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Old 15th May 2013, 10:06 AM   #31
DF96 is offline DF96  England
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Quote:
Originally Posted by borg7x9
they still recommend driving the single ended input with -10x the input impedance <60ohms, but say that the XLR input should work well at 600ohms matched. Do you agree with this opinion ??
The two inputs are essentially the same, except XLR is balanced and the other is not. The switch merely shifts the ground connection from the primary centre-tap to one end. Apart from the balancing, anything which would work with one would work with the other.
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Old 15th May 2013, 10:34 AM   #32
borg7x9 is offline borg7x9  New Zealand
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The two inputs are essentially the same, except XLR is balanced and the other is not. The switch merely shifts the ground connection from the primary centre-tap to one end. Apart from the balancing, anything which would work with one would work with the other.
DF96, thanks for that.
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Old 15th May 2013, 11:44 AM   #33
Pano is offline Pano  United States
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Do you have, or can you borrow, a voltmeter that has a low volt AC scale? 2V AC or less?
With that, you can measure the overall gain of the amp, then know if you really need the 17dB voltage gain of the input transformer. If not needed, it could be bypassed.

For that matter if you have some way to apply the signal at the 100K resistor and 1st grid, you'll find out very fast.
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Old 15th May 2013, 12:47 PM   #34
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As Godfrey mentioned, you need a headphone amp to drive this power amp. You could design one that was essentially your preamp also. It's no big deal to me anyway. While many opamps claim to drive 600 ohms by themselves (LME49710 comes to mind) at very low distortion (but I assume this is at unity gain), I'd feel better if it was muscled up with a power buffer like the BUF634 or LME49600. Have you tried using a headphone amp to drive this power amp?
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Old 15th May 2013, 11:12 PM   #35
borg7x9 is offline borg7x9  New Zealand
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Pano, I do have a digi multi meter that reads to .00 of a volt. How would I do that. I suspect I could get away with-out the extra gain. Currently ( using a cat sl1 preamp ) I can only usefully use the first four-five clicks on the Volume control its too loud thereafter.
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Old 15th May 2013, 11:18 PM   #36
borg7x9 is offline borg7x9  New Zealand
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Dirkwright, I have a schiit Lyr with a pre out that is a fairly good amp. Are you suggesting that I run a headphone jack to rca and see what that is like. This amp also has a pre amp output at 75 ohms. I tried this it was ok but it was noisy.

I could try the head-out if you think this will yield different results.
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Old 16th May 2013, 09:20 AM   #37
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by borg7x9 View Post
............. I do have a digi multi meter that reads to .00 of a volt................
You could buy a second DMM that can read down to 0.0000Vac i.e. the most sensitive scale reads 199.9mVac. These are available cheap.
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Old 16th May 2013, 12:01 PM   #38
borg7x9 is offline borg7x9  New Zealand
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You could buy a second DMM that can read down to 0.0000Vac i.e. the most sensitive scale reads 199.9mVac. These are available cheap.
Doh !! Actually mine will do that . It has a variable scale depending on magnitude of input signal.
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Old 17th May 2013, 05:52 PM   #39
Pano is offline Pano  United States
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If you have a CD player and a test tone CD you can check your meter. If not, I can make you some test tones that you can burn to CD or play back from your computer.
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