DSO Quad bandwidth

--DSO203

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flyingdave
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Re: DSO Quad bandwidth

Post by flyingdave » Sat Jul 23, 2011 7:42 pm

bielec

What hardware did you modify (2.2 or 2.6)?

I have just received my V2.60 DSO Quad and want to get the best performance possible. Is it worth me repeating your mods?

Thanks, Dave

bielec
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Re: DSO Quad bandwidth

Post by bielec » Sun Jul 24, 2011 2:32 am

Flyingdave,

My quad was the latest version. If you are using the scope for audio measurements then you won't notice any improvement by modifying it. The changes improve the upper frequency response and risetime on some of the voltage ranges. You would notice this when using the scope near the upper end of the frequency scale. The mods are fiddly so only attempt them if you are confident using a miniature soldering iron.

flyingdave
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Re: DSO Quad bandwidth

Post by flyingdave » Sun Jul 24, 2011 2:45 am

Bielec

Thanks. I might give it a try - my main use for the Quad is to look at PAL Video, so it would be good if 4.43 MHz wasn't too far down (<3db).

What size smd components did you use - most of my stock is 0805, which is probably too big?

Dave

bielec
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Re: DSO Quad bandwidth

Post by bielec » Sun Jul 24, 2011 7:13 am

I actually used a mixture of 1206 and 0805 s/m capacitors and for the smaller values I used two pieces of thin single core teflon insulated wire tightly twisted together. This arrangement could be adjusted to give best response.

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Re: DSO Quad bandwidth

Post by webmaster » Wed Jul 27, 2011 3:52 am

Hi,

Finally, what's the BW of the quad ?

Thanks

geshsoft
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Re: DSO Quad bandwidth

Post by geshsoft » Wed Jul 27, 2011 8:11 am

Well, mine stock had 3dB anywhere from 400kHz to 1Mhz depending on the vertical scale selection.
After patching up the front end the 3dB is now shy of 11Mhz for vertical scale settings. I implemented similar to bielec's solution (almost the same). The parts I used are low drift resistors (25ppm 0603) and NP0 0603 capacitors.

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Re: DSO Quad bandwidth

Post by glt » Wed Jul 27, 2011 1:21 pm

Anyone has example traces for >2Mhz?
When I hook up a signal (which I think is) >1.x MHz, I dont see the trace (flat), but the frequency counter says 2.x Mhz.

Thanks!

flyingdave
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Re: DSO Quad bandwidth

Post by flyingdave » Wed Jul 27, 2011 8:07 pm

geshsoft

What resistors did you change? bielec only mentioned capacitors.

Thanks

Dave

geshsoft
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Re: DSO Quad bandwidth

Post by geshsoft » Fri Jul 29, 2011 12:14 am

flyingdave my bad about the resistors - I changed 2 and reverted back to the original as they made no difference, so it is just capacitors really.

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Re: DSO Quad bandwidth

Post by noname » Mon Aug 22, 2011 12:44 am

ATTENTION, DO NOT BOTHER PERFORMING THE MOD BELOW. I just did it and I still have a damn sine wave on my screen when wave out is set to square wave at 6-8MHz (no improvement). How disappointing. This scope is pretty much worthless above 1 MHz. So much for the quad :(
bielec wrote:I have modified my scope to increase the bandwidth as follows....

For ch A.
Remove C73
C11=1.5pF
Across R17 3.3pF
Across R21 22pF
C9=1.5pF
Across R15 3.3pF
Across R19 12pF

For ch B.
Remove C74
C12=1.5pF
Across R18 2.2pF
Across R22 15pF
C10=1.5pF
Across R16 2.2pF
Across R20 12pF

I now get about 10MHz sinewave bandwidth on all ranges and good pulse response with minimal overshoot and rounding. Trigger and good display of sub 100nS pulses is now possible. As delivered, the scope had less than 1MHz B.W. and poor risetime which varied depending on range.

I would suggest the above values are used as a guide, for experimentation, and I hope it may help others get better performance.

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