[krmathis]

Quote:

Originally Posted by MrMajestic2 /img/forum/go_quote.gif Does that mean you are building one, or waiting for me to build one

Not building one right now. Undecided if I will build one, or use other transformers...

 

[MrMajestic2]

Quote:

Originally Posted by krmathis /img/forum/go_quote.gif Not building one right now. Undecided if I will build one, or use other transformers...

Now if there was only someone close by, say in another Nordic country, that could lend me a pair of Stax when I build this thing

 

[FrankCooter]

I'm a stax neophyte, but it appears to me that high voltage transmitting triodes such as the 845 may be better candidates for a Stax amp than any solid state device. Look at the plate curves for an 845. Huge amounts of very linear voltage swing at very high levels. I'm not aware of any solid state device that can do the same thing this well.
Correct me if I'm wrong, but isn't a Stax amp just like any other push-pull amp with the exception of a high voltage, high impedance output? I'd think a "Williamson" tupe push-pull amp with 845 finals and a 1:1 secondary on the output transformer would do the job nicely and might even take the Stax to a new level.

 

[pabbi1]

I know you really want to drop this post here - well, after a bit of a search... it is all things Stax, at least on this planet. Over 8000 posts strong - well, some stronger than others. I know 845 has come up in there many a time.

 

[ericj]

Has anyone checked the cost of commissioning one of the half dozen or so companies that offer custom toroids and r-cores to make transformers for a diy energizer?

Myself I'm not even sure how to describe the requirements to one of those companies.

 

[pabbi1]

Wlee, these guys claim to, but I have only used Victoria Magnetics, and they are very on top of whatever spec you can throw at them - for a price. Well, and a bit of a wait, like all custom order shops.

I always try Antek first - they have a LOT more than listed on eBay.

 

[MrMajestic2]

Quote:

Originally Posted by MrMajestic2 /img/forum/go_quote.gif I found a Dutch site that sells them. The LL1630 is 114 Euro and the LL1650 is 154 Euro Triple Audio Website:

Just a quote from Mr. Per Lundahl himself:

The three transformers including VAT and shipping is 3801:- SEK which is roughly €400 Euro. The price from TripleAudio was without shipping or VAT so buying directly from Lundahl is quite a bit cheaper.

 

[luvdunhill]

Quote:

Originally Posted by FrankCooter /img/forum/go_quote.gif I'm a stax neophyte, but it appears to me that high voltage transmitting triodes such as the 845 may be better candidates for a Stax amp than any solid state device. Look at the plate curves for an 845. Huge amounts of very linear voltage swing at very high levels. I'm not aware of any solid state device that can do the same thing this well. Correct me if I'm wrong, but isn't a Stax amp just like any other push-pull amp with the exception of a high voltage, high impedance output? I'd think a "Williamson" tupe push-pull amp with 845 finals and a 1:1 secondary on the output transformer would do the job nicely and might even take the Stax to a new level.

as matter of fact, I just bought a power transformer that was pulled from a 845 amp for cheap ...

 

[spritzer]

Quote:

Originally Posted by FrankCooter /img/forum/go_quote.gif I'm a stax neophyte, but it appears to me that high voltage transmitting triodes such as the 845 may be better candidates for a Stax amp than any solid state device. Look at the plate curves for an 845. Huge amounts of very linear voltage swing at very high levels. I'm not aware of any solid state device that can do the same thing this well. Correct me if I'm wrong, but isn't a Stax amp just like any other push-pull amp with the exception of a high voltage, high impedance output? I'd think a "Williamson" tupe push-pull amp with 845 finals and a 1:1 secondary on the output transformer would do the job nicely and might even take the Stax to a new level.

This has been discussed quite a bit over the years (mostly in PM's though) and there is even a 845 based design out there by Morgan Jones. That one uses a push-pull choke to mimic a primary on an output trafo but a 1:1 trafo would also work. It was intended to drive Quad ESL's but will work just as well for a Stax headphone. Kevin Gilmore has an all DHT amp design with Emission Labs tubes which he won't share unless you are prepared to build the thing.

 

[FrankCooter]

I've seen the Morgan Jones design (great book!). I searched the Stax thread and while there is a fair amount of 845/GM70 discussion, I'm not clear if anybody has an actual functioning amp. I have a pair of Cary Audio push-pull to push-pull interstage transformers. These were designed for 300Bs to drive 845s. I also have a quad of Chinese 845s laying around. These transformers will obviously not handle 845s run at full bore. The 845 actually sounds good at around 500v and 40ma. The Japanese DIY community does this and I've done it myself. Wondering if a "poor mans" 845 Stax amp might be a worthwhile project?

 

[luvdunhill]

Quote:

Originally Posted by FrankCooter /img/forum/go_quote.gif I've seen the Morgan Jones design (great book!). I searched the Stax thread and while there is a fair amount of 845/GM70 discussion, I'm not clear if anybody has an actual functioning amp. I have a pair of Cary Audio push-pull to push-pull interstage transformers. These were designed for 300Bs to drive 845s. I also have a quad of Chinese 845s laying around. These transformers will obviously not handle 845s run at full bore. The 845 actually sounds good at around 500v and 40ma. The Japanese DIY community does this and I've done it myself. Wondering if a "poor mans" 845 Stax amp might be a worthwhile project?

what sort of input stage would you consider, and what would the target gain be? Two important factors.

 

[FrankCooter]

On the breadboard at least, I'd want to keep this as simple as possible. I'd start out with a triode connected 7788 running a phase splitting interstage transformer, then straight to the grids of the 845s. I'd guess this this would be good for 45-50 db total gain

 

[spritzer]

Nobody has built an amp based on the large DHT's that I know of so you should definitely build one.

I went down the BH route along with Marc but it looks like I'll build an ES-1 as well for good measure.

 

[FrankCooter]

Another alternative, good for a bit more gain, would be a 6ea7. The high gain section directly coupled to the low gain/high current side and then the phase splitting transformer to the 845 grids as above. I'd be open to better ideas.

 

[marcus1]

I`m interested in building the Stax transformer as well - unfortunately I can`t offer much in the way of technical input but a member did send me the following PM when I posted a similar query about building the Stax transformer:....

Personally I would not use a system of diaphragm charge that used the audio signal. I would build a single Walton - Cockroft multiplier and charge both diaphragms off of that. Filter the crap out of the AC that driver the HT supply transformer and things should sound very good. ..........
Before you buy the Lundahl's you might want to try something interesting and very cheap. Get a couple of small (as in big wallnut size) 70 volt line matching transformers and wire them up backwards and drive your phones with them and see what you think. cost about ten bucks each if you look less if you look hard.