• FORTE Model 1 • INput impedance

rekupax · 24th December 2009, 07:45 AM

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!

labjr · 24th December 2009, 12:37 PM

Quote:

Originally Posted by rekupax

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.

AndrewT · 24th December 2009, 12:43 PM

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.

rekupax · 24th December 2009, 01:06 PM

schematic i used was like this:

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!

rekupax · 24th December 2009, 02:24 PM

schematic pic
http://i46.tinypic.com/2rcu6ub.jpg

jacco vermeulen · 24th December 2009, 02:52 PM

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)

Nelson Pass · 24th December 2009, 06:11 PM

I think you can drop them in.

rekupax · 24th December 2009, 07:38 PM

!! 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!

24th December 2009, 07:45 AM	#1
rekupax diyAudio Member Join Date: Dec 2009	• 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!

24th December 2009, 12:43 PM	#3
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	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. __________________ regards Andrew T.

24th December 2009, 02:52 PM	#6
jacco vermeulen diyAudio Member Join Date: Oct 2004 Location: At the sea front, just under Rotterdam	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) __________________ Looks like Sponge Bob has killed another thread.

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24th December 2009, 01:06 PM	#4
rekupax diyAudio Member Join Date: Dec 2009	schematic i used was like this: 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!

24th December 2009, 02:24 PM	#5
rekupax diyAudio Member Join Date: Dec 2009	schematic pic http://i46.tinypic.com/2rcu6ub.jpg

24th December 2009, 06:11 PM	#7
Nelson Pass The one and only Join Date: Mar 2001	I think you can drop them in.

24th December 2009, 07:38 PM	#8
rekupax diyAudio Member Join Date: Dec 2009	!! 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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