Sorry, that comes from over-eagerness to help. Yes, I was temporarily confused since I am used to the Teabag boards, not the DIY Audio boards.
Appreciate all the help I can get
If you only have hum when both inputs are connected, it's not the PSU. It could be some ground connections to it, but the PSU itself is not the issue.
Also, if it's 50Hz hum it's grounding. 100Hz hum is PSU noise.
I changed R5/R6 to 475 Ohm, but I have 2SJ201/2SK1530 output MOSFETs. So it depends on which output devices you have.
My railvoltage is around 32-33 Volt. I changed the resistors of the cascoding so I have around 12,5 Volt on the JFets.
Walter
Hi Walter,
Thanks for the input. Im thinking of running on a higher rail voltage to increase output. Lets say 100W or maybe less but my target is higher than 80W.
So if you are running 32-33V rails so you are still on V2? Even you have several output pairs? Im still learning....even I have F5T V2 running in experimental mode(1 channel only).
Cheers.
The difference between V2 and V3 is not defined by the voltage on the rails.
V1 - Parallel Outputs and Higher Voltage
V2 - Diodes added
V3 - Cascade transistors for the JFETs were added to handle higher voltage, but it is not required that you run higher voltage. In most cases, yes, that will be the deciding factor anyway for going the cascaded route. I did it just to protect my JFETs sothat they run cooler.
V1 - Parallel Outputs and Higher Voltage
V2 - Diodes added
V3 - Cascade transistors for the JFETs were added to handle higher voltage, but it is not required that you run higher voltage. In most cases, yes, that will be the deciding factor anyway for going the cascaded route. I did it just to protect my JFETs sothat they run cooler.
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Why are there positions for parallel JFETs (Q1//Q2 and Q3//Q4) on the store PCB? Option to increase the gain?
I got my store boards today and must have missed the reasons for this (I guess it is all in the article though....).
I have to thin about that for a bit. it would defintely lower noise, should lower/alter distortion. I guess gain is set by Idss through fets, so maybe you are right, but i have a feeling it altes total Yfs of that stage. Nelson uses two 109's in the J2 but that could correlate to more current "drive" for the gates of the SS.
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I think Yfs is the gain and that this would double by paralleling (twice the current swing for an equal change in voltage). Downside? Twice the input capacitance and therefore increased distortion
Yfs and gain are related, but not so directly as that. i was corrected on this point by ZM and EUVL, i brlieve. Higher Yfs has the effect of minimizing harmful capacitance. Nelson and Juma both confirmed this in a discussion with me. I am not saying it does not go up some, but it is partially offset by the increased Yfs. It will change the distortion spectra but to what degree, I am unsure.
Walter,
I have not seen the R5/R6 issue concerning SK1530/SJ201 outputs discussed anywhere. Would you mind telling what decided you to lower those values ?
Thanks,
Max