Gyraf Pultec Problems - Please help!!
« on: May 18, 2006, 03:36:10 PM »

First of all, I'd like to say that I'm a huge fan of this forum.  I've read hundreds of pages, but never posted anything myself.  I'd also like to say a huge thank-you to Jakob for making these projects possible, and to everyone who has shared their knowledge on the forum.

I've already built the G-SSL and the G-1176, and now I'm on to the Gyraf Pultec project.  I finished the prototype yesterday and I'm having some trouble with it.  I wasn't able to find any answers to these problems anywhere on the forum:

1.  I can't get the LED to work.  I've attached the LED using the slot for the 470R resistor right next to the LM317 regulator.   I attached a wire with the 470R resistor imbedded in it to the hole nearest the LM317, then attached that to the positive pole of the LED, and then sent the other wire to the other hole.  When I do this the LED does not light up, nor does the unit pass audio.  When I bypass the LED and simply connet the two wires the unit passes audio.  Is this not a good place to take power for the LED??  If not, where should I do so???  I checked the LED with my DMM and it works fine.  Perhaps the LED itself is inappropriate??  I bought it from Digikey, 67-1156-ND.

2.  Once I got the unit passing audio I set up a test as follows:  I played a chord on one of my synths and used the "hold" feature, so that I had a steady signal.  This went to my preamp and then to my computer.  I got the signal to run at about unity.  Then I sent the signal through the Pultec.  The signal drops considerably even when I have the filter section bypassed, and when I actually use the filter section it drops even more.  I can't say for sure how much it drops, but it's a lot.  

So, is something wrong here or am I misinformed about how this EQ is supposed to work??  

I followed ChuckD's pic and parts list as close as possible.  I'm using the Amveco 62062 for the primary transformer and the Triad (Digikey# 237-1046-ND) for the secondary transformer.  I followed the PCB layout and the pdf on the Gyraf site, so I've soldered in all the resistors (including the one shunting the unbalanced input, which I'm not sure I should have done).  I'm only using the transformer balanced input.  

I'd be incredibly grateful for any ideas you may have.  




Gyraf Pultec Problems - Please help!!
« Reply #1 on: May 19, 2006, 02:02:45 AM »
Hi Jay,

Welcome to the GroupDIY!

1) If you have heater voltage, your LED should light. Re-check orientation and resistor value.

2) Pultec has a VERY low input impedance - you neeed to drive it from a real 600 Ohm-capable source, otherwise you'll loose level.

Jakob E.
..note to self: don't let Harman run your company..


Gyraf Pultec Problems - Please help!!
« Reply #2 on: May 23, 2006, 04:51:14 PM »
Thanks very much for your reply, Jakob.   Sorry for not responding sooner...I was out of town for the holiday weekend here in Canada.

I haven't been able to fix any of the problems I'm having.  I sent audio to the G-Pultec using my converter, which I know is a 600 ohm capable source.  I still have losses when I use the Filter Section.  

Anyway, it is not my intention to push you for more answers, but simply to say thanks!



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