Neve 1272 Clicking in a shorting, 12 position, 3 deck Grayhill switch.

I just finished my N&2 Neve 1272 clone and there is a small problem.

When I switch the Shorting grahil switch there is an audible click on the forst 6 positions, which then becomes much quiter (almost inaudible) after that. What can I check? I'd hate to find it's a bad switch and have to try to remove that sucker! I wouldn't even know where to begin!

Also, I have it biased to measure 21.4 volts on the collector od the large transistor, but it seems like it is quick to distort. Any ideas on where to look or what to check. There are no shorts that I can see, and the power leads test as an open circuit so I am at a loss for where to look next.

Shane

I believe the switch you're refering to is actually non-shorting for the first 5 positions, then shorting after that. In this case the clicking is to be expected for the first 5 positions.

>>Also, I have it biased to measure 21.4 volts on the collector od the large transistor, but it seems like it is quick to distort. Any ideas on where to look or what to check. There are no shorts that I can see, and the power leads test as an open circuit so I am at a loss for where to look next.

Trace it with a scope, then a voltmeter if necessary. Adjust bias for even positive and negative clipping. I haven't looked at the circuit in quite some time so I'm not sure of exact voltages, but my guess would be that if everything else is OK and the only problem is early distortion, you have unsymmetrical clipping pos/neg. If you have distortion at low levels as well it could be another problem.
Have you tried reading Tim Ryan's instructions, and search on his forum? I'm pretty sure you will find the answer is there.

Thanks. the version i have built IS Tim Ryan's kit. It is a bit more difficult than the A12's were so i am sure there are plenty of things than could go wrong. The switch being non shorting for the first five positions is odd, but that would probably explain that! I set for symmetrical clipping the best I could with a scope, and then I measure the voltage as 21.72. Is that normal? Tim recommends 21.4 as a starting point.

Shane

Is it distorting on all frequencies?
What kind of output transformer?

It is a VTB1847. It is not "distorting" all the time, it just seems like it doesn't have as much headroom as it should. I haven't done too much testing.

Even after I set the unit for symmetrical clipping, the top of the waveform is clipping differently than the bottom.

Part of it (I think) has to do with the fact that it has an output fader. The A12's have a 6 db trim, so I normally have to set the gain at 6 or 7. The N72 gets the same gain at about 2 or 3 on the switch with the fader all the way up. Maybe the fader is meant to be at 1/2 or something. I can switc the fader to a 6db trim like the A12 has by swapping out a single resistor, so maybe I'll do that.

Is it really normal for the Grayhill to click in the first half of the switch positions? The switch I am using is 71bdf30-03-1-ajs

Shane

take off the fader and see how it sounds. I think the class A stuff has less headroom due to it being 24 volts instaed of say 36 like a dual supply.
i always set those trimmers by ear.

Thanks CJ. I may switch to the 6db trim as that may be more useful to me in the long run.

After rebiasing off of the scope I am not hearing the unit distort so obviously anymore. In fact, I just spent a half hour singing and "check 1-2"ing and it sounds rather good.

I wish there were something I could do about the switch clicking though. Grayhill lists that switch as shorting, so is Admin right in saying that hte first five clicks aren't shorting? I know there are some hybrid designs, but why would Tim Ryan spec one into his design?

The A12 uses the same switch, but the 2 deck version and it is inaudible during gain changes.


Shane

Hi Shane!
Feed a signal direct to the output stage and look on your scope! I think your problem is in the inputstage(s) the input stages doesen't clip symetrical. The output stage clips before the inputstages!

Check out the wiring and color codes for the 1847 to, there's two issies of that with diffrent lead coloring!

I use a non-shorting switch, no clicks.

Sounds like you might have a leaky cap or something, it doesn't take much dc to put pops in in that circuit.