The most recent F4 service manual. The notes on the bias setting are just below the schematic.
-Mal
p.s. what kind of Idss are people running in Q1 & Q2? I started with a pair at 6.8ma, Vp -0.6v, swapped them out for j74/k170bl's at 10ma, Vp -0.8v. To me the topend is sweeter, smoother for it. Had to correct for 200mv of offset (dif between channels less than 5mv) . Anyone know what might be happening here?
-Mal
p.s. what kind of Idss are people running in Q1 & Q2? I started with a pair at 6.8ma, Vp -0.6v, swapped them out for j74/k170bl's at 10ma, Vp -0.8v. To me the topend is sweeter, smoother for it. Had to correct for 200mv of offset (dif between channels less than 5mv) . Anyone know what might be happening here?
Ah-ha, there it is! I just didn't scroll down far enough.
I fired up my first F4 channel today. Neat!
I'm using IRF630b and IRF9630 FETs (I had a bunch, so why not?)
Anyway, I'm getting .400mV across the source resistors right out of the box--and that's with P1 at minimal setting (Bourns 3296W-1-502LF full counterclockwise; PD pcbs).
Aside from the FET change, I use a 26.85k resistor pair for R8--I didn't have the prescribed 27.4k on hand.
I'm not displeased that my bias is high, I just want more control over the setting. I could raise the value of R9. Does this sound like the correct thing to do?
I haven't hooked the amp up to my main speakers, yet. Sound from test speaker is promising.
I fired up my first F4 channel today. Neat!
I'm using IRF630b and IRF9630 FETs (I had a bunch, so why not?)
Anyway, I'm getting .400mV across the source resistors right out of the box--and that's with P1 at minimal setting (Bourns 3296W-1-502LF full counterclockwise; PD pcbs).
Aside from the FET change, I use a 26.85k resistor pair for R8--I didn't have the prescribed 27.4k on hand.
I'm not displeased that my bias is high, I just want more control over the setting. I could raise the value of R9. Does this sound like the correct thing to do?
I haven't hooked the amp up to my main speakers, yet. Sound from test speaker is promising.
Ahemmm....
Turns out that P1 is at max setting (not minimum) when turned fully counter-clockwise...
Fortunately, I attempted the simple procedure of turning the pot clockwise, vs. replacing R9.
Yes, I'm embarrassed.
I've dialed the amp bias down, and the source resistor voltage is now the suggested 200mV.
The little FETs run much cooler, and the amp sounds less stressed.
I've listened for a half an hour and love what I'm hearing. The tiny test speaker sounds marvelous. I can't wait until a get a pair of "Curvy Chang" full range horns fabricated with which to mate this little F4.
Turns out that P1 is at max setting (not minimum) when turned fully counter-clockwise...
Fortunately, I attempted the simple procedure of turning the pot clockwise, vs. replacing R9.
Yes, I'm embarrassed.
I've dialed the amp bias down, and the source resistor voltage is now the suggested 200mV.
The little FETs run much cooler, and the amp sounds less stressed.
I've listened for a half an hour and love what I'm hearing. The tiny test speaker sounds marvelous. I can't wait until a get a pair of "Curvy Chang" full range horns fabricated with which to mate this little F4.
Choky, I have to borrow my sweetie's digital camera......
Right now, the parts are not in an enclosure, soon they will be, then you can tell me what an "ugly" amp I have.
I'm going to start carving on my ugly little pumpkin soon. I have my receiver cranked all the way and can only get a moderate listen....
Today, one F4 laying bare naked on a table... tomorrow, dual bridged mono F4s per channel....this is getting exciting.
Right now, the parts are not in an enclosure, soon they will be, then you can tell me what an "ugly" amp I have.
I'm going to start carving on my ugly little pumpkin soon. I have my receiver cranked all the way and can only get a moderate listen....
Today, one F4 laying bare naked on a table... tomorrow, dual bridged mono F4s per channel....this is getting exciting.
Babowana said:
Did you use all matched MOSFETs?
I matched N fets to N and I matched P to P. The P channel VAS test result is 0.18 volts apart from the N channel.
I also match (ohm wise with a multimeter) all resistors that have a mate.
I made no attempt to match jfets. I just asked them to be blessed with the loving energy of the "golden ears" spirit.
The amp does hit the 50 degree mark, but holds steady--in fact, I'd swear that the fets get cooler when the amp is playing music.
carpenter said:
I matched N fets to N and I matched P to P. The P channel VAS test result is 0.18 volts apart from the N channel.
I also match (ohm wise with a multimeter) all resistors that have a mate.
I made no attempt to match jfets. I just asked them to be blessed with the loving energy of the "golden ears" spirit.
The amp does hit the 50 degree mark, but holds steady--in fact, I'd swear that the fets get cooler when the amp is playing music.
I think that I sent you matched 170/74 ; P to N
Here's a Wakefield 392-300AG heatsink given to me from a fellow carpenter. He had no idea what it was, but thought I might be able to put it to good use.
I purchased a mate for it at a cost of $160.00. This will be my first F4. For the rest of the F4s, I'm going to play with water cooling.
Caps in PS are 47,000uF each.
I purchased a mate for it at a cost of $160.00. This will be my first F4. For the rest of the F4s, I'm going to play with water cooling.
Caps in PS are 47,000uF each.
Attachments
Re: Re: N to P matching
0.18 volts you got per accident or you ordered or choosed or selected such an exact 0.18 V combination of P and N channel? Could it be 0.15 or 0.21 Volts for instance? (As far I understand 0.15 is better).
I try to understand what do I need to look/ask while ordering the set of IRFP's for my ballanced f4, two channels. In other words what is the most important: N to N matching (4xNNN in my case) and separately P to P matching (4xPPP) or matching all together what seams me to the best but probably not available for me (4xNNN AND 4xPPP). I see the IRFP240 and IRFP9240 curves are different. Sorry my language...-
a.
carpenter said:
0.18 volts you got per accident or you ordered or choosed or selected such an exact 0.18 V combination of P and N channel? Could it be 0.15 or 0.21 Volts for instance? (As far I understand 0.15 is better).
I try to understand what do I need to look/ask while ordering the set of IRFP's for my ballanced f4, two channels. In other words what is the most important: N to N matching (4xNNN in my case) and separately P to P matching (4xPPP) or matching all together what seams me to the best but probably not available for me (4xNNN AND 4xPPP). I see the IRFP240 and IRFP9240 curves are different. Sorry my language...-
a.