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Old 5th September 2006, 09:03 AM   #511
Mad_K is offline Mad_K  Norway
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Have a look at the latest OTA schematic I just posted, it should please you tube guys. Even more linear. Just adjust the input Z (47K connected to 100R at the gate) to suit whatever is driving the gate. 100K is a good value, but 470K not a problem either

http://www.diyaudio.com/forums/showt...017#post998017
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Old 5th September 2006, 09:10 AM   #512
hifryer is offline hifryer  Australia
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I am not a one eyed tube guy BUT I am interested in a comparison.

If a hybrid can equal a DHT SET itt is a great breakthrough for price / performance!

I checked your design earlier ( few minutes ago). It seems to me that cap quality will make or break this design.
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Old 5th September 2006, 09:14 AM   #513
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Yup, the coupling caps are very important. I have had good results with Elna RJH (for low power version, 4700uF) Comparable to Panasonic FC, Sanyo MV-AX/WX etc. For higher power I liked the Evox Rifa PEH 200. In my next OTA build I am going to use a chassis mounted 10000uF 63V PEH 200 bypassed with a 250V 2u2 Rifa PHE426. It MAKES
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Old 5th September 2006, 10:04 AM   #514
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I don't want to be seen as a cap snob but have you tried things more exotic than RIFA? Like Hovland, Auricap or Mundorf? I would see something this quality critical on the input cap at least.

Also I wouldn't under-estimate the effect of that bias bypass cap nor the last power supply electro.

With very simple low parts count zero feedback designs like this, the catch is you must pay up for the absolutely best available parts if you want the most out of the design. I know YOU know this.

cheers,

Bart
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Old 5th September 2006, 10:25 AM   #515
Mad_K is offline Mad_K  Norway
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Yes, I used to be fantaic about these things, but you know I am an engineer, so I guess that side of me keeps me from paying through my nose for any "audio" components. I use the best I can get from my electronic component supplier ( www.elfa.se ). For better sound, it is better to buy bigger/better trafo, supply caps, heatsinks, mosfets, voltage, current etc. IMHO. I know the passive components can significantly change/better the sound. I leave this to the individual tweaker

BTW, there has been a lot of talk and little actual building to be seen in this thread. What we NEED is to see some pictures of some ratsnests acually making music. Come on gys, show us, show us! Someone must have buildt something
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Old 5th September 2006, 12:12 PM   #516
hifryer is offline hifryer  Australia
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engineer accounts only for getting close to an approximation of good sound.

from there on in we can only trust our ears - admittedly subjective by personal bias but amazingly often agreed upon by large groups.

we pay larger sums for better parts hopefully only if these parts offer a worthwhile benefit / cost to our ears!

you cant get there merely as you say by bigger everything, sorry! you are wrong. in every place you mention, if correctly engineered, once quantity is adequate quality is everything.

look at the very best pre-amps from CAT and Conrad Johnson. This later refining very simple almost 30's designs for 30 years. They won't have an electrolytic capacitor ANYWHERE! both make their own caps.
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Old 5th September 2006, 12:19 PM   #517
Mad_K is offline Mad_K  Norway
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I am with you and I completely agree/understand these things. Remeber that I said "bigger/better". What I said, counts for me, and my experiences. I'm really not into listening to sound, only the music matters to me. Let's not get into this parts debate in this thread, please
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Old 5th September 2006, 12:44 PM   #518
hifryer is offline hifryer  Australia
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OK, fair enough. I also am only into music. My ultimate test is if it makes me cry!!
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Old 5th September 2006, 01:51 PM   #519
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Quote:
Originally posted by hifryer
My ultimate test is if it makes me cry!!

-Excactly
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Old 5th September 2006, 01:56 PM   #520
Mad_K is offline Mad_K  Norway
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Default Latest schematic

I guess I should post this in this thread also..

If you are planning to use the full 7W potential, I would use 30V rails and 5K6 for R1 to keep distortion down
Attached Files
File Type: pdf seward.sch.pdf (70.1 KB, 353 views)
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