@AndrewT;
I'll measure P1&P2 tonight.
@Jim;
I'm thinking the same thing
But I don't want to risk anything. I'll try to increase resistance. As I read Fairchild mosfets needs 4V to turn on.
Mine did fine with standard pot values, but I used Toshiba devices. I will say that I turned quite a bit before any reaction occurred on the meter. You may need the suggested pots from the BA-3 Power Amp build for the Fairchild units?
You will love the Pre!
Russellc
Success! Yes, pots needed lots of turns. Both channels biased to 1V. Mosfets temperature almost 55°C after half an hour. I need bigger heatsink IMO. Offset seems jumpy! Tried to minimize but I couldn't. It jumps to -15 to + 20mV all the time. Before cap, after cap measurement more or less same.
I'll connect BA-3 FE to my F5 for audition.. Late in here... baby sleeping.. I'll have to wait for tomorrow..
I'll connect BA-3 FE to my F5 for audition.. Late in here... baby sleeping.. I'll have to wait for tomorrow..
This "jumpy" output offset could be due to too small heatsinks, or due to lid off allowing draughts (drafts) to cool some parts, or due to a fault.
Check thoroughly to exclude a fault cause BEFORE you connect a speaker.
Think about adding a speaker protection relay while you are still experimenting with the amplifier.
Yes, I was having the greatest trouble with this.....with a ceiling fan overhead! Once I removed to another room all was well. Pearl 2 was even more touchy...exhaling over open top disturbed readings.
Russellc
Russellc
Finally I connected BA-3 FE to my system. First of all; it's working 
Whenever I connected BA-3 output to F5 input, jumpy offset gone to zero immediately and stayed around +/- 2mV.
BA-3 biased to 1V for both channels. Heatsinks will be replaced with bigger ones at the weekend.
Looks like 330ohm gain resistor is way too much for my speakers. I'll try 100 or 180ohm.
I had to use 12uf caps at the outputs, because I had them in my stash.
Soundwise, it's totally different from B1. I noticed higher frequencies sounds like there is a sibilance. Is it related with my output cap choise? Or is it time to play with P3?
Whenever I connected BA-3 output to F5 input, jumpy offset gone to zero immediately and stayed around +/- 2mV.
BA-3 biased to 1V for both channels. Heatsinks will be replaced with bigger ones at the weekend.
Looks like 330ohm gain resistor is way too much for my speakers. I'll try 100 or 180ohm.
I had to use 12uf caps at the outputs, because I had them in my stash.
Soundwise, it's totally different from B1. I noticed higher frequencies sounds like there is a sibilance. Is it related with my output cap choise? Or is it time to play with P3?
What lower limit do you want for the frequency passband?
What impedance loads the coupling capacitor?
Using Capacitance = 1/2piRFrequency you can select a suitable coupling capacitor value.
In my systems I generally use 100k as my Rin.
My passband is usually 2Hz to 200kHz (i.e. one decade wider than the audio band).
That allows me to use a plastic film coupling capacitor.
I can't tell the difference between a 1uF MKT and a 1uF MKP.
What impedance loads the coupling capacitor?
Using Capacitance = 1/2piRFrequency you can select a suitable coupling capacitor value.
In my systems I generally use 100k as my Rin.
My passband is usually 2Hz to 200kHz (i.e. one decade wider than the audio band).
That allows me to use a plastic film coupling capacitor.
I can't tell the difference between a 1uF MKT and a 1uF MKP.
In addition;
Is it a good idea to remove 12uf film cap and use 10uf Elna or Muse electrolytic and bypass them with 0.1uf pio caps?
I can also use 8.2uf mundorf polypropylene cap instead of 12uf. Unfortunately don't have any 10uf at hand
I also removed my film cap for an Elna 10uh. Better sound with a lot better soundstage. A premium film might be best but the Elna sounds so good why bother.
Is it normal to hear faint music coming from the BA-3 pcb itself?
I listen BA-3 and F5 tonight, then I turned off F5. When I try to reach BA-3 chassis on/off switch, I heard a very faint music coming from inside the chassis. Increasing with the volume.
Please tell me it's ok.
Or am I going insane?
I listen BA-3 and F5 tonight, then I turned off F5. When I try to reach BA-3 chassis on/off switch, I heard a very faint music coming from inside the chassis. Increasing with the volume.
Please tell me it's ok.
Or am I going insane?
Is it normal to hear faint music coming from the BA-3 pcb itself?
I listen BA-3 and F5 tonight, then I turned off F5. When I try to reach BA-3 chassis on/off switch, I heard a very faint music coming from inside the chassis. Increasing with the volume.
Please tell me it's ok.
Or am I going insane?
I will "listen" to mine tonight...in the mean time, Ahh, I don't know. I have heard of tubes making sounds but mosfets? I really have no idea.
Russellc
everything is making sound
in tube amps - output xformers mostly , then tubes
in sand amps - most singing creatures are old T03 case critters , then ceramic cased ones in much smaller scale
T03 being hollow , act as resonating box
it really depends on voltage swing through critters - greater the swing , greater parasitic s(w)inging
in tube amps - output xformers mostly , then tubes
in sand amps - most singing creatures are old T03 case critters , then ceramic cased ones in much smaller scale
T03 being hollow , act as resonating box
it really depends on voltage swing through critters - greater the swing , greater parasitic s(w)inging
I've gotten some on eBay for a reasonable price.. I know there are fakes out there but the ones I've purchased have all (well mostly all, I've gotten some fake K170s but not a big surprise though) checked out with a curve tracer and sound good to me. Some of the sellers will show you original packaging with lot# etc..
Check the eBay store for alweit. Seller from IL. It's where mine came from, and I believe others have bought from him as well. I seem to recall generg buying from him as well but the these could be false memories....