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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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#1
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Rotel Bias ...
Anyone know off the top of their head, or have the manual to check what the
correct bias figure for a Rotel RB970BX Mk II is ? Working along the lines of the 'standard' 20mA figure (about 5mV across the TPs which are across a 0.22 ohm emitter resistor) the output stages idle quite cool, and I see no signs of x-over distortion on the 'scope, but would be nice to know the correct recommended figure. Arfa |
#2
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Rotel Bias ...
Arfa Daily wrote: Anyone know off the top of their head, or have the manual to check what the correct bias figure for a Rotel RB970BX Mk II is ? Working along the lines of the 'standard' 20mA figure (about 5mV across the TPs which are across a 0.22 ohm emitter resistor) the output stages idle quite cool, and I see no signs of x-over distortion on the 'scope, but would be nice to know the correct recommended figure. 20mA sounds a bit low to me. I'd go for at least 30mA. Graham |
#3
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Rotel Bias ...
Arfa Daily wrote: Anyone know off the top of their head, or have the manual to check what the correct bias figure for a Rotel RB970BX Mk II is ? Working along the lines of the 'standard' 20mA figure (about 5mV across the TPs which are across a 0.22 ohm emitter resistor) the output stages idle quite cool, and I see no signs of x-over distortion on the 'scope, but would be nice to know the correct recommended figure. 20mA sounds a bit low to me. I'd go for at least 30mA. Graham |
#4
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Rotel Bias ...
"Arfa Daily" wrote in message ... Anyone know off the top of their head, or have the manual to check what the correct bias figure for a Rotel RB970BX Mk II is ? Working along the lines of the 'standard' 20mA figure (about 5mV across the TPs which are across a 0.22 ohm emitter resistor) the output stages idle quite cool, and I see no signs of x-over distortion on the 'scope, but would be nice to know the correct recommended figure. **8mV across TP1 & TP3 & Across TP2 & TP4. Those are the figures for the RB970BX. (Not MkII). I'll try to locate the data pertaining to the model you have. Trevor Wilson |
#5
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Rotel Bias ...
"Arfa Daily" wrote in message ... Anyone know off the top of their head, or have the manual to check what the correct bias figure for a Rotel RB970BX Mk II is ? Working along the lines of the 'standard' 20mA figure (about 5mV across the TPs which are across a 0.22 ohm emitter resistor) the output stages idle quite cool, and I see no signs of x-over distortion on the 'scope, but would be nice to know the correct recommended figure. **8mV across TP1 & TP3 & Across TP2 & TP4. Those are the figures for the RB970BX. (Not MkII). I'll try to locate the data pertaining to the model you have. Trevor Wilson |
#6
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Rotel Bias ...
If you have a distortion meter -- especially one that can show the levels of
each harmonic (eg, an audio spectrum analyzer) -- you might try adjusting for the lowest distortion or the least odd-order distortion. |
#7
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Rotel Bias ...
If you have a distortion meter -- especially one that can show the levels of
each harmonic (eg, an audio spectrum analyzer) -- you might try adjusting for the lowest distortion or the least odd-order distortion. |
#8
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Rotel Bias ...
"Trevor Wilson" wrote in message ... "Arfa Daily" wrote in message ... Anyone know off the top of their head, or have the manual to check what the correct bias figure for a Rotel RB970BX Mk II is ? Working along the lines of the 'standard' 20mA figure (about 5mV across the TPs which are across a 0.22 ohm emitter resistor) the output stages idle quite cool, and I see no signs of x-over distortion on the 'scope, but would be nice to know the correct recommended figure. **8mV across TP1 & TP3 & Across TP2 & TP4. Those are the figures for the RB970BX. (Not MkII). I'll try to locate the data pertaining to the model you have. Trevor Wilson Thanks very much Trevor. That equates to not far off Graham's figure of 30mA, so that's where it's now set, and going back to the shop this morning - it's one of those jobs where the owner is panicking the shop for it on a daily basis. Customers, don't you just love 'em !! d;~} Arfa |
#9
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Rotel Bias ...
"Eeyore" wrote in message ... Arfa Daily wrote: Anyone know off the top of their head, or have the manual to check what the correct bias figure for a Rotel RB970BX Mk II is ? Working along the lines of the 'standard' 20mA figure (about 5mV across the TPs which are across a 0.22 ohm emitter resistor) the output stages idle quite cool, and I see no signs of x-over distortion on the 'scope, but would be nice to know the correct recommended figure. 20mA sounds a bit low to me. I'd go for at least 30mA. Graham I can live with that, and 30 is pretty close to Trevor's figure (see his post). Thanks Arfa |
#10
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Rotel Bias ...
"William Sommerwerck" wrote in message ... If you have a distortion meter -- especially one that can show the levels of each harmonic (eg, an audio spectrum analyzer) -- you might try adjusting for the lowest distortion or the least odd-order distortion. I do have one, but it only shows THD. I was expecting the figure to be somewhere between 20 and 50mA, and was erring on the side of caution and cool running with 20mA. It's now set for about 30 per Trevor's useful info, and heatsinks are just barely off room temp at idle. I doubt that there would be too much to be measured as a difference in THD between 20 and 30mA, and the owner probably wouldn't be able to tell the difference ... :-) Arfa |
#11
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Rotel Bias ...
"Arfa Daily" wrote in message
... "William Sommerwerck" wrote in message ... If you have a distortion meter -- especially one that can show the levels of each harmonic (eg, an audio spectrum analyzer) -- you might try adjusting for the lowest distortion or the least odd-order distortion. I do have one, but it only shows THD. I was expecting the figure to be somewhere between 20 and 50mA, and was erring on the side of caution and cool running with 20mA. It's now set for about 30 per Trevor's useful info, and heatsinks are just barely off room temp at idle. I doubt that there would be too much to be measured as a difference in THD between 20 and 30mA, and the owner probably wouldn't be able to tell the difference... :-) I'd be foolish to suggest there even _might_ be an audible difference. However, the harmonic-distortion spectrum of transistor amplifiers can vary quite weirdly with bias and signal level. |
#12
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Rotel Bias ...
"Arfa Daily" wrote in message ... "Trevor Wilson" wrote in message ... "Arfa Daily" wrote in message ... Anyone know off the top of their head, or have the manual to check what the correct bias figure for a Rotel RB970BX Mk II is ? Working along the lines of the 'standard' 20mA figure (about 5mV across the TPs which are across a 0.22 ohm emitter resistor) the output stages idle quite cool, and I see no signs of x-over distortion on the 'scope, but would be nice to know the correct recommended figure. **8mV across TP1 & TP3 & Across TP2 & TP4. Those are the figures for the RB970BX. (Not MkII). I'll try to locate the data pertaining to the model you have. Trevor Wilson Thanks very much Trevor. That equates to not far off Graham's figure of 30mA, so that's where it's now set, and going back to the shop this morning - it's one of those jobs where the owner is panicking the shop for it on a daily basis. Customers, don't you just love 'em !! d;~} **Some. I have a few clients who are like gold. Some, OTOH, I just never want to see again. Trevor Wilson |
#13
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Rotel Bias ...
"Trevor Wilson" wrote in message ... "Arfa Daily" wrote in message ... "Trevor Wilson" wrote in message ... "Arfa Daily" wrote in message ... Anyone know off the top of their head, or have the manual to check what the correct bias figure for a Rotel RB970BX Mk II is ? Working along the lines of the 'standard' 20mA figure (about 5mV across the TPs which are across a 0.22 ohm emitter resistor) the output stages idle quite cool, and I see no signs of x-over distortion on the 'scope, but would be nice to know the correct recommended figure. **8mV across TP1 & TP3 & Across TP2 & TP4. Those are the figures for the RB970BX. (Not MkII). I'll try to locate the data pertaining to the model you have. Trevor Wilson Thanks very much Trevor. That equates to not far off Graham's figure of 30mA, so that's where it's now set, and going back to the shop this morning - it's one of those jobs where the owner is panicking the shop for it on a daily basis. Customers, don't you just love 'em !! d;~} **Some. I have a few clients who are like gold. Some, OTOH, I just never want to see again. Trevor Wilson Amen to that, Trevor !! Arfa |
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