Good catch my cryptic reply, Dennis!! I meant the MOSFET that is corresponding to the resister.
Hello,
I looked around but could not find the answer on the forum. I apologize preemptively if i am breaking any rules, I am not too versed in posting on forums. I am using the F4 power supply ( bought a year ago) to power the output stage of a hybrid ( Lm1875c based ) amplifier, that needs 21v. The power supply puts out 24 v. What is the best way to lower the output voltage? Also, do 3v make a difference? There are no trim pots on the amplifier's output board. THE ORIGINAL power supply consisted of four diodes and two 4700uf caps ( ,1uf in parallel) and sounded awful in comparison. I had measured 27v from that one. Thank you in advance
I looked around but could not find the answer on the forum. I apologize preemptively if i am breaking any rules, I am not too versed in posting on forums. I am using the F4 power supply ( bought a year ago) to power the output stage of a hybrid ( Lm1875c based ) amplifier, that needs 21v. The power supply puts out 24 v. What is the best way to lower the output voltage? Also, do 3v make a difference? There are no trim pots on the amplifier's output board. THE ORIGINAL power supply consisted of four diodes and two 4700uf caps ( ,1uf in parallel) and sounded awful in comparison. I had measured 27v from that one. Thank you in advance
Depending on how much... a some resistance may do the trick.
That depends
No need to reply here. I'd suggest finding the appropriate thread (or start a new thread) for the specific amp you're working with and ask something like...
I'm thinking of using my PSU from a First Watt F4 clone. Will this work? My PSU Schematic is attached below. When tested, it is +/- 24V under load and +/- 27V unloaded.
Change the details as needed and be sure to post the schematic and perhaps a picture or two of your PSU. Good luck and have fun!
Post #2088 from Mr. ggetzoff (I am assuming "g" for g force then "gets off" as I think he's a pilot 
) with detachable top plate.
F4 in 3U case
) with detachable top plate.F4 in 3U case
Got the L ch. up and running with the swapped FETs. Set Q3 source resistor drop to 130mV. After an hour, drops across respective resistors are:
Q3: 152mV; Q4: 138mV; Q5: 147mV; Q6: 148mV; Q7: 134mV; Q10: 159mV
A spread but within 20%. Looks like MOSFET swap had intended effect but the set may not be optimal. Later today, will get R ch. up and running and see where it all sits.
Q3: 152mV; Q4: 138mV; Q5: 147mV; Q6: 148mV; Q7: 134mV; Q10: 159mV
A spread but within 20%. Looks like MOSFET swap had intended effect but the set may not be optimal. Later today, will get R ch. up and running and see where it all sits.
Not so lucky on the R ch.
Q3: 147mV; Q4: 167mV; Q5: 106mV; Q6: 144mV; Q7: 128mV; Q10: 151mV
Something isn't right with Q5 but unsure how I'm going to proceed. I have all the parts (including a matched set of MOSFETs from Etsy) to build up another set of boards. Thinking best bet is to give a fresh build a chance and set aside the offending board for troubleshooting when I can get a real test bench set up.
Q3: 147mV; Q4: 167mV; Q5: 106mV; Q6: 144mV; Q7: 128mV; Q10: 151mV
Something isn't right with Q5 but unsure how I'm going to proceed. I have all the parts (including a matched set of MOSFETs from Etsy) to build up another set of boards. Thinking best bet is to give a fresh build a chance and set aside the offending board for troubleshooting when I can get a real test bench set up.
I guess that just means that at a common gate voltage Q5 conducts less current than Q3 and Q4.
Prior to swapping the parts, did you measure the gate voltages per post #3063?
Assuming you have new triplets that are well matched, I suggest you go ahead and use them and leave these existing ones for testing later. Whether you want to build completely new sets of boards will depend on how comfortable you are in desoldering the existing mosfets.
Prior to swapping the parts, did you measure the gate voltages per post #3063?
Assuming you have new triplets that are well matched, I suggest you go ahead and use them and leave these existing ones for testing later. Whether you want to build completely new sets of boards will depend on how comfortable you are in desoldering the existing mosfets.
Sadly, I did not. Got too focused on getting something done this long weekend.
with your input there about desoldering the MOSFETs and what I went thru the last 2 days, going to build new boards. The dinner table actually gets used for dinner. Unpacking and packing is getting old and tiring. Looking forward to buying a house and having a work bench.
with your input there about desoldering the MOSFETs and what I went thru the last 2 days, going to build new boards. The dinner table actually gets used for dinner. Unpacking and packing is getting old and tiring. Looking forward to buying a house and having a work bench.