Vintage Saba opt in SE-headphone amp - diyAudio
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Old 26th August 2009, 06:40 PM   #1
Stixx is offline Stixx  Germany
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Default Vintage Saba opt in SE-headphone amp

After having finished a very good sounding Aikido with parafeed output transformers I wanted to try a true SE headphone amp with output transformers. I breadboarded the amplifier and am currently using E810F wired as triode with LED bias (orange ones at around 21mA/1.9Vish) and fully regulated supplies.
As output transformers I was given a nice pair of Saba opt's out of the old famous radios (dunno which tube compliment). Those have three taps with two of them making a nice 6K:300R output transformer. I was able to confirm this by using a small 6V print transformer and measuring the respective voltages.

Q: Since the transformers don't have any markings of the taps I keep wondering how to correctly hook up the wires... I just hooked it up and it plays music nicely , but does it matter which way around I hook things up and how prim. and sec. are hooked up in respect to each other? Hope I could make myself clear enough in terms of language...

Please see attached image -->


Edit. Tubes in picture of course are not E810F! To test things I didn't want to run the risk of toasting the "precious" pentodes but used "cheap" 6N6P instead (wired correctly ;-))...
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Last edited by Stixx; 26th August 2009 at 06:45 PM. Reason: typo
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Old 26th August 2009, 06:50 PM   #2
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Very nice! What impedance are your headphones? I might be inclined to stick with the 6N6P, it's a very low distortion performer, especially CCS loaded (also the price is very attractive for longevity of the amp).
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Old 27th August 2009, 07:47 AM   #3
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Thank you Blade!

My Sennheiser headphones are 300 ohm which is why I was trying the Saba opt's. To be honest I don't now how sensititive a headphone amplifier is in terms of correct load of the plate... but I tried to achieve something like a 6K load.
I might also try the 6N6P's...only issue I am having here is that my regulated heater supply needs way more heatsinking to supply the needed 1500mA
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Old 28th August 2009, 07:35 AM   #4
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HF performance will be different because Fres of the OT will be lower when the primary is reversed. I noticed it the other day with an amorphous core. Although it happens at a supersonic frequency, the effect on the audio band can be heard. Don't know if the effects will be noticable when the OT has more / stronger shortcomings.
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Old 28th August 2009, 11:21 AM   #5
Stixx is offline Stixx  Germany
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Thank you Jaap...

So I can test the correct polarity by ear...
Any advice how to connect primary and secondary in respect to each other,
or doesn't hurt reversed connection here?
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Old 28th August 2009, 03:45 PM   #6
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Quote:
Originally Posted by Stixx View Post
Thank you Jaap...

So I can test the correct polarity by ear...
Any advice how to connect primary and secondary in respect to each other,
or doesn't hurt reversed connection here?
Hi,
It won't hurt but if you want optimal performance progress is achieved by correct connections. Look at those graphs. The red line is correct connection, blue is reversed.
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Old 29th August 2009, 09:34 AM   #7
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Quote:
HF performance will be different because Fres of the OT will be lower when the primary is reversed. I noticed it the other day with an amorphous core. Although it happens at a supersonic frequency, the effect on the audio band can be heard. Don't know if the effects will be noticable when the OT has more / stronger shortcomings.
This is true of the toroidal transformers I have used, but you want the orientation which produces the more rolled off frequency at the top end. This is because the rising response is due to a resonance between the leakage inductance and capacitance and with all the toroidals I have used usually peaks at about 60khz. Over time this makes for very fatiguing listening. Peaking can be as much as 6db. I also found that if the transformer was ringing - it also distorted the lowest frequencies the transformer could produce.

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Last edited by Shoog; 29th August 2009 at 09:37 AM.
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