First Watt F1 Compatible with Passive Preamp (Miller Capacitance)?

xand1x · 10th March 2008, 04:24 AM

Greetings everyone. I own a First Watt F1 Amplifier (using the XLRs). I'm in abit of a sticky situation because I have two passive preamps that seem to sound great with my setup but technically shouldn't (according to a knowledegable friend of mine). I have a Slim Devices Transporter as my source from the XLRs (Specs: 3Vrms, Impedance: 100Ohms) and AKG K1000 earspeakers as my "speakers". According to my friend the F1 Amplifier has a high miller capacitance which makes it a not so great candidate for passive/resistor based preamps because it forms a low pass filter with the output impedance of the preamp which rolls off treble. He said that a transformer volume control could work much better or an active preamp with low output impedance. I am a bit lost because I don't hear a rolled off treble in my system, yet curious, because if a passive isn't the best solution my rig is capable of much more.

The passive preamp(s) I have are Scott Endlers BALANCED ShotGun Attenuators (4k resistors): http://mysite.verizon.net/vze4c5pt/
as well as a Luminous Audio Axiom Balanced Passive with 2.5K output: http://luminousaudio.com/axiombal.php

I know this seems like alot to ask but I was just wondering if a passive can work with my First Watt F1 given my source specs or if the passives I have now are fine. I have little knowledge about this type of thing and I'm only really basing the above claim on what my friend said.

Regards and thanks for your time

Nelson Pass · 10th March 2008, 07:17 PM

It is correct that a higher source impedance will reduce the
bandwidth due to input capacitance. I would estimate the
rolloff with a resistive load slightly above 20 KHz, and if the
headphones have inductance, which I believe they do, then
you may get a little better.

If they sound good, then there you are. If you have the
opportunity to try them with a balanced active source, then
you might hear a difference.

xand1x · 10th March 2008, 08:07 PM

Thanks Nelson for your response. I don't mean to be a bother but I do have one more quick question about the F1 and it is in regards to input sensitivity. I've checked both the owners and service manual but haven't found any specs. Would you be able to tell me what the input sensitivity of the F1 is?

Best Regards,

xand1x

Nelson Pass · 10th March 2008, 08:35 PM

The amplifier's sensitivity is load dependent, as it is a current
source, however into 8 ohms the gain is 14 dB, which is 5x

The sensitivity is 1.8V input for 10 watts into 8 and .566 for 1 watt
into 8.

zycomatique · 12th March 2008, 08:38 AM

Hello,

my question is quite near...
I'd like to build a Pass kit and use a passive préamp to drive it.
To match it perfectly the source impédance must be 1kohm and the load impédance must be 100kohms: is there a pass diy amp wich could have such a load impédance (in assymétrical)?

Thanks: David

Nelson Pass · 12th March 2008, 06:32 PM

Quote:

Originally posted by zycomatique
To match it perfectly the source impédance must be 1kohm and the load impédance must be 100kohms

Why do you say that?

zycomatique · 13th March 2008, 03:33 PM

Hello,

It's what the dealer of the TVC told me...
Then I understood that a passive préamp works the finest with a low impédance source and a high impédance load...
Am I wrong?

I've found the notice of the Aleph J: that could match (242ohm impédance input). Is the diagramm and part list avaible?

Thank you: David

10th March 2008, 04:24 AM	#1
xand1x diyAudio Member Join Date: Mar 2008	First Watt F1 Compatible with Passive Preamp (Miller Capacitance)? Greetings everyone. I own a First Watt F1 Amplifier (using the XLRs). I'm in abit of a sticky situation because I have two passive preamps that seem to sound great with my setup but technically shouldn't (according to a knowledegable friend of mine). I have a Slim Devices Transporter as my source from the XLRs (Specs: 3Vrms, Impedance: 100Ohms) and AKG K1000 earspeakers as my "speakers". According to my friend the F1 Amplifier has a high miller capacitance which makes it a not so great candidate for passive/resistor based preamps because it forms a low pass filter with the output impedance of the preamp which rolls off treble. He said that a transformer volume control could work much better or an active preamp with low output impedance. I am a bit lost because I don't hear a rolled off treble in my system, yet curious, because if a passive isn't the best solution my rig is capable of much more. The passive preamp(s) I have are Scott Endlers BALANCED ShotGun Attenuators (4k resistors): http://mysite.verizon.net/vze4c5pt/ as well as a Luminous Audio Axiom Balanced Passive with 2.5K output: http://luminousaudio.com/axiombal.php I know this seems like alot to ask but I was just wondering if a passive can work with my First Watt F1 given my source specs or if the passives I have now are fine. I have little knowledge about this type of thing and I'm only really basing the above claim on what my friend said. Regards and thanks for your time

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Pentode Miller Capacitance, and which spec value to use?	flysig	Tubes / Valves	5	30th May 2009 08:59 PM
71a Line Stage and Miller Capacitance	dsavitsk	Tubes / Valves	32	2nd November 2006 12:19 AM
c3m + 300b + miller capacitance	Klimon	Tubes / Valves	6	25th October 2006 10:51 PM
Ultralinear Miller capacitance	rdf	Tubes / Valves	3	9th July 2005 03:18 AM
Miller capacitance	ding	Solid State	11	28th September 2001 07:01 AM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read


	Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving

10th March 2008, 07:17 PM	#2
Nelson Pass The one and only Join Date: Mar 2001	It is correct that a higher source impedance will reduce the bandwidth due to input capacitance. I would estimate the rolloff with a resistive load slightly above 20 KHz, and if the headphones have inductance, which I believe they do, then you may get a little better. If they sound good, then there you are. If you have the opportunity to try them with a balanced active source, then you might hear a difference.

10th March 2008, 08:07 PM	#3
xand1x diyAudio Member Join Date: Mar 2008	Thanks Nelson for your response. I don't mean to be a bother but I do have one more quick question about the F1 and it is in regards to input sensitivity. I've checked both the owners and service manual but haven't found any specs. Would you be able to tell me what the input sensitivity of the F1 is? Best Regards, xand1x

10th March 2008, 08:35 PM	#4
Nelson Pass The one and only Join Date: Mar 2001	The amplifier's sensitivity is load dependent, as it is a current source, however into 8 ohms the gain is 14 dB, which is 5x The sensitivity is 1.8V input for 10 watts into 8 and .566 for 1 watt into 8.

12th March 2008, 08:38 AM	#5
zycomatique diyAudio Member Join Date: Feb 2008 Location: south France near Avignon	Hello, my question is quite near... I'd like to build a Pass kit and use a passive préamp to drive it. To match it perfectly the source impédance must be 1kohm and the load impédance must be 100kohms: is there a pass diy amp wich could have such a load impédance (in assymétrical)? Thanks: David

13th March 2008, 03:33 PM	#7
zycomatique diyAudio Member Join Date: Feb 2008 Location: south France near Avignon	Hello, It's what the dealer of the TVC told me... Then I understood that a passive préamp works the finest with a low impédance source and a high impédance load... Am I wrong? I've found the notice of the Aleph J: that could match (242ohm impédance input). Is the diagramm and part list avaible? Thank you: David

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)