Driving balanced outputs - 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 28th February 2012, 02:28 AM   #1
diyAudio Member
 
astouffer's Avatar
 
Join Date: Jun 2004
Location: Pittsburgh, crumbling wasteland
Default Driving balanced outputs

A friend of mine asked me about building him a preamp for his acoustic guitar pickup. Seems simple enough except he asked for a balanced XLR output as well. Hmmm

So it looks like a phase splitter should work. My concern is the cable impedance and whatever input impedance the next amp has. I'm trying to think of an elegant solution where a phase splitter has two cathode outputs. Any ideas?
  Reply With Quote
Old 28th February 2012, 02:35 AM   #2
diyAudio Member
 
Join Date: Jul 2008
balanced signal paths are always good, but you can drive XLR using unbalanced circuitry and a transformer, differentially arranged resistors, or a circuit that provides separate paths for the inverted and non inverted inputs.
  Reply With Quote
Old 28th February 2012, 02:44 AM   #3
diyAudio Member
 
leadbelly's Avatar
 
Join Date: Dec 2002
Location: Calgary, Alberta
Quote:
Originally Posted by astouffer View Post
I'm trying to think of an elegant solution where a phase splitter has two cathode outputs. Any ideas?
Don't think you'll find anything that meets both. If you want a CF output stage, you will need another stage such as concertina or LTP to do the splitting. If you are looking for good drive capability via fewest parts, then CCS loading a pentode LTP will do the job.
__________________
Aerodynamics are for people who can't build engines. Enzo Ferrari
  Reply With Quote
Old 28th February 2012, 07:57 AM   #4
diyAudio Member
 
Join Date: Jan 2002
Location: nowhere
Remember you want galvanic isolation, (that is, it is preferred, tho many live without), but if you include balanced out, it will likely go to a mixer input and maybe a local amp. As soon as he wants to plug into more than one device, he should have at least one of the outputs isolated from the other.
Edcor's transformers are not bad for the price, but should be made shielded if you use them, if he wants best he'll pay for Lundahl or Jensen.
Going standard you could use E88CC into Edcor 10k:600 transformer. Has worked for me.
  Reply With Quote
Old 28th February 2012, 08:05 AM   #5
diyAudio Member
 
artosalo's Avatar
 
Join Date: Feb 2010
I would try a LTP with a cathode followers for both outputs.
A douple triode 6DJ8 or 6N6P would be my favourite.
  Reply With Quote
Old 28th February 2012, 09:10 AM   #6
diyAudio Member
 
Join Date: Jan 2002
Location: nowhere
Here's something I've used. It is KISS, but works. The phase splitting, or symmetry at the output, is surprisingly good.
You want some kind of gain/level adjust of course, a 1megohm pot at input works. If you want more flexibility a prestage with gain and tone controls can be put in front.
Not sure about acoustics, but electrics are sensitive to input impedance, and >1megohm is usually prefered. Obviously, if the guitar has a built in preamp, the input impedance can (should?) be much lower.
Attached Images
File Type: jpg simple_DI.jpg (206.3 KB, 204 views)
  Reply With Quote
Old 28th February 2012, 11:04 PM   #7
diyAudio Member
 
astouffer's Avatar
 
Join Date: Jun 2004
Location: Pittsburgh, crumbling wasteland
Thanks everyone. Looks like transformer coupling is best.
  Reply With Quote
Old 28th February 2012, 11:12 PM   #8
diyAudio Member
 
tubelab.com's Avatar
 
Join Date: Jul 2005
Location: West Virginia panhandle
Quote:
I would try a LTP with a cathode followers for both outputs.
Well, maybe its just me but I would use an LTP with a mosfet follower on each output.
__________________
Too much power is almost enough! Turn it up till it explodes - then back up just a little.
  Reply With Quote
Old 29th February 2012, 10:42 AM   #9
diyAudio Member
 
artosalo's Avatar
 
Join Date: Feb 2010
Quote:
Thanks everyone. Looks like transformer coupling is best.
How come ?
  Reply With Quote
Old 29th February 2012, 12:03 PM   #10
diyAudio Member
 
Join Date: Jan 2002
Location: nowhere
1. In a musical instrument world you will often benefit from the galvanic isolation the transformer provides. (All high-end pro gear has in-out transformers).
2. For most instruments you usually do not want wide bandwidth as in HiFi. It will take many alpha-numeric symbols to xplain, so I'll leave it for you to google it.
3. For it's simplisity it makes for a good se-balanced conversion.
4. Musical instruments often like the 'vintage' way of doing things. Most musicians prefer the time tested tones of vintage tube and transformer gear.
5. You can chose exotic hand wound transformers and ave apiece of kit costing it's weight in gold...or just go edcor. Many fun options.
6. Ah, running out of ideas.
  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
Balanced versus unbalanced outputs ksporry Analogue Source 2 22nd February 2011 06:08 AM
Balanced (preamp) Outputs - Why ? ronzeman Solid State 9 24th January 2009 10:44 AM
Balanced outputs used as inverting & Non-inverting preamplier outputs gni Solid State 4 19th September 2008 04:25 AM
Preamp with balanced outputs miguel2 Chip Amps 9 5th May 2004 03:19 PM
What's the better option and how (Balanced in/outputs) king30 Pass Labs 9 4th December 2002 11:45 AM


New To Site? Need Help?

All times are GMT. The time now is 09:53 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