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Old 28th April 2006, 10:14 AM   #1
GD3 is offline GD3  United States
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Default Transformer Coupling and Headphones? (Toob Noob)

I have no experience but I am tube curious.. ;-)

All the DIY tube headphone amps I've seen generally use tubes for voltage gain followed by various solid state buffers.

Does anyone use transformer coupling to drive headphones? Are there any particular characteristics or problems with its sound?

Can anyone comment on SE vs. P-P sound?
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Old 28th April 2006, 01:03 PM   #2
lndm is offline lndm  Australia
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Some do use transformer coupling. A quality output transformer provides quality sound. Still, many seem to see a headphone amp as an opportunity to take the next step and drive the headphones directly (with different circuitry).

PP and SE can both sound good. Some, like myself believe the SE is the slightly better choice. The main disadvantage is its lower power output. In the case of a headphone amp though, maybe that's a non issue
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Old 28th April 2006, 02:20 PM   #3
Rocky is offline Rocky  Norway
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I use transformer coupling in my amp, built for horns but also serves my headphone needs (low impedance headphones)

It is SE DHT and I am happy to report there are no problems. From earlier experiences I've also done SE with single tube 6C45P and E810F (in triode), also transformer coupled, also very good for headphones.
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Old 28th April 2006, 07:21 PM   #4
rdf is offline rdf  Canada
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I second Rocky's experiences with the 6C45 SE, excellent sound and objective measured performance. Headphones are, in an amp context, high impedance devices and respond to voltage, not power. They also present a light load to both tube and transformer, further reducing distortion. I waaaaay prefer a good transformer in the path to the large electrolytic required in all the OTL headphone schematics I've seen.
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Old 29th April 2006, 08:48 AM   #5
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I have used 12V mains toroidal transformers as output transformers in a ECL82 headphone amplifier, they sound good. This is a parafeed design so has a cap on the output as well. The bass is a little rolled off because of the use of mains toroidals. This can be compensated for by introducing a small resonance into the bass response of the output transformer, with the use of partial / plate to plate feedback. Alternatively use air gapped output transformers.
The ECL86 is a better candidate for a headphone amp, this is because the ECL82 has difficult operating points.

Shoog
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Old 29th April 2006, 03:43 PM   #6
GD3 is offline GD3  United States
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Thanks for your replies everybody.

I am now off to get more info on the physics of transformers, something I have a poor understanding of.

I was under the impression that there is some inherent form of distortion associated with their use. Don't they introduce hysteresis when a magnetic field changes polarity? Or does that only come into play when you reach saturation?
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Old 6th May 2006, 09:26 PM   #7
dado5 is offline dado5  United States
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I use an Electra Print SE transformer for a single stage ECC99 tube amp. The transformer has a 17:1 ratio and is 65ma rated (way over rated). I use Grado phones and this amp sounds better with them than any I have used before, tube or solid state.

One big point is that the power supply needs to be VERY well filtered as noise is very apparent with phones. I recently switched to choke input and it did reveal some very low level detail that apparently had been masked by noise.
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Old 8th May 2006, 04:25 PM   #8
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Probably the biggest reason not to do transformer coupling is cost... a good transformer is a little pricey.

I've had very good luck with Sowter headphone xfmrs. A 6C45pi driving a Sowter 9351 works really well. Very much single-ended in character.

I also did an ECC99 SRPP parafeed using the Sowter 8665. Details here:

http://www.pmillett.com/ecc99_srpp_headphone_amp.htm

As for PP vs. SE, I've never tried a true PP headphone amp. But to me, most headphones benefit from a little SE sound... to me it tends to tame some of the harshness that most have.

Pete
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Old 19th May 2006, 03:29 PM   #9
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Hi,

I was a AKG K1000 user & recent was testing the 6EM7 transformer coupling headphone amp. detail will post later.

thx

thomas
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Old 20th May 2006, 05:55 AM   #10
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I have a decent parafed E/PCL86 headphone amp design if you're interested - gives more flexibility on the transformer type
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