Can you start by measuring the voltages across Z1 and Z2? Do you get about
6.8V? Also please confirm your values for R7 and R8.
If Z2 voltage is ok then measure the voltage across between the negative rail and R10.
What do you see? Now try adjusting P2 slightly. Does this voltage change?
6.8V? Also please confirm your values for R7 and R8.
If Z2 voltage is ok then measure the voltage across between the negative rail and R10.
What do you see? Now try adjusting P2 slightly. Does this voltage change?
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Thanks for your help. Measured across Z1 and Z2 you mentioned around 6.8V I measured 6.64V R7 and R8 are both 10k ohm resistors. The initial voltage between R10 and negative rail was 0.003V. slight adjustment of P2 and voltage changed to 0.720
When you said that P2 didn't seem to do anything, how much of the range of P2
did you go through? Did you just turn it a little and saw no voltage across R2,
or did you go through the range of adjustment on P2 and saw nothing across R2?
Is it possible you haven't turned the pot P2 enough to turn on Q2? You need about
3 to 4V between the gate pin (where Q2 connects to R12) and source pin (where
Q2 connects to R2) for the current to start flowing.
did you go through? Did you just turn it a little and saw no voltage across R2,
or did you go through the range of adjustment on P2 and saw nothing across R2?
Is it possible you haven't turned the pot P2 enough to turn on Q2? You need about
3 to 4V between the gate pin (where Q2 connects to R12) and source pin (where
Q2 connects to R2) for the current to start flowing.
I went through the entire range of the pot. I found some additional posts recommending the 3.3k resistors in conjunction with 6.8 zener diodes. At present I have 10k resistors so just ordered those to try as well for R7 and R8.
Changing R7 and R8 out to something lower is a good idea to help stabilize
the voltage of the zeners (and the bias), but in this case that's not your problem
(since they are in the right ball park.)
Can you try measuring the DC voltage between the gate and source pins as mentioned
above as you adjust through the range of P2? What range do you get? At the same
time measure the DC across R2 to confirm you are not seeing any current.
the voltage of the zeners (and the bias), but in this case that's not your problem
(since they are in the right ball park.)
Can you try measuring the DC voltage between the gate and source pins as mentioned
above as you adjust through the range of P2? What range do you get? At the same
time measure the DC across R2 to confirm you are not seeing any current.
you guidance was spot on and I did get to 3.8v however lost sight of the fact the bias and offset needed to be adjusted in balance with each other. Conducted a smoke test but happy that I now understand the procedure. Ordering some components. Will report back when I get some parts in. Thanks again
I guess both the full kit and PCB + transformers kit are out of stock now.
If you can't locate a kit, you can try putting one together:
PCBs and input jfets: from the diyaudio store.
Jensen transformers: directly from Jensen, or from a dealer. I've
ordered from these guys before:
Jensen Transformers JT-123-FLPCH Line Output Transformer, PCB Mount
The rest of the parts should be a single digikey or mouser order.
If you can't locate a kit, you can try putting one together:
PCBs and input jfets: from the diyaudio store.
Jensen transformers: directly from Jensen, or from a dealer. I've
ordered from these guys before:
Jensen Transformers JT-123-FLPCH Line Output Transformer, PCB Mount
The rest of the parts should be a single digikey or mouser order.
If you're in need of doing something before the store is back in stock and/or don't feel comfortable sourcing the components, PM me. I think we can work something out. Note - I won't be able to check my stash until 20th July earliest, but I am 90+% confident I have some spares of everything - boards, Jensen transformers, matched MOSFETs, and all other components minus the JFETs. They won't be the identical resistors etc. used in the store kits, but comparable.
I won't get around to building them until Sept earliest, so I can part with them and replace later.
I won't get around to building them until Sept earliest, so I can part with them and replace later.
Dear audio friends,
It has been a half year from now that you guys helped me during the built of my First Watt F6, and due to several things in life I was not able to reply sooner than this.
I want to thank all of you who helped me during the build and faultfinding, without you guys I was lost. The result is an amazing amplifier, clarity, dynamic, and full grip on the bass! I never want to listen to music without the First Watt anymore!
For 2021 I am planning to build The Loudspeaker (Troels Gravesen's design), and for that I am planning to build two First Watt M2 monoblocks (Mountain View version).
For now, I am just enjoying the First Watt F6 together with the Discovery 3 way Classics, also designed by Troels. This is really a great speaker, very detailed, and the First Watt F6 is the best amplifier that was paired with it. It just does everything right! Even the sensitivity of the 3 way classics is only 88dB, it fills my small room (4x4 meters) with ease.
Again a big thank you to all of you who took the time to guide me, looking forward to a new project next year! :-D
Regards,
Koos
It has been a half year from now that you guys helped me during the built of my First Watt F6, and due to several things in life I was not able to reply sooner than this.
I want to thank all of you who helped me during the build and faultfinding, without you guys I was lost. The result is an amazing amplifier, clarity, dynamic, and full grip on the bass! I never want to listen to music without the First Watt anymore!
For 2021 I am planning to build The Loudspeaker (Troels Gravesen's design), and for that I am planning to build two First Watt M2 monoblocks (Mountain View version).
For now, I am just enjoying the First Watt F6 together with the Discovery 3 way Classics, also designed by Troels. This is really a great speaker, very detailed, and the First Watt F6 is the best amplifier that was paired with it. It just does everything right! Even the sensitivity of the 3 way classics is only 88dB, it fills my small room (4x4 meters) with ease.
Again a big thank you to all of you who took the time to guide me, looking forward to a new project next year! :-D
Regards,
Koos
Is there a resource similar to this thread but for non-DIY F6s? I have a "Pilot Run" model right now, and it doesn't seem to match even the schematic from the 2012 presentation PDF. I need to adjust the bias and offset, but have no idea what the bias should be on this revision.
About an amp over any of the source resistors... Post a photo or two when you get a chance and we can point it out.
Yeah take some close up photos of the pcbs around the mosfets.
Bias it around 1.3A to 1.5A whatever the heatsinks will dissipate without getting bloody hot.
Well bloody hot is probably ok, but you don't want to be saying CRIKEY that's bloody hot.
Seriously ! consider using a pair of Tannoy dual concentric speakers. IMO you will find them clearly superior to the Troels efforts.. and as a perfect match to your F6... You won't need yet more amps 😉
I took some closeups of the top side of the PCB. The final image is a panorama, so please excuse the slight distortion.
First Watt F6 Pilot Run - Album on Imgur
First Watt F6 Pilot Run - Album on Imgur
Looks like bias measurement is taken across the White Block Resistor.
Bias and DC offset is adjusted at the trimpots as labelled on the PCB.
Bias and DC offset is adjusted at the trimpots as labelled on the PCB.
Thank you for the response.
The resistor is a 3W R05J (0.05 ohm). I know how to adjust the bias and offset because I've done it for other amps (Beta 22, M^3), but I didn't know what to measure on this particular version of the F5.
If the bias is measured at that block resistor, does that mean for 1.3 A, I would want 0.065 V across that 0.05 ohm resistor?
The resistor is a 3W R05J (0.05 ohm). I know how to adjust the bias and offset because I've done it for other amps (Beta 22, M^3), but I didn't know what to measure on this particular version of the F5.
If the bias is measured at that block resistor, does that mean for 1.3 A, I would want 0.065 V across that 0.05 ohm resistor?