Hello,
Just wanted to be clear about bias circuit. To my knowledge whatever you use to achieve stable bias/offset will not affect sound quality.
i have purchased the kit First watt F6 and I am able only to get on R1 or R2 with only 0.3V when I turn the Bias to the end. Everything seems to be right but I cannot get 0,5 V.It’s the same on the both PCB.From power PCB I’m getting 24.6V.
Have you experienced same problem ?
Have you experienced same problem ?
What are your Z1 and Z2 zener values? If they are 5.1V, apparently your kit has some ~6V ones you can try.
While you're at it, if you're using 10K for R7 and R8, consider replacing them with something lower (say 3 to 5k)
While you're at it, if you're using 10K for R7 and R8, consider replacing them with something lower (say 3 to 5k)
I used Z1 and Z2 5.1 V , P2 -5k, R7,8 - 10k.Tomorrow I will try change Z1 and Z2 for 6v from kit.
Thank you in at advance.
Or at some point just do this,https://www.diyaudio.com/forums/pas...a-amps-possibly-dumbest-idea-post6851970.html
Hello all, I have changed Z1 and Z2 as recommended and now the bias is fine. Thank you all for the very helpful advices! Cheers!
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@ 2 picoDumbs
Please forgive the noob question but...
All else being equal, what does the increase capacitance achieve?
If I'm not mistaken the original design had 60000uF per bank.
Honestly, not all that much. These are class-A amps that have a pretty steady and smooth draw on the PSU, so bigger cap banks are mostly a drain on the wallet.
I have been following the F6 "alteration" threads over the years but unfortunately have not written them down.
This means that my fading memory is now totally confused!
I am currently running with the zenner mod.
I have found reference to altering output devices to FQH44N10, and also to the green LED mod.
I seem to remember alterations to R1 - R2, but can't find them now.
I wonder if anyone can post a summary of the modifications, possibly with listening results to help my decisions. 😵
Schematic in use at the moment.
This means that my fading memory is now totally confused!
I am currently running with the zenner mod.
I have found reference to altering output devices to FQH44N10, and also to the green LED mod.
I seem to remember alterations to R1 - R2, but can't find them now.
I wonder if anyone can post a summary of the modifications, possibly with listening results to help my decisions. 😵
Schematic in use at the moment.
Hello Colin ,
Please see this thread. I haven’t made many changes to my F6 but the green led bias circuit was definitely one of them
https://www.diyaudio.com/community/...sibly-my-dumbest-idea-yet.348969/post-6851970
I haven’t as yet tried the 150 mosfets
Regards
I use FQH44N10 as Q1 and Q2 with good effect, and of course the green led bias solution. I have not used any other mosfet as output device so can't compare directly. I changed R11 and R12 to 100 R as a result of my tests with my ACA. Less than 60 ohm for the gate resistor gave a harsh upper register and 120 ohm a bit more muted sound for whatever reason. How that will apply for F6 I don't know.
I leave changing the values for R1 and R2 for for now, maybe add 50 mOhm to the source leg of Q1 as a test at some point. That is relatively easy to do, just cut off the right leg of Q1 and add a small resistor as a crutch.
As it is right now, distortion levels are at about 0.04% at one watt and with very equal levels of 2nd and 3rd harmonics.
I leave changing the values for R1 and R2 for for now, maybe add 50 mOhm to the source leg of Q1 as a test at some point. That is relatively easy to do, just cut off the right leg of Q1 and add a small resistor as a crutch.
As it is right now, distortion levels are at about 0.04% at one watt and with very equal levels of 2nd and 3rd harmonics.
I'm Lucky Bstrd, having spent some time with Elephants, so I can't hear difference of 60R, when mosfet gate resistor is in case
I have done some modifications to my F6. The first intention was to "correct" bias pots working the wrong way.
New pots fitted and all correct and logical now.
Whilst doing this I changed the bias from lm329 to three green leds. This went well, it just needs attention in getting the diode clusters in the correct orientation. (opposite way to the zenners.)
Biasing (measured across original 0.47 resistors) to 650mv was easy and very stable.
Also, I changed the big fets from IRFP240 to On Semi FQU44N10-F133 which has been mentioned previously.
This was done just as an experiment "because I could."
Listening now and any change is subtle. If anything, the overall sound is "warmer" with very slightly less harshness at the top end.
(BUT! This might just be psychological listening to new mods.)
Feed from BA3pre into Dallas II horns.
Now, can anyone (simply) modify the bias on a BA3 pre to be this stable and easy? 🤔
New pots fitted and all correct and logical now.
Whilst doing this I changed the bias from lm329 to three green leds. This went well, it just needs attention in getting the diode clusters in the correct orientation. (opposite way to the zenners.)
Biasing (measured across original 0.47 resistors) to 650mv was easy and very stable.
Also, I changed the big fets from IRFP240 to On Semi FQU44N10-F133 which has been mentioned previously.
This was done just as an experiment "because I could."
Listening now and any change is subtle. If anything, the overall sound is "warmer" with very slightly less harshness at the top end.
(BUT! This might just be psychological listening to new mods.)
Feed from BA3pre into Dallas II horns.
Now, can anyone (simply) modify the bias on a BA3 pre to be this stable and easy? 🤔
Wow, 650 mV bias, I have to try that. I'm still at about 550 mV.
The best thing about the green led mod is that when you put the lid back on the bias current is stable or even a bit less than without the lid.
The best thing about the green led mod is that when you put the lid back on the bias current is stable or even a bit less than without the lid.