Step-up transformer design - Page 26 - diyAudio
Go Back   Home > Forums > Loudspeakers > Planars & Exotics

Planars & Exotics ESL's, planars, and alternative technologies

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 March 2013, 07:39 PM   #251
diyAudio Member
 
bolserst's Avatar
 
Join Date: Jun 2005
Location: Fort Worth, Texas
Quote:
Originally Posted by Legis View Post
Can I use regular toroidal transformer, with 1:8 step up ratio to drive basic dynamic tweeter load (16ohm compression driver + 200R series resistor). Is the bandwidth enough to reach ultra frequencies without much phase shift? Lets say the primary inductance is for example 166mH. If that kind of trafo is a low pass filter with that load, which kind of transformer should it be? Bifilar wound pri and sec, minimal primary turns...? Should I use a electrostatic shield or not between the pri and sec?
Should be doable to keep phase < 30deg at 20Khz.
How low in frequency will the transformer have to operate? and what Vrms will it need to handle?


Quote:
The reason if anyone is wondering, is that I will be current driving the compression drivers, the step up trafo is just to boost the output level back to almost normal.
The current drive is approximated by the use of the 200R series resistance?

Quote:
Actually when I measure the two primaries in series, the inductance reads 166mH, but when the primaries are in parallel the inductance is vanishingly low 0,03mH. Secondary is unshorted in both cases.
Any chance you need to swap polarity on one of the primaries when wired in parallel?
  Reply With Quote
Old 7th March 2013, 07:58 PM   #252
Legis is offline Legis  Finland
diyAudio Member
 
Legis's Avatar
 
Join Date: Dec 2009
Quote:
Originally Posted by bolserst View Post
Should be doable to keep phase < 30deg at 20Khz.
How low in frequency will the transformer have to operate? and what Vrms will it need to handle?



The current drive is approximated by the use of the 200R series resistance?


Any chance you need to swap polarity on one of the primaries when wired in parallel?
Hi Steve, thank for answering. I will be using 1st order line level low pass between 300 and 600Hz. 11Vrms is the maximum continuous drive voltage, the power dissipation in the two 100R resistors gets too high after that. They can handle 2-3x the power at short peaks, but the SPL at 11V is quite high already (it translates to ~8Vrms across the 110dB/2,83V compression driver I think).

Yes the series resistor acts as the main "V/I converter" so the non-linear V/I conversion of the voice coil gets smaller. The amount that the nonlinearities (caused by electric motor forces) are reduced at maximum, can be estimated by (200R + 16R [+ secondary R]) / 16R = ~13,5 times = ~22,6dB. I did not take the R of the secondary in the account, but it should be pretty low.

I connected the center wire of pri A with the side wire of pri B. If I connect the center wires of both pri A and B, the inductance goes to 0,01mH. And actually the measuring frequency is ~65kHz, this ebay meter changes it's frequency depending on the load.

What kind of design would be best? 50 turn on that size core is quite oversized regarding saturation. So maybe 25 turn pri? Bifilar would pri and sec (at least pri)? How about the electrostatic shield, good or not? Should I connect it to the chassis of the driving amplifier for fully balanced operation, or leave it floating?

Last edited by Legis; 7th March 2013 at 08:04 PM.
  Reply With Quote
Old 7th March 2013, 11:12 PM   #253
diyAudio Member
 
JonasKarud's Avatar
 
Join Date: May 2008
I think that when you are measuring the paralleled inductance, you must change the polarity on one of the coils so that you get a correct reading of 166/2 = 83 mH.

Driving a dynamic speaker with a 8 times stepup trafo is not an good idea due to
the enormous impedance mismatch...it will give 16/(8*8) impedance = 0.25 ohm......
  Reply With Quote
Old 7th March 2013, 11:19 PM   #254
Legis is offline Legis  Finland
diyAudio Member
 
Legis's Avatar
 
Join Date: Dec 2009
Quote:
Originally Posted by JonasKarud View Post
I think that when you are measuring the paralleled inductance, you must change the polarity on one of the coils so that you get a correct reading of 166/2 = 83 mH.

Driving a dynamic speaker with a 8 times stepup trafo is not an good idea due to
the enormous impedance mismatch...it will give 16/(8*8) impedance = 0.25 ohm......
Hi, each individual primary measures 0,04mH when measured separately. For some reason both primaries in series show much higher inductance. If I connect them in series "the wrong way", then the inductance also reads below 0,1mH. Could it be from the bifilar wounding that's causing this... Maybe the "correct" series connection negates the bifilar wounding's inductance cancelling effect.

Like was mentioned, there will be 200R resistor (or more likely 2 x 100R) in series with the 16ohm driver, so the load that the amp sees will be closer to ~3,38ohms.

Last edited by Legis; 7th March 2013 at 11:23 PM.
  Reply With Quote
Old 8th March 2013, 09:21 AM   #255
diyAudio Member
 
JonasKarud's Avatar
 
Join Date: May 2008
If you don't have any inductance in a coil then you don't have a coil...
How are yoy measuring the inductance?
I cant see the reason for first stepping up the voltage 8 times, then reducing it 200/16=12.5 times with a resistor? All that you will achieve is a reduced sensitivity
and a impedance at 3.4 Ohm instead of 16.....
  Reply With Quote
Old 8th March 2013, 09:46 AM   #256
Legis is offline Legis  Finland
diyAudio Member
 
Legis's Avatar
 
Join Date: Dec 2009
Quote:
Originally Posted by JonasKarud View Post
If you don't have any inductance in a coil then you don't have a coil...
How are yoy measuring the inductance?
I cant see the reason for first stepping up the voltage 8 times, then reducing it 200/16=12.5 times with a resistor? All that you will achieve is a reduced sensitivity
and a impedance at 3.4 Ohm instead of 16.....
I use this kind of meter: http://www.ebay.com/itm/L-C-F-Induct...item3f0e13fb9d

You can read more about the current driving here: Current-Drive - The Natural Way of Loudspeaker Operation

I have used 33R over a month in series with the same drivers and have been liking what I hear. I want to use more current drive, and still get good sensitivity, that's why the bigger series res and the step-up trafo.

Last edited by Legis; 8th March 2013 at 09:52 AM.
  Reply With Quote
Old 8th March 2013, 12:09 PM   #257
Legis is offline Legis  Finland
diyAudio Member
 
Legis's Avatar
 
Join Date: Dec 2009
The transformers' specifications that I ordered:

- Core's area ~11,5cm2, material is grain oriented silicon steel, Bmin = 1.7T
- 2 x 30 turn bifilar wound primaries (2,0mm2 wire)
- 2 x 120 turn bifilar wound secondaries (0,44mm2 wire)
- Primay is wound close to the core, secondary on top.
- Electrostatic shield
- Electromagnetic shield

What do you think, will it have high enough bandwidth when operated at 1:8 and 200R series resistance prior the driver? There is also possibility to use just ~100R series resistance and connect the trafo at 1:4 step-up by connecting the secondaries in parallel.

Last edited by Legis; 8th March 2013 at 12:13 PM.
  Reply With Quote
Old 8th March 2013, 03:10 PM   #258
diyAudio Member
 
bolserst's Avatar
 
Join Date: Jun 2005
Location: Fort Worth, Texas
Quote:
Originally Posted by Legis View Post
What do you think, will it have high enough bandwidth when operated at 1:8 and 200R series resistance prior the driver? There is also possibility to use just ~100R series resistance and connect the trafo at 1:4 step-up by connecting the secondaries in parallel.
Based on measurement of other small toroidal power transformers, if transformer is wound with layers taking up full circumerence of toroidal core, I think it will. The only thing I am not sure about is how much space the electrostatic shield takes up, as I have not yet measured any with it. Any added space between primary and secondary increases leakage inductance. Primary of 30 turns should provide plenty of core capability for the frequency range you plan to drive it in.

Concerning measurement of primary inductance:
My guess is that your meter is trying to determine inductance at too high a frequency and is getting confused by other parasitics like winding capacitance. You need to have a meter you can set the measurement frequency to something low(< 200 Hz) where the primary inductance dominates the impedance.

Attached below is a simple test setup to calculate primary inductance based on voltage measurement across a series resistor(VR) and across the primary(VL). I'd recommend input voltage of 1Vrms @ 60Hz using series resistor R = 10 ohm.
Attached Images
File Type: gif Lp_test.gif (20.2 KB, 138 views)
  Reply With Quote
Old 9th March 2013, 01:17 AM   #259
diyAudio Member
 
alexberg's Avatar
 
Join Date: Oct 2009
<- 2 x 120 turn bifilar wound secondaries (0,44mm2 wire)>
Never do bifilar winding for HV windings, doing so you create too much capacitance. Look at Tesla's patent Patent US512340 - NIKOLA TESLA - Google Patents
  Reply With Quote
Old 9th March 2013, 01:27 AM   #260
Legis is offline Legis  Finland
diyAudio Member
 
Legis's Avatar
 
Join Date: Dec 2009
Quote:
Originally Posted by alexberg View Post
<- 2 x 120 turn bifilar wound secondaries (0,44mm2 wire)>
Never do bifilar winding for HV windings, doing so you create too much capacitance. Look at Tesla's patent Patent US512340 - NIKOLA TESLA - Google Patents
What is the negative side effect of extra capacitance in this application (dynamic driver and non-inductive resistor as load)? 120 turns is still quite low, ESL output transformer with several thousand turns would be a different story...

Last edited by Legis; 9th March 2013 at 01:43 AM.
  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
Step Down Transformer Ropie Power Supplies 3 15th October 2006 10:42 AM
Can I use a step-up transformer as step-up? cviller Parts 5 6th September 2006 07:32 PM
help design SE preamp with mosfet buffer and step-up transformer. AudioGeek Solid State 0 19th January 2005 04:02 AM
Help Newbie Design X-over Step-by-Step Kongen Multi-Way 3 21st November 2004 03:32 AM
Using one transformer to step down another. Shoog Solid State 9 28th August 2003 11:00 PM


New To Site? Need Help?

All times are GMT. The time now is 10:26 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