Hmmmm....
Start by setting front-end bias a little bit low, 1.3V with minimum offset at T18.
Re-check once it's warmed up.
Then set the output bias (across R32) a bit low also, 90mV, with minimum offset.
Remember to make small adjustments, and go slow. Since your Vfet are installed, and the feedback loops working, everything reacts with everything.
Can you get minimum offset at both locations?
Also, as mentioned earlier, if you don't have 3 DMM, it's time to get more. The very inexpensive Chinese ones are good enough, just make sure they have a fresh battery!
Thanks so far, it is indeed the interactions that make it a little complex.
I have 3 multimeter's at hand so I try the advise above this evening (taking my time).
If this doesn't work I still am tempted by the idea of removing the drain screws only (replace them one by one by plastic screws to maintain mechanical tension) so you can adjust T18 without VFET interaction. But only if I have to...
I have 3 multimeter's at hand so I try the advise above this evening (taking my time).
If this doesn't work I still am tempted by the idea of removing the drain screws only (replace them one by one by plastic screws to maintain mechanical tension) so you can adjust T18 without VFET interaction. But only if I have to...
When I first tried setting the bias with one meter I was not able to adequately do it. When I hooked up another meter to monitor the DC offset and saw what was going on it became much easier to understand the relationship between adjusting pots.
In fewer words, I believe you just have one pot turned too much in relationship to the other.
In fewer words, I believe you just have one pot turned too much in relationship to the other.
Assuming that you have not reached the limit of any pots involved, you
should be able to do it.
Earlier in this thread we discussed a step-by-step procedure. The key is to
adjust all the pots in rotation, moving toward the desired measured values
a little bit at a time.
To quote the manual for a user assembled bicycle from Asia,
"Assembly of bicycle requires great piece of mind."
should be able to do it.
Earlier in this thread we discussed a step-by-step procedure. The key is to
adjust all the pots in rotation, moving toward the desired measured values
a little bit at a time.
To quote the manual for a user assembled bicycle from Asia,
"Assembly of bicycle requires great piece of mind."
Everyone on the waiting lists has now had a chance to purchase one of the VFET kits. There are still some left over, mainly due to us imposing a restriction of a limit of 1 per member for the second batch to ensure as many members as possible have the chance to build this rare amplifier.
People who did not join the waiting list because they thought they wouldn't get a chance, but are watching this thread, are now invited to secure their kits.
Please note:
To order click the appropriate links:
To add both items to your cart, just click both links and add to your cart.
If you are perhaps interested in a Deluxe 4U or Deluxe 5U chassis, we are offering a $10 discount on all 4U and 5U Deluxe chassis. Just enter code 10OFFDELUXE4VFET at checkout.
If you have any questions just reply to this email or mail contact@diyaudiostore.com.
Thank you very much for your patience and good luck building your amplifier
People who did not join the waiting list because they thought they wouldn't get a chance, but are watching this thread, are now invited to secure their kits.
Please note:
- VFET essential kits will ship in around 2 months
- VFET supplemental kits will ship in 2-3 months
Please only purchase up to the quantity of "VFET essential kits" you requested, with a maximum of 1 kit per diyAudio member. You can order as many "VFET supplemental kits" as you like. - Members from EU zone have the option of not purchasing the brackets in order to save some customs fees. The brackets will be able to be purchased intra-EU from Hifi2000 directly, on a case-by-case basis. Please orders without brackets, and then email contact@diyaudiostore.com if you would like to do this, and we will tell you the process.
- All orders will be held until they can be manually verified. This may create a delay of 1-2 days as we manually check each order.
- One order, one shipment - please read the note on the VFET essential kit product page. We only ship one time per order, so if some items you order are pre-order, you will have to wait until all items in your order are ready before it ships. Because this is a pre-order, we will make up your order over the next 2 months and aim to ship it around December 1st 2016.
To order click the appropriate links:
- VFET essentials kit- Sony VFET kit - Batch 2 - diyAudio Store
- VFET supplemental kit - Pass VFET Power Amp Supplemental Kit - diyAudio Store
To add both items to your cart, just click both links and add to your cart.
If you are perhaps interested in a Deluxe 4U or Deluxe 5U chassis, we are offering a $10 discount on all 4U and 5U Deluxe chassis. Just enter code 10OFFDELUXE4VFET at checkout.
If you have any questions just reply to this email or mail contact@diyaudiostore.com.
Thank you very much for your patience and good luck building your amplifier
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Well, I retried the offset trimming on the fully populated VFET pcb...
I noticed a cold bias startup at 108mV, I reduced it to 98mV and suddenly all offsets are in the 0-15mV range, a little tweaking improved this... My balanced/bridged set plays on old Sony test speakers, they like the VFET's!
In the end I have peace of mind. I was actually planning on assembling a bicycle, I am sure I will remember Nelson's saying on that "piece of mind"
I noticed a cold bias startup at 108mV, I reduced it to 98mV and suddenly all offsets are in the 0-15mV range, a little tweaking improved this... My balanced/bridged set plays on old Sony test speakers, they like the VFET's!
In the end I have peace of mind. I was actually planning on assembling a bicycle, I am sure I will remember Nelson's saying on that "piece of mind"
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I would REALLY like to get another VFET-Kit for my envisioned bi-amp build, but since the idea is to ensure that as many members as possible have the chance to build this rare amplifier, I shall abstain (in hope that members hogging kits get weeded out).
The question is, for how long? When is it okay to get greedy?
The question is, for how long? When is it okay to get greedy?
I like your whisky; not too bad for the "peace of mind" and best for enjoying together with the VFETs !
Quite a few people from Group 2 chose not to buy, so there are enough spare for anyone who wants to build two amps to order a second kit.
We were possibly a bit heavy handed on the "1 per member" rule for Group 2, but we wanted to ensure everyone on the list got a chance. It didn't look like there would be enough to go around. Everyone has now had their chance to order, and there are still plenty of kits left. So if you're genuinely going to build a second amp and not just horde the parts, anyone who wants to is welcome to go ahead and order a second set to bring their total to 2.
Apologies in advance for any additional shipping charges this causes anyone. If your existing outstanding order is currently being held, we may be able to combine the orders (Email contact@diyaudiostore.com with your previous order number to see if it's possible before placing your new order).
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Great.
I was like you when I first tried to set the bias. I thought there was something wrong with my build. This was when I was only using one meter. Using 2 or more meters makes adjusting bias and setting offset much easier to understand. Following Nelson's instructions "precisely" is the key to setting the bias with low offset.
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speaking of Japanese Bicycle ...... most popular quote is certainly :
you can explore it(s context) here , read something (short) about (even taking a pdf) here , or just drool here
edit .... which reminds me - Papa's is making amps with big Chissel ........ but extremely sharp
you can explore it(s context) here , read something (short) about (even taking a pdf) here , or just drool here
edit .... which reminds me - Papa's is making amps with big Chissel ........ but extremely sharp
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Japan San.. Clearly doesn't Own a suitable sized Lathe.
That method is too labour intensive.. at best.
Notably that Craftsman erm.. Forgot? that a piece of wood like that requires a deepish longitudinal kerf.
Or it will develop an Ugly longitudinal crack. As one is already starting to do.
Lotsa Folklore involved. Mostly BS imo.
Local Wood merchants Sell Only complete Logs to the Japanese Market Because they Claim they won't buy dressed timbers.
I say: Let them grow their own Damn Primo Quality trees .. so they can 'better' cut them themselves
Went to see the (in) famous Greene and Greene house.. widely held as the epitome of 'Murican wood craftsmanship skills.
Went in behind the Tourist Areas
Bent over nails, split wood, bad joins, too short cuts.
Same quality of work as found on most Any cheap/ crappy tract house.
Depressing actually.
That method is too labour intensive.. at best.
Notably that Craftsman erm.. Forgot? that a piece of wood like that requires a deepish longitudinal kerf.
Or it will develop an Ugly longitudinal crack. As one is already starting to do.
Lotsa Folklore involved. Mostly BS imo.
Local Wood merchants Sell Only complete Logs to the Japanese Market Because they Claim they won't buy dressed timbers.
I say: Let them grow their own Damn Primo Quality trees .. so they can 'better' cut them themselves
Went to see the (in) famous Greene and Greene house.. widely held as the epitome of 'Murican wood craftsmanship skills.
Went in behind the Tourist Areas
Bent over nails, split wood, bad joins, too short cuts.
Same quality of work as found on most Any cheap/ crappy tract house.
Depressing actually.