I tried to buy a series of the earlier amps and kits, but got burned.
I built up a more recent version. I am not impressed. Adequate would be my description.
Hi,
I double checked my wiring for the external bias board.
Upon power up the voltage across the 10ohm resistor measures 400mV
The negative rail 100mV less.
The problem Im having the bias voltage keeps increasing, after maybe 30 seconds
It increased to 700mV without any adjustment?
How stable is the bias voltage? Or do I have to wait 30 minutes to get stable?
I do have shorting plugs on the inputs.
How stable is it overall? Any issues with open chassis?
Thanks
I double checked my wiring for the external bias board.
Upon power up the voltage across the 10ohm resistor measures 400mV
The negative rail 100mV less.
The problem Im having the bias voltage keeps increasing, after maybe 30 seconds
It increased to 700mV without any adjustment?
How stable is the bias voltage? Or do I have to wait 30 minutes to get stable?
I do have shorting plugs on the inputs.
How stable is it overall? Any issues with open chassis?
Thanks
check the trimpot position. is it correct ? last exp i cant adjust it coz my trimpot is upside down. second check driver bd139 should be fasten to read the heat and it should be one heatshink or mount above it. . other wise it will continue to increase. if it short the 10 R should be hot. if not than you are ok. despite heat that generate from high bias. (thats all i know coz i'm new comer 
)
goodluck
)goodluck
Hi Bengali,
Just a couple of points that may help.
IMHO the 10 ohms protective resistor should only initially be in the circuit to ensure the circuit has been built correctly and the Vbias pot is set roughly correct. The Vbias should be set without the 10 ohm resistor in place. You don't need the input shorted to adjust Vbias. The stability of Vbias will depend on size of heatsink and where you mounted the Vbias transistor.
DC offset will vary slightly. Short the input for DC offset measurements. Single digit mV is more than adequate. When you turn the amp on and off the DC offset will change dramatically. DC offset is a function of how closely the LTP input transistors have been matched and current through these transistors. Personally, I am happy with 30mV DC offset.
I haven't played with the DX amp for many years, but I think the adjustment DC offset effects the Vbias also. So you need to adjust the DC offset and recheck the Vbias, then the DC offset. IMO the Vbias setting is more important than the DC offset.
regards
Just a couple of points that may help.
IMHO the 10 ohms protective resistor should only initially be in the circuit to ensure the circuit has been built correctly and the Vbias pot is set roughly correct. The Vbias should be set without the 10 ohm resistor in place. You don't need the input shorted to adjust Vbias. The stability of Vbias will depend on size of heatsink and where you mounted the Vbias transistor.
DC offset will vary slightly. Short the input for DC offset measurements. Single digit mV is more than adequate. When you turn the amp on and off the DC offset will change dramatically. DC offset is a function of how closely the LTP input transistors have been matched and current through these transistors. Personally, I am happy with 30mV DC offset.
I haven't played with the DX amp for many years, but I think the adjustment DC offset effects the Vbias also. So you need to adjust the DC offset and recheck the Vbias, then the DC offset. IMO the Vbias setting is more important than the DC offset.
regards
Thank you Greg.
I guess now its just hooking up some speakers and trying it out.
I did remove the 10 ohm resistors. DC offset still jumping around but still under 30mV
What is considering damaging for turn on thump? I dont have a scope dont know what the duration is but I definately see it with the volt meter. I will increase range and see what it is if I can catch it.
under closed chassis, at temperature rises, the the bias voltage increase or decrease?
I guess now its just hooking up some speakers and trying it out.
I did remove the 10 ohm resistors. DC offset still jumping around but still under 30mV
What is considering damaging for turn on thump? I dont have a scope dont know what the duration is but I definately see it with the volt meter. I will increase range and see what it is if I can catch it.
under closed chassis, at temperature rises, the the bias voltage increase or decrease?
Hello andrewT
I have 30 0 30 AC with 3A transformer can I get 100 watts stereo through Dx with this supply.And can you suggest good pre-amplifier for DX amplifier.
I have 30 0 30 AC with 3A transformer can I get 100 watts stereo through Dx with this supply.And can you suggest good pre-amplifier for DX amplifier.
Do the math. 30-0-30 Volts = 60 Volts. Multiply that wit 3 Amps, thats 180 Watt.
You can (roughly) get one channel with 100 Watt on a good day.
Best regards Ebbe
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