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Old 8th October 2012, 07:13 PM   #21
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Its not that terribly bad. I ordered Spencer DAC kit and soldered everything by myself (excluding SMD parts). Worked just fine. But thats just PCB with all needed elements etc. Im afraid of collecting all parts by myself, matching transistors etc.
Dont need any chassis for now. Im searching best solution for me - Ill think about chassis when i find it.
All I know is to go DIY path as many commercial products or projects dont have proper application. I like sound of Hifimans (I tried a lot of different HP). Regarding headamp i only compared it to Woo Audio WA 6 SE and it was better. Not mention to other chinese clones of BCL. One of friends who listened to it at meeting said its class A+ and he really heard massive stack of equipment.
On the other hand if we only look at measurements shouldnt O2 amp be the best in the world theoretically? Only guessing, maybe Im wrong.
800 USD is too much for testing
PSU shouldnt be problem. I use 2x12V accumulators for headamp
Friend also makes me 2 Salas PSU.

Last edited by zibra; 8th October 2012 at 07:15 PM.
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Old 8th October 2012, 07:33 PM   #22
jcx is online now jcx  United States
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Default "drives 32 Ohms" isn't too informative

what's the bias current/Class A output current range of the Marsh amp? (a JLH outupt stage delivers less than 2x the bias in push-pull due to Q beta mismatch and modulation)

the HE-5LE are way low sensitivity @87.5 dB/mW compared to say Grado 32 Ohm headphones @ 98 dB/mW and requires more current and V to reach the same SPL as typical near 100 dB/mW headphones - >10x more power

Last edited by jcx; 8th October 2012 at 07:35 PM.
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Old 8th October 2012, 07:58 PM   #23
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Ah I noticed theres review in english language already. I have now that headamp. Its IC based but again: are there any real advantages of using discrete designs when both solutions are theoretically well implemented?

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Old 8th October 2012, 08:16 PM   #24
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Quote:
Originally Posted by jcx View Post
what's the bias current/Class A output current range of the Marsh amp? (a JLH outupt stage delivers less than 2x the bias in push-pull due to Q beta mismatch and modulation)
The Marsh headphone-amp is a Class-A/B output stage (see attached topology schematic from the article abstract), the circuit values might have to be adjusted to "crank-up" the standing bias current. In my own experiences with my HiFiMan HE-6's, I've found that we really need about 200mA bias-current in a Class-A/B output-stage to make the planar-magnetics really "come into their own" from a sonics standpoint.

Quote:
the HE-5LE are way low sensitivity @87.5 dB/mW compared to say Grado 32 Ohm headphones @ 98 dB/mW and requires more current and V to reach the same SPL as typical near 100 dB/mW headphones - >10x more power
As I mentioned, I haven't had an opportunity to read Richard Marsh's article on his headphone-amplifier in Linear Audio, but I would assume if we run with at least +/- 24VDC power-supply rails and 200mA bias-current in the output stage, we should be in good shape for driving the HiFiMan beasties (Richard noted that he himself uses this circuit with HiFiMan planar-dynamics...).
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Old 8th October 2012, 08:26 PM   #25
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Quote:
Originally Posted by zibra View Post
Its not that terribly bad. I ordered Spencer DAC kit and soldered everything by myself (excluding SMD parts). Worked just fine. But thats just PCB with all needed elements etc. Im afraid of collecting all parts by myself, matching transistors etc.
Dont need any chassis for now. Im searching best solution for me - Ill think about chassis when i find it.
All I know is to go DIY path as many commercial products or projects dont have proper application. I like sound of Hifimans (I tried a lot of different HP). Regarding headamp i only compared it to Woo Audio WA 6 SE and it was better. Not mention to other chinese clones of BCL. One of friends who listened to it at meeting said its class A+ and he really heard massive stack of equipment.
On the other hand if we only look at measurements shouldnt O2 amp be the best in the world theoretically? Only guessing, maybe Im wrong.
800 USD is too much for testing
PSU shouldnt be problem. I use 2x12V accumulators for headamp
Friend also makes me 2 Salas PSU.
The problem with pursuing a DIY solution is that it's pretty difficult to find an existing implementation to audition prior to committing to constructing your own instance. I constructed a half-dozen prototypes before I built my current prototype that I briefely described earlier (John Curl-designed JC-80 as the core engine, Erno Borbely-designed all-FET shunt power-supply regulator, and relay-based 128-step attenuator). I'll likely build Richard Marsh's headphone-amplifier PCB's and insert them into my current prototype for an audition; that's what DIY audio is all about, after all...

Without the ability to audition most of the circuits, you'll eventually reach a point where you'll just have to commit to a given circuit, build it and see what you think...

Good luck!
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Old 9th October 2012, 12:13 PM   #26
RNMarsh is offline RNMarsh  United States
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each half of the output stage runs at 90mA. throw in another series diode for more class A if you need it and more heat-sink. -RNM
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Old 9th October 2012, 12:23 PM   #27
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Richard,

Thanks for the information. So, about 180mA of current delivered into a 32-ohm load or just a tick over 1W of Class-A power before transitioning into Class-A/B operation. That should be head-pounding SPL's while staying in Class-A operation!

Excellent!
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Old 27th October 2012, 05:39 PM   #28
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Someone made nice math for power needs of HE5LE:


120dB - 1778mW or 8.22VRMS
115dB - 562mW or 4.62VRMS
110dB - 177mW or 2.6VRMS
105dB - 56mW or 1.45VRMS

Can you please tell me what numbers are in case of HE6? Im weak at it.
HE6 is specified as 50 Ohm, 83.5dB/mW
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Old 27th October 2012, 06:28 PM   #29
qusp is offline qusp  Australia
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just for clarity, Nelson contracted the now bankrupt Semisouth to make him a SIT all of his own to his specifications, the transistor used in that amp linked is a standard sic power JFET, not a SIT, different things. I do hope that kickstarter guy managed to buy his jfets before Semisouth went belly up last week, there really isnt an easy substitute except a mosfet*,which i'm sure wouldnt go down well with the backers of the project. (*at least if it was using the depletion mode Semisouth parts, they were fairly easily dropped into many projects that use Mosfets with a simple change of bias),



Quote:
Originally Posted by mullardel34 View Post
Zibra,

Static Induction Transistors (SiT's) are a relatively new genre of solid-state gain devices which offer transfer-function characteristics similar to those of triode vacuum-tube devices. As you noted, Nelson Pass is among the first noted audio designer to invest in the production of suitable SiT's for audio-reproduction purposes. These devices cannot be just substituted for more conventional solid-state devices on a "drop-in" basis; instead, the circuit must be tailored to the devices in order to exploit their "special" characteristics...

Richard Marsh is a retired key researcher in High Energy Physics R&D at Lawrence Livermore National Laboratory and a published member of IEEE and AES. He recently published his "diamond" topology-based headphone amplifier design in Volume 3 of Jan Didden's "Linear Audio" bookzine (www.linearaudio.net - home). I'm a bit behind on my audio-design journal reading, so I haven't read the article as yet, but the abstract illustrates a simple/elegant topology which could be built in a "bridged" configuration to easily drive balanced-drive headphones such as the HiFiMan planar magnetics...

Just my $0.02's worth...

Last edited by qusp; 27th October 2012 at 06:31 PM.
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Old 29th October 2012, 12:17 PM   #30
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Default Hifiman HE6

Hi, those nice numbers for the HE6

120dB - 4467mW or 14.95Vrms
115dB - 1413mW or 8.41Vrms
110dB - 447mW or 4.73Vrms
105dB - 141mW or 2.65Vrms

Hope thats helpfull

Paul.
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