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.
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.
Attachments
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.
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
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.
Thank you Zen Mod…..
with a little help from my friends…..
http://www.myvideo.de/watch/4962176/With_a_little_help_from_my_friends
with a little help from my friends…..
http://www.myvideo.de/watch/4962176/With_a_little_help_from_my_friends
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Thanks for the answer guys!
One more simple question - didn't find the answer after some searching... so I'll have to admit how much of a beginer I am in electronics...
What is the minimum power rating for the resistors (not including the specified 3W resistors)? Is Dale RN55D 1/8W useable or should it be 1/4W?
One more simple question - didn't find the answer after some searching... so I'll have to admit how much of a beginer I am in electronics...
What is the minimum power rating for the resistors (not including the specified 3W resistors)? Is Dale RN55D 1/8W useable or should it be 1/4W?
Dale RN55 are 50% de-rated as they are mil-spec. They are actually a 1/4W resistor.
1/4 or 1/8W s ok.
Ready to start this thing up... Power supply tested. Both mono sides give +/-25.8 VDC.
Got one multimeter on the speaker outputs to measure the DC off set. Another multimeter between amp -23V input and power supply to measure the current.
How about the pots? They should be turned 'down' to start with. Would that be anti clock wise or clock wise?
Anything I'm missing or should account for?
Got one multimeter on the speaker outputs to measure the DC off set. Another multimeter between amp -23V input and power supply to measure the current.
How about the pots? They should be turned 'down' to start with. Would that be anti clock wise or clock wise?
Anything I'm missing or should account for?
She lives!
Wow… everything's gone smooth and fine. No problems at all... I'm a little amazed...
Biased both cannels up to 1.55 Amps. They will go higher but I’ll stop here for now at least.
Connected my desktop speakers, cellular phone and Chris Jones via Spotify. Sounds pretty deasent already. Especially noteworthy is how deep the soundstage is and how the speakers disapper. Will be interesting to put in the main rig.
I’ll but in a pic or two of the finnished amp once we get enough light for a decent photo here in Finland. Still have to get the front plate done though.
But for now a hugh thanks(!) for all you who have helped me along the way. This is my first propper electric project – appart from some simple kits. Wouldn't have been able without you.
So thanks guys! And Nesson… well… your generosity is special. Greatfull!
Wow… everything's gone smooth and fine. No problems at all... I'm a little amazed...
Biased both cannels up to 1.55 Amps. They will go higher but I’ll stop here for now at least.
Connected my desktop speakers, cellular phone and Chris Jones via Spotify. Sounds pretty deasent already. Especially noteworthy is how deep the soundstage is and how the speakers disapper. Will be interesting to put in the main rig.
I’ll but in a pic or two of the finnished amp once we get enough light for a decent photo here in Finland. Still have to get the front plate done though.
But for now a hugh thanks(!) for all you who have helped me along the way. This is my first propper electric project – appart from some simple kits. Wouldn't have been able without you.
So thanks guys! And Nesson… well… your generosity is special. Greatfull!
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