Critique my noise gate

craigmillard · March 29, 2018, 06:19:14 PM

The chip is a that4301 that has a vca, RMS detector and a few op amps in one.

I'm not 100% on how the RMS detector part is working, I have basically followed the datasheet here for the most part:

http://www.thatcorp.com/datashts/dn100.pdf

I understand the majority just not how the threshold is supposed to be working ?

Sent from my Plus E using Tapatalk

craigmillard · March 29, 2018, 06:23:36 PM

From the datasheet:

U2A and U2B are connected as comparators, with VR3 providing a means for adjusting the threshold. While the signal is above threshold, the LM393 steals all the current from Q1,and the output of U2B is forced low. In the steady state condition, the output of U3A (weused a FET input op-amp) will be high.

This makes sense but I can't get the pot to act right with guitar, its all or nothing: (

Sent from my Plus E using Tapatalk

Kipper4 · March 29, 2018, 07:39:40 PM

Is it Intended for line out use?

craigmillard · March 30, 2018, 05:19:23 AM

Originally I believe so.. Any idea to adjust it down to guitar levels?

Sent from my Plus E using Tapatalk

Kipper4 · March 30, 2018, 06:21:26 AM

Or maybe bring it up to line level

https://cgs.synth.net/modules/cgs60_sba.html

craigmillard · March 30, 2018, 06:42:00 AM

Had thought of it that way! The datasheet states its set for -10dbu and guitar is about -20dbu... So if I set the first buffer as a amp to increase it a bit and see what happens, might need to switch the first path around so the side chain doesn't effect the signal chain and boost that! What do you think?

Thanks for the help kipper, good to have someone to bounce this off:)

Sent from my Plus E using Tapatalk

craigmillard · March 30, 2018, 06:48:07 AM

Hadn't*

Sent from my Plus E using Tapatalk

craigmillard · March 31, 2018, 07:09:30 PM

Had a go at boosting the guitar in and it didn't make too much difference. Although for some reason q1 now heats up and magic smoke appears:(

I have messed about with this board to much now so thinking of re cutting and starting from scratch!

While hunting for what is causing q1 issues I noticed an odd trace on my board, looks like my CNC couldn't get between this bit and left copper remnants! Its bridging the threshold pot to the RMS input cap, I suspect this has been my problem all along!!! The track looks like its ment to be there so never questioned it, so frustrating!!

Anyhow, if anyone has ideas on why q1 is heating up that would save me yet more time getting this f%£ker to work.. from what I can tell it all looks good to me, I have verified the ICS in another board and all the diodes test good..

Sent from my Plus E using Tapatalk

craigmillard · March 31, 2018, 07:10:36 PM

Had a go at boosting the guitar in and it didn't make too much difference. Although for some reason q1 now heats up and magic smoke appears:(

I have messed about with this board to much now so thinking of re cutting and starting from scratch!

While hunting for what is causing q1 issues I noticed an odd trace on my board, looks like my CNC couldn't get between this bit and left copper remnants! Its bridging the threshold pot to the RMS input cap, I suspect this has been my problem all along!!! The track looks like its ment to be there so never questioned it, so frustrating!!

Anyhow, if anyone has ideas on why q1 is heating up that would save me yet more time getting this f%£ker to work.. from what I can tell it all looks good to me, I have verified the ICS in another board and all the diodes test good..

Sent from my Plus E using Tapatalk

News:

Critique my noise gate