Hello Zen Mod
I found a difference between the circuit you posted and the one in the F4 manual.
The circuit in the manual takes DC power after the 1k resistor to power the jfet front end. The circuit you posted feeds power directly to the jfet drains.
Both versions work.
Is the manual incorrect or has the circuit been revised?
Just finished my F4 after years of the kit sitting to the side. Unfortunately both channels have problems.
The first channel will bias to a minimum of .2V. DC offset is at 18.7 Volts (Rail at 27.8V). P2 does not affect bias. I don't think it's a bad pot, any thoughts on where else to look?
The other channel is blowing fuses, so I need to get a new incandescent bulb in my tester before I can start to look there.
Cheers,
The first channel will bias to a minimum of .2V. DC offset is at 18.7 Volts (Rail at 27.8V). P2 does not affect bias. I don't think it's a bad pot, any thoughts on where else to look?
The other channel is blowing fuses, so I need to get a new incandescent bulb in my tester before I can start to look there.
Cheers,
The output of the PSU is currently 27.8V. The other channel is disconnected. I believe both channels will settle to about 25.5V when they are both up and running.
All components appear to be properly oriented. Closer inspection revealed a lifted pad on R6 (though the resistor feels sturdy). Seems like this may be the culprit. Other than measuring R6, anything else I should get a measurement of before I disassemble?
All components appear to be properly oriented. Closer inspection revealed a lifted pad on R6 (though the resistor feels sturdy). Seems like this may be the culprit. Other than measuring R6, anything else I should get a measurement of before I disassemble?
Last edited:
please , be precise
what secondaries you have on xformer(s) (Vac)
what rectifier config ?
what size of cap bank
PSU is bipolar , so , for clarity sake , you must write +/- something Vdc , not just 27.8V
what secondaries you have on xformer(s) (Vac)
what rectifier config ?
what size of cap bank
PSU is bipolar , so , for clarity sake , you must write +/- something Vdc , not just 27.8V
PSU: universal v3, follows standard Bom, no snubbers
Secondaries: 20V
Cap Bank: 8x 22,000uf
And voltages at PSU output measure +27.8Vdc and -27.8Vdc
I went digging around and found no voltage across R6. Unsurprisingly R6 had a lifted pad.
Secondaries: 20V
Cap Bank: 8x 22,000uf
And voltages at PSU output measure +27.8Vdc and -27.8Vdc
I went digging around and found no voltage across R6. Unsurprisingly R6 had a lifted pad.
well , having both channels faulty , that means you made some systematic mistake
what you need is to recheck JFets (just in case) , put new TL431 in , and start with just one pair of outputs (checked at least with diode/ohmmeter , if not with common mosfet testing jig) per channel
when you get them working as that , install rest of outpouts
what you need is to recheck JFets (just in case) , put new TL431 in , and start with just one pair of outputs (checked at least with diode/ohmmeter , if not with common mosfet testing jig) per channel
when you get them working as that , install rest of outpouts
(Aside to the audience)
Now you see the value of the mighty ZM, doing all the work while
I lounge around listening to Pepe Deluxe.
😎
Now you see the value of the mighty ZM, doing all the work while
I lounge around listening to Pepe Deluxe.
😎
Zen, you overestimate me. I very likely made several mistakes and probably all over the place.
some zen interlude for ya : https://youtu.be/TnBQ_Ffz0Cg
after that , I can recommend these steps :
check JFets (matching jig)
check Mosfets (matching jig)
put just TL431 in pcb , power it up and confirm it's setting voltage span , say from 4 to 9Vdc between lower and upper mosfet gates junctions
if that is OK , put just one pair of mosfets , set them - both Iq and DC offset
if that is OK , populate rest of mosfets , recheck Iq and offset
after that , I can recommend these steps :
check JFets (matching jig)
check Mosfets (matching jig)
put just TL431 in pcb , power it up and confirm it's setting voltage span , say from 4 to 9Vdc between lower and upper mosfet gates junctions
if that is OK , put just one pair of mosfets , set them - both Iq and DC offset
if that is OK , populate rest of mosfets , recheck Iq and offset
F-4 TURBO?
Hi,
Is there a finished design for a F4 that is as powerful as an F-5 Turbo? I need more watts than 20W to power a pair of electrostatic panels. I want to use a tube preamp/SET amp since I prefer tube amps for my midrange horns.
One option is to use F4 monoblocks, but they are balanced in? I think Zen Mod wrote that balanced would give a stronger signal, but maybe mono blocks requires a balanced tube preamp, something I don't have. I also read that balanced would be preferrable to get higher voltage from the preamp. Any ideas?
Hi,
Is there a finished design for a F4 that is as powerful as an F-5 Turbo? I need more watts than 20W to power a pair of electrostatic panels. I want to use a tube preamp/SET amp since I prefer tube amps for my midrange horns.
One option is to use F4 monoblocks, but they are balanced in? I think Zen Mod wrote that balanced would give a stronger signal, but maybe mono blocks requires a balanced tube preamp, something I don't have. I also read that balanced would be preferrable to get higher voltage from the preamp. Any ideas?
Last edited:
100W isn't enough ?
ya read article?
I read the F4 manual now. Is this article you referred to? I would like to use an unbalanced preamp into two balanced F4 mono block. How would that work?
simple phase splitter (unity gain) in front of it
or nice repeater with CT secondary
all that for bridged
for SE : put BA3 FE in front of it , crank the PSU and call it BA3
or nice repeater with CT secondary
all that for bridged
for SE : put BA3 FE in front of it , crank the PSU and call it BA3
If I have a 3.5 watt 2A3 tube amplifier, would that reduce gain too much?
Unity gain, any disadvantages?
I have a feeling that there must be some huge disadvantage to use an unbalanced preamp or amplifier with the F4 balanced mono blocks that I don't know about yet.
Where can I read about how to build the F4 mono blocks and set up right?
Last edited:
define what you need , regarding output power and gain (thus input sensitivity)
then ask again
then ask again
I will get the ER Audio 505 mini electrostatic panels later this week. I will test them with the standard F5 and see how strong amplifier I need. According to the manufacturer called Rob from Australia they are around 88-90dB at 2.83V, and they will be used down to 250Hz. The max output is 100dB, but they need "a lot of current", according to Rob.