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Old 19th January 2013, 04:50 PM   #461
Pano is offline Pano  United States
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My rule of thumb for Grados is "Ouch, that hurts my ears!".
Orthodynamic on the other hand I love the sound of. (What I've heard of them)

Interestingly I'm just getting hum with my prototype, not buzz or rizz. Hope to clean that up some. DC heaters help, I guess.
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Old 19th January 2013, 05:05 PM   #462
iko is offline iko  Canada
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Pano, if you don't already have Rod Coleman's filament supply have a look at this little circuit which is based on the same idea, a CCS after the filament, and a bjt filter before it. I have used both Rod's circuit and mine in my 26 preamp and could not tell the difference (sound or measurement wise). All kind of different power bjts can be used, of course. I developed this after ordering a pair of Rod's supply because I ran out of patience.
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Old 19th January 2013, 07:03 PM   #463
Pano is offline Pano  United States
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Thanks Iko! I'll look into it. At the moment I'm running the filaments in CV mode from a lab power supply. Overkill, but convenient for prototyping. I could run in CC mode, too.

Below is the output circuit that I'm running now. The DC voltages are from the sim'd model and agree with measurements. The 330R is the DCR of the primary.
Even in the messy wiring stage noise is OK, about 27mV into an 8 ohm load. With the vintage Tamura iron I'm running the -3dB points are 12Hz-38Khz. Not bad, really.
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Old 19th January 2013, 08:24 PM   #464
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Yes, there will be transformers for parafeed drive. Let me test them first. I started a headphone 6W amp project about an year ago, then when potential partner became inpatient the project had been canceled, then the plant I contacted before come with some solution, so may be I will re-open the project if transformers are really as nice as they claim.
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Old 19th January 2013, 09:39 PM   #465
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Quote:
Originally Posted by merlin el mago View Post
The Russian company will make 300 ohms transformers?
You don't need 300 Ohm transformer. If you will try to drive 300 Ohm headphones from 300 Ohm secondary of 2W amp you will be deaf, and your headphones fried.

Speaking of 32 and 50 Ohm 2 and 6W headphones, we mean special planar drivers that have very low sensitivity. For conventional dynamic headphones 2W will be too much.
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Old 19th January 2013, 09:42 PM   #466
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But Wavebourn, certain headphones out these days require more power than speakers do. The efficiency is extremely low. Matching becomes very important.
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Old 19th January 2013, 09:50 PM   #467
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Quote:
Originally Posted by cotdt View Post
But Wavebourn, certain headphones out these days require more power than speakers do. The efficiency is extremely low. Matching becomes very important.
Yes, it is exactly what I meant. I never saw 300 Ohm headphones that require 2-6W of power. Nor never heard.
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Old 19th January 2013, 10:38 PM   #468
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Maybe I should try the Speaker Voltage Test on my headphones. (HD 580). Would be interesting to see what the voltages are.

The 600 ohm tap on my OPT puts out wayyyyyy too much voltage for the headphones. A 300 ohm tap would, too. I suppose the "Ear Speaker" types really need an amp suited to low efficiency speakers.
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Old 20th January 2013, 07:58 AM   #469
regal is offline regal  United States
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Quote:
Originally Posted by ikoflexer View Post
Pano, if you don't already have Rod Coleman's filament supply have a look at this little circuit which is based on the same idea, a CCS after the filament, and a bjt filter before it. I have used both Rod's circuit and mine in my 26 preamp and could not tell the difference (sound or measurement wise). All kind of different power bjts can be used, of course. I developed this after ordering a pair of Rod's supply because I ran out of patience.
What would be a real (as in something that is available off the shelf) qd44h11transistor ?
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Old 20th January 2013, 08:38 AM   #470
iko is offline iko  Canada
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The venerable D44H11 like here: D44H11 STMicroelectronics | Mouser

However, I've used D1912 successfully as well.
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