Finally a comparison to the HP339a:
Me thinks the HP339a has lower distortion products.
Buy a long shot too.
Don't take my word on it, see for yourself, here:
So if I read This right, I kould start with -108.9 dB then add -10 dB equals _118.9dB.
So that should be total distortion for the H:339A? Not too bad. IF I did the maths right.
Cheers yall. Ok we've got to find someone else to figure out how to make these things
function better. So who's all interested in making theirs better?
I am (Sync)
Euro21?
SkiDave?
Maybe some guys from the -- Dead thread.
Any one else ready have one or interested?
Come on down, we'll lstart right away.
We've got two baselines and with Ski, we can have 3 or more before we start.
What do you think, ready to make a go at it>
Cheers,
Me thinks the HP339a has lower distortion products.
Buy a long shot too.
Don't take my word on it, see for yourself, here:
So if I read This right, I kould start with -108.9 dB then add -10 dB equals _118.9dB.
So that should be total distortion for the H:339A? Not too bad. IF I did the maths right.
Cheers yall. Ok we've got to find someone else to figure out how to make these things
function better. So who's all interested in making theirs better?
I am (Sync)
Euro21?
SkiDave?
Maybe some guys from the -- Dead thread.
Any one else ready have one or interested?
Come on down, we'll lstart right away.
We've got two baselines and with Ski, we can have 3 or more before we start.
What do you think, ready to make a go at it>
Cheers,
Last edited:
Sync, big delays on my part due to cold crappy weather. It will be some time before I get some measurements... Sorry about that. Send some warm DRY weather my way!
SKI,
I would but you know down here in Texas we NEED some warm
dry weather ourselves. Hope you had a good vacation.
Cheers,
Sync, can you summarize what are the pending issues/improvements you want to make (your wishlist).
If the genererator is working and within its specs, there is probably little that can realistically be done
If the genererator is working and within its specs, there is probably little that can realistically be done
Elvee,
Ja,
I'd like to lower distortion and noise of the unit.
Have more tuning accuracty of the pots for the better accuracy.
Was trying ot replace the 741 opamps, didn't know how to
optimize them when changing.
Wondering then if the output devices themselves might be
replaced with lower noise units.
If replacing electrolytics, with better units, any virtue
with going 2x or more on uF value?
The unit is specd at .5% or -46 dB, was wondering
the possibility of getting it down to .01 % or -80dB.
For a reduction of about 20 dB. Doable
or pie in the sky kind of stuff?
Ja,
I'd like to lower distortion and noise of the unit.
Have more tuning accuracty of the pots for the better accuracy.
Was trying ot replace the 741 opamps, didn't know how to
optimize them when changing.
Wondering then if the output devices themselves might be
replaced with lower noise units.
If replacing electrolytics, with better units, any virtue
with going 2x or more on uF value?
The unit is specd at .5% or -46 dB, was wondering
the possibility of getting it down to .01 % or -80dB.
For a reduction of about 20 dB. Doable
or pie in the sky kind of stuff?
Frequency Caps
I was expecting a lot of drift in the caps,
especially the caps for frequency adjustment,
yes I know, I actually adjust the pot.
Figured they drifted a bit, but no. They were
all pretty close to being spot on. Surprising me
further was the low D they all had, from 0.00 to 0.03
for the higher frequency caps. That is,
until I went back through the parts list and
read they were all Mica caps, even the 10uf 100V
cap. And here I thought they were all film
and drifted....
I was expecting a lot of drift in the caps,
especially the caps for frequency adjustment,
yes I know, I actually adjust the pot.
Figured they drifted a bit, but no. They were
all pretty close to being spot on. Surprising me
further was the low D they all had, from 0.00 to 0.03
for the higher frequency caps. That is,
until I went back through the parts list and
read they were all Mica caps, even the 10uf 100V
cap. And here I thought they were all film
and drifted....
Distortion can be reduced by trimming the triangle to sine circuit. Check that the amplitude of the triangle input has exactly the correct value, that is the most sensitive parameter.
You have to identify the origin of the noise to cure it: is it ripple intruding from the PSU, HF oscillation, noisy component like a resistor?
Use better pots: cermet, plastic track or similar
The 741's are used for non-critical, mainly DC jobs. There is little to be earned by changing them.
For the ones having no offset trim connected, you could always sub TLO81's, but I don't think you'll see a difference
That won't make a difference
Replacing the electro's is probably a good idea, but I am not too sure about systematically doubling their value: in principle, it should be OK, but you always find exceptions here and there
No way: this kind of sine generation arrives at the very best at 0.1% for top notch instruments, a more normal value is 0.2, 0.3%.
If you are unlucky with your instrument, you will stay stuck at 0.5%: not each and every component in the sine converter is adjustable, and if the tolerances conspire in the wrong direction, that will remain the floor whatever....
Thanks, Elvee.
Will have to look at that triangle to sine part of circuit closely.
It is pretty clean right now.
No body seems to like the 741 opamp, the other
Leader thread here had several that were going to rid
themselves of the 741.
Opamp swap was an easy swap for me as sockets
were already installed. But circuit was non optimized.
I could probably fool around but might make things worse.
Just plugging in opamps didn't help.
When I checked the output pin, 6 of the 741s
I didn't see any "ugliness" or bad signal on
my scope.
I also can't look confidently below about 20 Hz
and above 24kHz with my little QA400, it does
its job.
Caps, I'm wondering what I can get away with
in the PS Filtering. The other electrolytics
look like are mainly used for shunts, why
not increase filtering to ground?
Danke
Will have to look at that triangle to sine part of circuit closely.
It is pretty clean right now.
No body seems to like the 741 opamp, the other
Leader thread here had several that were going to rid
themselves of the 741.
Opamp swap was an easy swap for me as sockets
were already installed. But circuit was non optimized.
I could probably fool around but might make things worse.
Just plugging in opamps didn't help.
When I checked the output pin, 6 of the 741s
I didn't see any "ugliness" or bad signal on
my scope.
I also can't look confidently below about 20 Hz
and above 24kHz with my little QA400, it does
its job.
Caps, I'm wondering what I can get away with
in the PS Filtering. The other electrolytics
look like are mainly used for shunts, why
not increase filtering to ground?
Danke
Sync,
Finally caught up on weather related issues at home (for now). Here is how my unit measures.
This is .5 volts out with a 50 ohm terminator:
I checked the THD+N on my HP 8903 and it matches.
What Euro21 said about the sine wave quality is correct. Function generators have their place...not for testing equipment distortion! But...it is all that I had way back when. I've come far and have a way to go!
Dave
Finally caught up on weather related issues at home (for now). Here is how my unit measures.
This is .5 volts out with a 50 ohm terminator:
I checked the THD+N on my HP 8903 and it matches.
What Euro21 said about the sine wave quality is correct. Function generators have their place...not for testing equipment distortion! But...it is all that I had way back when. I've come far and have a way to go!
Dave
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