My JFET samples were bought years ago and obviously come from other batches. But...I had proactively asked Tea to send me non matching leftovers from the batch he did the matches so I can breadboard odd needs closer to what you guys got. Just in case they would bias bit differently. He sent me a few but varying enough in range, fortunately they arrived a few days ago. Thanks Tea.
So I found one close to your IDSS. I will breadboard it for proper Iq after higher R2 tests so you will lose 4dB according to my modeling, but I want you to also inform me the voltage you got from Q1's drain to GND. To be 100% based on your situation.
I guess so, but I did not put much attention to tonal balance yet. I concentrated over load and gain. I assume I'll be back to C2Y after load and gain.
Sure, first things first, I just wanted to know if something seems obviously out or not. It would attract early attention if it was.
My JFET samples were bought years ago and obviously come from other batches. But...I had proactively asked Tea to send me non matching leftovers from the batch he did the matches so I can breadboard odd needs closer to what you guys got. Just in case they would bias bit differently. He sent me a few but varying enough in range, fortunately they arrived a few days ago. Thanks Tea.
So I found one close to your IDSS. I will breadboard it for proper Iq after higher R2 tests so you will lose 4dB according to my modeling, but I want you to also inform me the voltage you got from Q1's drain to GND. To be 100% based on your situation.
I'll measure Q1's drain to GND voltage today at night. Let you know soon.
Thank you very much for a compliment.
I spent some time to make it right-matched.
I'll wait patiently for your advise.
So quick...
I'm speechless about your support.
Thank you very much!
Unfortunately, I do not have these values (beside 3.3k which I have -> Kiwame 2W, but I doubt if I can use it there). 18R I need to order from partsconn (PRP PR9372), so I'll order 3.3k 1W PRP too.
I'll get back with results ASAP.
Measuring Hfe
My 2sa970's arrived today, less than 2 weeks from Hong Kong to eastern Canada in December, I am amazed.
They were sold as a matched set, with hfe supposed to be matched within 2%, median value 493. Maybe not as high as I hoped, but >350 which is what the build guide says. So I measured them to choose a well-matched pair, hopefully at the high end of the range sent. My DMM doesn't have a transistor test function, so I used the info here Transistor matching to test. My resistor values didn't match the author's exactly (no 50K so I used 47K, no 5K so used 5K6), but the results I got were quite different, a lot higher than I expected.
The label on the bag of transistors indicates that they were tested with Ic 1.8mA and Vcc 10V. I was testing with Vcc closer to 8V and a lower collector current as well, more like 1.2mA. There were a couple of outlyers, but they mostly measure hfe around 600 (578 to 661, with most clustered around 610). Discarding the few outlyers they are within 2%. I went back and double-checked a couple, and my measurements were consistent and repeatable (one where the base current was a lot lower than the others measured the same when I tried again later). That said, the voltage across the base resistor was mostly in the range 3.7-3.9 mV, and I would not expect my meter to be very accurate in that range.
The BC560's I measured on a similar jig (same resistors) and same batteries gave results around 700. So, whether my results are way off or not, the 2sa970's have hfe not too far below the BC560's. So I will use them. I hope they are real.
Does anyone have any solid info on measuring hfe? I would love to have a test setup where the voltage drop across the base resistor was higher.
My 2sa970's arrived today, less than 2 weeks from Hong Kong to eastern Canada in December, I am amazed.
They were sold as a matched set, with hfe supposed to be matched within 2%, median value 493. Maybe not as high as I hoped, but >350 which is what the build guide says. So I measured them to choose a well-matched pair, hopefully at the high end of the range sent. My DMM doesn't have a transistor test function, so I used the info here Transistor matching to test. My resistor values didn't match the author's exactly (no 50K so I used 47K, no 5K so used 5K6), but the results I got were quite different, a lot higher than I expected.
The label on the bag of transistors indicates that they were tested with Ic 1.8mA and Vcc 10V. I was testing with Vcc closer to 8V and a lower collector current as well, more like 1.2mA. There were a couple of outlyers, but they mostly measure hfe around 600 (578 to 661, with most clustered around 610). Discarding the few outlyers they are within 2%. I went back and double-checked a couple, and my measurements were consistent and repeatable (one where the base current was a lot lower than the others measured the same when I tried again later). That said, the voltage across the base resistor was mostly in the range 3.7-3.9 mV, and I would not expect my meter to be very accurate in that range.
The BC560's I measured on a similar jig (same resistors) and same batteries gave results around 700. So, whether my results are way off or not, the 2sa970's have hfe not too far below the BC560's. So I will use them. I hope they are real
.Does anyone have any solid info on measuring hfe? I would love to have a test setup where the voltage drop across the base resistor was higher.
One more question...
Since I'm going to re-solder these parts, does it make sense also to replace R1x for Caddock MP930 15R (I have these new at my home)?
I'm using Vishay CFP 15R 100PPM now which came with Tea's mini-kit.
I assume that Caddock is just a better resistor for shunt than Vishay CFP.
BTW, I can use these un-soldered 15R CFPs for RC Raw PSU. I hope 15R will be not too high for V-drop there with 4700uF Caps and I'll cutoff at 2,26 Hz.
Since I'm going to re-solder these parts, does it make sense also to replace R1x for Caddock MP930 15R (I have these new at my home)?
I'm using Vishay CFP 15R 100PPM now which came with Tea's mini-kit.
I assume that Caddock is just a better resistor for shunt than Vishay CFP.
BTW, I can use these un-soldered 15R CFPs for RC Raw PSU. I hope 15R will be not too high for V-drop there with 4700uF Caps and I'll cutoff at 2,26 Hz.
The BC560's I measured on a similar jig (same resistors) and same batteries gave results around 700. So, whether my results are way off or not, the 2sa970's have hfe not too far below the BC560's. So I will use them. I hope they are real
They better be because they are nice parts. Three times less internal resistance also.
Look for a Camsemi paper about practical bjt measurements, has some simple methods.
Is that why I saw quite a bit less Vce than on BC560's with the same circuit and batteries?
The difference is in the base resistance. Rbb. Affects its noise figure performance. Such Rbb class common transistor is 2N4403 by the way. In this case bcs in cascode the main noise contributor is the JFET.
Your advise
Hi Salas,
Merry Christmas to you and to all the community.
I have been gattering my BOM for the Folded (waiting for the parts to come from Parts Connexion), In the meantime, I have measured all my semiconductors, and measure like this:
Q1=11,23mA; 11,23mA
Q2=(Not used, I will go for the 43dB version for Dynavector 10X5)
Q3Z=462; 456 HFE
Q4=8,50mA; 8,40mA
Q5=8,08mA;8,07mA
Q6=8,90mA;8,89mA
Q7=4,57mA; 4,48mA
Regulator:
Q2X=3,52mA; 4,16mA
Q3X=4,84mA; 4,73mA
Q4X=638; 638 HFE
Q5X=4,89mA; 4,93mA
Do you think these are ok?
The rest of components will be as in your manual, Takman and Vishay resistors, Vishay 1837, Elna Silmic II, Obbligato gold, Mundorf Supreme and EVO, and so on. Will keep you updated on the build.
Thanks for your time.
Kind regards,
Hi Salas,
Merry Christmas to you and to all the community.
I have been gattering my BOM for the Folded (waiting for the parts to come from Parts Connexion), In the meantime, I have measured all my semiconductors, and measure like this:
Q1=11,23mA; 11,23mA
Q2=(Not used, I will go for the 43dB version for Dynavector 10X5)
Q3Z=462; 456 HFE
Q4=8,50mA; 8,40mA
Q5=8,08mA;8,07mA
Q6=8,90mA;8,89mA
Q7=4,57mA; 4,48mA
Regulator:
Q2X=3,52mA; 4,16mA
Q3X=4,84mA; 4,73mA
Q4X=638; 638 HFE
Q5X=4,89mA; 4,93mA
Do you think these are ok?
The rest of components will be as in your manual, Takman and Vishay resistors, Vishay 1837, Elna Silmic II, Obbligato gold, Mundorf Supreme and EVO, and so on. Will keep you updated on the build.
Thanks for your time.
Kind regards,
What is the preamp and amp gain, the speakers sensitivity? Seems like you got spare enough voltage amplification in that system. You mentioned once it is a tubes based system? Now with the new resistors the phono is going to hold back by 4dB and it should be tracking along the CD on average, but still it seems like a trigger happy system gain. When you use 40% on CD is it as loud as you can stand, or simply as loud as it satisfies your listening habits?