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Old 23rd October 2009, 08:26 PM   #651
AKSA is offline AKSA  Australia
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Hi Michael,

Thank you for your post. Yes, nice little forum, most grateful to the owner, so I thought it would be nice to give something back.

5401s are rated to 150V, reasonably fast. This application is low voltage, so 557Bs would be better as they are faster, lower Cob, and much higher beta. The VAS is the best I've yet used, 1.8pF, 150V, 200MHz, 50mA, and inexpensive. The outputs are much faster than the usual choice, MJE15030/31, and while not so high current, their linearity is as good and they are cheaper. For this application, very good choice.

On top of that, all these are commonly available except the 3423, and I have plenty of stock of all of them (though not for resale!).

Cheers,

Hugh
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Old 23rd October 2009, 08:41 PM   #652
AKSA is offline AKSA  Australia
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Default HP Amp Amendment

Michael's comment reminded me I had not simulated the Loop gain for BC557B, so I did it again today and came up with slightly different lag compensation and phase lead values. This has resulted in a full two degree reduction in phase shift at 100KHz, which is no bad thing. Apologies, it's set in concrete now!

Cheers,


Hugh
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Old 23rd October 2009, 09:59 PM   #653
keantoken is offline keantoken  United States
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Hugh, I realized I should ask you this. Until now I haven't thought to understand how exactly you made your choice of devices.

How much do you believe the actual performance curves of an individual transistor (Ic vs Hfe/Vbe, etc.) affect it's sound as opposed to passive factors such as Cob, Ft and AC characteristics?

I'm sort of asking you how important DC performance is as opposed to AC performance.

PS, the amp is awesome I think, painfully nitpicked and scrutinized, it has had a rough childhood but will surely be strong for it. A masterpiece I believe.

- keantoken
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Old 23rd October 2009, 10:22 PM   #654
Bigun is offline Bigun  Canada
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Aspen Headphone Amp
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Originally Posted by keantoken View Post
the amp is awesome I think, painfully nitpicked and scrutinized, it has had a rough childhood but will surely be strong for it. A masterpiece I believe.
It's the mid-teenage years that worry me - when we start building and listening there will be more subjective emotions coming into things - and I share your optimism for a very positive outcome !
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Old 24th October 2009, 02:54 AM   #655
keantoken is offline keantoken  United States
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Yes, though if he acts up we may have to cut an arm off and replace it with something better. Or perhaps restrain him a little to keep him under control. They're under a lot of pressure these days because of the internet - it cultivates (sometimes incredible) expectations.

EDIT: Hugh, I've sent you one or two emails, in case they got buried in spam or perhaps you just haven't had the time.

- keantoken
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Last edited by keantoken; 24th October 2009 at 03:00 AM.
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Old 24th October 2009, 03:17 AM   #656
AKSA is offline AKSA  Australia
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Kean/Bigun,

Presently at a friend's on the other side of Melbourne, will answer on return.

This is Step #1, no amp is yet built, so I could never be sure this is the cat's meow. We must be patient, lay out the pcbs, and build it (though in reverse order, preferably!)

Hugh
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Old 24th October 2009, 03:24 AM   #657
Luke is offline Luke  New Zealand
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what are crossfeeds?
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Old 24th October 2009, 03:43 AM   #658
keantoken is offline keantoken  United States
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Normal sounds in nature are always blended because both your ears hear the noise. But in headphones, the ears are isolated. This can cause fatigue when your ears are hearing completely different sounds that were designed to be played on speakers where there is always natural crossover.

So in order to make headphones perform better for those who have these issues, someone of years past designed a crossfeed which mixes the left and right channels in a way that is natural to the brain.

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Old 24th October 2009, 03:57 AM   #659
Luke is offline Luke  New Zealand
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thanks Keantoken,

so I guess its a personal preference thing?
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Old 24th October 2009, 04:00 AM   #660
keantoken is offline keantoken  United States
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Yes, but recordings aren't consistent in how they record left and right channels, so we (if I understand the committee) figure it's better to be safe than sorry. I'm not sure, but I believe there is a bypass switch for the crossfeed.

EDIT: the schematic shows a variable crossfeed pot, so you get a knob to determine how much you want. Perhaps then a bypass switch is not necessary?

- keantoken
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