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Old 8th September 2010, 02:35 PM   #1
adamus is offline adamus  United Kingdom
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Default help me decide,headphone amp - parafeed or normal tx ?

I am building and amp for friend who has large budget.

He wants a valve based headamp. To my mind that conjures a couple of good options

1) CSS or choke load parafeed with sowter transformer (Sowter Type 8650 Headphone Output transformer)

2) Single ended with sowter gapped transformer (SOWTER HEADPHONE TRANSFORMERS) - the 8968

3) CSS or choke load parafeed with a magnequest autoformer (TL-404)

Both look like they will work well with a myriad of tubes (d3a, 6h30p...the list goes on, i could even use DHTs).

My question is, given a very large budget, which would you build and why. I havent heard a parafeed amp, but sites such as epc.cc seem to like them very much. I also asked the question on head-fi a while ago, but its crunch time and i need to start building. He will be using them predominantly with HD650's, and very occasionally with grado's.

Has anyone done both with relatively highend iron, any comparisons?

Last edited by adamus; 8th September 2010 at 02:38 PM.
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Old 8th September 2010, 06:54 PM   #2
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Originally Posted by adamus View Post
I am building and amp for friend who has large budget.

He wants a valve based headamp. To my mind that conjures a couple of good options
4) SRPP parafeed with transformer.
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Old 8th September 2010, 07:09 PM   #3
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Parafeed controls the signal current loops better, allows the use of better quality transformers, keeps the PS caps out of the signal path, and sounds better. Single feed only makes sense if you need the added efficiency it provides ... which you probably don't. Same goes for choke loading, by the way.

http://www.ecpaudio.com/pdf/parafeed_basics.pdf
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Old 8th September 2010, 07:14 PM   #4
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My personal suggestion is one of Gary Pimm's self-bias CCS loads for a 5687 tube, with parafeed magnequest, electraprint, or lundahl magnetics. Something in the 4:1 or 5:1 ratio range. See the Espressivo Espressivo Headphone Amplifier but the modern self-bias CCS no longer needs a pentode at these power levels.

If you really have the money to burn, build exactly this http://www.nutshellhifi.com/Raven-MarkII.gif
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Old 8th September 2010, 07:26 PM   #5
adamus is offline adamus  United Kingdom
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Thanks gents, you have made my mind up.

I am going to go with lundahl magnetics, 6h30p.. led bias, dact attenuator, dn2450 cascode ccs.

Two chassis build to avoid hum, PS tube rectifier, clcl - probably lundal chokes, obbligato film caps.

or to simplify things, i may ask jack (electraprint) to do all the magnetics - people speak very highly of his transformers.

Last edited by adamus; 8th September 2010 at 07:30 PM.
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Old 8th September 2010, 07:48 PM   #6
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Jack's stuff is great, especially getting custom power trans for exactly what you need. He doesn't seem to be a big fan of choke-input supplies, and when I've asked him about using his chokes as choke-input, he usually seems wary. I've successfully used the large hammond enclosed chokes as choke-input as long as you run the current way under the rating. (~120ma in my 300ma choke). No mechanical hum in mine but the magnetic field is colossal, keep those OPT's far, far away from choke input supplies.

Or alternatively, hook up the supply w/ a dummy load and put a scope or FFT software onto the disconnected output transformers, you can then twist/move the transformers around possible mounting spots and find the dead zones where the field lines are all at right angles and the hum is minimum. I found I can mount my opt's about 12" in front of the choke, if they are perfectly in line vertically, and horizontally about 3" to either side, the hum is extremely low (measurable but not audible) and I didn't need a separate chassis.
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Old 8th September 2010, 09:22 PM   #7
Arnulf is offline Arnulf  Europe
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Originally Posted by adamus View Post
Thanks gents, you have made my mind up.
Pitty. IMHO "tube sound" is as much of a "tranformer sound" as it is that of the tubes so the output - if buyer desires the "tube sound" - should incorporate both of these, and nothing else.

Parafeed = less OPT sound and more capacitor sound which probably isn't what the buyer is looking for.

Somebody wit large budget might also be interested in tube amplifier because of its "bling" value rather than actual sound so CCS (and other 3+ legged sandy components in general) won't be a big selling point for him.

My choice would therefore be a normal (SE) OPT in straightforward configuration suitable for speakers, driving higher Z load that is headphones. Alternatively a load-matched OPT could be used, but this will provide waaaay too much output (speaker OPT into high-Z headphone load = awesome damping factor and enough swing regardless as less power is required).

With generous budget you mentioned you might as well build 2 or 3 architectural alternatives and have him keep the one he likes the most ... who knows, it just might be the CCS load parafeed variant suggested above.
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Old 8th September 2010, 09:33 PM   #8
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If it's just the ultimate sound quality you want, I'd use a 2a3 output - low anode resistance and wonderful sound. And for the ultimate in performance feed it direct coupled from a 26 in filament bias. I don't expect you to build this, but I'm going to!! I have AKG K-701s which are 50 ohms, and I'm scratching my head about what SE output transformer to use, or indeed if I should use parafeed. Parafeed maybe even with a toroidal mains transformer with the right step-down ratio. Still at the pondering stage but it wouldn't be hard to knock together - take a day I imagine since I already have power supplies and filament supplies in separate cases. Useful to be modular!

andy
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Old 8th September 2010, 09:35 PM   #9
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Except that in a normal SE output you still have the capacitor, it's just the final power supply cap instead of the parafeed cap.

Unless you use some 3 legged sandy components and make a regulated supply.
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Old 8th September 2010, 10:07 PM   #10
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Except that in a normal SE output you still have the capacitor, it's just the final power supply cap instead of the parafeed cap.

Unless you use some 3 legged sandy components and make a regulated supply.
But then you just swap the capacitor for the regulated supply - i.e. swapping a simple and improvable component for a complex circuit!
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