AC ground on Gyraf Pultec?

Just a stupid question comes to mind after giving myself a huge jolt of 220V...

Where does the AC ground on the Gyraf Pultec hook up?


Thanks

Chuck

The ground from the mains inlet?

That goes - as always - to the chassis grounding point at the input XLR.

At the input XLR, pin1 is connected to chassis ground, and this is our input reference.

Jakob E.

Do you mean connect XLR pin 1 to the chassis and AC ground to the chassis as well?

-Chuck

Yep, that's it.

And this point is your input signal reference, your "centre ground" if you need it later for hum-tracing/cancelling.

Jakob E.

Here's some photos....


http:////www.pillarsofnein.com/Images/DSCN0724.jpg[img]
[img]http:////www.pillarsofnein.com/Images/DSCN0725.jpg[img]
[img]http:////www.pillarsofnein.com/Images/DSCN0727.jpg[img]

I'll send some more results when I get a chance to test it!!

-Chuck

Damn that didn't work !!

Looks great!

What are the jack connectors for?

Jakob E.

Chuck,

Nice work!

Yep, make sure you connect a mains ground to the case. Just before you power back up, check and double check that there are no stray connections from the HT supply to the chassis (an accidental "stray" strand of wire etc can easily brush against the chassis etc)

It's just that when you said you got a kick of 220V, I presume (from where you live!) you mean DC HT and not AC mains! (a DC shock is very different from an AC shock- I HATE AC shocks ) I wanted to make sure that you didn't get the shock touching the chassis itself. This would indicate an accidental connection from the circuit to the chassis, which when a mains earth is added may pop a fuse.

Just checking. I've done this before myself and spent hours thinking "...now why did this stop working when I added a safety ground?"

:thumb:

Mark

Thanks,

The Jack connectors are for the unbalanced input and I was thinking of either adding an unbalanced output or a TRS 1/4" output so I added the jack.

I am taking it to my work lab today to run a signal generator through it and test it. I wanted to see what the actual frequencies each setting represented.

I remember someone (Kev?) had some curves on his unit but I can't seem to find it?

-Chuck

Preliminary Test Results of the Pultec:

Test equipment : Signal Generator and Scope

1. From what I can tell the Gyraf Pultec works very well with little to no signal loss.

2. It seems to Work very well with the low frequency in both boost and cut. Frequencies go from 30Hz to about 100Hz.

3. The High Frequency Boost works very good as well and it's frequencies go from 2-3 Khz to 10-12Khz.

4. THe High Cut doesn't do what I thought it would. It seems to just give a LPF in varing levels of ampiltude and not a Notch at varing frequencies. The frequency doesn't change that much at all when the selector switch is moved. It does provide a great LPF though.

5. The High Q function works well and can be seen against the High Boost on the scope. One thing I noticed was that my knob goes from 6 oclock to 4oclock and the Q is the sharpest at the begining (6 oclock) and the smoothest at the other end (4 oclock). I thought it would be the opposite. Maybe the pot is backwards?


Now I will give it the listening test and post my findings soon...

Comments?


-Chuck

I don´t see the star ground point on your unit. Make sure to do the star ground thing correctly!

yeah,
I put that in after the picture late last night...

You're right the way it was in the picture would produce quite a shock!!
I felt it!

What do you think of my results? The High Cut doesn't appear to work like I thought... Any comments on this?

-Chuck

I have an annoying hum in my stereo pultec, it's around 80-100hz and comes up after a few seconds, when the tubes had lighten up...

the pin1 of both input xlr is connected to ac ground, to the groundplanes on the board and to the chassis... (the same as starground ?? )
all pin1s of all xlrs arec onnected together

both trafos are packed in grounded aluminium boxes to prevent magnetic interferences...

so do you have any idea what could be the reason for this strange hum...
maybe bad parts??
my main trafo makes a little noise itself, when it gets power
my tubes are valvo nos e88cc

???


thank you

mat

Chuck,

Your HF cut seems to act normally - it is simply an adjustable lowpass filter with three different cutoff frequencies - different from the "high boost", that actually is a variable bandpass.

Matthias,

Check for ripple in your HT voltage. Maybe too small a resistor between the two psu caps?

Jakob E.

@jakob:

I just started a new thread with more info and pics


mat