Critique my noise gate

[craigmillard]

Hi Guys,

I have drawn up a schematic for a noise gate using the THAT4301 audio processor and am looking for a bit of critiquing before i begin designing the board!

Anything wrong with it or any improvements??


You can open it in a new tab and it will be bigger too.

Cheers all
Craig

[DDD]

MAX1044 is extremely unreliable at input voltages higher than 9 Volts as well as at output current close to its specified maximum.
I had a problem with Devi Ever Silver Rose fuzz, and producers informed me of that fact and advised to change originally installed MAX1044 with LT1054 (if I remember properly).
So, if you want to avoid problems... bla-bla-bla...

[craigmillard]

Hi DDD, thanks for the input, I have had issues with the max device before so was planning on using the Lt device, I just don't have an eagle symbol for it!:) any thoughts on the rest?

[Govmnt_Lacky]

this probably won't be a high current draw device. I would recommend going with either the TC1044S or the ICL7660 for the charge pump. Good up to 12VDC input and should be able to handle the current demand for this circuit.

These pumps have the built in frequency doubler if you connect Vcc to Pins 1 and 8 

[midwayfair]

this probably won't be a high current draw device. I would recommend going with either the TC1044S or the ICL7660 for the charge pump. Good up to 12VDC input and should be able to handle the current demand for this circuit.

These pumps have the built in frequency doubler if you connect Vcc to Pins 1 and 8 

The 7660's max is 12v, the LT1054 has a higher input voltage rating, a very high clock frequency, and more current available. Unless you absolutely need to save a dollar, I can understand using anything else on a circuit above regulated 9v. I also suspect that the current draw will be a little higher than you suspect when the effect is opening the gate.

[Govmnt_Lacky]

The 7660's max is 12v, the LT1054 has a higher input voltage rating, a very high clock frequency, and more current available. Unless you absolutely need to save a dollar, I can understand using anything else on a circuit above regulated 9v. I also suspect that the current draw will be a little higher than you suspect when the effect is opening the gate.

Yes, the LT1054 does have a higher input voltage however, the standard clock frequency (without supporting and external components being added) is 25KHz. The TC1044 can go up to 45KHz without any other components being added. Simply jumpering Pins 1 and 8.

Also, you hit upon the pricing. The TC wins in that department and for this project... I think it is a good choice 

[DDD]

As per Devi Ever producer's advice, I simply cut MAX1044 away from the PCB and soldered LT1054 instead.
No any other changes, and the gadget works as it should do.
*** LT products are of a very high engineering and production quality, so they are reasonably expensive.
-----------------
Fix advice by Mr. Ken Schurer of Infanem 
(Extracts)

There has been a problem with early Silver Roses frying their charge
pumps. Devi is offering repairs so beginner DIYers don't get in over their heads
on work that's available from the builder.

The offending part is the SOIC-8 sized MAX1044 toward the bottom left
of the PCB. In later pedals, an LT1054, capable of handling greater
voltage spikes and load, is used in that position to eliminate the
issue. It requires a bit of ingenuity to mount, though, as they are
only available in PDIP-8 or SOIC-16 wide packages. Should you decide
to make the swap, the PDIP version is a pin-for-pin substitute except
for leaving pin 1 of the LT1054 open.

[slacker]

I don't know anything about the 4301 so i can't comment on that part of the circuit but I noticed a couple of things. R22 and R25 are connected to VA which is 9 Volts, if the opamps are powered from +-9 Volts they should be connected to ground. You don't need IC2A, C18 can go from the output of IC1B. You can get rid of C1 or C17 you don't need them both.
I wouldn't use polarised electro caps in the signal path, your opamp outputs are centred around ground and so is the other end of the caps so you'll get negative voltages across the caps, you could lower the values to 1uF or 2.2uF which are easy enough to get as film caps.
You might want more filtering on the charge pump, especially on -VA, maybe add a series resistor and another filter cap to the output.

[Govmnt_Lacky]

The offending part is the SOIC-8 sized MAX1044 toward the bottom left
of the PCB. In later pedals, an LT1054, capable of handling greater
voltage spikes and load, is used in that position to eliminate the
issue. It requires a bit of ingenuity to mount, though, as they are
only available in PDIP-8 or SOIC-16 wide packages. Should you decide
to make the swap, the PDIP version is a pin-for-pin substitute except
for leaving pin 1 of the LT1054 open.

The TC1044 comes in SOIC-8 

[craigmillard]

Thanks guys! I have made some changes:



With regards to the noise gate its essentially a replica of the THAT datasheet
http://www.thatcorp.com/datashts/dn100.pdf

[Transmogrifox]

This looks good.  I particularly like the send/return loop.  Really good idea since you can gate on incoming noise prior to amplifying it in a distortion.  It gets really hard to gate noise after something high gain because noise gets amplified, and signal is clipped (lower SNR), so you have to gate a lot higher, which doesn't work any more when you turn off the distortion because your signal isn't high enough to turn on the gate unless you really dig in.  The loop solves all those problems.  You detect at the input and attenuate after all of the noise-adding loop .  Very nice.

I don't think it's warranted for you to redesign at this point, but the hold/release functions could be made much simpler for guitar use.  I see why they did it this way:  the constant current mirror creates a nice linear ramp that turns into a more faithful exponential in the VCA.  You could actually put numbers on your dial that have some kind of industry standard meaning in terms of dB/ms-- it's engineered for a professional rack unit, probably.

For guitar use, it could probably just be a simple RC time constant for hold and another simple buffered RC for release and it would sound fine on the release...but for you it's more work to redesign it to something more simple than it is to just build it as designed

[craigmillard]

Thanks for the input on this Guys! I have finally built this up but am having a few issues!

The gate works but causes a popping sound when it kicks in or comes off and the hold release section seams to have little effect
Oh i subbed 2n3906's for 2SA1015 in that section but believe these are a suitable equivalent?
Any one spot anything up with the schematic?

The popping sounds like DC pops although i understand this is because the VCA is instantly switching instead of gradually fading the signal out??

Any help would be much appreciated! I want to get this thing verified and get the transfer up:)

[craigmillard]

Im stumped on this one!:(

Any ideas??

[slacker]

C1 on the example schematic is 220n, your schematic has 22n in that position. From reading the description in the example that would affect the release time which might explain the problem.

[craigmillard]

C1 on the example schematic is 220n, your schematic has 22n in that position. From reading the description in the example that would affect the release time which might explain the problem.

Thanks slacker although I had already spotted that and the 300k for 47r at the sym on the vca..
How much do you think the nlc has an impact on it?

[craigmillard]

C1 on the example schematic is 220n, your schematic has 22n in that position. From reading the description in the example that would affect the release time which might explain the problem.

Thanks slacker although I had already spotted that and the 300k for 47r at the sym on the vca..
How much do you think the nlc has an impact on it?

Got it! I had my opamps the wrong way round![emoji35]

Works great now the release and hold function very well!

I just want to change the threshold a bit so it allows a low level set, currently it cuts to hard I think. Looking at r3 and r5 at the mo.. Any thoughts?

So close!

[craigmillard]

sorry for dragging this up again, finally got round to looking at this again..

Im still struggling with the threshold, can someone explain to me how this is working as im struggling to grasp it?

Currently the threshold pot is not doing anything with the resistor set at 150k.. it also causes the gate to cut out at either end of the pot with a little spark on the carbon trace of the pot..

Iv tried different resistor values but nothing seems to change it, i have also rebuilt it on a new board with the same result.

any ideas?

[Kipper4]

Can I ask what chips you are using lm358 or the 393 ?

The threshold likes like an offset for the op amp/comparator inverting input.

[craigmillard]

its the lm393, the 358 is on the schematic as it was the part i used and relabeled.. havent removed for some reason.

[Kipper4]

Ok thanks.
I'm not to sure what the ug chip is either.
The bottom four op amps look like a complex pulse generator.
Is that so?