Quantcast
Adding a low Z mic to an amp with a hi Z input - Gearspace.com
The No.1 Website for Pro Audio
Adding a low Z mic to an amp with a hi Z input
Old 21st September 2012
  #1
Gear Head
 
🎧 5 years
Adding a low Z mic to an amp with a hi Z input

Hi, sorry for asking about a lo-end amp in a high end forum, I couldn't find a low-end thread.

I am hooking up a lo-Z mic (600 ohms) to my David Bogen HE10 that has a mic preamp and an input for a hi-Z mic, but I did use a 600ohm-50K ohm input matching transformer, but you have to have the volume at MAX for it to have decent normal volume. Its still low sounding.. but clear and clean.

My question is, do I have to swap out the resistor that is grounded between the mic and the preamp tube to match the ohms of the mic? (600 ohms?) Also should I leave the capacitor in place and wire straight to the tube?

See the schematic..

Thanks in advance!
Rob

Old 21st September 2012
  #2
Gear Head
 
🎧 5 years
Any takers?
Old 22nd September 2012
  #3
Lives for gear
 
Richard Crowley's Avatar
 
🎧 10 years
Study this circuit...
http://www.jensentransformers.com/as/as020.pdf

It is a reference design for connecting an input transformer to a tube gain stage.
Low impedance mics are not a very good match for high-impedance mic input circuits. That is why we typically use an input transformer. A transformer has MANY benefits, not the least of which is that it makes low-impedance mics compatible with fire-bottle circuits. Of course you don't have to use a $100 Jensen transformer if your application doesn't warrant that level of quality.
Old 22nd September 2012
  #4
Lives for gear
 
JohnRoberts's Avatar
 
🎧 10 years
One minor point a 600 ohm mic in modern context is a high impedance mic. Low Z mics are 150-200 ohm with some down to 50 ohm.

The Jensen ref is probably just what you need.

JR
Old 22nd September 2012
  #5
Gear Head
 
🎧 5 years
Thanks guys, I really appreciate the help!

Rob
πŸ“ Reply
Topic:
Post Reply

Welcome to the Gearspace Pro Audio Community!

Registration benefits include:
  • The ability to reply to and create new discussions
  • Access to members-only giveaways & competitions
  • Interact with VIP industry experts in our guest Q&As
  • Access to members-only sub forum discussions
  • Access to members-only Chat Room
  • Get INSTANT ACCESS to the world's best private pro audio Classifieds for only USD $20/year
  • Promote your eBay auctions and Reverb.com listings for free
  • Remove this message!
You need an account to post a reply. Create a username and password below and an account will be created and your post entered.


 
 
Slide to join now Processing…

Forum Jump
Forum Jump