Transformers MIC and Phono - 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 8th August 2014, 03:18 PM   #1
BRSHiFi is offline BRSHiFi  United States
Previously known as kingden
 
Join Date: Aug 2008
Location: Evanston, IL
Default Transformers MIC and Phono

I read an application note on Sowter where someone used a step up transformer for a Moving Magnet Cartridge as well as Moving Coil (where it is almost a must).

What would the detriments be if I had a unit made that took a 47k ohm primary and stepped it up to 235k (1:5 turns ratio)? The active circuitry would produce 25 dB of gain instead of 40 after RIAA to lower the noise floor.

For moving coil mode, I could add taps that step it up even higher.

Edcor makes small signal transformers that look to me as if they can perform this task. Given that they are unshielded, hum I suppose could be an issue if they are not enclosed in a chassis. One reason I like Edcor is they are made in the US, not China or Europe (high shipping costs).
  Reply With Quote
Old 8th August 2014, 05:57 PM   #2
Merlinb is offline Merlinb  United Kingdom
diyAudio Member
 
Merlinb's Avatar
 
Join Date: May 2006
Location: Lancashire
I suspect you'll find it seriously difficult to find a transformer that can deliver a decent bandwidth while achieving a 47k load!

In fact, I suspect its winding resistance would be so high that the Johnson noise would actually be no better than the noise of the amplifier stage you would have used instead.

Last edited by Merlinb; 8th August 2014 at 06:00 PM.
  Reply With Quote
Old 8th August 2014, 08:06 PM   #3
gofar99 is offline gofar99  United States
diyAudio Member
 
Join Date: Jan 2007
Location: Arizona USA
Default Transformers

Hi, As much as I like Edcor transformers (great folks there) and use them in my designs exclusively they will not do well at what you are trying. I thought I could do something similar and found that the lack of shielding was a serious problem. To achieve the results I wanted I eventually used ones by Lundahl. They are designed for such applications and are well shielded with Mu metal. Yes there is a considerable price difference, but in this case IMO it is necessary and worth it.
__________________
Good Listening
Bruce
  Reply With Quote
Old 12th August 2014, 08:20 PM   #4
BRSHiFi is offline BRSHiFi  United States
Previously known as kingden
 
Join Date: Aug 2008
Location: Evanston, IL
What do you think of the idea of a 1:5 ratio transformer after the RIAA stage? Between the RIAA and transformer is a current sourced cathode follower that allows the driving of 600 ohms. After that is another lower gain stage. Or yet, another CF followed by another transformer.
  Reply With Quote
Old 12th August 2014, 08:32 PM   #5
Merlinb is offline Merlinb  United Kingdom
diyAudio Member
 
Merlinb's Avatar
 
Join Date: May 2006
Location: Lancashire
Quote:
Originally Posted by kingneb View Post
What do you think of the idea of a 1:5 ratio transformer after the RIAA stage?
I think it would be a pointless waste of money and heat.
  Reply With Quote
Old 12th August 2014, 10:16 PM   #6
sreten is offline sreten  United Kingdom
diyAudio Member
 
Join Date: Nov 2003
Location: Brighton UK
Quote:
Originally Posted by kingneb View Post

What would the detriments be if I had a unit made that took a 47k
ohm primary and stepped it up to 235k (1:5 turns ratio)?
Hi,

1:5 will step up 47K to 1.2M, no transformer exists that will work well.
The nearest is 1:2.5 giving 47K to 294K, but I can't see the point.

rgds, sreten.


Note a MM is only a "47K" device inductively at high frequencies.
MC's don't have the inductance issues.
__________________
There is nothing so practical as a really good theory - Ludwig Boltzmann
When your only tool is a hammer, every problem looks like a nail - Abraham Maslow

Last edited by sreten; 12th August 2014 at 10:25 PM.
  Reply With Quote
Old 13th August 2014, 12:34 AM   #7
BRSHiFi is offline BRSHiFi  United States
Previously known as kingden
 
Join Date: Aug 2008
Location: Evanston, IL
No, what I mean is a cathode follower driving a transformer that steps 600 ohms up to 15000 ohms. This would appear after a passive RIAA stage. Another lower gain stage would appear after the transformer.
  Reply With Quote
Old 13th August 2014, 07:49 AM   #8
Merlinb is offline Merlinb  United Kingdom
diyAudio Member
 
Merlinb's Avatar
 
Join Date: May 2006
Location: Lancashire
Sounds like you're just desperate to use a transformer...
  Reply With Quote
Old 13th August 2014, 05:20 PM   #9
diyAudio Member
 
Wavebourn's Avatar
 
Join Date: Sep 2006
Location: Pleasant Hill, CA
Send a message via Skype™ to Wavebourn
I once managed to order nice mic input transformers from ALTRAN directly. They were nice. 200 Ohm primary, 39K secondary. Usually they take big order from "brand names" known for their famous audio transformers. My friend in Israel used one pair of them for MC cartridges, and was impressed by results.
For MM you better go without any transformers. Just a 47K trimpot, because it is a good idea to start EQing before the 1'st stage to increase headroom that is vital due to the nature of scuffs and particles that produce fast and high peaks.
__________________
The Devil is not so terrible as his math model is!

Last edited by Wavebourn; 13th August 2014 at 05:23 PM.
  Reply With Quote
Old 13th August 2014, 07:29 PM   #10
diyAudio Member
 
Join Date: Jun 2004
Location: Copenhagen
Quote:
Originally Posted by kingneb View Post
What do you think of the idea of a 1:5 ratio transformer after the RIAA stage? Between the RIAA and transformer is a current sourced cathode follower that allows the driving of 600 ohms. After that is another lower gain stage. Or yet, another CF followed by another transformer.

Hi King!
Try a search fo Susan Parker and her Zeus amplifier. She uses this approach.
Thorsten
  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
Masco C-10 Mic/Phono Amp CraigNS Tubes / Valves 7 1st February 2013 12:42 PM
MIC input transformers..... camusmuse Instruments and Amps 5 18th May 2008 08:24 AM
Mic pre transformers Tim Wyatt Tubes / Valves 2 25th June 2006 11:00 PM
HELP with PHONO and MIC preamps. P Lazkao Tubes / Valves 10 23rd June 2006 01:42 PM
Mic Splitting Transformers Mikeym Parts 1 18th August 2004 08:09 AM


New To Site? Need Help?

All times are GMT. The time now is 02:35 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