On 7/10/19 9:18 AM, wrote:
On Monday, 1 July 2019 16:36:27 UTC+1, blisca wrote:
Hi to all the people here

I bought the old preamplifier,i remember it as pretty silent,and
the "apparent" S/N ratio is further increased by the proprietary
noise gate called "H.U.S.H." This is a good pic of the board ,found
on a website
https://images.reverb.com/image/uplo...aqvapl3ygx.jpg


I'm finding it a bit too noisy,and this noise sounds as "digital
noise",more than white noise..it sounds like the frequencies
composing the noise are related to the activity of the segments
digits of the display.Adding a piece of wire as antenna to the
resistors between IC driver and display increases some particular
frequency to the heared noise,confirming my impression . I tried
shorting ground points with good cables,it does not change
anything. I tried adding some metallic shield with minimal or null
impact. I ask your opinion about the decoupling capacitors,they are
1uF ceramic capacitors,with relatively long leads.Do yout think
that it is worth replacing them?Maybe with SMD capacitor directly
to IC VDD and GND? Another idea is to replace the displays with new
ones more efficient,needing much less current,and then ,to increase
the resistor values,less current=less noise,but i still dont know
if such display exists. I would like to know your opinion. Thanks
for your time Diego

The simple way to find out if replacing a cap will help is to bridge
it with another cap. If the original is ok, it makes no difference.
If the original is bad, it solves the problem. Sometimes you can just
hold the 2nd cap & touch it onto other caps one after another to dx a
fault.

That's a great way to blow stuff up, too.

Cheers

Phil Hobbs


--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com