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Output coupling cap and transformer mod...? - Page 3

post #31 of 38

Base on the information provided by the manufacturer, the primary impedance is 5.5k ohm,

 

As the impedance of the transformer cannot be measured by a simple muitmeter, I can only reply on the provided information. 

 

 I am not very sure it is 100% correct. 

 

I think frequency affect the impedance of the transformer,

 

any idea on how to measure the impedance of the transformer ?

 

 

 

I do not have a oscilioscope.  To determine if 4.7uf is sufficeint or not,   I used the internet site which provides sounds in 30Hz.  See if I can hear the signal (sound) pass thro the transformer to the headphone.  Any other suggestions?

 

English is not my mother language, I am sorry if I present my idea in a strange way.

 

Sam

post #32 of 38

This is nice because it does not require working on high voltage stuff to test.. 

 

Connect your cap, transformer, and a SS amplifier using alligator jumpers. I would recommend a cmoy or O2 for this test. If you want to be VERY realistic in this test add a 100ohm resistor (or whatever the actual output impedance of whatever you will connect the transformers to is) between the amp and cap.

 

Listen to the other side. 

 

If you have RMAA or are handy with PC based oscilloscopes feel free to measure. 

post #33 of 38
Quote:
Originally Posted by nikongod View Post

This is nice because it does not require working on high voltage stuff to test.. 

 

Connect your cap, transformer, and a SS amplifier using alligator jumpers. I would recommend a cmoy or O2 for this test. If you want to be VERY realistic in this test add a 100ohm resistor (or whatever the actual output impedance of whatever you will connect the transformers to is) between the amp and cap.

 

Listen to the other side. 

 

If you have RMAA or are handy with PC based oscilloscopes feel free to measure. 

That's a great idea.

You should be able to get large enough signal output to measure rms voltage on a DMM too.

post #34 of 38
Pair of Hammond 119DA and misc mounting parts inbound. I'd like to get a blank chassis from Woo and put it in that....I've not approached them yet on availability. Would make a neat stack.
Quote:
Originally Posted by kramer5150 View Post

Cool... please post back your results if you decide to give it a try.  This little box now has me eye-ing other small OTL amps... always wanted to try an LDII or III.  The only new addition I have made to mine is the addition of a DPDT switch, ON-OFF-ON.  I have the 125 and 500 ohm primary loads wired to the ON positions so I can toggle back and forth different settings.  The Earmax sounds best with the 500 ohm and the darkvoice works best with the 125.  I flip to the middle OFF position when I swap cans.  I have "hot swapped", and even flipped the switch back and forth, neither amp seems to mind... although I don't make doing that a habit.

Some other threads of interest.

Elliottstudio has some excellent THD and FR plots here:
http://www.head-fi.org/t/629661/a-lo-cost-ht-supply-true-transformer-coupled-tube-headphone-amplifier/90#post_9172063

fullcompass.com has a decent selection of affordable speaker output transformers.

A mini transformer discussion / build. (I might try one of these just for the heck of it).
http://www.head-fi.org/t/553094/continued-sidetrack-discussion-from-tiniest-portable-amp-i-can-build-nikongod-microtransformer-based-impedance-step-down-box

Here's the disturbing thing. I am not really plugged into an amplifier circuit anymore.  I am plugged into a coil listening to an oscillating magnetic field... and it sounds BETTER than the actual circuit I was plugging into before.
post #35 of 38
Well, this is definitely a neat mod. You need about 45 degrees more volume knob to maintain the same loudness on a WA3. Music is clear and detailed and you can go a bit louder before distorting with lower impedance headphones (HD558). I'm perceiving a slight reduction in crazy impulse dynamic range (Trifonic 'Terminal A' track). Sax sounds great, as does strings. Bass is all there, along with sub bass and great imaging (Strauss Also Sprach Zarathustra Saint Saens Symphony #3 organ). There may be a ever so slight loss of air, but that could be placebo at work and the tubes I'm running. This is definitely a keeper and will get packaged nicely (and creatively) at some point. Right now it's just a cluster of jumpers...I'm using the 8 ohm tap.

Edited by GrindingThud - 4/4/13 at 4:06pm
post #36 of 38
Thread Starter 

Nice grinding... where did you get the 119DA?  I can't locate them for less than ~$30-35

post #37 of 38

Mouser has them for $27.25, which is where these came from. 

Quote:
Originally Posted by kramer5150 View Post

Nice grinding... where did you get the 119DA?  I can't locate them for less than ~$30-35

post #38 of 38
I got mine from mouser. Free delivery when you spend more than a hundred. Not bad when you consider the total cost including postage.
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