Control board
- Thread starter FredR
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Ed said Quote "You may also want to measure the value of the 10 ohm resistors (R128 and R180) located in the output stage. Most amplifiers had carbon composition type which are going up in value with age, etc. Ideally they should be 10 ohms which makes adjusting the bias a little easier. However they are usually a 10% tolerance part and the "DC voltage drop" will measure differently between the (2) resistors when the resistors are not closely matched in there values. I am beginning to replace these as a matter of course as they have caused me some grief."
Are these 1/2W resistors from Mouser a good choice to replace the 10 Ohm bias resistors in PL amps?
https://www.mouser.com/ProductDetail/660-MF1-2CCT52R10R0F
Are these 1/2W resistors from Mouser a good choice to replace the 10 Ohm bias resistors in PL amps?
https://www.mouser.com/ProductDetail/660-MF1-2CCT52R10R0F
I guess I was confused. If the temp swing is no more than 45C, then why spec a resistor to 230C?
Sorry, it is taking me awhile to get back into this fantastic hobby after being away for awhile. There have been some improvements in technology over the past five years. Some of the parts I previously used are no longer available. I just want to use the best engineered parts, consistent with availability and value, for the designed functionality. I like to hear what parts & techniques other forum members are using, and I like to do independent research. Please excuse me if I go too far afield, sometimes I find myself talking to the only person in the room, me.
Sorry, it is taking me awhile to get back into this fantastic hobby after being away for awhile. There have been some improvements in technology over the past five years. Some of the parts I previously used are no longer available. I just want to use the best engineered parts, consistent with availability and value, for the designed functionality. I like to hear what parts & techniques other forum members are using, and I like to do independent research. Please excuse me if I go too far afield, sometimes I find myself talking to the only person in the room, me.
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Hi Mark
They rate these resistors for applications much more severe than we use them in. These resistors are loafing with a huge amount of derating in our typical application. For the bias application, the dissipation is ~13mW but the resistors are rated for 1000mW which means that our derating factor is 98.7%. Huge.
On tempco, if we see a 45C swing inside the chassis then something is seriously wrong (like all the air vents have been blocked up. So that 45C swing we talked about really represents a corner case.
They rate these resistors for applications much more severe than we use them in. These resistors are loafing with a huge amount of derating in our typical application. For the bias application, the dissipation is ~13mW but the resistors are rated for 1000mW which means that our derating factor is 98.7%. Huge.
On tempco, if we see a 45C swing inside the chassis then something is seriously wrong (like all the air vents have been blocked up. So that 45C swing we talked about really represents a corner case.
Sometimes I think of myself as George Bailey, "...this business of nickels and dimes and spending all your life trying to save three cents on a length of pipe."
I see how the bias resister function could be accomplished with a wet Popsicle stick, but we love these amplifiers and simply want the best, so we derate or over-rate the specifications of the resistors (and other parts) to some degree that makes engineering sense. How much engineering sense and associated cost is a subjective decision. I myself enjoy the hunt for the best parts that I can find, to effectively do the job at the least cost, if cost is a factor; and I think it should be while some may disagree. I would say no to $600 interconnects when the $24 Radio Shack cables perform just as well, subjectively, to me.
I see how the bias resister function could be accomplished with a wet Popsicle stick, but we love these amplifiers and simply want the best, so we derate or over-rate the specifications of the resistors (and other parts) to some degree that makes engineering sense. How much engineering sense and associated cost is a subjective decision. I myself enjoy the hunt for the best parts that I can find, to effectively do the job at the least cost, if cost is a factor; and I think it should be while some may disagree. I would say no to $600 interconnects when the $24 Radio Shack cables perform just as well, subjectively, to me.
Joe, thank you for clarifying. The side note part of the release notes mention the .33 ohm emitter resistor, but I thought that only applied to the backplane kits. I ignored that because I was not using the kits this time around. Re-reading the note, I see it is a general, and not a specific, change in the application of the specs of the emitter resistors and the base-emitter resistors for the pre-drivers.
Are these the ones from Mouser that you use?
660-MOSX3CT631RR33G
Are these the ones from Mouser that you use?
660-MOSX3CT631RR33G
Last edited:
Ed Is this correct I'm little confused.
Converted the text to this as I read it, w ***
700 series II fully comp amp PL-36 pc boards.
1. This involves removing the 120pF cap (C106/C206) that is in series with the 12K ohm resistor (R128/R129) next to Q106/Q206 ******** R119/R219************************
2. and installing a 56pF cap in parallel with the 12K ohm resistor. This will greatly reduce the classic crossover notch and THD levels (particularly at lower volume levels) that you see with many Phase Linear amps (at 1kHz, 1 watt, 8 ohms). In which case the bias should be adjusted to approximately ********************Add Jumper?*************
3. 385mV (which also works better when the 10 ohm resistors are nearer the nominal value of 10 ohms).
I have made 2-drawing and this is the second one which I think is correct? (I love Drawing not Text)
Thanks anybody who has done this?
Converted the text to this as I read it, w ***
700 series II fully comp amp PL-36 pc boards.
1. This involves removing the 120pF cap (C106/C206) that is in series with the 12K ohm resistor (R128/R129) next to Q106/Q206 ******** R119/R219************************
2. and installing a 56pF cap in parallel with the 12K ohm resistor. This will greatly reduce the classic crossover notch and THD levels (particularly at lower volume levels) that you see with many Phase Linear amps (at 1kHz, 1 watt, 8 ohms). In which case the bias should be adjusted to approximately ********************Add Jumper?*************
3. 385mV (which also works better when the 10 ohm resistors are nearer the nominal value of 10 ohms).
I have made 2-drawing and this is the second one which I think is correct? (I love Drawing not Text)
Thanks anybody who has done this?
