Does anyone have any schematics for a parafeed SET amp?

[zman3]

Hello all,

I was just wondering if anyone had schematics for a parafeed SET amp (2A3, 6AS7, etc.). There just doesn't seem to be much of anything out there besides the stuff on the Magnequest site. I'm sure those are some great-sounding amps, but I just don't have that kind of money for iron right now!

I seem to remember a 6EM7 parafeed amp floating around on this forum in the past, and that sounds like it's right up my alley. At any rate, I'd appreciate any sort of help or wisdom anyone could share on this matter...

Thanks!

[alexg]

I built a 6080/6as7 parafeed amp using 12at7 as driver and using a Talema mains toroidal transformer as OPT.

I have not drawn the schematic, as soon as I do, I will post it here.

It sounds quite good.

[Sheldon]

Originally posted by zman3
Hello all,

I was just wondering if anyone had schematics for a parafeed SET amp (2A3, 6AS7, etc.). There just doesn't seem to be much of anything out there besides the stuff on the Magnequest site. I'm sure those are some great-sounding amps, but I just don't have that kind of money for iron right now!

I seem to remember a 6EM7 parafeed amp floating around on this forum in the past, and that sounds like it's right up my alley. At any rate, I'd appreciate any sort of help or wisdom anyone could share on this matter...

Thanks!

You can take any single ended design and make it parafeed. You just need a choke, cap and output transformer. This site gives some good guidelines for choosing the choke and cap. The OPT just needs to have the right impedance ratio (same as it would be for regular single ended, but no gap needed): http://www.siteswithstyle.com/VoltSe...afeed_fun.html

You can maybe get away with more ripple on the B+, as the choke load provides better isolation that a SE transformer, otherwise everything else can remain exactly the same.

Sheldon

[Ryssen]

You just need a choke, cap and output transformer.

Can one use a SS CCS instead of the choke.

[ErikdeBest]

Hi Ryssen

Is that a statement or a question? In either case, a SS CCS can be used, but that will require about twice the B+ of a choke loaded parafeed.

[dsavitsk]

To add to what Erik said, with a choke load, the output signal can swing above B+. With a CCS, you are limited to swinging how much you drop across the CCS. CCSes work great where not a lot of voltage swing is necessary (line stages, etc.) but are tougher to use on the output of a power amp.

[Ryssen]

It was a question,and here´s anotherone Why twice the B+?
Ok,posted to late...

[Sheldon]

Originally posted by Ryssen
It was a question,and here´s anotherone Why twice the B+?
Ok,posted to late...

Full explanation here: http://members.aol.com/sbench/outstru.html

[zman3]

There are some really good replies here, folks - thanks!

To alexq: The 6AS7/6080 amp sounds like a good candidate. I'd love to see the schematics for that one.

Now for another question: Are any changes to the power supply section necessary when converting a conventional amp to parafeed configuration? I ask because I seem to remember reading somewhere that a higher B+ is needed for parafeed amps...

Thanks again!

[dsavitsk]

Originally posted by Sheldon


Full explanation here: http://members.aol.com/sbench/outstru.html

That article makes the point that parafeed has the trouble of that "extra" cap in the signal path. This is true, but it ignores all the caps that are in the signal path with single feed, too. This is a little over simplified, but might prove helpful in comparing topologies: http://nutshellhifi.com/library/ETF.html