Hamlet Delay Whine...

[clipman3]

So a while ago (Spring of 2013) I bought a black Hamlet Delay board (before JMK started making Hamlet+ boards), and I finally got around to finishing it. The thing works and sounds beautiful, props to Jon, aside from two issues with noise I'm having.

1) My 2399 is noisy as heck. Probably just cuz I went through Tayda though; I'll get them from Smallbear or something next time.

2) My LT1054 is oscillating well into the audible spectrum.
I took my time and researched fixes for the 1054's whine, but all I could really find is the datasheet trick that calls for a 5-20pF cap between pins 2 and 7. I tried a few values, and they all (ironically) LOWERED the oscillation frequency and made it quite a bit louder. Without the chip the pedal works fine, and without noise, but it does sound a lot better with the extra voltage.

I went through and checked voltages, and everything was normal except for the pump's output. I measured the voltage at the resistors connected to the output of the pump, and it read something like 16.5v. It should be 18v. The pump's voltages are:
1 - 4.29v
2 - 4.26v
3 - Gnd
4 - 188.6mV
5 - 380mV
6 - 4.72v
7 - 4.44v
8 - 8.7v

My first guess would be that the chip somehow got ruined, but I thought I'd ask here first in case I'm missing something.

Thanks guys

[MrStab]

hi Jordan,

1. may not be the issue, but there are reports of fake PT2399s with less-than-optimal performance. see here: http://www.diystompboxes.com/smfforum/index.php?topic=99723.0

2. do you have a picture of the PCB layout? how isolated is the LT1054 from the rest of the circuit, in terms of grounding and physical proximity? keep the charge pump ground(s) on separate wires and away from signal ground at all costs.

you may also have heterodyning going on - clocks/pulses from both chips combining to produce new frequencies altogether. admittedly, i don't know much about that. but a consistent whine doesn't strike me as that kinda problem - sounds more like issues i had with charge pumps in more tone-shaping-type circuits when i first started messing with them (now i wear a tinfoil hat whenever using them).

just some thoughts.

[clipman3]

Thanks, Mr. Stab for your quick reply!

1. may not be the issue, but there are reports of fake PT2399s with less-than-optimal performance. see here: http://www.diystompboxes.com/smfforum/index.php?topic=99723.0

Yeah, that's what I've heard. I've read that Tayda also has pretty hit or miss shipments of them, too. The crappy ones have a tendency to motorboat.

2. do you have a picture of the PCB layout? how isolated is the LT1054 from the rest of the circuit, in terms of grounding and physical proximity? keep the charge pump ground(s) on separate wires and away from signal ground at all costs.

you may also have heterodyning going on - clocks/pulses from both chips combining to produce new frequencies altogether. admittedly, i don't know much about that. but a consistent whine doesn't strike me as that kinda problem - sounds more like issues i had with charge pumps in more tone-shaping-type circuits when i first started messing with them (now i wear a tinfoil hat whenever using them).

just some thoughts.

Here's the thread, with the schematic and layout.

The chip is a little close to the audio line, but I think people have built it using the same board without a problem. The chips seem a little far apart for heterodyning, but I could be wrong. To my ears, it just sounds like power supply noise. It has to be from the 1054, though, because it doesn't whine without the chip. It also doesn't affect the delay line at all.

[midwayfair]

What's your power supply?

If you're still on the test board, put a 47R between the power supply and the +9V input. This might drop the voltage a bit (probably not enough to worry), but you can at least determine if it's power filtering issue.

I'm pretty sure you can just pull the LT chip and see if you still have noise. the supply voltage end up something like 8.5V.

I've had charge pumps whine when they were about to die. If you have another, try just swapping the chip.

Finally, check where your noise/tone trim is set. If it's all the way down, you might be getting some PT noise.

[italianguy63]

Doesn't pin 7 of the LT1054 need to go to ground via a 5pf to 20pf cap?!  (Frequency boost)

But, sure sounds like a bad IC... swap it.

MC

[clipman3]

What's your power supply?

If you're still on the test board, put a 47R between the power supply and the +9V input. This might drop the voltage a bit (probably not enough to worry), but you can at least determine if it's power filtering issue.

I'm pretty sure you can just pull the LT chip and see if you still have noise. the supply voltage end up something like 8.5V.

I've had charge pumps whine when they were about to die. If you have another, try just swapping the chip.

Finally, check where your noise/tone trim is set. If it's all the way down, you might be getting some PT noise.

It's just a typical planet waves wall wart. I use it with all my pedals. I've been using the board without the LT and it's worked fine, without noise, so I'm definitely going to order another chip.

Doesn't pin 7 of the LT1054 need to go to ground via a 5pf to 20pf cap?!  (Frequency boost)

In the datasheet it said that connecting pin 7 to ground would lower the frequency. However it also said that connecting pin 2 to pin7 would raise the frequency (which it did not), so it could be worth a shot.

Thanks for your help and suggestions guys

[italianguy63]

I'm sorry.  Ignore me.

From the datasheet:

The frequency can be increased by
adding an external capacitor (C2, Figure 2, in the range
of 5pF to 20pF) from Pin 2 to Pin 7.

You had it right!  Still.  Sounds like a bad charge pump IC.  I have had one do that before too (low output).

MC

[chuckd666]

So I just finished my build of this, and had the whine spoken of here. Turns out all the LT1054s I purchased from eBay all whined brutally and could not be fixed or bettered by any small caps between pins 2 and 7 or 7 and ground or whatever it was. I DID however have another LT1054 proven to work (from diyguitarpedals.com.au) and I put it in and my whine was gone. ALLLL "LT1054s" purchased from eBay were out of spec. They were charge pumpin' to 14V~, but alas... whiny. Get a proper one and life will be easier I guess?

[midwayfair]

So I just finished my build of this, and had the whine spoken of here. Turns out all the LT1054s I purchased from eBay all whined brutally and could not be fixed or bettered by any small caps between pins 2 and 7 or 7 and ground or whatever it was. I DID however have another LT1054 proven to work (from diyguitarpedals.com.au) and I put it in and my whine was gone. ALLLL "LT1054s" purchased from eBay were out of spec. They were charge pumpin' to 14V~, but alas... whiny. Get a proper one and life will be easier I guess?

Thanks for reporting what fixed it. If anyone else ever has the problem I'll show them this post!

[chuckd666]

No prob Jon! Great circuit! Have been in the recordin studio with it today. Gonna throw my TC Electronics Repeater in the trash now haha.