm75]

Quote:

Originally Posted by BoilermakerFan /img/forum/go_quote.gif If we have a PS transformer that has the heater windings, is there any reason why it can't be used for a SS amp? I'm assuming it can be used without damage as long as the leads do not short out, correct?

I know Pabbi1 already reported but just wished to confirm. No problem with not using a winding what-so-ever. And like you said, electrical tape the unused ends. Matter of fact, I picked up a old/unmarked transformer for this project and pretty sure (or assume to be safe) the 6.3V winding will not be able to deliver 2.5+ A. They will go unused and I'll have a separate filament transformer for 6.3VAC (on the hybrid).

 

[luvdunhill]

you might see higher voltages if all the windings are not utilized, depending on the specs of the transformer.

 

[Beefy]

Quote:

Originally Posted by pabbi1 /img/forum/go_quote.gif Yes, that is my experience, though mine is normally that the heater windings are 6.3v and 5v, where the 5v just gets clipped, or tied off, with the liquid electrical tape applied to the ends.

I would use a terminal block personally......

 

[BoilermakerFan]

Quote:

Originally Posted by Beefy /img/forum/go_quote.gif I would use a terminal block personally......

That was my plan. I have those sweet miniature 15mm DIN rail terminal blocks.

 

[macm75]

Guys,
Just powered the PS with dummy load minutes ago. I get 238-0-238VAC in and adjusted P1 and P2 to get the desired 360mV and 410mV respectively. I do not get greater than +320V and -320V at T1 and T3. I measured +298V and -298V (same as the output at the dummy loads) - can I move forward or is this an issue?
Thanks, Joe

 

[Beefy]

Well, it would say to me that you are essentially getting no regulation. Far from ideal.

Refresh my memory...... what transformer are you using?

 

[macm75]

Quote:

Originally Posted by Beefy /img/forum/go_quote.gif Well, it would say to me that you are essentially getting no regulation. Far from ideal. Refresh my memory...... what transformer are you using?

Transformer comes out of an old tape recorder. I have another to use but cannot see why transformer would be the issue.
I powered it up again and found another issue. New concern is T1-T2 and T3-T4 only sit at there desired voltage for moments. After about 30 seconds, they start drifting lower and LED's go out.
At first I'd ask what transistors do I need to replace but the issue is with both sides. Rats - transformer is the only thing that is common to both sides but all the while the PT continues to hold at 238-0-238VAC.

 

[Beefy]

Quote:

Originally Posted by macm75 /img/forum/go_quote.gif Transformer comes out of an old tape recorder. I have another to use but cannot see why transformer would be the issue. I powered it up again and found another issue. New concern is T1-T2 and T3-T4 only sit at there desired voltage for moments. After about 30 seconds, they start drifting lower and LED's go out. At first I'd ask what transistors do I need to replace but the issue is with both sides. Rats - transformer is the only thing that is common to both sides but all the while the PT continues to hold at 238-0-238VAC.

No, I think it is definitely the transformer.

While the amp is cold, and the zener string is cold, the voltage reference is close to the 'proper' value of 291V. As long as the T1-T3 voltage is higher than this, current will flow through the shunt transistors and the LEDs lighting them up.

But as the PSU/zener string warms up, the voltage reference gets higher due to the zener's positive tempco - it rises into the 300-310V range. If this is higher than the T1-T3 voltage, no current flows through the shunt transistors or LEDs.

 

[macm75]

Quote:

Originally Posted by Beefy /img/forum/go_quote.gif Well, it would say to me that you are essentially getting no regulation. Far from ideal. Refresh my memory...... what transformer are you using?

OK Beefy, transformer is the issue. Way back I remember Alex saying we need (if I remember correctly) between 320V and 350V at the caps. I'm short - I only get 295 - I obviously need some overhead to regulate.
I'm getting the other transformer out - I believe it supplies more voltage.
These transformers are free so I cannot complain so far.

Edit, I wrote mine as while you posted. As I said, you're on the money. Thanks.

 

[macm75]

New PT is in. Better but still not at the specified T1/T3 values. I now have 315V on T1 and 312V on T3. T1-T2 and T3-T4 are steady at 360/410mV.
I'm assuming I'm out of luck with my free-bee's but...
instead of replacing a PT, can I replace my 91V zeners with say ~80V and run B+ at -290V and +290V. Surely the circuit does not care about 10V difference in supply voltage.

 

[Beefy]

Yeah, you could do that and it wouldn't hurt too much. Just a few less volts maximum swing...... or a little bit less permanent deafness, if you prefer to look at it that way

 

[macm75]

Thanks for the support Beefy. Luckily I found an ebay seller with 75 and 82 volters located less than an hour from my house. Wait (although not easy) will not be long.