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. 😱
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 🙂🙂🙂
Im about to rewire the whole Power supply for 3rd time in hope of getting rid of this intrusive hum.
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.
Hi Walter,
This is great information. Have you change the value of R5/R6(V3 Schematic)
to 2.2K or you stay at 1K. Just making sure for me to avoid rework.
BTW, what is your rail voltage for your V3?
Cheers.
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
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?Yes It will not be used. Cascode transistors are marked as Q5/Q6, I will used 2SA1837/2SC4793 for these. Im referring with Q1,Q2,Q3,Q4 which is a parallel jfet slot. BTW im referring with the store PCB.
I got my store boards today and must have missed the reasons for this (I guess it is all in the article though....).
Because the slots were there I tried doubling gr instead of bl grade fets.It did not work for me but I think I had fakes I think it should work with genuine parts.
It increases the gain of the input pair which should affect FE gain, total gain, total feedback , and distortion profile.
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.
Highly noted Henry and thanks.
It increases the gain of the input pair which should affect FE gain, total gain, total feedback , and distortion profile.
I thought it would 'only' increase current 'drive'
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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Pretty much got rid of all the hum! so will post at some point for others how Ive wired up. very faint hum now.
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😕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.
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.
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
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
They have lower Vgs for same current level, so less resistance is need to set proper bias. This also affects gain structure.
Pretty much got rid of all the hum! so will post at some point for others how Ive wired up. very faint hum now.
Wonderful!
What did you do?
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