Ribbon Microphone Preamp - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

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
Reply
 
Thread Tools Search this Thread
Old 27th April 2013, 01:17 PM   #1
diyAudio Member
 
Join Date: Aug 2012
Default Ribbon Microphone Preamp

Hi, Perhaps this may be a quick question:

So I am in the process of designing a ribbon microphone. I am getting alot of my info from "http://www.diyaudiocomponents.com" and was wondering what a suitable preamp would be for a 4mm wide 2.5u thick ribbon in between two neodymium magnets (2"x1/4"x1/4").

I prefer a simple and minimal component count preamp design and I think I landed on one. Check out the image below. A single pentode wired like a triode? Whatever it may be, I enjoy the concept of single stage amps.

Click the image to open in full size.

Being that I didnt fabricate the microphone yet, I dont know the impedance of the ribbon. But when I do measure the impedance of the microphone, what is the process for setting the proper resistor value at the input to match the impedance?

I also heard somebody mutter the idea of using a potentiometer to accommodate a wide range of impedances. But my question as well is how do you tell by ear that the microphone is loaded properly?

Some Preamps have input attenuation and output (gain) control. Should I consider all that? This one schematic I supplied doesn't feature any of those.
  Reply With Quote
Old 27th April 2013, 01:24 PM   #2
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
This will be extremely noisy. A ribbon impedance is likely to be an ohm or less, and the equivalent noise resistance of a pentode will be 1k or more. If you use a step up transformer (30:1 is typical), the source impedance seen by the tube is going to be several hundred ohms, which is at least in the ballpark for triodes- then you have to fight the effect of the input capacitance on the transformer... Tube preamps for low output, low source impedances are NOT trivial to design!
__________________
You might be screaming "No, no, no" and all they hear is "Who wants cake?" Let me tell you something: They all do. They all want cake.- Wilford Brimley
  Reply With Quote
Old 27th April 2013, 01:32 PM   #3
diyAudio Member
 
Join Date: Aug 2012
Oh wait, I dont know if this adds to your statement, but on the microphone, there will be a step up transformer inside from Edcor.
EDCOR - RMX1

This transformer is 1:37. The output DCR of the transformer is 87 Ohms. Will this make it more apropriate for a tube preamp to function less obnoxiously?
  Reply With Quote
Old 27th April 2013, 01:36 PM   #4
diyAudio Member
 
Join Date: Aug 2012
Also on a second note, I am not married to the concept of using a 6AU6 pentode. I have some nice luxurious D3A tubes but that may require me to seriously reconsider every component surrounding it.
  Reply With Quote
Old 27th April 2013, 01:47 PM   #5
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
D3a is a MUCH better choice. This still won't be ultra quiet, but it will be a phuc-ton quieter than a 6AU6!

You'll want a much quieter supply (DC on heaters, elevated heater potential, common mode filtering, snubbered HT secondary), since a pentode will not have good power supply rejection.
__________________
You might be screaming "No, no, no" and all they hear is "Who wants cake?" Let me tell you something: They all do. They all want cake.- Wilford Brimley
  Reply With Quote
Old 27th April 2013, 06:46 PM   #6
diyAudio Member
 
Join Date: Aug 2012
If I were to use a D3A in this schematic, should I go about using this similar layout, (no cathode resister) etc or should I do cathode bypass like this:
Click the image to open in full size.

How would you recommend going about redesigning for the D3A? What about impedance matching? attenuators for load matching?

The power supply I'm not too worried about, I have some chokes I can use etc.
  Reply With Quote
Old 28th April 2013, 12:10 AM   #7
diyAudio Member
 
Join Date: Apr 2004
Location: Monroe Township, NJ
RCA was/is famous for their "velocity", AKA ribbon, microphones. They used a SUT into a 6SL7. Other than RIAA equalization, this situation is quite analogous to that found in handling a LOMC phono cartridge.

If you're willing to "wrestle an alligator", consider the Russian 6C45П (6s45p), as the 1st tube the signal "hits". That tube, like the 5842, comes perilously close to oscillating, while being stored in its cardboard box. EXTREME measures that suppress parasitic oscillation are very much in order. Place a 5.6 KOhm carbon composition "stopper" on both grid connection points. Place a 100 Ω carbon film "stopper" on the plate connection point. Finally, place ferrite beads on the heater power wires, as close to the socket as you can get.
__________________
Eli D.
  Reply With Quote
Old 28th April 2013, 12:31 AM   #8
diyAudio Member
 
Join Date: Aug 2012
Oh man, I never heard about this Russian magic before,
DIY 6c45 Amplifier
sounds like a cult classic. It probably isnt realistic to have a 6s45p be OTL right?

In fact, is there a OTL preamp thats minimal like this? Regardless, Im realy starting to dig this mini magic trick
  Reply With Quote
Old 28th April 2013, 02:20 AM   #9
diyAudio Member
 
Chris Hornbeck's Avatar
 
Join Date: May 2011
Location: Little Rock
You might end up going through *two* input transformers to get things acceptably quiet, one in the mic and one in the preamp. Ribbon mic output levels are measured in mouse farts per furlong, and that's on a good day. Sounds like a fun project, fersure. What are you using for magnets?

All good fortune,
Chris
  Reply With Quote
Old 28th April 2013, 03:42 PM   #10
diyAudio Member
 
Join Date: Aug 2012
I figured a output transformer on the preamp would be necessary,

The two magnets would be 2" x 1/4" x 1/4" neodymium bars.

I figure Edcor would be a healthy solution for all transformers required
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
DIY ribbon microphone preamp question efabric Instruments and Amps 2 14th June 2012 08:30 AM
DIY Ribbon Microphone Tutorial RickshawRecords Analogue Source 13 29th September 2011 10:50 AM
WTB: Cheap Ribbon Microphone Transformer for Experiment exp jst Swap Meet 0 10th June 2011 09:03 PM
Ribbon microphone jzagaja Planars & Exotics 12 23rd May 2008 10:48 PM
Stereo Ribbon Microphone GB magicalpig Group Buys 1 11th March 2007 09:02 AM


New To Site? Need Help?

All times are GMT. The time now is 05:14 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2