Studio Tube 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 December 2005, 02:53 AM   #1
diyAudio Member
 
Join Date: Aug 2005
Default Studio Tube Preamp

Built this Instrument Preamp from plans by Fred Nachbaur. Amp works except I can not get the tone controls to work. Being a newbie ( other than a simple repair) I'm not sure where to start. I've checked and rechecked my wiring and I really can't find anything that looks out of place. One mod was I eliminated the bypass and ran directly to the tone controls. Any suggestions?

Freds Web Link http://www.dogstar.dantimax.dk/tubestuf/instpre.htm

MoreBass
Attached Images
File Type: jpg instpres.jpg (81.5 KB, 907 views)
  Reply With Quote
Old 27th December 2005, 04:25 AM   #2
diyAudio Member
 
Geek's Avatar
 
Join Date: Sep 2004
Are the controls connected correctly as per pinout and in the right place on the board?
  Reply With Quote
Old 27th December 2005, 08:26 AM   #3
dhaen is offline dhaen  Europe
diyAudio Moderator Emeritus
 
dhaen's Avatar
 
Join Date: Jun 2002
Location: U.K.
Ensure that the phasing of Sw1 sections is correct.
Did you fit a component in the position of Ctwk? If so, remove it for now.
  Reply With Quote
Old 27th December 2005, 11:46 PM   #4
diyAudio Member
 
Join Date: Aug 2005
Default Tube preamp

Pinouts of my pots look OK and I eliminated SW1ab completely (bypassing the flat response switch. Just ran signal directly to the tone stack). No cap in the tweek before C3 either. Being my first post and new to this I appreciate your responses.
Perhaps a better question about my nonfuntioning tone controls is should this schematic work as designed? From Freds web site on this project he said he did not construct this project but felt it is correct in design. I haven't found anyone else who may have built this preamp to compare notes, and I know there are a lot of knowedgeable people on this forum, so if others can say this design is solid, I'll assume the problem is on my end and troubleshoot my construction.

Thanks,
MoreBass

Freds Web Link http://www.dogstar.dantimax.dk/tubestuf/instpre.htm
Attached Images
File Type: jpg instpres.jpg (81.5 KB, 588 views)
  Reply With Quote
Old 28th December 2005, 02:57 AM   #5
diyAudio Member
 
Geek's Avatar
 
Join Date: Sep 2004
I was a personal friend of Fred (RIP) and can indeed attest to it's working good. Even got PCB's here for it
  Reply With Quote
Old 28th December 2005, 04:11 AM   #6
diyAudio Member
 
Join Date: Aug 2005
Default Tube Preamp

Geek, I appreciate your response and from what I've read, Fred was a wealth of knowledge and most willing to share it, that's what prompted me to build his design. By eliminating the possibility of a flaw in the schematic, I know the problem is on my end. Was not aware boards were available but building it point to point and constructing an enclosure was part of the fun and education to understand tube design.
When time permits, I'll go over my build and post any progress.

MoreBass
  Reply With Quote
Old 28th December 2005, 07:44 AM   #7
diyAudio Member
 
Geek's Avatar
 
Join Date: Sep 2004
No problem! Good luck

IIRC, DigitalJunkie has the majority of those PCB's now. Maybe he'll shoot you a couple for a buck or two.
  Reply With Quote
Old 28th December 2005, 01:21 PM   #8
dhaen is offline dhaen  Europe
diyAudio Moderator Emeritus
 
dhaen's Avatar
 
Join Date: Jun 2002
Location: U.K.
I too think it should work, and have confidence in Fred's work.
For the tone controls to work, there must be gain - lots of it as they are in the feedback path.
Try removing the feedback take out C15, and see if the gain jumps right up (it may go unstable)..
Also, are the regulator tubes glowing? If not, measure some voltages and report.
  Reply With Quote
Old 4th January 2006, 12:12 AM   #9
diyAudio Member
 
Join Date: Aug 2005
Default Studio Preamp

Busy Holidays, but found time to trouble shoot.
In my first post I mentioned I deviated from the orig. design by eliminating the bypass switch, so thinking that may be the problem, I installed the switch for tone/bypass with no better results. Switching to tone gives me good sound but no control of tone; bypass produces more noise and ocsillation.
Bypassed C15 resulting in distorted low volume(neon bulbs did not light), so I probed some voltages which are represented on the left. On the right are recommended voltages from Freds Phono Preamp(similar design, not sure if applicable).

B+ 366V 360-390V
Plate V1A( bottom of R6) 204V 190-210V
Cathodes V1(pin 3&8) 31.5V 26-32V
Grid Supply V1A(+ side C2) 29.5V 1.5V less than Cathodes
Grid Supply V1B(+ side C4) 29.9V 2V less than Cathodes
Grid V2(pin 2) 207V Same as V1A(190-210V)
Grid V2(pin 7) 288V N/A
Cathode V2(pin 3) 202V 1.5V higher than Grid V2
Plate V2 (pin 1) 288V 290-310V
Filaments +- 6.5V +- 6.3V
R9 and L1 191V N/A
C15 (- side) about 30V N/A

Thanks Again for the Suggestions
MoreBass
  Reply With Quote
Old 4th January 2006, 02:30 AM   #10
diyAudio Member
 
Geek's Avatar
 
Join Date: Sep 2004
Leaky caps? I saw the RA-100 this was designed for and Fred used low-leakage sweep/SMPS caps.

Also, 12AT7's are kinda finicky unless you're used to them.
  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
Does anyone interested PSE STUDIO SL Preamp ? ANALOG GUY Solid State 5 19th April 2006 04:00 AM
A.R.T. tube mp studio preamp music321 Chip Amps 3 25th December 2005 03:36 AM
behringer dcx + passive preamp + studio pa leifislive Digital Line Level 3 3rd March 2004 08:28 AM
Balanced Mic Preamp, Transistors...and Studio Equipment iCebReakEr409 Solid State 4 28th December 2003 08:03 AM
balanced stereo tube preamp for a recording studio zdpinet Tubes / Valves 12 15th July 2002 03:53 PM


New To Site? Need Help?

All times are GMT. The time now is 01:09 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