transformer output dynamic amp

[kevin gilmore]

well the stax mafia has been fairly busy the last few days.

 

So a person over there was asking about a specific amplifier that they

thought was WAY overpriced, and significantly under performing. Helped out

by the fact that a certain moderator over there was shilling the hell out of it and

doing his typical hatchet job on various posts etc.

 

Well that's enough to get us involved. Combined with a picture of high enough

resolution posted on the 6 moons website. Guys, seriously talk about giving

away the farm. Well...

 

http://gilmore.chem.northwestern.edu/alostudio6.pdf

 

What a massive piece of crap this is.  If you really want to build one, its trivially

easy to do it point to point. And dirt cheap.

power transformer $80

http://www.classictone.net/40-18086.html

 

chokes, pick your favorite Hammond chokes

 

output transformer  $28 each

http://edcorusa.com/p/505/gxse10-16-5k

slightly bigger output transformer $38 each

http://edcorusa.com/p/542/gxse15-16-5k

 

expensive coupling caps, go cheap, or go silly expensive

 

now I sent this schematic to someone whose opinion I trust who actually knows tubes/transformer

circuits better than I do, and his answer was exactly as I expected...

 

we can do better. WAY better.

 

For one thing, that power supply is pure crap. almost dual mono.

that's just like "almost a room temperature super conductor"

proprietary circuitry.  Does anyone see any proprietary circuitry.

And what about that solid state for the filaments... Guess that does not

count in the "all tubes" thing... And stacked gas tubes?

(represented on the schematic by zeners because I'm lazy)

 

looks like a bad rip of this.

http://www.cascadetubes.com/Tube_Site/The_6V6_Lacewood_Amp.html

 

happy new year.

 

The Donald north amplifiers are next 

[luvdunhill]

Would be fun to populate the four outputs and the input and see how high you can get THD+N. I bet you could do 5%.

[luvdunhill]

DC heater with like 1VAC ripple might be proprietary. AC-DC heaters ?

[nikongod]

R2 is totally un-necessary. R3 will bleed the whole circuit without any help. 

 

C1 should be smaller. 22uF tops, but 5-15uF would not hurt anyone or anything. Have we learned nothing about the perils of big input caps from the WOO amps and countless Chinese piles of fail? I guess the guy who designed this did not. 

 

R12 should probably be 470ohms. Probably a typo, but it should really be a few LEDs in series. Or a funky voltage source/CCS like Doug uses. 

 

What choice did the designer have for the heater supply? AC heaters? That is not an option in an amp like this - if someone puts in a microphonic tube (but its my absolute favoritest) it will hum like what. This is true even if you bias the heaters well above ground. And then you are responsible for building a $4100 amp that hums when the same tube did not hum in my old amp - it is clearly something wrong with your amp. no I will not try another tube, this is the best tube I have. What? You say its microphonic and I should smash it up with a brick? You are a fool! No, the tube you sent with the amp does not hum, but its a cheap eastern-block tube. This tube was handed down through my family from mr RCA (what the fuck!) himself who gave it to my grand-dad. Yea it was buried in the back shed for a few years behind an old Ford Fairmont, but we could not get the old radio out from behind the car until we got the car working again, and that never happened. As luck would have it the shed fell over in a storm and all I could salvage was this tube and by golly I'm going to use it. In your fucking huming amp. Except your amp hums. so I'm not going to use it. Is now the wrong place to say what filaments? 5ar4 is indirectly heated, with the heater hooked up to the cathode on one side of the heater supply. Tube rectified heater supply? LOL WUT? 

 

Whats with the hate? Its an overpriced amp, clearly. But, that seems to be the overwhelming trend in hi-fi. 

I hope anyone with the skills to p2p this takes the extra hour or 3 to design their own thing at least this nice and get some extra pride from that. Anyone who wants to build it on a PCB should sit down for a few hours and learn to wire things p2p then design something better.

 

I wish the circuit were just a little more interesting so that more people could learn from it though that is a shame. 

 

The DNA stuff is as boring as you would expect. 

[naamanf]

To be expected from ALO. Reminds me of the $600 amp they were selling that was nothing more than a cheap headphone chip amp, but it did have V-Caps 

 

Edit:Then again I'm sure Ken and Ray talk about all the Lamborghinis they have owned.

Edited January 8, 2014 by naamanf

[dsavitsk]

In a single feed amp, the point of transformer loading a tube is that it increases efficiency. That is, the power supply voltage represents the midpoint of the tube's possible plate voltage as it can swing above and below this point. This is as opposed to a resistor load where the power supply represents the limit of the tube's swing. This makes sense to do in a speaker amp where you need to squeeze all the power out of a tube you can. For instance, a 300B loaded with a transformer can put out around 15W of power with a 350V supply. In order to do the same with a resistor load would require a power supply over 600V with considerable heat lost across the load.

 

This efficiency benefit comes at a cost which is that single feed transformers are necessarily compromised in quality. They must be gapped to avoid saturation, they must be made from non-exotic materials to avoid bass loss (and saturation), the core needs to be larger and the wire thicker to accommodate the DC both of which lower the fidelity, and they require more windings (to generate the necessary inductance) which increases winding capacitance, increases impedance, and further hurts quality.

 

In a speaker amp where fidelity is not as sensitive as with headphones, these tradeoffs may well be worth it to keep amplifiers reasonable. However, in a headphone amp, this hardly seems to be the case. The power needed is easy to generate, and while they may be wildly inefficient, even inefficient headphone amps don't really use that much electricity.

 

The two primary ways* to transformer couple and avoid compromised single feed iron are via parafeed and with push-pull. Indeed, push-pull actually maintains most of the benefits of the lower more efficient power supply, corrects most of the issues with single feed transformers, and adds the benefit of dropping into class B when necessary. And they sound better, too.

 

So my objection here would be that is it just another amp that is just a scaled down power amp rather than being designed with headphones in mind.

 

All that aside, even within the single feed paradigm, the above referenced amp does everything pretty badly -- poor quality power supply, poor loading of the driver, poor quality biasing methods, showy but noisy regulator, etc. So even if you think single feed amps are better in some way, this one is just not that good.

 

 

* Intact winds DHT transformers with an additional winding which uses the filament current to counteract the B+ DC.

[spritzer]

That's my point exactly, everything here is done badly but the Alo Studio Six is billed as the best there is by shills/reviewers.  It must be awesome as it has 4 TRS sockets which all will drive your headphones equally badly and some tubes that can be rolled endlessly.  What more could anybody want? 

 

Well the PSU is fubar and so it the heater supply.  I'm all for running the tubes off DC but any good designer would use a custom transformer which has enough headroom to regulate said DC.  Pehaps Marc is right and the high ripple was part of the design...  Then we have the 47uf cap after the rectifier which guarantees that the owners of this pile of fail will be rolling rectifiers like crazy to try and find one that tolerates being run on the limit.  Not quite as bad as the Woo crap but that also takes a special level of skill. 

 

As for the actual amp section, I agree with Doug that there isn't a chance in hell this was designed to drive headphones.  Also any tube amp will also only be as good as the transformers it uses so the best they could do is the cheapest Edcor?  This is a 4200$ amp not some 500$ Chinese ebay job. 

[Pars]

^ They must follow the Mike Elliot (counterpoint) school of design. In the preamp I had, he used an EZ81 / 6CA4 rectifier with a CRC filter of 100uf / 500 ohms / 100uf. Datasheet for that rectifier has 50uf max after the tube, and I'm sure it likely performs better with something more like 20uf. When he was doing "upgrades" he was selling EZ80 / 6V4s and claimed they sounded "amazing" in place of the EZ81, Coupled with poor layout of the heater supply (ripple special). Lots of similarities.

[spritzer]

That's the same BS Woo are up to.  In the WES it's the tube, followed by one of those ultra cheap Chinese bridges and into a 100uf cap.  Makes less sense than usual... 

[PretentiousFood]

Just came to point out how amazing that schematic is.

 

It really looks like they took a regular CRC filter and replaced a T of the filter with some underrated caps with glow tubes. Are those supposed to be voltage balancing resistors across the glow tubes?

 

If anyone wants to upgrade this to parafeed, Edcors are $10 per transformer. 

[kevin gilmore]

I think those resistors are to make sure the gas tubes actually start. Something Mikhail had problems with.

the resistor after the gas tubes was because otherwise they would oscillate into the output capacitor.

[justin]

while the gas tubes look cool i'd probably be unable to use them in a headphone amp, as unfortunate as that is -- inexpensive, so easy to stick them in as no heater supply required. However they are noisier than a zener despite what the internet says, and most of them don't work properly anymore. Some of the later made Russian ones might still function ok but quality is more likely to be suspect. The voltage reference tubes like 85A2 (10mA max) or 5651 (3mA) max i think were still being produced into the late 80s, so those may be a better option, and then increase the current capability with a triode/pentode or a transistor. I have done neither but i suspect it would work better.

[dsavitsk]

However they are noisier than a zener despite what the internet says, and most of them don't work properly anymore.

 

They are definitely noisy, and the impedance is surprisingly high -- upward of 300 Ohms. Where I have had OK luck with them is fed by a CCS and used as a bias for a pass transistor like an IRF810 or something. In that case, the impedance does not matter as the current across them is constant. However, they really are all for show as a zener still works more reliably, is quieter, and can be bypassed without creating an oscillator.

[PretentiousFood]

while the gas tubes look cool i'd probably be unable to use them in a headphone amp, as unfortunate as that is -- inexpensive, so easy to stick them in as no heater supply required. However they are noisier than a zener despite what the internet says, and most of them don't work properly anymore. Some of the later made Russian ones might still function ok but quality is more likely to be suspect. The voltage reference tubes like 85A2 (10mA max) or 5651 (3mA) max i think were still being produced into the late 80s, so those may be a better option, and then increase the current capability with a triode/pentode or a transistor. I have done neither but i suspect it would work better.

 

I've had good luck using something like this, but you need to make sure the triode filaments come on before b+ or you'll exceed the VR tube's current rating for a short time. 

http://i.imgur.com/smuyUlc.png

 

At this point they really aren't acting as much more than a pilot light and it's probably smarter to do something like the Heathkit supplies.

[spritzer]

All the audiophools need are pilot lights that can be rolled for piece of mind.   

 

If somebody wants to read about the proper use of caps with tube rectified PSU's I recommend the EML datasheets.  These will die an early death in the Woo amps and this shows exactly why. 

[spritzer]

On this subject take a look at this:

 

http://www.siliconray.com/audio-amateur/amplifiers-w-case/low-price-6p3p-single-ended-tube-amplifier-kit.html

 

So this is a fully featured tube amp kit for 241$ shipped.  It uses 6P3P which is a Chinese version of the 6L6 and 6N1 driver.  It is trivial to use 807, 6BG6, 6L6 or indeed 6V6 and swap the driver for 6N1P-EV or indeed 6CG7 (aka 6SN7).  Now all the components included are probably crap so it's just the chassis, sockets and transformers that are usable.  Good excuse to get some Koa SPR's and rework the circuit to perform better.  The PSU needs work but the small Wima 10uf caps are cheap so make for an excellent input cap after the tube.  Add another choke, some new caps and we are in business. 

 

All in something like this could cost 500$ with very nice parts and crush the Alo piece of crap.  Hell there is plenty of space on that front panel for six TRS sockets if you think that helps...    The Edcor output transformers are only 50$ and should fit the top plate perfectly. 

 

I just bought one but I'll do it a bit differently.  I'll fit some Lundahl iron and turn this into a Stax amp.  Might even add some input transformers and balanced inputs.  XLR in, then single ended to balanced output. 

[DefQon]

lol 

 

I showed that schematic to a local builder who has been building and repairing amps mainly tube speaker and some solid state designs since the VFET days, he just giggled. 

 

I actually didn't know the price of the ALOStudio6 until Spritzer mentioned it while ago with it using shit trafo's what the fucking fuck $4k for something that looked $1k max sort of like the Woo stuff, big, intimidating and nice chassis but underwhelming sound for the price.

 

 

On this subject take a look at this:

 

http://www.siliconray.com/audio-amateur/amplifiers-w-case/low-price-6p3p-single-ended-tube-amplifier-kit.html

 

So this is a fully featured tube amp kit for 241$ shipped.  It uses 6P3P which is a Chinese version of the 6L6 and 6N1 driver.  It is trivial to use 807, 6BG6, 6L6 or indeed 6V6 and swap the driver for 6N1P-EV or indeed 6CG7 (aka 6SN7).  Now all the components included are probably crap so it's just the chassis, sockets and transformers that are usable.  Good excuse to get some Koa SPR's and rework the circuit to perform better.  The PSU needs work but the small Wima 10uf caps are cheap so make for an excellent input cap after the tube.  Add another choke, some new caps and we are in business. 

 

All in something like this could cost 500$ with very nice parts and crush the Alo piece of crap.  Hell there is plenty of space on that front panel for six TRS sockets if you think that helps...    The Edcor output transformers are only 50$ and should fit the top plate perfectly. 

 

I just bought one but I'll do it a bit differently.  I'll fit some Lundahl iron and turn this into a Stax amp.  Might even add some input transformers and balanced inputs.  XLR in, then single ended to balanced output. 

Coincidentally I bought one of the 6P1 amp's from that site while ago, for the price $200 shipped, you are bang on the money with the crappy quality parts used (generic resistors, caps and shit soldering and wiring technics), but for the price just for the trafo, chassis and some of the re-usable parts it's pretty good and with a bit of extra $$ and time to fix either fucked up CCS or SRPP stage used as output it actually sounds nice, you can go further with an O-scope and make sure you get no fucked oscillating noise from the circuit and go further fixing it up, still worth it in my books definitely good way to learn about diy tube amps rather than just theorising all the Morgan Jones diy tube book in your head without an actual project to work on.

 

Some of these big shill companies should just fuck off already and leave us alone, especially the clueless fucks on head-fi thank fucking god I ain't active on that shit anymore (excuse and pardon some of the few folks there that actually do provide non shill input to the threads).

 

Now I'm pissed.

Edited January 13, 2014 by DefQon

[spritzer]

The 6P1 amp is even cheaper (less than 200$) so yeah, great to learn from.  You could also modify it to take EL90's which are pretty good. 

 

I picked the bigger amp as it had a better PSU setup and I have a pile of nice 807's that will work perfectly.   My only problem is with the chassis height as it simply might not be enough for all the film PSU caps I want to put in there.  The 100uf/500V aren't exactly small...  I'll also probably add DC heaters for the front end, maybe a CCS on it too. 

[spritzer]

A month to the day and the amp kit shows up at my door yesterday.  Classic China shipping with everything thrown into one box with little to no padding between the fragile chassis and a 2.5kg transformer...    Well it is serviceable but the real WTF moment are the components that are included.  Now the power transformer is pretty decent and run way below max so that will be just fine.  The output transformers also look to be nice enough and ditto on the psu choke. Similar to what you find in the Woo, ALO and DNA amps at 15 times the price... 

 

What is of no use are the caps, resistors, volume pot, connectors and even the bloody tube sockets.  Not a chance in hell any of those caps are real despite the Nichicon or Nippon Chemicon markings.  Wasn't expecting anything else but it's still funny.   

 

Now what to do with this thing, clearly destined for Stax duty so some Lundahl 1660's on the top panel, add a DC supply for the front end tube, perhaps a simple regulator for it as well and a CCS

[nopants]

If the chassis didn't explode en route, I consider that a win.

 

So if I understand things correctly, you're going to make a "normal" tube amplifier with the output transformers, and then stick lundahls after that? 

[spritzer]

Nope, the output transformers will be ditched and I'll use different output transformers which step up the voltage and acts as a phase splitter.   Something like this...