Hi
I have had some hum problems which I thought were caused by bad grounding or lack of sheilding, which was more than likey considering my current "prototype-test" setup
.
I've discovered to my surprise that it is my preamp which isn't too happy driving my active XO
(read: it oscillates big time 
)
My preamp is a pot infront of 3 stacked buf634.
Adding a series resistor to the output of the preamp fixed the problem. Currently I'm using a 800 ohm resistor (lowest value I had around) which I would think is way too high (unqulified guess).
What resistor value is normal to use for this???
I have had some hum problems which I thought were caused by bad grounding or lack of sheilding, which was more than likey considering my current "prototype-test" setup
.I've discovered to my surprise that it is my preamp which isn't too happy driving my active XO
(read: it oscillates big time )My preamp is a pot infront of 3 stacked buf634.
Adding a series resistor to the output of the preamp fixed the problem. Currently I'm using a 800 ohm resistor (lowest value I had around) which I would think is way too high (unqulified guess).
What resistor value is normal to use for this???
J P,
why stacking ? isn't 250mA enough ?
OK, what did you do with pin#1, aka the BandWith pin, ?
Leave it unconnected for less BW, but still more than enough for audio.
The application notes suggest an input R of 25 to 200 ohm.
I for myself had good experience with small input resistors at high speed buffers to eliminate oscillations.
Also the output R is advised between 10 to 150 ohms, but for each unit like Jan says, if still staggering.
Hope this helps
Dick.
why stacking ? isn't 250mA enough ?
OK, what did you do with pin#1, aka the BandWith pin, ?
Leave it unconnected for less BW, but still more than enough for audio.
The application notes suggest an input R of 25 to 200 ohm.
I for myself had good experience with small input resistors at high speed buffers to eliminate oscillations.
Also the output R is advised between 10 to 150 ohms, but for each unit like Jan says, if still staggering.
Hope this helps
Dick.
>OK, what did you do with pin#1, aka the BandWith pin, ?
>Leave it unconnected for less BW, but still more than enough for audio.
A 100 ohm resistor to the - rail. People claim it sound better this way. I only know it gets a bit warm
Regarding the stacking:
In the "Combining an amplifier with the buf634" application note they stack 3 buf634 with no seperate input or output resistors only one common ouput resistor (50 ohm).
I read somewhere that the buf634 has an output impedance of 10 ohm, so I though the an isolation resistor wasn't needed.
When I open my eyes and read the buf634 datasheet, it says: "Best response is usually achieved with a series input resistor of 25 to 200 ohm, depdending of the signal source. Response with some loads (especially capacitive) can be improved with a resistor of 10 to 150 ohm in series with the output".
A pot infront of the buf won't that act like a series resistor?
>Leave it unconnected for less BW, but still more than enough for audio.
A 100 ohm resistor to the - rail. People claim it sound better this way. I only know it gets a bit warm
Regarding the stacking:
In the "Combining an amplifier with the buf634" application note they stack 3 buf634 with no seperate input or output resistors only one common ouput resistor (50 ohm).
I read somewhere that the buf634 has an output impedance of 10 ohm, so I though the an isolation resistor wasn't needed.
When I open my eyes and read the buf634 datasheet, it says: "Best response is usually achieved with a series input resistor of 25 to 200 ohm, depdending of the signal source. Response with some loads (especially capacitive) can be improved with a resistor of 10 to 150 ohm in series with the output".
A pot infront of the buf won't that act like a series resistor?
Probably not oscillating
If you have used the stacked BUF634 in high bandwidth mode they are going to throw out a lot of heat even when not driven. Three stacked ones in high bandwidth mode will run 45 mA undriven. See p. 5 of the info sheet.
There's no functional need to run in full bandwidth mode. A 300 ohm resistor for each BUF634 will give you 3 x 7mA and still good bandwidth. Norman
If you have used the stacked BUF634 in high bandwidth mode they are going to throw out a lot of heat even when not driven. Three stacked ones in high bandwidth mode will run 45 mA undriven. See p. 5 of the info sheet.
There's no functional need to run in full bandwidth mode. A 300 ohm resistor for each BUF634 will give you 3 x 7mA and still good bandwidth. Norman
>"Passive Buffered"? How the hell did you determine that? It is either one or the other.
I didn't come up with that name. It is a copy of http://www.stereophile.com/amplificationreviews/54/
I skiped one buf634, so I could fit input and putput resistors to the 2 that was left.
The guys at headwize stacks buffers, ok they drive headphones and not amps, but I thought why not try when I have them around anyway.
I didn't come up with that name. It is a copy of http://www.stereophile.com/amplificationreviews/54/
I skiped one buf634, so I could fit input and putput resistors to the 2 that was left.
The guys at headwize stacks buffers, ok they drive headphones and not amps, but I thought why not try when I have them around anyway.
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