worth using the Mains Bulb Tester for first Power ON.
If the bias is inadvertently set high, then the bulb will glow and maybe brightly, indicating excess current draw.
After that safe Power ON has confirmed that the bias pots are set to zero ohms, one then powers ON direct from the mains and sets the bias using pots p1 & p2.
If the bias is inadvertently set high, then the bulb will glow and maybe brightly, indicating excess current draw.
After that safe Power ON has confirmed that the bias pots are set to zero ohms, one then powers ON direct from the mains and sets the bias using pots p1 & p2.
Thanks Andrew. It is biasing nicely. cooking now at about 900mV, lid on. Offset about 30-40mV. I don’t know the moment I should try it with amp. By the way, the DMM for the offset I attached it to the lead of R12 that looks into C3, as the lead of C3 is absolutely not reachable. I reckon it is the same.
Just make sure there is no dc after the cap (you can test at the rca jack) and you should be ready to try it out. Since you have the bias and dc offset adjustments acting correctly and this preamp has an output cap there is not really much that can go wrong. It will likely work fine. If it doesn’t it’s likely the input or output wiring. If you are worried about hooking it up to your speakers try it first with a cheap pair of headphones. The ba-3 can also be used as a headphone amp although it’s not a very good one.
I’d try to get as much bias as possible... 1v is good. I think I had about 1.25v on mine. Watch the heatsink temp. Depending on your heatsinks you may be able to go higher. Bias effects dc offset so you need to go through the biasing/dc nulling process again if you change bias. But 1v is a good starting point.
I’d try to get as much bias as possible... 1v is good. I think I had about 1.25v on mine. Watch the heatsink temp. Depending on your heatsinks you may be able to go higher. Bias effects dc offset so you need to go through the biasing/dc nulling process again if you change bias. But 1v is a good starting point.
Sorry guys, too busy with work and preparing for a christmas journey. I will be back in a couple of weeks and recheck everything. So far I'm listening to the preamp quite happily. Sound improvement? Well, my F6 sounded quite well already, so not much to comment. What I have is a bit of hiss at high volumes. But nothing bothering.
Thanks a lot for your advice. And have a nice Christmas time.
Thanks a lot for your advice. And have a nice Christmas time.
Can anyone advice on the heat sink which fits diyStore PCB for this preamp: Burning Amplifier Gain Stage for BA-3 – diyAudio Store
Power MOSFETs are pretty close together so I don't like to end up with too big one, but it also needs to be able to dissipate enough heat assuming standard bias with some room for experiments.
Power MOSFETs are pretty close together so I don't like to end up with too big one, but it also needs to be able to dissipate enough heat assuming standard bias with some room for experiments.
They don't have to be very big. Something like this HEAT SINK would work.
I can't tell you exactly what part # I used in my build. I can't access my history at Mouser for some reason. Anyone else have this problem?
Edit: sorry for the bad link. Should be fixed now
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Good to know. I was thinking about a bit bigger one: 504222B00000G Aavid Thermalloy | Mouser Ireland It seems just about to fit so I guess I'll stay with it.
