Re: Toying with little xfrs for headphone stage

[Robert Casey]

>
>
>
>First I tried a simple grounded cathode gain stage
>(ECC82/12AU7 both triodes paralleled) with the
>transformer primaries in series as plate load,
>and then a combination of a ECC82 grounded cathode
>gain stage followed by a 6CG7 cathode follower
>(both triodes paralleled), with the transformer
>primaries in the cathode path.
>
>The results in both cases were - ummm - interesting,
>but far from being disappointing. I guess with some
>further experimentation the results may even be quite
>acceptable, if one does not expect the impossible from
>such an unconventional, but simple setup.
>
>
With the two primaries avaliable, you could create a push-pull circuit.
Using a dual triode like the 12AU7. You'll need a phase splitter, though.

[Tom Schlangen]

Hello Ian,

> You might try distributed load...one winding on cathode and one on
> anode,

Great idea, since there is no need for the splitter stage
as suggested for a micro p-p amp. On the other hand, there
is DC flowing thru that ungapped tranny and probably
core saturation is the reason for that "interesting" sound
I got with the tranny used eiter as a plate load or
cathode load.

And the symetrical windings/loads when using distributed
load are probably far from ideal, but what the heck, I'll
try it anyway :-)

But I'll try distributed load, of course.

> assuming the insulation is up to it (perhaps not up to the
> inter-winding voltage...but if you're having fun a bit of smoke and
> ozone, and some of those fried enamel smells, might be a welcome
> addition).

Yes, the safety aspect of tubed headphone amps shouldn't be
underestimated. I let the circuit work into a dummy load
resistor at least for 1/4 hour before plugging in the
headphone, which is convenient time to take some measurements,
too.

Up to now the little tranny survived and my brain isn't
cooked.

> Also possibly PP/splitter combined.

Robert and Ronald suggested that too, and I tried it
already as a quick hack. This gave a large improvement
in sound, probably because the little cores didn't
saturate in p-p operation.

Tnx2u,

Tom

--
The large print giveth, the small print taketh away.
- Tom Waits

[Tim Williams]

I used some small trannies parafed from an RC stage for my h'fon. amp:
http://webpages.charter.net/dawill/Images/WOT_Amp2.jpg
http://webpages.charter.net/dawill/Images/WOT_Amp1.jpg
http://webpages.charter.net/dawill/Images/WOT%20Headphones%20Amp.gif

Tim

--
In the immortal words of Ned Flanders: "No foot longs!"
Website @ http://webpages.charter.net/dawill/tmoranwms

"Tom Schlangen" > wrote in message
...
> Hi RATs,
>
> just for the fun of it and to see (and hear) what
> happens I tried some spare very little transformer
> I intended to use in other projects for bias voltage
> supply as micro-OPTs to drive a headphone.
>
> The transformers have the following specs: Two
> primary windings 110 volts, two secondary windings
> 9 volts; nominal max. secondary current being 50mA per
> secondary. The primary ohmic resistance for each
> winding measures ~1,6 kOhm, the secondaries are
> at 20 ohms each. One transformer fits easily
> into 1 cubic inch, there is a photo of it at
> http://www.ndh.net/home/schlangen/roehren/ecl82pset/transformer.html
> at the bottom of that page. The origin of that type
> is unknown; I bought (5) of them for 1 Euro on Ebay ...
>
> When using primaries and secondaries in series, the
> turns ratio is ~12, with my ~20 years old AKG K240
> headphones (600 ohms studio version, this studio
> version is quite different to what was/is sold as a
> consumer version) this gives a reflected load of
> ~86,5 kOhms.
>
> First I tried a simple grounded cathode gain stage
> (ECC82/12AU7 both triodes paralleled) with the
> transformer primaries in series as plate load,
> and then a combination of a ECC82 grounded cathode
> gain stage followed by a 6CG7 cathode follower
> (both triodes paralleled), with the transformer
> primaries in the cathode path.
>
> The results in both cases were - ummm - interesting,
> but far from being disappointing. I guess with some
> further experimentation the results may even be quite
> acceptable, if one does not expect the impossible from
> such an unconventional, but simple setup.
>
> Hey, toying around with tubes by try & error & improve
> is fun :-)
>
> Tom
>
> --
> Knowledge is power - knowledge shared is power lost.
> -- A. Crowley

[Tim Williams]

"Tim Williams" > wrote in message
...
> http://webpages.charter.net/dawill/Images/WOT%20Headphone%20Amp.gif

Oops... no plural on hfon's. Above link will woik..

Tim

--
In the immortal words of Ned Flanders: "No foot longs!"
Website @ http://webpages.charter.net/dawill/tmoranwms

[Robert Casey]

Tim Williams wrote:

>"Tim Williams" > wrote in message
...
>
>
>>http://webpages.charter.net/dawill/Images/WOT%20Headphone%20Amp.gif
>>
>>
>
>
>
I did something similar, see:
http://home.netcom.com/~wa2ise/radios/pcm61pt6112-8fq7.jpg
and http://home.netcom.com/~wa2ise/radios/tubedac.htm for
the commentary. About 3/4 the way down the page.