Suggestion for this 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 13th July 2008, 05:48 PM   #1
diyAudio Member
 
Join Date: Jan 2005
Location: montreal
Default Suggestion for this tube preamp

I looking to buy this tube preamp kit. Is this kit any good?
Can i use the same 6.3v for the heaters or I have to follow the schematic.
Attached Images
File Type: gif 6n3c.gif (23.5 KB, 430 views)
  Reply With Quote
Old 13th July 2008, 06:35 PM   #2
diyAudio Member
 
Join Date: Aug 2005
Location: Seattle
Send a message via AIM to audiowize
You can share the winding between the rectifier and the 6SN7. This schematic is actually similar to a Bottlehead Foreplay II. I would mention, however, that if you don't bias the filaments for the 6SN7 up around 60v, you will get significant noise. Also, R7 can be tied to the other plate without the R3/C3 combination. With a cathode follower, this just isn't necessary.
  Reply With Quote
Old 13th July 2008, 07:07 PM   #3
diyAudio Member
 
Join Date: Jan 2005
Location: montreal
Planning to use this to drive Nelson's F4 amp.
This kit is around $100 to build.
First time to build with tubes, don't know how good is the sound between tubes and solid state. Or I should go with the Aikido kit which may cost 2 times or more???
  Reply With Quote
Old 13th July 2008, 07:11 PM   #4
diyAudio Member
 
Join Date: Aug 2005
Location: Seattle
Send a message via AIM to audiowize
If you're planning to build this kit point-to-point, you will learn a lot more than you ever could by stuffing a PCB. Also, this should have nice low output impedance to drive a solid state amp (although the best would likely be a transformer coupled preamp)

-Paul
  Reply With Quote
Old 13th July 2008, 10:08 PM   #5
diyAudio Member
 
Join Date: Apr 2004
Location: Monroe Township, NJ
A significant difference between that circuit and a FP is the presence of a global NFB loop.

Frankly, I'm not at all comfortable with loop NFB being applied to the I/P grid, without a DC blocking cap. being present. Also, the NFB ratio varies with the setting of the volume control. The value of the O/P coupling cap. is too small. To work into the IHF "standard" 10 KOhm load, a minimum of 3.3 μF. is needed. TANSTAAFL always applies and I suspect that kit is not a good value.

Jim McShane is finally getting to work on a back burnered project that could fill this need nicely. Look here.
__________________
Eli D.
  Reply With Quote
Old 14th July 2008, 05:30 PM   #6
diyAudio Member
 
Join Date: Aug 2005
Location: Seattle
Send a message via AIM to audiowize
Yeah, it seems odd to put feedback in a preamp that doesn't have a whole ton of gain to begin with. I try to stay out of the feedback arguments, however, but in this case it makes very little sense. Removing the feedback and that extra RC stage in the power supply ought to make this a listenable preamp. The coupling caps could always be changed later, I see plenty of solid state and tube amps alike with 50+k input impedance now.
-Paul
  Reply With Quote
Old 14th July 2008, 06:20 PM   #7
EC8010 is offline EC8010  United Kingdom
diyAudio Moderator Emeritus
 
EC8010's Avatar
 
Join Date: Jan 2003
Location: Near London. UK
I don't think this circuit is likely to work very well. As pointed out by others, the 10k input resistance will load that 100k pot very heavily. Further, there's not very much global feedback - you either want none or shed-loads of it. I suspect this circuit was developed rather than engineered.
__________________
The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...
  Reply With Quote
Old 14th July 2008, 09:02 PM   #8
diyAudio Member
 
Join Date: Oct 2004
Location: Maui, Hawai'i, USA
I used global feedback like that at one point on Bruce Rosenblit's original Mu Follower 12AU7 circuit.  It worked okay, but the problem is that the volume pot is (part of) the bottom resistor of the feedback voltage divider, so that the amount of feedback you have depends on the volume setting.  That's the reason for the 10K additional resistance in the input circuit; it's not a 'stopper', since it's outside the feedback loop, it's there to stabilize the feedback circuit somewhat.

In any case, you don't get really a lot of feedback, about 3dB most (volume control in the middle position).  You can leave it, and the 10K resistor out of there, it won't change the sound or drive much.  That circuit is much more common than a Foreplay, by the way.  It's about nine tenths of all the linestages ever made.  It actually has pretty good technical performance, though it can be difficult to dehum.  I just don't like the sound of cathode followers.

Aloha,

Poinz
  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
Preamp suggestion required pls milen007 Tubes / Valves 4 19th September 2009 03:53 AM
Need suggestion for tube MC pre-pre inertial Analog Line Level 18 8th March 2009 08:28 PM
Suggestion for a bass preamp.. Dxvideo Chip Amps 4 29th July 2008 01:47 PM
Suggestion on the input transformer for tube preamp bee696 Tubes / Valves 3 2nd August 2006 04:43 AM
PREAMP suggestion for my IRAUDAMP. pat allen Class D 3 21st March 2005 12:42 AM


New To Site? Need Help?

All times are GMT. The time now is 08:41 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