Weekend Fun with Tubes - Guitar 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 7th October 2007, 05:25 PM   #1
diyAudio Member
 
Join Date: Nov 2006
Smile Weekend Fun with Tubes - Guitar Preamp

Hi friends,
Great fun modeling new guitar preamps
at weekend, so this is a new design based
in a lot of things, comments welcome:

http://server4.pictiger.com/img/1426.../prototipo.gif

I will put the tonestack curves next.

Thanks
Blinsjc
  Reply With Quote
Old 7th October 2007, 05:47 PM   #2
diyAudio Member
 
Join Date: Nov 2006
So, the tonestack switch effect (in theory):
http://server7.pictiger.com/img/7154.../tonestack.gif

The intention is a mid base move from 500Hz
to something about 800Hz-1KHz, and get some
metal tones with scooped mids.

Thanks
Blindsjc
  Reply With Quote
Old 7th October 2007, 06:42 PM   #3
Merlinb is offline Merlinb  United Kingdom
diyAudio Member
 
Merlinb's Avatar
 
Join Date: May 2006
Location: Lancashire
Looking good! Some comment (ignore at will!)

Your input grid stopper is pretty large, seems a shame to throw away some gain right at the input. I'd go with about 22k or so, after the grid leak.
Also, why have yet another divider right after the first stage? I can't see the signal being that big by that point...

Your high/low gain switch has a problem. In the high gain setting, V2b is DC coupled to V2a anode, in the normal way. But in the low gain setting it isn't. You'll end up with a REALLY cold biased clipper in that setting, which I can't see being good at all. I suggest you either arrange for it to be DC coupled in both settings, or change the V2b cathode follower to an AC coupled version.

I like your tone stack switching though!
  Reply With Quote
Old 7th October 2007, 07:54 PM   #4
diyAudio Member
 
Join Date: Nov 2006
Hi Merlin,
Thanks a lot for your comments,
I really want to mod this initial project
and find errors with help of experienced
people like you.

So, about your comments:
Changed the first stopper to after leak
resistor, but value is a standard radio
frequency blocker, but I will test 22K and
see (hear).

The second voltage divider was there
to take care of a wild gain (I was worried
about it), but you made me think... the standard
divider in this point, imagine it without the pot,
would be a fixed divider of 470K/470K...so, the
pot alone (1M) will handle it and add some freedom
to user. Finally... Divider removed.

Mods applied:
http://server7.pictiger.com/img/7161.../prototipo.gif

About the high/low gain switch... you made me
confused... Used a analog solution in my ax84
Lead preamp and it works fine... Take a look at
this mod in the third page of this schematic.

http://www.ax84.com/static/corepream..._Schematic.pdf

So, if you can tell me more details about this switch
will be fine, remember that I'm not a professional in
any way.

Thanks a lot
Blindsjc
  Reply With Quote
Old 8th October 2007, 02:36 PM   #5
diyAudio Member
 
Join Date: Nov 2006
(1) put a coupling cap on the plate from V2A

(2) the input grid stopper should be mounted right on the tube. Not sure about the 22k resistor though. For a resistance of 22k with 12ax7 millar capacitance of about 150pF this would give an RC cutoff value of 48kHz. 68k, which is common in guitar amps will give a more reasonable 15khz cutoff. This is much more suitable to eliminating frequencies you don't want in your amp. There will be very little signal loss with a 68k resistor.

(3) you will have a lot of gain in this amp. Try keeping the voltage dividers, then adjust to taste.

If you like, post it on the forum at hoffman amps, there are quite a few designers there specifically for guitar amps.

d1
  Reply With Quote
Old 10th October 2007, 11:49 AM   #6
diyAudio Member
 
Join Date: Nov 2006
Man,
Thanks for your reply.
I think I will need to try it alone,
no replies at ax84 or hoffman amps.
Don't know if my bad english doesn't
allow people to understand what I'm
trying to do.

Thanks
Blindsjc
  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
Any 100W DIY Tubes Guitar Amp ? willycom Instruments and Amps 9 24th July 2007 10:08 PM
Good Source for NOS tubes for guitar Daveis Instruments and Amps 1 29th May 2007 03:09 PM
Guitar Amps, Overdrive Pedals, and Space Charged Tubes Turbo7MN Tubes / Valves 14 14th November 2006 12:38 AM
Riviera 725 guitar tubes amp Jeffy74 Tubes / Valves 1 10th October 2004 08:15 PM
low voltage tubes (space charge, etc.) for guitar amp? needtubes Tubes / Valves 4 31st October 2003 01:45 AM


New To Site? Need Help?

All times are GMT. The time now is 12:27 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