Warhead Lamp and Pulse LED operation question

[JakeFuzz]

So I just finished up my Warhead vibe. It is like 12 at night so I cant test it but I was playing around with the lamp and pulse LED function. Had a few questions for the few folks who have built this. First of all my pulse LED lights but the pulses are super shallow and at the lowest speed setting both the main lamp and LED aren't pulsing really at all. As the speed increases the main lamp acts exactly as it should but the pulse LED just barely pulses. Is this normal? If it is is there a way decrease the lower bound of the pulse to zero? 

[JakeFuzz]

So I raised the value of the LED resistor to 14.7K but that just made things worse, I couldn't get a pulse out of anything. Maybe lower resistor value? I am thinking this is happening because I am using an ultra bright LED for the indicator.

[madbean]

You can lower the value down to 2k2 or 3k3 from 4k7.

[cjkbug]

I got the two working with careful adjustment of the trimmers. Although I did experience the same behavior that you described. In every vibe project I've built the pulse is always shallower at slow speeds. R.G. Keen describes this quirk in the neovibe docs. It's common in this kind of circuit. When I got a nice vibe throughout the entire range, the lamp and led worked properly. In my experience you need to use your ears to adjust and not your eyes, preferably in a darkened room. I used a superbright blue led in my warhead.

[madbean]

A diffused LED probably will not be as noticeable in terms of brightness variation.

[Jargo]

I'm currently building the NeoVibe...I remember reading about this, but it's been a few months since then...thanks for the heads up.

I'll be sure to put up some samples!!

[JakeFuzz]

Okay, swapped to 2K2 and it looks much better. Audio testing today shows some distortion on very loud, heavy attack bass notes. Sounds like little fizzles that decay very quickly and they get a little less noticeable with lower light bias settings. Other than that everything works as it should and sounds so awesome!

I don't think the distortion can be attributed to the resistance change as it is just in the lamp driver/lfo section. Ill have to do some troubleshooting when I get back in a few days and find out wot's... uh the deal. 

[madbean]

How are you powering the effect? This can have a direct impact on distortion (ie you need ample current).

[cjkbug]

I had distortion on my neovibe when powering it on my iso5 with every socket spoken for. with just the vibe it was fine.

[madbean]

I used an 18v AC adaptor and the on-board rectifier with no issues.

Optimal would be 18v DC @ 200mA I'm told. I've gotten away with an LT1054/charge pump but the result is not as good (ie distortion).

[JakeFuzz]

Sorry for the delay just got back. I am using an 18V AC at 500mA wall adapter from smallbear.

[madbean]

That's the one I used.

Distortion could mean an incorrect value in an emitter resistor, too. I had one build where I swapped R4 and R5 and it sounded horrible.

Are you using mostly 2n5088?

[JakeFuzz]

That's the one I used.

Distortion could mean an incorrect value in an emitter resistor, too. I had one build where I swapped R4 and R5 and it sounded horrible.

Are you using mostly 2n5088?

Yeah that's what I was thinking too. Yeah mostly 2N5088 and that one 5089 in Q1. Ill go through and check all the emitter resistors today. I am also using BC549CG which has the same specs as BC549C so I think that should be okay.

[JakeFuzz]

Checked all resistor and caps value and went through most of the traces (cant get to the ones under the pots). Still getting strange distortion. Very slight crackly distortion. After the rectifier bridge I read 21 volts (with some ripple) on the meter, but this shouldn't effect anything because it goes through a regulator. I moved the LED resistor back to 4.7K and removed the power to the second LED. I also went through with a BC108c and replaced the trannies not in the phase section one by one and I still couldn't get rid of it. 

[JakeFuzz]

Interesting, I found an old ampage archive where a guy had the exact same problem as me. It is late so I will test the theory in the next two days:

http://archive.ampage.org/threads/1/fxgd/003265/Univibe_clipping-2.html#003354

The issue was a bad 330pf cap, I am not sure my cap is bad but the problem sounds the same. Keen said it was self oscillation in the preamp feedback amplifier and gave a number of solutions which I will run through and report back with results.