fed up with bosoz

[Magura]

According to my experience the BOSOZ runs off pretty much anything between 25 and 80V, it supposedly sounds better with lower distortion around 50VDC and up, but I have not been able to hear any difference.

Magura

[cowanrg]

do you think having an 80VA per channel would be a good idea? it looks like two of those would fit perfect in the case as is. and price-wise it would be decent as well.

i just hope thats the problem!

[Magura]

80VA is plenty. I have seen people run it off 25VA trafos.

Magura

[cowanrg]

so, im re-opening this thread!

im tired of the preamp just sitting there collecting dust. i ordered a 1.7 kit from a guy on here, but after 2 months, he has yet to ship it, and still have my money. im still working it all out, he claims it was lost in the mail, but still, it sounds fishy.

anyways, i want this thing fixed and working. i have a scope now! im not entirely sure how to use it, but im pretty sure it works, and i have test leads.

i hooked it up to the wall outlet and looked at the AC voltage coming in from the wall. it looked like a nice sine wave, with just a tiny bit of distortion at the peaks. i went step by step hooking up the preamp. i started with just the transformer, and looked at it through the scope. it looked pretty much the same, nice and smooth lines.

then i hooked up the power supply board. i got +-59v, a little low, but fine. however, i tried to stick the scope probe on it, but all i got was a solid line, no matter how many knobs and dials i messed with. so obviously im doing something wrong there. or maybe it is supposed to look like that. but it was always pretty much perfect.

i hooked up the preamp circuit and measured it all, the voltages are perfect. i put the scope on the output, and same story, straight line. it kicks up and down when the amp turns on an off, but other than that, it looks the same as if the probe wasnt even plugged in...

ill try hooking up a source and see what it sounds like. maybe staying away from it for so long has made it work finally. haha, yeah right.

so, can someone tell me how i can use the scope to diagnose this problem?

[cowanrg]

an update:

i threw on an RCA connector for the output on the preamp board and plugged it into an amp i have in my shop that i use for testing. i hooked the scope up to the outputs on the amp. after fiddling with a lot of settings, i got a something that was interesting.

with the preamp off, the scope just shows a pretty much perfect straight flat line. with the preamp on, it goes a little nuts on startup (i get a buzzing at startup through the speakers, so the scope shows this), and then it shows a line that is "decent", but has some bumps in it and is a bit fuzzy or looks kinda like static. its not a perfect line anymore. and when i kick the preamp off again, or unplug it, the line jumps around a bit (turn off thump), and then stabilized to an almost perfect line again.

SO, im seeing whats going on. what can i do from here to troubleshoot? ive checked and rechecked all my components for the most part. i THINK all the components are fine. ive replaced ALL fets twice or more. where should i go from here?

[lgreen]

Originally posted by cowanrg
an update:

i threw on an RCA connector for the output on the preamp board and plugged it into an amp i have in my shop that i use for testing. i hooked the scope up to the outputs on the amp. after fiddling with a lot of settings, i got a something that was interesting.

with the preamp off, the scope just shows a pretty much perfect straight flat line. with the preamp on, it goes a little nuts on startup (i get a buzzing at startup through the speakers, so the scope shows this), and then it shows a line that is "decent", but has some bumps in it and is a bit fuzzy or looks kinda like static. its not a perfect line anymore. and when i kick the preamp off again, or unplug it, the line jumps around a bit (turn off thump), and then stabilized to an almost perfect line again.

SO, im seeing whats going on. what can i do from here to troubleshoot? ive checked and rechecked all my components for the most part. i THINK all the components are fine. ive replaced ALL fets twice or more. where should i go from here?

1. If your bosoz is making 60hz humming noise, you should be able to see it on the scope, turn your timebase down to 60hz, which is about 1/60= 16.6ms/div, so use 20 or 10ms/div. Your trace will slow down, as it goes across the screen.

then turn your v/div on the input amps up till you see the hum as a pattern of waves or partial waves on the screen.

2. turning up the v/div on the input amps will show you all the noise that is there, the straight line will not be so straight after all once you start cranking the amp. However, you have to play with the timebase to learn where the noise is in frequency as HF and LF noise cannot be seen on the low/fast speed (ns) settings.

3. If you want to see AC make sure you select "AC couple" the waveform will not shift position if there is DC on it. this is good to look at the noise on your 60V rails, for example. You may want to see if noise is coming in from your power rails, check them out, if they have bumps then your MOSFETs are probably working right, your power supply might be bleeding the AC to the circuit.

4. You might want to look at the output and rails/input simultaneously on the screen to see if the bumps are happenning at the same time or not in the ps and amp circ.


did this help?

[sklimek]

Originally posted by cowanrg
so, im re-opening this thread!

i have a scope now! im not entirely sure how to use it, but im pretty sure it works, and i have test leads.

so, can someone tell me how i can use the scope to diagnose this problem?

Hi cowanrg, I too hope to get a scope soon, in the meantime I have been reading/studying on which ones to get on Ebay. I found a great tutorial from Tektronics on oscilloscopes that may be helpful.

http://www.tek.com/Measurement/cgi-b...=oscilloscopes

Stan

[cowanrg]

thanks for the help guys. unfortunately, i cannot see ANYTHING connected just to the preamp itself. it always shows a straight line, no matter how many knobs and dials i turn. this is also true for my meter, the meter registers almost no voltage out on the preamp. in theory, its quite.

however, here is what i see when hooking it up to an amplifier:
(no making fun of my scope)

[cowanrg]

this is with no input into the preamp at all. the phoenix connectors are completely empty. the outputs just a single rca going from + and GND to an RCA jack. then, an interconnect connects that RCA to the amplifier. i put the probe at the positive output of the amp's speaker terminal. i could of course be picking up noise from the amp itself, but without the preamp connected, there is just a straight line. so, the preamp is introducing it.

it SEEMS like its a ground loop issue, but ive tried everything. ive lifted grounds, ive shorted inputs, etc... it never goes away. and the preamp board is almost 2 feet away from the transformer, etc... this is a perfect test condition. and the power supply appears to be pretty clean.

the settings i used are: 1ms/cm, .05 v/cm, AC input.

i hope that tells someone SOMETHING. i just found a very small plitron transformer at a surplus shop. its rated at 30 watts and has 55v secondaries i believe. im going to make a small power supply using that, a couple bridge rectifiers, and some caps. i will get rid of the regulated supply and xformer, as they might be the issue. ill see if i still have noise then.

[cowanrg]

well, well, well.

i finally used a completely different power supply and the results are interesting. previously, i used the transformer that was in the original build and removed the PSU boards and just made a simple linear unregulated supply. i had the same results as with the regulated PSU boards.

well, it was said that it could be the transformer causing the issues because it was so oversized. i used this little 30 watter i got to test that theory. in the writeup for the bosoz, nelson says that you can use 30-60v rails, but at 60v, you get lowest distortion. this transformer gave me 30v rails loaded. i just used a single bridge rectifier and a pair of smaller value caps. nothing fancy at all.

the exact same noise was still there, but now it was louder. that was probably due to the lower voltage supply, and noisier supply. here is what it looked like (is that what oscillation looks like?):