I really need help with this 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 24th June 2003, 05:06 PM   #1
diyAudio Member
 
Join Date: Jul 2002
Location: usa
Default I really need help with this preamp!

I need a preamp for my recording studio at home. I have been tinkering with this design for a while, although I haven't built it yet. My problem is, if this doesn't look like it's going to work well, I'm going to sell my parts and just buy a preamp instead. I really want to build it, I just don't want to be dissapointed.

My plan is to have a seperate box for the power supply, probably the Allen Wright SuperReg, and of course I'll need phantom power for the condenser mics.

My main questions are these:

What would the gain be of this preamp?
What is the gain of each stage?
How can I implement a SIMPLE optical limiter? (Silonex LDR modules?):
http://www.silonex.com/audiohm/application.html

What about a simple EQ?
How would I plug a guitar into this circuit?

I'm afraid that the Limiter and EQ might steal too much gain.

My idea for the limiter was to just strap the LDR across the inputs to the 6H30, and then build a control circuit. This would bring the 2 phases together and cancel/reduce volume.

Please help with this. Any tips or comments are welcome. I'm not really a pro at electronics, I just love building things and elctronics, so I'm sorry for some of the questions if they are too basic.

Thanks!

Matt
Attached Images
File Type: gif micpreamp.gif (8.3 KB, 569 views)
  Reply With Quote
Old 24th June 2003, 05:46 PM   #2
Joel is offline Joel  United States
diyAudio Member
 
Joel's Avatar
 
Join Date: Oct 2002
Location: Brooklyn, NY
Default Re: I really need help with this preamp!

Quote:
Originally posted by mwmitchell
What would the gain be of this preamp?
What is the gain of each stage?
How can we know until you fill in the circuit values?
  Reply With Quote
Old 24th June 2003, 05:57 PM   #3
diyAudio Member
 
Join Date: Jul 2002
Location: usa
Hey Joel. Sorry about that. Here is a revised schematic with values. Thanks for your reply!

Matt
Attached Images
File Type: gif micpreamp.gif (9.6 KB, 534 views)
  Reply With Quote
Old 25th June 2003, 01:51 PM   #4
diyAudio Member
 
Join Date: Jul 2002
Location: usa
Default Do I really need a regulated supply for this?

I'm wondering if I really need a regulated supply for this. It's all balanced so noise shouldn't be an issue, and as far as the supply sagging from transients, can that really happen with a mic preamp?

Matt

p.s. anyone feel free to have a look at the schematic and PLEASE let me know as much as you can about it. Thanks.
  Reply With Quote
Old 25th June 2003, 02:04 PM   #5
diyAudio Moderator Emeritus
 
Bas Horneman's Avatar
 
Join Date: Apr 2002
Location: The Netherlands
Blog Entries: 18
Hi Matt,

Also try posting at K&K audio at the AudioAsylum distributor of Lundahl in the US.

Hate to see you sell everything and just buy a preamp!

Cheers,
Bas
  Reply With Quote
Old 25th June 2003, 02:42 PM   #6
diyAudio Member
 
Join Date: Jul 2002
Location: usa
Yeah, believe me I don't want to do that. I just want to make sure that this is a good design first.

I figured this would be the best place to do it. Thanks for the info on KK forums. I'll do that.

Cheers!

Matt
  Reply With Quote
Old 25th June 2003, 11:51 PM   #7
diyAudio Member
 
Sch3mat1c's Avatar
 
Join Date: Jan 2003
Location: Milwaukee, WI
Send a message via ICQ to Sch3mat1c Send a message via AIM to Sch3mat1c
Oh yeah, I think I was gonna add something to this thread...

What are the cathode resistors for?
How is the output going to be balanced if it's not a CT output winding?

Tim
__________________
Seven Transistor Labs
Projects and Resources
  Reply With Quote
Old 26th June 2003, 12:41 AM   #8
diyAudio Member
 
Join Date: Jul 2002
Location: usa
Well, the center tap on the secondary would be grounded. So it would be balanced. I messed up the drawing!

As far as the cathode resistor, I don't need one before getting to the constant current source? Please tell me why? Would the current source determine the current all by itself?

Please let me know what would be best. I was thinking about using Kevin Kennedys current source, but also thought about an LM317 with its adjust tied to ground and the output tied to ground thru a current limiting resistor. the input would be tied to the cathodes.

If you have any input on this at all, please let me know. I'm ready for all comments! More than a completed preamp, I want to learn!

Matt
  Reply With Quote
Old 26th June 2003, 02:57 AM   #9
diyAudio Member
 
Sch3mat1c's Avatar
 
Join Date: Jan 2003
Location: Milwaukee, WI
Send a message via ICQ to Sch3mat1c Send a message via AIM to Sch3mat1c
Quote:
Originally posted by mwmitchell
Well, the center tap on the secondary would be grounded. So it would be balanced. I messed up the drawing!
I see.

Quote:
As far as the cathode resistor, I don't need one before getting to the constant current source? Please tell me why? Would the current source determine the current all by itself?
Uhm....well....uh.....that's its job by definition, um yea.... *choking back snickers* J/K.

Quote:
Please let me know what would be best. I was thinking about using Kevin Kennedys current source, but also thought about an LM317 with its adjust tied to ground and the output tied to ground thru a current limiting resistor. the input would be tied to the cathodes.
Personally I'd probably jump for a signal pentode CCS, but I don't have experience in anything else A HV transistor or MOSFET based CCS would work as well.

Quote:

If you have any input on this at all, please let me know. I'm ready for all comments! More than a completed preamp, I want to learn!
Ok!

Tim
__________________
Seven Transistor Labs
Projects and Resources
  Reply With Quote
Old 26th June 2003, 03:32 AM   #10
diyAudio Member
 
Join Date: Jul 2002
Location: usa
Thanks for the response.

I get the current source thing. OK, that's funny. So, the resistor is not needed because the CCS is there, and no signal is being taken from the cathode. Is that right? Couldn't you adjust gain with a cathode resistor in this configuration?

Please understand, I'm NOT a pro. I just pic up info from different places. I'm hoping I can learn something from this, and maybe somday I'll teach you something!

Please people, tear me up if you have to, but share the knowledge!

Matt
  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
Tube Preamp Popping on Source Input Change (?) / 6DJ8 Preamp On Chip Amps MartyM Tubes / Valves 3 16th October 2008 04:52 AM
Guitar Preamp = MIC Preamp = other preamp ,,are they all same? Paswa Solid State 1 12th March 2008 05:16 PM
twisted pear Preamp/other suggestions for Preamp kit LukeDuke Chip Amps 1 1st February 2008 09:57 PM
Electret mic preamp - will phono preamp work? darthmullet Analogue Source 6 12th October 2007 07:32 AM
wiring preamp outs on a preamp bonsai171 Solid State 4 22nd March 2004 10:13 PM


New To Site? Need Help?

All times are GMT. The time now is 07:58 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