[Bluetick]

If you could build (or have built for you) ANY tube head amp based on a schematic that is public domain-what would it be? Why??

 

[slwiser]

any Berning amp

 

[tomb]

At the moment, probably Dsavitsk's Less Pressivo. It looks like the best bang for the buck for a pure tube amp, is not OTL, and has big iron that doesn't cost mega-bucks.

I'm still scared of the 460V, though, but one day soon ...

 

[dsavitsk]

Quote:

Originally Posted by tomb /img/forum/go_quote.gif At the moment, probably Dsavitsk's Less Pressivo. It looks like the best bang for the buck for a pure tube amp, is not OTL, and has big iron that doesn't cost mega-bucks. I'm still scared of the 460V, though, but one day soon ...

I'm flattered. A version using the same OPTs as the original Espressivo or some parafeed 5K:32 would be the way to make it expensive ... and better. I have to say, I am on the fence between parafeed and single feed. Both are good, and both are better than OTL

I have also been working with some differential parafeed circuits lately, and I think there are some promising ways to go there.

For best circuits, you can't do better than old Western Electric ones. And, there are really no non-public domain circuits out there. There have been very few new things in tube circuits in quite a while, and the best circuits are from the 1930's.

Also, if you haven't seen it, Jim Hagerman has a new headphone amp coming out that amounts to a Less-pressivo but with choke loads instead of the CCS (these are some Hammond chokes, and you could certainly use them in a Less-pressivo built too -- they cost about $12 each). He has it as a PCB project which I think is a little silly, and he uses a single 6H30 for the tube, but it might be a way for people uncomfortable with high voltages to get started.

 

[fierce_freak]

I'm a tube noob, but how about this?

 

[Bluetick]

Quote:

Originally Posted by dsavitsk /img/forum/go_quote.gif I'm flattered. A version using the same OPTs as the original Espressivo or some parafeed 5K:32 would be the way to make it expensive ... and better. I have to say, I am on the fence between parafeed and single feed. Both are good, and both are better than OTL I have also been working with some differential parafeed circuits lately, and I think there are some promising ways to go there. For best circuits, you can't do better than old Western Electric ones. And, there are really no non-public domain circuits out there. There have been very few new things in tube circuits in quite a while, and the best circuits are from the 1930's. Also, if you haven't seen it, Jim Hagerman has a new headphone amp coming out that amounts to a Less-pressivo but with choke loads instead of the CCS (these are some Hammond chokes, and you could certainly use them in a Less-pressivo built too -- they cost about $12 each). He has it as a PCB project which I think is a little silly, and he uses a single 6H30 for the tube, but it might be a way for people uncomfortable with high voltages to get started.

I just read the Less-pressivo page. Very interesting. At first it seems very bare bones, but it is nicely thought out. I'm not sure about 6c(s)45 tubes, though. You did give some options...

So which CCS did you prefer with the Less-Pressivo? c45 or the 10m45??

Has anyone here built one?

 

[tomb]

Quote:

Originally Posted by Bluetick /img/forum/go_quote.gif I just read the Less-pressivo page. Very interesting. At first it seems very bare bones, but it is nicely thought out. I'm not sure about 6c(s)45 tubes, though. You did give some options... So which CCS did you prefer with the Less-Pressivo? c45 or the 10m45?? Has anyone here built one?

Colin Toole, the Millett MAX designer, built one - or has it mostly finished, I believe. He used a couple of DN2540 FETs in a cascode(?) arrangement for the CCS and Edcors wired as autoformers on the output.

Just as an aside, Colin is not really a tube guy - the MAX was a deviation for him. Yet, he saw enough potential in Dsavitsk's design that it was his choice for a pure tube amp. That seems a pretty good testament to me.

 

[amphead]

Hmmm...... Maybe Dsavitsks NOOT (no output transformer) (OTL) amp is what I should do. Quiet is always a plus for a tube amp. I get the impression it would be warm and midrange focused on the frequency response, which wouldn't be bad with K701s. Dsavitsk?

 

[Rescue Toaster]

I would put quite a bit of money that the best is the Raven built with 5687's. The LL1676 transformer phase split & push-pull operation has some real advantages over diff amp connections. It is not really public domain though Lynn's not gonna be angry if you build one yourself. Might be easier to use a CCS other than Gary's since he's off the grid afaik, but Gary's are the best.
http://www.nutshellhifi.com/Raven-MarkII.gif
If I ever have a real bucketload of money that's what I'd build probably.


For single-ended, the basic parafeed w/ CCS is the only way to go. 5687's are probably best but can be very expensive, maybe the 6h6/6n6 or ECC99 for a budget. My opinion is avoid the 6c45 unless you *absolutely* need that much gain. They are just plain not as linear. I'm not certain about TL-404 vs LL1674, but those would be the two best options realistically. Go as crazy as you can on the power supply... choke-input and ccs-fed shunt regulated if possible. I left my cathodes unbypassed on purpose to let me use a smaller parafeed cap, but LED or battery bias may ultimately sound better.

 

[Bluetick]

Quote:

Originally Posted by Rescue Toaster /img/forum/go_quote.gif I would put quite a bit of money that the best is the Raven built with 5687's. If I ever have a real bucketload of money.....

Yeah, I've drooled over that design for some time but the cost of all that iron had me spinning!

It's just one of those things where you could NOT skimp anywhere. Not much wiggle room with that one but it is be-he-ute-he-ful!!

 

[rb67]

How much do those transformers run around for the Raven design?

I'm considering building another amp, something a step above a Bijou.

 

[Blooze]

If I could build one amp I would build the BCJ. Someday when I can gather all the bits.

 

[Rescue Toaster]

Quote:

Originally Posted by rb67 /img/forum/go_quote.gif How much do those transformers run around for the Raven design? I'm considering building another amp, something a step above a Bijou.

2x LL1676: $210
2x LL1680: $230
1x LL1672: $90
1x LL1683: $160

A nice pair of 5687's can run $40-60. The capacitors don't have to be anything amazing, and regulator tubes & damper diodes are CHEAP. The whole point of the circuit is to keep parts OUT of the signal path so just your transformers & tubes are the critical components. This will be an expensive amp but if you are in that price range, I don't see a way to beat it.




The nice thing about the parafeed SE design is you can start CHEAP (only expensive part is a nice power trans ~$80 which you should do from the get-go, no Hammond please). ECC99's are cheap, you can use a simple K&K Audio CCS for the power supply CCS and a Bottlehead C4S kit (or some DIY designs around) for the plate loads. I started with SUPER cheap ($12!) XSM10K:600 output transformers from Edcor, wired them as 5:1 autoformers and they are amazing for the price. Then you can over time go to 5687's, Lundahl 1674's or MQ TL-404 output transformers, upgrade your parafeed caps, move to cascoded MOSFET current sources etc..etc.. And hear all the changes for yourself.

The difference between a real medium-voltage SE transformer'd tube stage w/ proper signal current control and ANY hybrid out there (especially ones that use low voltage tubes that suck) will absolutely astound you.

Here's the thread where I started my SE parafeed amp. It's grown a bit since then but even the original was a delight. Most expensive part was the custom wound power trans from electraprint and I still use that.
http://www.head-fi.org/forums/showthread.php?t=181469

 

[fierce_freak]

Great info, Rescue Toaster. I'm planning on building a tube circuit for my Grado RS-1 (and only the Grado RS-1), but for a first time out with tubes I'll probably use a more generic, less specific design. Is the parafeed SE design like the Less-pressivo a good choice for that? I noticed that dsavitsk uses the RS-1, so I'm assuming so. There are a couple other basic designs that interest me, too, like a directly heated triode design with the 2A3 or various push-pull designs.

 

[Rescue Toaster]

Quote:

Originally Posted by fierce_freak /img/forum/go_quote.gif Great info, Rescue Toaster. I'm planning on building a tube circuit for my Grado RS-1 (and only the Grado RS-1), but for a first time out with tubes I'll probably use a more generic, less specific design. Is the parafeed SE design like the Less-pressivo a good choice for that? I noticed that dsavitsk uses the RS-1, so I'm assuming so. There are a couple other basic designs that interest me, too, like a directly heated triode design with the 2A3 or various push-pull designs.

Unless you're really shooting for the $100 tag on the Less-pressivo, you should go for a more ambitious power supply like the one I used (see my link to old thread). SE Iron for grados... I'm not quite sure. Mayble the TL-404's on the 50 ohm tap with a really hot ~30ma 5687.

As for push-pull, you've got me thinking now and I'm gonna take some time to look for iron that might be used for a more affordable raven-style amp.