The point of the cascode is to protect the low voltage input FET from the high voltage rails -- it would otherwise blow.
It also has other effects, one of which is increased bandwidth, which may lead to instability. However, the compensation caps on the F5T boards seem to take care of that nicely.
See: https://www.passdiy.com/project/amplifiers/cascode-amplifier-design
See: https://www.passdiy.com/project/amplifiers/cascode-amplifier-design
Transformer wiring connection
Some may feel this is a stupid question but I will ask it anyway.
The Antek 800VA transformer that I have has secondary wires that are 12AWG stranded. I was going to solder them directly onto Teabag's diode boards but find that the holes on the board are too small for 12 AWG stranded wire and can only accept either 12AWG solid wire or 14 AWG stranded. So what is the best way to go about this? Solder the 12AWG stranded to 12 AWG solid, solder 12 AWG Stranded to 14 AWG stranded, insert as many strands of the 12AWG into the hole as I can and then solder , or some other idea?
Thanks.
Nash
Some may feel this is a stupid question but I will ask it anyway.
The Antek 800VA transformer that I have has secondary wires that are 12AWG stranded. I was going to solder them directly onto Teabag's diode boards but find that the holes on the board are too small for 12 AWG stranded wire and can only accept either 12AWG solid wire or 14 AWG stranded. So what is the best way to go about this? Solder the 12AWG stranded to 12 AWG solid, solder 12 AWG Stranded to 14 AWG stranded, insert as many strands of the 12AWG into the hole as I can and then solder , or some other idea?
Thanks.
Nash
Thanks. I found one that accepts 12AWG wire within the 5.0mm pitch.
Invalid Request
Any other suggestions?
Radioshack sells quick connects that are compression fittings that have a pin end on them. You can crimp the wire, solder, and then the pin will lsip right into the hole. You can then solder that as well.
NTE 76-IPT12L - PVC Ins Pin Term 12-10 AWG (50 PK) : Pin Terminals | RadioShack.com
NTE 76-IPT12L - PVC Ins Pin Term 12-10 AWG (50 PK) : Pin Terminals | RadioShack.com
And if you prefer to solder the connections (vs crimping), McMaster-Carr sells a non-insulated version that may be easier to solder (on the wire side):
McMaster-Carr
My personal preference is soldering over crimping.
McMaster-Carr
My personal preference is soldering over crimping.
Unfortunately the diameter of the pin is too large. The specs to accept a 12 AWG wire indicate a diameter of 0.12in for the pin while the hole size in the PCB is 2.0mm.
Wouldn't getting the wire into the PCB hole with as many strands as possible and then soldering it be the best electrically, maybe not the easiest?
I have read of people enlarging the holes a bit; you will lose the thru plating but should be good if you solder on both sides? Or is this stupid.
Wouldn't getting the wire into the PCB hole with as many strands as possible and then soldering it be the best electrically, maybe not the easiest?
I have read of people enlarging the holes a bit; you will lose the thru plating but should be good if you solder on both sides? Or is this stupid.
traditionally speaking, i do not think that it is a good idea not to solder all parts of a stranded wire. It may not be important for power connections, but would be a ad idea for signal connections. Is there an aversion to using the suggested options? You will not hear the connector or terminal block.
thanks, I was building a turbo a few months back it kept blowing up , Im thinking of trying again this time cascoded and with the new diyaudio PCB boards. the ones i used before were proto's. Id take my time building the amp this time...
also been wondering what other amps are in this class, perhaps the older Krells ?
Not really. I suppose this is getting academic. Just looking for ideas, maybe "best DIY accepted practice".
Thanks again to all.
Nash
Newbie to this forum but not to building audio components. 🙂
I am looking at building the F5 Turbo V3 and I have a couple of toroid transformers , 1 kVA 36 vac x2 outputs, which I removed from a pair of Threshold SA1s to put in 2.4KVA Toroids. Since they are just laying around I would like to use them. These transformers give a 48v rail voltage which is 50% higher than the 32v rails in the schematic. I am looking at what changes would need to be made, and while I am not much on design, I came up with changing R5 and R6 from 1k ohm to 1.5K ohm to keep the current the same through the input JFETs and cascode parts. Also R25 and R26 which sets the input voltage of Q7 and Q8 would be changed from 10k to 15k ohm to keep the voltage the same, or would R27 and R28 also have to change as this is a voltage divider?
Analysis, opinions, feedback?
Thanks, John
I am looking at building the F5 Turbo V3 and I have a couple of toroid transformers , 1 kVA 36 vac x2 outputs, which I removed from a pair of Threshold SA1s to put in 2.4KVA Toroids. Since they are just laying around I would like to use them. These transformers give a 48v rail voltage which is 50% higher than the 32v rails in the schematic. I am looking at what changes would need to be made, and while I am not much on design, I came up with changing R5 and R6 from 1k ohm to 1.5K ohm to keep the current the same through the input JFETs and cascode parts. Also R25 and R26 which sets the input voltage of Q7 and Q8 would be changed from 10k to 15k ohm to keep the voltage the same, or would R27 and R28 also have to change as this is a voltage divider?
Analysis, opinions, feedback?
Thanks, John
I figured different voltages had been discussed with 324 pages but how to find it. 🙂
Much Appreciated.
John
Much Appreciated.
John
Ok, I have taken some time to read through about 30 pages of this thread, all very interesting. Then I went back to the schematic. With the 32v supply rails the voltage divider R25/R27 and R26/R28 (4.75k/10k) is passing about 2ma and the base of Q7 and Q8 see about 10.3v. I calculate that for 48v rails the resistors would be 4.75k and 19.2k to keep the voltage and current at the base the same R5 and R6 would be to 1.5k to keep the current to the front end devices the same.
I saw Daze2 is using 58v so wouldn't R25 and R26 need to be 24.2k and R5 and R6 be 1.8k? For testing your devices see Nelson's article Building the A75 Part II for the setup.
Also, I have found some of the Jfets from China claiming to be J74 and K170 are not, but something relabeled. Be aware.
Have a good one,
John
I saw Daze2 is using 58v so wouldn't R25 and R26 need to be 24.2k and R5 and R6 be 1.8k? For testing your devices see Nelson's article Building the A75 Part II for the setup.
Also, I have found some of the Jfets from China claiming to be J74 and K170 are not, but something relabeled. Be aware.
Have a good one,
John
From NP's F5Turbo article "In the example of cascode Q7, a voltage reference is set by resistors R25 and R27 between V+ and Ground so that the Jfets see about 1/3 of the rail voltage."Folks here say that the Jfets need to see anywhere between 12-15V. Using the same values for R25 and R 27 as in the schematic keeps you in that range.
How did you calculate R5, R6 as 1.5K?