5k trim pot
I found a new 12-turn bourns trim pot I was thinking of using instead of the multi turn 3266.
Anyways, I hooked up my multi-meter (between 1 side and the wiper) and it also trims up to about 3200ohms before it conks out. I could try another meter, but shouldn't you get a range of ~0 to ~4999 ohm from a 5k trim pot?
Maybe something else might be wrong? I'll order some of the multi-turn bouns 5k pots anyways.
I found a new 12-turn bourns trim pot I was thinking of using instead of the multi turn 3266.
Anyways, I hooked up my multi-meter (between 1 side and the wiper) and it also trims up to about 3200ohms before it conks out. I could try another meter, but shouldn't you get a range of ~0 to ~4999 ohm from a 5k trim pot?
Maybe something else might be wrong? I'll order some of the multi-turn bouns 5k pots anyways.
Have you done what you were told and disconnected one end of each of the parallel resistors?
When you are measuring 3200 ohms, it this JUST across the pot, WITHOUT it being in the circuit, right? Reason I'm asking: I started getting screwy readings with my trusty digital multimeter--voltage readings (AC and DC) were fine, but all resistance ranges below 100 Kohms was reading way off..... (Fortunately, I wasn't doing anything that required critical resistance readings at the time....). That DMM is now scrapped...
As a quick check, grab several fixed (i.e., non-variable) resistors of about 3-5 Kohms and read them on your meter. Compare the expected resistance (resistor's color code) to your actual reading--this will give you confidence in your meter (or tell you it's defunct!). You have put fresh batteries in your meter, haven't you?
OK, the chassis is a bit expensiveD) .
OK..... trick question: How do you make a DIY F5 look like a $1,500 commercial amp???
Answer: Start by gutting a $2,700 commercial amp....!
Nice job, Cassiel--look great. How does the F5 compare to the old F15, audio-wise?
I did check the pot with another multi-meter, and it had better results.
So I pulled apart my Fluke meter and replaced the battery (it was around 7v).
(The Fluke is more accurate now.)
So, maybe there wasn't anything wrong with the pot in the first place. I still have it , and I'll double check it.
So I pulled apart my Fluke meter and replaced the battery (it was around 7v).
(The Fluke is more accurate now.)
So, maybe there wasn't anything wrong with the pot in the first place. I still have it , and I'll double check it.
hmm, well I put that P1 back into the circuit and still having the same problem.
I've got the pots turned all the way counter clock wise unit they click.
When I power it up R11 & R12 give me .00v and .35v, and I noticed dc offset is also ~ .0v.
When I tweak the pots, I can't get them close enough to .59v each - there's always about .4v difference between the sides.
I have noticed that my dc offset doesn't move from .0v.
I've got the pots turned all the way counter clock wise unit they click.
When I power it up R11 & R12 give me .00v and .35v, and I noticed dc offset is also ~ .0v.
When I tweak the pots, I can't get them close enough to .59v each - there's always about .4v difference between the sides.
I have noticed that my dc offset doesn't move from .0v.
I think they're MJ15024 and MJ15025. Relabeled by MF so not completely sure. 4/4 per channel on the F15. No idea to the second question but it must be pretty good because I can beat the five seconds rule easily with the F5.
EDIT: Heatsinks are extremely heavy and divided in two pieces per channel. Screwing them to chassis is a nasty job.
EDIT: Heatsinks are extremely heavy and divided in two pieces per channel. Screwing them to chassis is a nasty job.
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minor surgery
I took it apart, both pots, r3/ r4 they all checked out fine (out of the circuit).
I also checked the other resistors, the only thing that I messed up on was R21/R22. I had 22k in, I replaced it with 10k.
I'm kind of confused, hmm, just looking at Nelson's schematic from the service guide, and cviller's guide they got different values.
So maybe there's no big deal with this discovery?
I'll have to wire it back up to power and inputs/outputs to see if anything has made a difference.
I took it apart, both pots, r3/ r4 they all checked out fine (out of the circuit).
I also checked the other resistors, the only thing that I messed up on was R21/R22. I had 22k in, I replaced it with 10k.
I'm kind of confused, hmm, just looking at Nelson's schematic from the service guide, and cviller's guide they got different values.
So maybe there's no big deal with this discovery?
I'll have to wire it back up to power and inputs/outputs to see if anything has made a difference.
Thanks!
I'll have to find some 22k's then.
I replaced my pot P2 with a 12 turn 5k trimmer (bourns something).
What are the max value of r3/r4 when you spin up your pots fully? I'm getting around 30ohms - not sure that sounds right - I could check to see what my other boards values are.
When biasing the F5, if you turn them both fully counter clockwise is one mosfet on and the other off? I mean, across R12 - I'll be getting ~ .00v and across R11 I'm at ~.35v.
It's been pretty tough to this board at .59v and a dc offset of ~ 0v.
I'll have to find some 22k's then.
I replaced my pot P2 with a 12 turn 5k trimmer (bourns something).
What are the max value of r3/r4 when you spin up your pots fully? I'm getting around 30ohms - not sure that sounds right - I could check to see what my other boards values are.
When biasing the F5, if you turn them both fully counter clockwise is one mosfet on and the other off? I mean, across R12 - I'll be getting ~ .00v and across R11 I'm at ~.35v.
It's been pretty tough to this board at .59v and a dc offset of ~ 0v.
CW or CCW - that depends of pcb and pot orientation and I can't see a reason for remembering that , just because there isn't any standard regarding that what needs to be change in which direction
just be sure that both are in shorted position before first powering up , then observe on DSMs what's happening , while you're fiddling with pots
just be sure that both are in shorted position before first powering up , then observe on DSMs what's happening , while you're fiddling with pots
Should the pot's be set to the minimum or the mosfets?
My brother tells me that the NPN mosfet should be set to the P2 pot min, and the PNP mosfet at the P1 pot. max - so both mosfets power up closed - (and R11 & R12 = ~ .000v)
(and start adjusting the bias from that starting point).
I know the service guide says both pots to their minimum.
I got one board successfully biased, this other side is giving me headaches.
My brother tells me that the NPN mosfet should be set to the P2 pot min, and the PNP mosfet at the P1 pot. max - so both mosfets power up closed - (and R11 & R12 = ~ .000v)
(and start adjusting the bias from that starting point).
I know the service guide says both pots to their minimum.
I got one board successfully biased, this other side is giving me headaches.