V76

Dave P · 8th May 2006, 07:59 PM

I have made a V76 type mic pre with a White follower output stage. (2x EF86, 1x12BH7). I have basically copied the first stage of a V76. There are 2 problems I need help with as Iv'e been working on this for months and I need fresh ideas! First problem is a very low frequency (about 2Hz) on the output which unless I have a 2k resistor across output ,spoils the 90dB S/N ratio. second problem is that the Bass rolls off from 100Hz to about 3/4 of 1KHz value by about 40Hz. Otherwise frequency response is flat to 35KHz.

By the way, I have translated from the telefunken braunbuch the technical descriptions for the V72,V77 & V78 circuits. I would be happy to place them somewhere accessible for members but I don't know how, this is my first ever post!

all the best
Dave P

Netlist · 8th May 2006, 08:17 PM

Dave,
welcome.

Shall I move your thread to tubes or analogue?

If the Telefunken descriptions are not copyrighted material, you can host them here if the files size is <100k and max 800X600 pixels.

/Hugo

Dave P · 8th May 2006, 10:50 PM

Hi Hugo,
I 'm not sure where to post, I'll be guided by you.
There are 3 pdfs of about 50k each, I did the translation so the work is mine and I got the German version freely off the web, what do you think?
best
Dave

Dave P · 8th May 2006, 10:50 PM

Hugo,
On second thoughts better to post it to tubes
thanks
Dave

Netlist · 9th May 2006, 06:33 AM

Dave,
50k will be no problem, you can only attach one file per post.
I'm looking forward to read them.

/Hugo

Dave P · 9th May 2006, 08:25 AM

Hugo,
This is first translation:- V72
Dave

Dave P · 9th May 2006, 08:25 AM

V77

Dave P · 9th May 2006, 08:25 AM

V78

EC8010 · 9th May 2006, 08:33 AM

Now I know what my EF804s were for! The screening on the mains transformer is to protect other circuitry from the extraneous field it generates, not to protect the mains transformer.

I await diagrams with interest.

Dave P · 9th May 2006, 11:58 AM

Thats right, this is one of the reasons why they managed to obtain such amazing S/N ratios (~120dB). Although the tubes are not canned, the steel chassis wraps around the tubes quite closely as well. The Mains TX screening stops the mic TX picking up hum in such a confined space, the components are really packed in.
Dave P

8th May 2006, 07:59 PM	#1
Dave P diyAudio Member Join Date: Dec 2005 Location: Welsh Hills	V76 I have made a V76 type mic pre with a White follower output stage. (2x EF86, 1x12BH7). I have basically copied the first stage of a V76. There are 2 problems I need help with as Iv'e been working on this for months and I need fresh ideas! First problem is a very low frequency (about 2Hz) on the output which unless I have a 2k resistor across output ,spoils the 90dB S/N ratio. second problem is that the Bass rolls off from 100Hz to about 3/4 of 1KHz value by about 40Hz. Otherwise frequency response is flat to 35KHz. By the way, I have translated from the telefunken braunbuch the technical descriptions for the V72,V77 & V78 circuits. I would be happy to place them somewhere accessible for members but I don't know how, this is my first ever post! all the best Dave P

9th May 2006, 08:33 AM	#9
EC8010 diyAudio Moderator Join Date: Jan 2003 Location: Near London. UK	Now I know what my EF804s were for! The screening on the mains transformer is to protect other circuitry from the extraneous field it generates, not to protect the mains transformer. I await diagrams with interest. __________________ The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...

9th May 2006, 11:58 AM	#10
Dave P diyAudio Member Join Date: Dec 2005 Location: Welsh Hills	V76 Thats right, this is one of the reasons why they managed to obtain such amazing S/N ratios (~120dB). Although the tubes are not canned, the steel chassis wraps around the tubes quite closely as well. The Mains TX screening stops the mic TX picking up hum in such a confined space, the components are really packed in. Dave P

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8th May 2006, 08:17 PM	#2
Netlist diyAudio Moderator Join Date: Jan 2003	Dave, welcome. Shall I move your thread to tubes or analogue? If the Telefunken descriptions are not copyrighted material, you can host them here if the files size is <100k and max 800X600 pixels. /Hugo

8th May 2006, 10:50 PM	#3
Dave P diyAudio Member Join Date: Dec 2005 Location: Welsh Hills	Hi Hugo, I 'm not sure where to post, I'll be guided by you. There are 3 pdfs of about 50k each, I did the translation so the work is mine and I got the German version freely off the web, what do you think? best Dave

9th May 2006, 06:33 AM	#5
Netlist diyAudio Moderator Join Date: Jan 2003	Dave, 50k will be no problem, you can only attach one file per post. I'm looking forward to read them. /Hugo

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