27 & 6SN7 Preamp - Crossover - Page 3 - 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 26th October 2009, 04:12 AM   #21
kevinkr is offline kevinkr  United States
diyAudio Moderator
 
kevinkr's Avatar
 
Join Date: Sep 2004
Location: Boston, Massachusetts
Blog Entries: 6
Quote:
Originally Posted by coldcathode View Post
Kevin,

I have used similar couplings without the diode, I might just leave it out.

I know the phono stage itself is non inverting, but running it into the 27 inversion stage then inverts it the rest of the way to the amps. Since the amps I plan to use will be non-inverting and I would rather not have to invert the speaker leads I think I will increase the gain on the second stage of the phono section and bring the signal in to the grid of the follower. I can use a switch arrangement that "shorts" the input to the 27 and switches in the Phono lineout. I can then just add another 2 section pot to adjust the level of the Phono.

I do not have much experience with Phono Cartridges but my guess is that I can expect about 4-5mV? So overall gain of 500+ should be ok?
I'm a bit confused I guess - I had assumed that you had other sources which would also probably have non-inverting output phase in most cases. You can probably use the additional gain with the phono stage as opposed to the other line sources which are presumably a cd/dvd player with a nominal output of 2Vrms at FS.

Depending on cartridge 4 - 5mV @ 5cm/sec lateral recorded velocity is in the ball park (Grado certainly) but some high output MC and many MM are about 6dB lower than this. If you need 40dB of gain at 1kHz you will need ~60dB @ 20Hz to be close to RIAA equalization requirements at the low end. 40dB of gain incidentally will give you only about 400 - 500mVrms at the reference velocity (re 4 - 5mV) and 1kHz. It might be enough, but lower output cartridges could make the proposal marginal.

Then again depending on the speakers you use polarity may not be a big issue. I find only on a very small number of recordings I have that it matters - but it might be a function of the design of my speaker system which is multi-way (Onken 3 - way) with 2nd order butterworth x-o. (I think it is relatively linear phase, but not phase coherent - I didn't design it with that criteria in mind. I have measured FR which was reasonably flat, but I have no recollection of whether I measured the system phase response and if so what it was like.) So YMMV..
__________________
"Extraordinary claims require extraordinary evidence." - Carl Sagan
  Reply With Quote
Old 26th October 2009, 04:35 AM   #22
diyAudio Member
 
coldcathode's Avatar
 
Join Date: Jan 2009
I trust your opinion and since my turntable is less than "ideal" I think I will just "live" with the inversion, which BTW as you point out will happen with the other sources anyway.

I have played around with this project in the planning stage so much that I lost track of where I was at. I had "tunnel" vision and only thought in terms of the "Phono" input.

I think it is now time to get out the soldering iron and get busy. I found an interesting source for chassis. Walmart has 9"x13" baking pans made of welded aluminized steel. They have a rolled lip on them and a quite sturdy and for $8 each sound good to me.

I figure I can make a nice hardwood base with a groove for the rolled lip. Considering a Hammond steel box is $26 they look like a bargain to me.

I plan to use a 6"x6" for the PS chassis and then the 9x13 for the preamp/crossover. I will start laying it out and see if I can comfortably fit the Phono section on the same chassis or maybe another 6x6?

I have just about used up my supply of NOS 6SN7's for this so maybe I go with 6J5 for the followers, or use 12SL7 & 12SN7 and use a 12VDC Regulated "wallwart" for the filaments on the phono preamp.

Clean DC to the filaments on the high gain phono section sounds like an idea to me?
  Reply With Quote
Old 11th November 2009, 03:59 PM   #23
diyAudio Member
 
albertli's Avatar
 
Join Date: Nov 2004
Location: Vancouver
Coldcathode,

How is your project going???? I'm patiently waiting and really would love to hear the result of the crossover. Would you release a formula to calculate the crossover point !!!
Thanks

Albert
  Reply With Quote
Old 11th November 2009, 09:01 PM   #24
diyAudio Member
 
Join Date: Mar 2003
Location: Zürich
Hi Coldcathode

Sorry not answering anymore, but I think you sorted things out for yourself! Good luck with the build!

to Albertli:

scroll down this page you find a link to a simple but effective X-over calculator (12 and 24dB LR). Just fill in two of the three values, and it will calculate the third for you!
__________________
my surname is indeed 'de Best': neither misspelling nor snobbism! Ask SY!
  Reply With Quote
Old 12th November 2009, 02:39 AM   #25
diyAudio Member
 
albertli's Avatar
 
Join Date: Nov 2004
Location: Vancouver
ErikdeBest,

Thanks

Albert
  Reply With Quote
Old 15th November 2009, 04:26 AM   #26
WBS is offline WBS  Tibet
diyAudio Member
 
Join Date: Jan 2007
Quote:
Originally Posted by ErikdeBest View Post

scroll down this page you find a link to a simple but effective X-over calculator (12 and 24dB LR). Just fill in two of the three values, and it will calculate the third for you!
A Microsoft program, damn! Do you know of a Mac based calculator for a 24dB LR?
  Reply With Quote
Old 15th November 2009, 02:47 PM   #27
diyAudio Member
 
albertli's Avatar
 
Join Date: Nov 2004
Location: Vancouver
Quote:
Originally Posted by ErikdeBest View Post

to Albertli:

scroll down this page you find a link to a simple but effective X-over calculator (12 and 24dB LR). Just fill in two of the three values, and it will calculate the third for you!
Eric,

As of site provided, I did the cal and found there might be some mistake on the R value on HP. If 22nf is used, the number of R I got was 72.34K, not 710K.
Please correct me.
Thanks

Albert
  Reply With Quote
Old 15th November 2009, 04:14 PM   #28
diyAudio Member
 
coldcathode's Avatar
 
Join Date: Jan 2009
Quote:
Originally Posted by albertli View Post
Eric,

As of site provided, I did the cal and found there might be some mistake on the R value on HP. If 22nf is used, the number of R I got was 72.34K, not 710K.
Please correct me.
Thanks

Albert
Albert,

Was is the desired crossover point you are looking for?
  Reply With Quote
Old 15th November 2009, 04:19 PM   #29
diyAudio Member
 
coldcathode's Avatar
 
Join Date: Jan 2009
Actually,

The problem is in your conversion to nF it is 2.2nF not 22nf.
  Reply With Quote
Old 15th November 2009, 04:20 PM   #30
diyAudio Member
 
coldcathode's Avatar
 
Join Date: Jan 2009
Albertli

use this link and download the capacitor program. It wil convert anything and everything as far as capacitor values.

cncfreak_capacitor_setup.zip
  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
Which 6SN7 preamp should I build? chrisvw Tubes / Valves 48 12th August 2010 12:08 AM
The complete 6SN7 preamp Joel Tubes / Valves 103 14th March 2008 10:32 AM
Help with 6SN7 preamp tubedude63 Tubes / Valves 7 9th October 2006 12:31 AM
12AY7/6SN7 preamp PSU check porkchop61 Tubes / Valves 100 2nd October 2006 09:13 PM
Preamp with 6sn7 & 6sl7 SRPP ??? Gregouille Tubes / Valves 4 18th June 2002 10:41 PM


New To Site? Need Help?

All times are GMT. The time now is 07:55 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