strange preamp - diyAudio
Go Back   Home > Forums > Live Sound > Instruments and Amps

Instruments and Amps Everything that makes music, Especially including instrument amps.

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 17th May 2013, 03:43 PM   #1
scrimpu is offline scrimpu  United States
diyAudio Member
 
Join Date: Jan 2012
Location: Grand Rapids, Mi
Default strange preamp

What type of preamp is this? I have never seen one wired quite like this. Its from a Baldwin organ amp I plan to convert for guitar use.
Attached Images
File Type: jpg Baldwin pre.JPG (53.5 KB, 137 views)
  Reply With Quote
Old 17th May 2013, 03:57 PM   #2
diyAudio Member
 
Join Date: Jul 2005
Location: North Derbyshire
I would suggest it's probably been drawn out wrongly?.

The left half is a common cathode stage, the right half a common anode stage giving a low (in valve terms) output impedance from it's cathode.
__________________
Nigel Goodwin
  Reply With Quote
Old 17th May 2013, 04:00 PM   #3
scrimpu is offline scrimpu  United States
diyAudio Member
 
Join Date: Jan 2012
Location: Grand Rapids, Mi
I drew this from the actual amp, it is correct. I am unable to find a schematic.
  Reply With Quote
Old 17th May 2013, 07:48 PM   #4
diyAudio Member
 
Join Date: Jul 2005
Location: North Derbyshire
Quote:
Originally Posted by scrimpu View Post
I drew this from the actual amp, it is correct. I am unable to find a schematic.
I presumed you're drawn it, and I 'presume' it's not quite correct - there should be something (an output) connected to the second cathode, pin 8. Assuming this is hard wired? (and not a PCB) sometimes it's easy not to be able to see a connection.
__________________
Nigel Goodwin
  Reply With Quote
Old 17th May 2013, 08:19 PM   #5
scrimpu is offline scrimpu  United States
diyAudio Member
 
Join Date: Jan 2012
Location: Grand Rapids, Mi
It is point to point not a PCB. I do now see another wire from the second cathode, It goes to a cap then on to a socket for an external speaker cabinet. I didn't notice it before, it is quite cramped in there. Now it makes sense, thank you for pointing that out.
Attached Images
File Type: jpg Baldwim2.JPG (60.2 KB, 103 views)
  Reply With Quote
Old 17th May 2013, 08:58 PM   #6
diyAudio Member
 
chrispenycate's Avatar
 
Join Date: Aug 2006
Location: Geneva, Switzerland
What's the thing driven from? I thought at first the .001F on the input was a bootstrap, but there's a cathode bypass capacitor, so it's essentially rolling off high frequencies.

And while the cathode follower is giving a decently low output impedance, with that 47k it's not capable of driving current into it.
  Reply With Quote
Old 17th May 2013, 09:33 PM   #7
scrimpu is offline scrimpu  United States
diyAudio Member
 
Join Date: Jan 2012
Location: Grand Rapids, Mi
The organs tone generator was connected to the input, the first output goes to the power amp and internal speakers, the second output would have gone to an optional amplified speaker cabinet.
  Reply With Quote
Old 17th May 2013, 09:54 PM   #8
scrimpu is offline scrimpu  United States
diyAudio Member
 
Join Date: Jan 2012
Location: Grand Rapids, Mi
This is the preamp for the reverb channel, I don't quite get this one either.
Attached Images
File Type: jpg BaldwinAmp2.JPG (68.7 KB, 81 views)
  Reply With Quote
Old 17th May 2013, 10:56 PM   #9
scrimpu is offline scrimpu  United States
diyAudio Member
 
Join Date: Jan 2012
Location: Grand Rapids, Mi
Opps,heres the correct schematic. I get it now.
Attached Images
File Type: jpg B3.JPG (66.8 KB, 70 views)
  Reply With Quote
Old 18th May 2013, 05:18 AM   #10
JMFahey is offline JMFahey  Argentina
diyAudio Member
 
JMFahey's Avatar
 
Join Date: Mar 2009
Location: Buenos Aires - Argentina
Those are quite standard circuits used since the 50's in guitar amplifiers.

Check the tone stack driver used in Fender Tweed Bassman or all Marshalls or VOX Top Boost.

Click the image to open in full size.
  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
Mic preamp - strange high frequency roll off problem Andyroid Tubes / Valves 31 6th January 2013 09:08 PM
Very Strange Preamp Issue Davec113 Tubes / Valves 12 6th August 2012 02:33 PM
6DJ8 preamp w/balanced input - strange schematic lordearl Tubes / Valves 7 20th November 2011 07:01 AM
Strange: Preamp Xformer Overheating but Not Blowing Fuse and Supplying Right Voltages dtm1962 Parts 4 29th January 2008 12:18 AM
Brazil, and some strange laws, not too much strange! destroyer X Everything Else 0 11th September 2004 12:38 PM


New To Site? Need Help?

All times are GMT. The time now is 12:01 PM.


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