analag

mic pre
« on: December 28, 2018, 01:29:26 PM »

Sharing thing this one before I build it. Lately I have been having fansties about some black plate 12SL7s and 12SN7s I have laying around. Mind you 6SL7 and 6SN7 will work. In fact I plan to get a couple of those new Tung Sol offering I see on the market. I have grown a love for the sound of the CCS triode stage. You see you can use it to hold even a crappy reproduction tube in it's sweet spot. Dynamic plate resistor kicks as, period!  Let the beatings begin
Audio engineering suffers from misinformation, disinformation, and downright lying more than most fields of endeavour.


analag

Re: mic pre
« Reply #1 on: December 28, 2018, 01:32:48 PM »
Trannys will be 1:10 in and 15:1 out. R 14 will be variable and will bottom out at 10K
Audio engineering suffers from misinformation, disinformation, and downright lying more than most fields of endeavour.

benb

Re: mic pre
« Reply #2 on: December 28, 2018, 04:12:12 PM »
How often are tubes used in an op-amp type configuration like this, for a preamp or otherwise? I don't think I've ever seen such other than the pre-709 times when all op-amps were made with tubes.

EmRR

Re: mic pre
« Reply #3 on: December 28, 2018, 04:39:44 PM »
There's a Fred Forssell drawing out there which has an article in Glass Audio #3 (1995).

https://www.forsselltech.com/media/attachments/VT_Opamp.PDF

Different for many reasons.

May or may not relate to his Millenia M-2B preamp. 

Best,

Doug Williams
Electromagnetic Radiation Recorders

"I think this can be better. Some kind of control that's intuitive, not complicated like a single knob" - Crusty

"Back when everything sounde

analag

Re: mic pre
« Reply #4 on: December 28, 2018, 06:19:21 PM »
Close but not quite
Audio engineering suffers from misinformation, disinformation, and downright lying more than most fields of endeavour.

ruffrecords

Re: mic pre
« Reply #5 on: December 28, 2018, 06:35:05 PM »
Trannys will be 1:10 in and 15:1 out. R 14 will be variable and will bottom out at 10K

If C6 really is 5 picoFarads then the max gain from the tube stage is 20dB. With 20dB from the input transformer that gives 40dB in total but a 15:1 output transformer this drops by 23.5dB to just 16.5dB

Do you really mean 15:1 ratio at the output? Did you really mean 5:1?

I think you need more gain in the tube stage but maintaining stability over a reasonable gain range will not be easy.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

abbey road d enfer

Re: mic pre
« Reply #6 on: December 29, 2018, 03:49:33 AM »
If C6 really is 5 picoFarads then the max gain from the tube stage is 20dB. With 20dB from the input transformer that gives 40dB in total but a 15:1 output transformer this drops by 23.5dB to just 16.5dB

Do you really mean 15:1 ratio at the output? Did you really mean 5:1?
If the OT was 5:1, that would probably make it the most useful mic pre for recording pop/rock; I've found that most of the times I use between 25 and 35dB of gain.
Now, one would ask why making it so complex?
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.

gyraf

Re: mic pre
« Reply #7 on: December 29, 2018, 10:34:09 AM »
Build the micamp, tune it in to suit your taste, and report back here.

Simulation games leave too much to be wished really

Jakob E.
..note to self: don't let Harman run your company..


 

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