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Old 26th June 2010, 07:35 PM   #31
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Originally Posted by bobodioulasso View Post
If you feel unconfortable with the volume at maximum, it is perhaps a matter of sensitivity of the amp, or wrong potentiometer value. In no way it can be a lack of power with earphones. Either you will be the first one in my knowledge.

That's interesting finally!

Consider that it works with 40 volts actually in front of 70 volts for the 400 watts in 8 ohms (I don't need them obviously!).

It is possibile that the problem could be the pot: I'm using a temporary pot before finish the project in his case with an Alps 100K: I'll try to change it.

But it is more interesting the possible sensitivity problem: if it is too low for the headphone purpose (remember that this amplifier was projected for loudspeakers), what could I do?


Thank you sincerely
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Old 26th June 2010, 08:15 PM   #32
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Which source do you use? How many millivolts it produces, at which impedance?
Dou you know the input impedance of your amp, its sensitivity?
All these need to match either you cannot feed properly your amp with the signal.

Have you hooked speakers to this amp, you should feel the same problem. If there is a mismatch this will not affect the headphones specially.

Last edited by bobodioulasso; 26th June 2010 at 08:18 PM.
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Old 26th June 2010, 08:26 PM   #33
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Originally Posted by bobodioulasso View Post
Which source do you use? How many millivolts it produces, at which impedance?
Dou you know the input impedance of your amp, its sensitivity?
All these need to match either you cannot feed properly your amp with the signal.

Have you hooked speakers to this amp, you should feel the same problem. If there is a mismatch this will not affect the headphones specially.

Thank you, I see. Tomorrow I'll measure and I'll say the values.

By the way, I believe to remember (I checked it) that the amplifier input impedance is 500k ohms about.

The source I usually use are standard cd players, sometimes also a cheap portable player (I study music and I need to move from a room to another very often: i can't carry everything everytime).

I Thank you very much. See you soon.
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Old 26th June 2010, 08:49 PM   #34
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Quote:
Originally Posted by bobodioulasso View Post
Which source do you use? How many millivolts it produces, at which impedance?
Dou you know the input impedance of your amp, its sensitivity?
All these need to match either you cannot feed properly your amp with the signal.

Have you hooked speakers to this amp, you should feel the same problem. If there is a mismatch this will not affect the headphones specially.
The cd player I used for testing and for the first listenings to the amp is a 800.000 ohms output impedance (measured with really professional analog multimeter) and the amplifier near 500.000 ohms input.
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Old 26th June 2010, 09:00 PM   #35
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You can't measure an impedance with an ohm meter.

Feeding a power amp from a CD player should work fine.

Your pot value is may be quite high, try 50k or 22k
But it looks like your amp is particularly unsensitive.
Try with speakers.

Last edited by bobodioulasso; 26th June 2010 at 09:03 PM.
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Old 26th June 2010, 09:07 PM   #36
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I know that it need an oscilloscope, but I haven't it... sorry...


Thank you for your time and availability.
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Old 27th June 2010, 03:18 AM   #37
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Hi Hammerklavier,

Do you really hook up your headphones to the amplifier to speaker output? Could you draw a simple circuit to show us how you hook up your headphones to your amp? I am very curious.

Wachara C.
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Old 27th June 2010, 09:18 AM   #38
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Originally Posted by Hammerklavier View Post
Risus abundat in ore stultorum
http://edvinas.sideris.googlepages.com/AV400.pdf
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Old 28th June 2010, 06:05 AM   #39
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Build EUVL's Dao Follower amp and incorporate a Salas shunt regulator.
Hard to beat.
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Old 5th July 2010, 09:24 PM   #40
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Default Smells fish?

Now this was a weird thread. Maybe it should have just died here. On the other hand, I just couldn't resist

You see, I own a pair of AKG 702's (among several other equally good 'phones). And the 702's are happy with just about everything I throw at it. I've tried Grace, Musical Fidelity, Benchmark...... Too little level is never a problem! Connect it directly to a non-valve CD-player output, and it's LOUD! Way too LOUD!

So, since this is a site for people with some technical knowledge, here's the spec's for the 702:
Sensitivity: 105 dB/V
Rated impedance: 62 ohms
Max. input power: 200 mW

Now, if we combine these spec's, we'll find:
1. Max. input VOLTAGE = 11 volts
2. SPL at 11 volts = 126 dB

So - do you smell fish now? An amplifier putting out levels far above what the 'phones can handle -- and it's still not loud enough?

There have been some hints to the source of the "not loud enough" problem. Did the thread starter ever answer to them?
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