Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

6SC7 Phono pre amp
6SC7 Phono pre amp
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 February 2018, 09:53 PM   #21
knockbill is offline knockbill  United States
diyAudio Member
 
knockbill's Avatar
 
Join Date: Feb 2013
Location: SE PA
Quote:
Originally Posted by PRR View Post
> I'd like to try something that could use the 6SC7s...

Use the 6SC7!! I only simmed with 12AT7 because I do not have a SC7 model; and to some degree tubes is tubes.

(However I am uncomfortable with the results I got. I suspect SC7 is not as hot-rod as AT7; also my AT7 model may be hotter than reality.)

You need that many R and C in the NFB EQ to define RIAA well. Anything with fewer parts 'cheats'. One cheat is that cartridge loading, no longer fashionable (data not available). Another is like PR6, let the "50Hz" corner happen where the tubes run out of gain (so low NFB in an important part of the spectrum, and wide variation with tubes).

Also you do not use my 1V grid batts with real vacuum tubes; the model does not have real electron clouds so does not simulate what really happens for 22Meg Rg.
I can build a new mule from your sim, if I can assemble the caps... I'll need a new PS, as the PT I used for this PS won't have 250V B+...
A couple questions,,, First, eliminate the batteries and run 22M grid resistors to grd? 2nd,, whats the 1VAC in the bottom Left corner of the schem?

I think the 6SC7 may be a little hotter than 12AT7,,, its basically replacing a 12AX7 in a phono amp, correct? I'll try 10k loading the Shure first...
Thanks for the continued support, it may just work out!
__________________
Regards,
John

Last edited by knockbill; 7th February 2018 at 09:56 PM.
  Reply With Quote
Old 7th February 2018, 10:58 PM   #22
knockbill is offline knockbill  United States
diyAudio Member
 
knockbill's Avatar
 
Join Date: Feb 2013
Location: SE PA
Tried the 10K on one channel with the Shure,,, no joy,,, I'll get the parts together and try to build a new mule...
__________________
Regards,
John
  Reply With Quote
Old 8th February 2018, 12:06 AM   #23
PRR is offline PRR  United States
diyAudio Member
 
PRR's Avatar
 
Join Date: Jun 2003
Location: Maine USA
I've confused you.

The preamp you have now.

There is a 120K+0.0027u network from pin 2 to pin 5.

Disconnect one end of that.

Build the 4-part network shown. Put it from pin 2 to pin 5.

In simulation this gives accurate RIAA.
Attached Images
File Type: gif GE-6SC7-preamp.gif (62.8 KB, 94 views)
  Reply With Quote
Old 8th February 2018, 12:12 AM   #24
knockbill is offline knockbill  United States
diyAudio Member
 
knockbill's Avatar
 
Join Date: Feb 2013
Location: SE PA
Will do,,, and thanks again for your support!! Its just a matter of having the caps to match...
__________________
Regards,
John
  Reply With Quote
Old 9th February 2018, 12:07 AM   #25
cogsncogs is offline cogsncogs  United States
diyAudio Member
 
cogsncogs's Avatar
 
Join Date: Jul 2003
Location: Wayne, West Virginia
Quote:
Originally Posted by PRR View Post
> I'd like to try something that could use the 6SC7s...

Use the 6SC7!! I only simmed with 12AT7 because I do not have a SC7 model; and to some degree tubes is tubes. ...
Code:
* ==============================================================
* 6SC7 Hi-mu twin triode
* Koren model (5 parameters): mean fit error 0.0418049mA
* Traced by Wayne Clay using Curve Captor v0.9.1 on 5/21/09
* from RCA data sheet (1940)
* 6SC7-RCA LTSpice model
* ==============================================================
.subckt 6SC7  P G K
    Bp  P K  I=
+ (0.01302262338m)*uramp(V(P,K)*ln(1.0+exp((7.848813146)+(7.848813146)*
+ (74.21318947)*V(G,K)/sqrt((7.786192876k)+(V(P,K))**2)))/(7.848813146))**(1.07495152)
    Cgk G K 2.4p ; 0.2p added (2.2p)
    Cpk P K 3.7p ; 0.7p added (3.0p)
    Cgp G P 2.7p ; 0.7p added (2.0p)
    d3  G K dx1
.model dx1 d(is=1n rs=2k cjo=1pf N=1.5 tt=1n)
.ends 6SC7
__________________
Sent from my Linux desktop computer using a keyboard and a mouse.
  Reply With Quote
Old 9th February 2018, 10:50 AM   #26
knockbill is offline knockbill  United States
diyAudio Member
 
knockbill's Avatar
 
Join Date: Feb 2013
Location: SE PA
Quote:
Originally Posted by PRR View Post
I've confused you.

The preamp you have now.

There is a 120K+0.0027u network from pin 2 to pin 5.

Disconnect one end of that.

Build the 4-part network shown. Put it from pin 2 to pin 5.

In simulation this gives accurate RIAA.
I have the resistors to build this network,,, the caps will need to be paralleled,,,,, what is max tolerance, 10-15% ?
__________________
Regards,
John
  Reply With Quote
Old 9th February 2018, 01:03 PM   #27
knockbill is offline knockbill  United States
diyAudio Member
 
knockbill's Avatar
 
Join Date: Feb 2013
Location: SE PA
Close as I could get,,, well under 10%,,, I'll tack em in later, and we'll see...
Thanks again for the sim work....
Attached Images
File Type: jpg P9170007.JPG (81.7 KB, 59 views)
__________________
Regards,
John
  Reply With Quote
Old 9th February 2018, 02:56 PM   #28
knockbill is offline knockbill  United States
diyAudio Member
 
knockbill's Avatar
 
Join Date: Feb 2013
Location: SE PA
Getting closer,,, this network sounds right... Bass is back, not booming but full... highs are just right, not exaggerated as before...

Volume is not loud as originally, but its probably due to the added network and/or big coupling caps (10x original) that are still installed... I'll keep tweaking, but we seem to be on the right page now....
Attached Images
File Type: jpg P9170010.JPG (82.4 KB, 53 views)
__________________
Regards,
John
  Reply With Quote
Old 10th February 2018, 05:39 AM   #29
PRR is offline PRR  United States
diyAudio Member
 
PRR's Avatar
 
Join Date: Jun 2003
Location: Maine USA
Quote:
Originally Posted by knockbill View Post
... Bass is back, not booming but full... highs are just right, not exaggerated as before... Volume is not loud....
Good. And there's only so much gain you can get from one 6SC7.

(Higher supply voltage *would* help some, because the NFB loop does not cover the whole amp. Gm of V1 is uncontrolled and will rise with I which will rise with B+. I don't know what "noise" you fear unless you are running out of B+ filtering, or have damp sockets that crackle with >100V across them.)

(An output FET would help slightly, by making V2's life easier.)

What you really want is a Test Rig. Stable audio sine source, reverse RIAA network, and decent AC voltmeter. Taking a frequency response is a BASIC audio skill. If you are sure the output cap does not leak DC, you can do it on a PC soundcard.
  Reply With Quote
Old 10th February 2018, 12:16 PM   #30
knockbill is offline knockbill  United States
diyAudio Member
 
knockbill's Avatar
 
Join Date: Feb 2013
Location: SE PA
Filters are adequate, its very quiet,,, caps should be big enough to easily raise B+...

I'll study on the Test Rig,,, seems a reverse RIAA network can be built,,, I have a Ballentine ACV meter,,, should be just the thing for low ACV readings, as it works well for reading input signals...

Thanks for all your help/info,, guess I need to catch up on some BASICS...
__________________
Regards,
John
  Reply With Quote

Reply


6SC7 Phono pre ampHide 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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
6SJ7 and 6SC7 not on roll chart famousmockingbird Tubes / Valves 5 21st November 2015 04:01 AM
How Can I connect A Balanced RIAA Phono Pre-Amp to a Phono Plug amp input jmartinbaugh Analogue Source 3 25th April 2011 01:24 PM
6sc7 vs. 6su7 in LTPI duty aletheian Tubes / Valves 3 25th November 2006 01:17 AM


New To Site? Need Help?

All times are GMT. The time now is 05:22 AM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.00%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio
Wiki