adding line out to guitar tube preamp - Page 2 - 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 15th April 2010, 09:43 PM   #11
diyAudio Member
 
Join Date: Apr 2010
Location: Belgium
All this is very interesting. Thanks to all of you for helping me, I learn more each time.

If I am right, the output of the opamp is the right place to connect the line out jack but it 'll only work if the led is on. So I have to install the new circuit only to get the correct output when bypass is on (led is off).

See schematic in attachment (I guess the gain pot is the one indicated in red?)
Attached Images
File Type: jpg VT911schematic+lineout3.jpg (60.4 KB, 102 views)
  Reply With Quote
Old 15th April 2010, 10:28 PM   #12
diyAudio Member
 
Join Date: Mar 2010
I don't like that gain method. The bandpass of the amplifier becomes a major issue, and you could be changing the amplifier response as well as inviting oscillation. The volume control on the right is all the gain control you should need. If you find that the system has too much gain, I'd sooner recommend a passive control.

Also, don't connect the outputs of the source follower and opamp together like that. If you use the opamp you can dispense with the source follower.

There are so many options that it's best you decide exactly what you want this thing to do and configure it accordingly.
  Reply With Quote
Old 16th April 2010, 01:38 AM   #13
diyAudio Member
 
Join Date: Apr 2010
Location: Belgium
When you talk about the gain, is it the one indicated in red?
If yes, this does not seems to be the best schema for gain control and, you are right. The major complain regarding this stompbox is that the gain pot is reacting too strongly (even with a log 500 K pot). I thought it was related to the tube but you might have put your finger on the real cause. Nevertheless, this preamp is used for guitar and should only have responding frequencies from 100 Hz to 4000 Hz (or so). Maybe it is not affecting the sound too much? Anyway, your suggestion is to remove the opamp just under the gain pot? I am right?

Regarding the outputs of the source follower, the 10F cap is polarized. Is it not enought to protect to source follower?

If I remove the source follower there 'll be big decrease of the signal when the stompbox is switched off (true bypass). I need to have a low impedance signal also when it is off. Any suggestion?
  Reply With Quote
Old 16th April 2010, 01:47 AM   #14
diyAudio Member
 
Join Date: Mar 2010
I don't know if removing that opamp will sacrifice too much gain. If it works without it, take it out.

The line out is being driven by two amplifiers, which is bad practice. They are conflicting and the output should be a single stage, either the source follower or the opamp on the right. The capacitor isn't the problem.

You will not have true bypass with the power off because the source follower will not work. You need to switch the input to the output and disconnect the rest in order to get a true bypass. Your DPDT switch can do that.
  Reply With Quote
Old 16th April 2010, 04:43 AM   #15
diyAudio Member
 
Wavebourn's Avatar
 
Join Date: Sep 2006
Location: Pleasant Hill, CA
Send a message via Skype™ to Wavebourn
I did not see the thread before, sorry.

Actually for a line out you need to add a line transformer, nothing more. Take one 10K:600 Ohm, and connect 600 Ohm output to tip and ring of TRS socket; a sleeve end connect to ground.

That's it.

Standard line out to connect to mixer or recording device has to be symmetrical, 600 Ohm. Even if input is 10K and asymmetrical, such an output helps you to eliminate possible interferences because of a ground loop absence.
__________________
The Devil is not so terrible as his math model is!
  Reply With Quote
Old 16th April 2010, 12:25 PM   #16
diyAudio Member
 
Join Date: Apr 2010
Location: Belgium
Thanks, I 'll give it a try and let you know.
  Reply With Quote
Old 16th April 2010, 03:47 PM   #17
diyAudio Member
 
Join Date: Apr 2010
Location: Belgium
Hi Wavebourn,

If I just add a line transformer, when the pedal is switched off, the volume 'll drop down, no? I want the pedal volume to be almost the same on or off.

Regarding the symmetrical connection, you are right, this 'll avoid interferences (specially if the cable to recorder is long).

So now I have to add a line trans. to the previous schema and reconnect it to avoid the signal going to line out to pass by two opamp when the effect is on.

I don't see how to do that without a 3pdt switch. Any suggestion?

Last edited by hacaira; 16th April 2010 at 03:52 PM.
  Reply With Quote
Old 16th April 2010, 04:07 PM   #18
diyAudio Member
 
Join Date: Apr 2010
Location: Belgium
Here is what you suggested (see attachment).

I 'd like to have your opinion on the volume difference between effect on and off. Do you think that the level 'll be very different?
Attached Images
File Type: png VT911schematic+lineoutUsingLT.png (163.4 KB, 91 views)
  Reply With Quote
Old 16th April 2010, 04:29 PM   #19
diyAudio Member
 
Wavebourn's Avatar
 
Join Date: Sep 2006
Location: Pleasant Hill, CA
Send a message via Skype™ to Wavebourn
Yes, such a way when you switch off an effect your guitar's output is loaded on a transformer. I would suggest you to take direct output from the 1'st opamp (buffer) instead of from input.

Also, why do you crossed out by red a stage that overdrives tubes and allows to control overdrive?
__________________
The Devil is not so terrible as his math model is!
  Reply With Quote
Old 16th April 2010, 06:12 PM   #20
diyAudio Member
 
Join Date: Apr 2010
Location: Belgium
Yes, such a way when you switch off an effect your guitar's output is loaded on a transformer.

Does it mean that the volume level 'll be acceptable when effect is off?

Also, why do you crossed out by red a stage that overdrives tubes and allows to control overdrive?

Well, the idea was that it might be obsolete. If the overdrive is only controlled by a pot, is it not enought? In fact I was looking for the reason why the overdrive is raising so quickly (after turning the pot just a little bit).

I 'll redraw and post it soon.
  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
need diy tube preamp (line-stage) recommendation and general tube advice Musiclover4 Tubes / Valves 16 18th May 2013 04:19 PM
tube preamp: adding headphone out then_dude Headphone Systems 10 19th July 2012 12:02 PM
Looking for tube guitar preamp high-fi Tubes / Valves 10 24th May 2006 03:27 PM
Multi-purpose tube amp (line and guitar inputs) smsmonster Tubes / Valves 28 20th May 2006 01:12 AM
Guitar Tube Preamp Kaiowas Tubes / Valves 5 24th April 2004 11:21 PM


New To Site? Need Help?

All times are GMT. The time now is 07:19 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