?I have not directly measured the JFET transconductance, but have measured the output impedance of the Teaser-6 under the following conditions:
Feedback network: 50R/10R.
Closed loop gain approx 4.7
Rs=0, ie. AC coupling directly to JFET source
Rsens=0R12
Ibias=1.3A
Zo = 0R334
Measured open-loop-gain: 153
(Based on AC voltage measurement across transformer primary at 60Hz.
Not sure about accuracy.)
Feedback network: 50R/10R.
Closed loop gain approx 4.7
Rs=0, ie. AC coupling directly to JFET source
Rsens=0R12
Ibias=1.3A
Zo = 0R334
Measured open-loop-gain: 153
(Based on AC voltage measurement across transformer primary at 60Hz.
Not sure about accuracy.)
Thank you lhquam. Actual Zo = 0.334 Ohms = 1/2S. Solve for S= 1.5 mho. Possible right answer?
I am not sure what you are trying to calculate. The feedback loop must be considered.
The actual transconductance of the JFETs is something like OLG/(2*Rload).
Rload is 8R || 60R approx 7R. We get S=10.77mho. That is consistent with the R100 datasheet.
The actual transconductance of the JFETs is something like OLG/(2*Rload).
Rload is 8R || 60R approx 7R. We get S=10.77mho. That is consistent with the R100 datasheet.
Last edited:
Switched Xformers and changed caps to Elna Silmics II 470uF. Stereo running now. Clean and sweet midrange. Definitely need more gain from Pre IMO. I think or me personally, I would like a little more bloom. Don't know yet for sure. What if top cap is connected below fet and bottom cap is connected on bottom of Rs or attached to pot across Rs? I have an itch to play with harmonics. Also. If i were to run FE off Salas Shunt, how do i take care of the gronuding issue considering two psu's present and two sides of xformer?
JBL inspired biasing for the F6
Having thought a little bit more, I suggest the following schema as a possible option for the bias.
It is in line with the JBL schema except that where they use a reference diode/zener I think the bias reference (I use 1k2 with an 2SK30 of Idss of 3,1 mA) should suffice.
The bootstrap ensures the current source sees the same potential all the time.
I have a bootstrap both sides just for the sake of symmetry.
JBL Energizer:
View attachment JBL Energizer.pdf
Having thought a little bit more, I suggest the following schema as a possible option for the bias.
It is in line with the JBL schema except that where they use a reference diode/zener I think the bias reference (I use 1k2 with an 2SK30 of Idss of 3,1 mA) should suffice.
The bootstrap ensures the current source sees the same potential all the time.
I have a bootstrap both sides just for the sake of symmetry.
JBL Energizer:
View attachment JBL Energizer.pdf
- The diode is a special diode, and as far as I understand it zeners at 1,0V.
- Else the bias voltage is generated across the 6,2 Ω resistor and the diode just acts as some kind of safety device.
Agree totally - I am just trying to pathethic over a small detail - the compression factor of the CCS, that will influence the operating point. I have no idea if there is a difference; simulation could show that.
lhquam: As you continue to tweak and listen to Teaser-6 [JFET], you have the experience and skills [build and sims] to start a new thread entitled [if you wish] "Teaser-6 [SIT] Amplifier". Zen Mod was the one to first suggest using SIT depletion-mode devices instead of JFETs in Conceptual F6. My gut feeling is that SIT devices will quickly find their place in a Conceptual F6 design. It is not a question of if; but rather when; in your case you can make it happen soon.
Who's bogarting the SITs? None of my good friends have sent any to my door.
Probably easier to find diamonds in the backyard. I'll just be happy when F6 schematic arrives. Either on this thread or in my Inbox. Until then, I have plenty of amplifiers that already please my ears. It's just overindulgence and licking the earth from here.Unfortunately Zen Mod, I do not have the skill and the experience which you, lhquam and others have to even begin to tackle the current Conceptual F6 [like you all are excelling at] let alone the SIT mod. I leave this challenge to the experts.what's stopping ya to do the same ?
Last edited:
How do I obtain SITs? The 2SK82 appears to be available from acronmanelectronics through Ebay, but Nelson's SIC SITs are not. I cannot even find a datasheet for the 2SK82.
Tea-Bag. I find the word plenty in your remark about having plenty of amplifiers remarkable. Is it a private collection of how many amps, and/or any up for sale? My ideas can always be seen and discarded as cheap talk. Just communication for whatever worth.Who's bogarting the SITs? None of my good friends have sent any to my door.
I remember a slightly different line from the original song, but it fits, i think.
@antionel
I got 4
not for sale, no way.buzzforb and Tea-Bag. Fortunately, I do not have SIT and JFET or any other hardware for sale [or plan to]. I leave this valuable activity and service to the experts.I remember a slightly different line from the original song, but it fits, i think.
@antionel
I got 4
Last edited:
Mr. Pass and Mr. Rothacher pioneered and/or revived the use of SIT devices. Their articles; especially the two practical ones by Mr. Rothacher and the Thread entitled "L'Amp: A simple SIT Amplifier" are a gold mine of info. Actually, Mr. Rothacher devised his own test equipment and method to generate the Characteristic Curves of 2SK82 in his first article.