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Old 25th December 2013, 09:26 PM   #5561
jugi63 is offline jugi63  Finland
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Have Merry Christmas guys!
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Old 2nd January 2014, 03:53 AM   #5562
anilva is offline anilva  India
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Default F6 build completed

Finally after months of waiting to finish the F6 project, I managed to complete during the Christmas holidays. This is based on Tea-bag's boards, Jensen transformers and Semisouth Power Jfets bought sometime back.

I am using a single blue LED on each side for bias. Also implemented degeneration resistors on input JFets and the FET are at 8.7 mA IDSS rating.

Everything else pretty much as per Papa's buffered circuit. No degeneration resistors on the outputs.

Biased well and stable. Only small hitch is that I am able to push one of the channel's bias current to max of 1.3 Amps and not beyond that. The preset has reached it's wiper end. The second channel has no such problem though and is able to go to 1.5 Amps bias.

Did a basic sound check and there is no hum or any other distortion. Need to do full listening sessions. The chassis and power supply are from an earlier F5 build. Attached are couple of pictures. Excuse me for the wiring, I will tidy up soon.

Thanks to Mr. Pass for this wonderful gift.

Cheers.
Attached Images
File Type: jpg F6_1.JPG (717.6 KB, 609 views)
File Type: jpg F6_2.JPG (701.8 KB, 586 views)
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Old 2nd January 2014, 07:23 PM   #5563
anilva is offline anilva  India
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Quote:
Originally Posted by anilva View Post
Finally after months of waiting to finish the F6 project, I managed to complete during the Christmas holidays. This is based on Tea-bag's boards, Jensen transformers and Semisouth Power Jfets bought sometime back.

I am using a single blue LED on each side for bias. Also implemented degeneration resistors on input JFets and the FET are at 8.7 mA IDSS rating.

Everything else pretty much as per Papa's buffered circuit. No degeneration resistors on the outputs.

Biased well and stable. Only small hitch is that I am able to push one of the channel's bias current to max of 1.3 Amps and not beyond that. The preset has reached it's wiper end. The second channel has no such problem though and is able to go to 1.5 Amps bias.

Did a basic sound check and there is no hum or any other distortion. Need to do full listening sessions. The chassis and power supply are from an earlier F5 build. Attached are couple of pictures. Excuse me for the wiring, I will tidy up soon.

Thanks to Mr. Pass for this wonderful gift.

Cheers.
Did some listening today with my favourite tracks. Sounds simply amazing. One of the best amps I have heard in all of the amps that I made of Mr. Pass's designs. Has terrific dynamics, amazing clarity and sweet sound. One channel is running slightly lower bias at 1.3 Amps compared to the other channel which is running at 1.5 Amps bias. Cannot make any difference in their sound. The amp is feeding Fostex FE 206E based Back Loaded Horn speakers and they sound wonderful.

I will try and add a second blue LED in series to the first one to increase the Bias voltage to be able to set the other channel to 1.5 Amps bias as well. Am I in the right direction? Any suggestions and help is appreciated.

Cheers.
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Old 2nd January 2014, 07:34 PM   #5564
Zen Mod is offline Zen Mod  Serbia
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just go for it

wind back bias pots prior to powering up , but I'm sure you already know that
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Old 10th January 2014, 06:56 PM   #5565
anilva is offline anilva  India
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Two blue LEDs on each side sorted the problem of full bias. Both the channels work now with 1.5 Amps bias each.

Amp sounds wonderful.

Cheers.
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Old 14th January 2014, 05:49 PM   #5566
jugi63 is offline jugi63  Finland
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Hi there!

Got the enclosure and power supply about ready, now populating the boards...

Before I solder the Semisouths in, a question about matching tightness rosed up. It seems matching is important (read through all the 5000+ posts, huh!) But how closely is "good enough"? That is good enough to get the "magic"?

The reasoning here is that are the R100As I've got good enough or would it be wise to pay for (maybe) better matced pairs from Semisouthfan?

I think these are originally from Teabag and the values as writen on minigrip bags are:

1.48 Vgs & 1.50 Vgs
1.50 Vgs & 1.51 Vgs
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Old 14th January 2014, 05:56 PM   #5567
generg is offline generg  Germany
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I see no problem using them, because you can trim possible small mismatch with the distortion pots to the "right" sound!
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Old 14th January 2014, 06:27 PM   #5568
OllBoll is online now OllBoll  Sweden
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Quote:
Originally Posted by jugi63 View Post
Hi there!

Got the enclosure and power supply about ready, now populating the boards...

Before I solder the Semisouths in, a question about matching tightness rosed up. It seems matching is important (read through all the 5000+ posts, huh!) But how closely is "good enough"? That is good enough to get the "magic"?

The reasoning here is that are the R100As I've got good enough or would it be wise to pay for (maybe) better matced pairs from Semisouthfan?

I think these are originally from Teabag and the values as writen on minigrip bags are:

1.48 Vgs & 1.50 Vgs
1.50 Vgs & 1.51 Vgs
If I remember correctly Vgs didn't matter much in this amp but rather transconductance. So unless they are matched there the best option is probably to build EUVLs variable distortion version and shape the distortion to your liking.

Keep in mind that everyone has a different definition of magic, what someone else likes and calls magic you might not like at all =) In the end the variable version is probably the safest to build since then you can build two amps, change the distortion on one then compare them and continue until you are satisfied.
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Old 14th January 2014, 07:01 PM   #5569
Zen Mod is offline Zen Mod  Serbia
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variable distortion ....... AKA Zen Amount Pot(s) is , if anyone's , mostly Generg's
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Old 14th January 2014, 07:16 PM   #5570
generg is offline generg  Germany
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Thank you Zen Mod…..

with a little help from my friends…..

http://www.myvideo.de/watch/4962176/...rom_my_friends
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Last edited by generg; 14th January 2014 at 07:19 PM.
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