transimpedance amplifier - Page 2

Gluca · 7th February 2010, 05:45 AM

I am working of a EF184 with servo bias actually. 6SN7 was there just to understand how things go.

Gluca · 7th February 2010, 06:24 AM

OK, a schematic is worth 1000s words

Gianluca

cetoole · 7th February 2010, 07:23 AM

That isnt a servo, and I really dont think it will what you want at all. You should get more like 70ohm input impedance at the cathode of the ef184. Also, I cant think that it will be happy with a 470ohm plate load.

Gluca · 8th February 2010, 02:08 AM

Quote:

Originally Posted by cetoole

That isnt a servo, and I really dont think it will what you want at all. You should get more like 70ohm input impedance at the cathode of the ef184. Also, I cant think that it will be happy with a 470ohm plate load.

I am probably very wrong, but do you mind elaborating a bit your comments?

cetoole · 8th February 2010, 03:40 AM

The opamp isnt working as a DC servo at all, no integration cap or input resistor, so therefore the whole circuit wont work as you are expecting.

Gluca · 8th February 2010, 05:22 PM

Quote:

Originally Posted by cetoole

The opamp isnt working as a DC servo at all, no integration cap or input resistor, so therefore the whole circuit wont work as you are expecting.

umpf ... I stand corrected. And the load onto the dac is in the 50ohm ballpark: too high. I-ll look somewhere else.

cetoole · 02:45 PM

Quote:

Originally Posted by Gluca

umpf ... I stand corrected. And the load onto the dac is in the 50ohm ballpark: too high. I-ll look somewhere else.

You wont get the input impedance any lower without more transconductance, or some nfb. EC8020 would be fun. How do you feel about a bit of sand, MOSFET/triode CFP would really drop it down.

I use something kinda similar in my system, but using BJTs for an open loop common base amplifier.

Gluca · 9th February 2010, 03:45 PM

Sand is welcome: I am putting all the parts together for a rboer IV. For the time being I am more than happy with a R (22ohm) and a step-up transformer into a tube preamp. I just want to explore other possibilities. It's fun.

Bas Horneman · 9th February 2010, 04:08 PM

Sorry for the off-topic. But what is a rboer IV?

Gluca · 9th February 2010, 04:32 PM

Quote:

Originally Posted by Bas Horneman

Sorry for the off-topic. But what is a rboer IV?

Simple I/V for TDA1541

many variants and updates exist.

ciao

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7th February 2010, 05:45 AM	#11
Gluca tarmac ripper diyAudio Member Join Date: Nov 2004 Location: Back to Italy	I am working of a EF184 with servo bias actually. 6SN7 was there just to understand how things go.

7th February 2010, 06:24 AM	#12
Gluca tarmac ripper diyAudio Member Join Date: Nov 2004 Location: Back to Italy	OK, a schematic is worth 1000s words Gianluca

7th February 2010, 07:23 AM	#13
cetoole diyAudio Member Join Date: Mar 2005 Location: Maryland, USA	That isnt a servo, and I really dont think it will what you want at all. You should get more like 70ohm input impedance at the cathode of the ef184. Also, I cant think that it will be happy with a 470ohm plate load.

8th February 2010, 03:40 AM	#15
cetoole diyAudio Member Join Date: Mar 2005 Location: Maryland, USA	The opamp isnt working as a DC servo at all, no integration cap or input resistor, so therefore the whole circuit wont work as you are expecting.

9th February 2010, 03:45 PM	#18
Gluca tarmac ripper diyAudio Member Join Date: Nov 2004 Location: Back to Italy	Sand is welcome: I am putting all the parts together for a rboer IV. For the time being I am more than happy with a R (22ohm) and a step-up transformer into a tube preamp. I just want to explore other possibilities. It's fun.

9th February 2010, 04:08 PM	#19
Bas Horneman diyAudio Moderator Emeritus Join Date: Apr 2002 Location: The Netherlands Blog Entries: 18	Sorry for the off-topic. But what is a rboer IV?

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