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Old 24th December 2009, 07:45 AM   #1
rekupax is offline rekupax  Russian Federation
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Default • FORTE Model 1 • INput impedance

Hi all!
Anyone knows what resistance one should use as passive amp for the Forte Model 1 Power amp?
I've just connected 2 Volts CD-Player through 50 kOm potentiometer (500 - 2M Ohms total resistance) --- signal in incredibly low!

Anyone tried?

Forte sounds a way better without my MBL preamp, so getting right attenuator would make me happy!
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Old 24th December 2009, 12:37 PM   #2
labjr is offline labjr  United States
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Quote:
Originally Posted by rekupax View Post
Hi all!
Anyone knows what resistance one should use as passive amp for the Forte Model 1 Power amp?
I've just connected 2 Volts CD-Player through 50 kOm potentiometer (500 - 2M Ohms total resistance) --- signal in incredibly low!

Anyone tried?

Forte sounds a way better without my MBL preamp, so getting right attenuator would make me happy!
I think the model 1 input impedence is 47K and input sensitivity was like 1 volt or less for full power output so shouldn't be a problem with a CD player. Make sure your pot is hooked up right.
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Old 24th December 2009, 12:43 PM   #3
AndrewT is offline AndrewT  Scotland
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2M total resistance measured!
How have you wired up the pot and how did you measure that resistance?

A 47k input impedance would work better with a 10k log pot.
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Old 24th December 2009, 01:06 PM   #4
rekupax is offline rekupax  Russian Federation
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schematic i used was like this:


Click the image to open in full size.



i didn't measure any resistance yet, i read it in manufacturer's datasheet.
"Total Resistance 500Ω ~ 2MΩ"

thanks, i'll try 10k pot tonight and compare!
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Old 24th December 2009, 02:24 PM   #5
rekupax is offline rekupax  Russian Federation
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schematic pic
http://i46.tinypic.com/2rcu6ub.jpg
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Old 24th December 2009, 02:52 PM   #6
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The Forté Audio Model 1 has a bipolar input.
Not an easier way for a passive pre to swap for a matched JFET pair ? (equivalent to the Model 1A)
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Old 24th December 2009, 06:11 PM   #7
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I think you can drop them in.

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Old 24th December 2009, 07:38 PM   #8
rekupax is offline rekupax  Russian Federation
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!! thank you all, i've solved the problem (cables were pseudo-balanced, rewired now). WORKS!
but now it's too powered. i can use just about 20 degrees angle rotation for non-extreme volume adjustment. ( 50K potentiometer )
i finally enjoy the sound ))

how MBL pre can be so poor in a circuit?... it's vintage though

cheers!
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