gyraf

Re: G-PULTEC problems, please help!
« Reply #760 on: March 24, 2020, 12:51:20 PM »
I'm seeing a -3dB point of maybe 95 Hz? Too high, should reach down to ca. 25Hz at least

What transformers are you using? Driven by what source impedance?

Amplifier output coupling capacitors?

How is your frequency response BEFORE the output amplifier (so that we know where it messes up)?

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


Re: G-PULTEC problems, please help!
« Reply #761 on: March 25, 2020, 04:04:23 PM »
Hello Jakob,

I don't know exactly why but today the frequency response is better. ;D
Maybe because the connection of the (bad) header from the filter board on the main board wasn't good...
 
What transformers are you using?
By the way, my power transformer is from Don-Audio. And the audio transformers are the Lundhal LL5402.
As you did.

Amplifier output coupling capacitors?
The coupling cap (if you mean the big 4,7uF/250V ) is a big red WIMA MKP4

Driven by what source impedance?
The signal is coming from my RME and it's a 75 Ohm output.

How is your frequency response BEFORE the output amplifier (so that we know where it messes up)?
Check the curves BEFORE and AFTER the output trafo
« Last Edit: March 25, 2020, 04:12:57 PM by lars on »

Re: G-PULTEC problems, please help!
« Reply #762 on: March 25, 2020, 04:09:05 PM »
I know it's less than one db difference but I wonder from where this bump and hollow are coming from.

gyraf

Re: G-PULTEC problems, please help!
« Reply #763 on: March 26, 2020, 02:01:04 AM »
Looks correct now. The bump is transformer inductance vs. coupling capacitance, you can tune vith out capacitor value if you like, but 4u7 and LL5402 sounds pretty nice.

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

groselicain

Re: G-PULTEC problems, please help!
« Reply #764 on: June 07, 2020, 10:50:21 PM »
Please forgive me if I'm asking a silly question. Thank you so much for this project, and even more for your continued help in troubleshooting builds.

I've got two channels built that pass audio and all the filters work as they should. However, I've been trying to get the zeroed (all gain pots set to zero) output to match the bypassed output. I tried the 1k trimmer on the high cut pot and got some gain, but nowhere near what I needed to make up the difference. One strange thing that I noticed is that when I was using my multimeter to measure the input XLR AC  on pins 2 and 3 against the output XLR, touching a probe to pin 3 of the output XLR boosts the output—without touching the other probe to anything. Touching a probe in the same manner to pin 2 of the output XLR adds additional noise. Additionally, if I unsolder pin 2 from the output, my noise goes down. Here are voltages from one of the channels—both channels are nearly identical in all respects. This is measured receiving +4db from a Whirlwind Qbox, which in the real world rarely puts out exactly +4dBu/1.227 V for me.
Input XLR
Pin 2 reference to Pin 1= .646 V
Pin 3 reference to Pin 1= .594 V
Pin 2 + 3 = 1.236 V

Output XLR
Pin 2 reference to Pin 1= .004 V
Pin 3 reference to Pin 1= .651 V
Pin 2 + 3 = .655 V

AC at pin 2 of LL5402 = 1.336 V

I'm pretty confused. I'm using the LL5402 on the output. Looking at those voltages, is there some really simple problem I'm overlooking? Thank you so much.
« Last Edit: June 07, 2020, 10:58:54 PM by groselicain »

gyraf

Re: G-PULTEC problems, please help!
« Reply #765 on: June 08, 2020, 03:43:19 AM »
..for transformer balanced, you need to measure between XLR pins 2 and 3

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

groselicain

Re: G-PULTEC problems, please help!
« Reply #766 on: June 08, 2020, 09:58:49 AM »
..for transformer balanced, you need to measure between XLR pins 2 and 3

/Jakob E.

Right, which is why I included that measurement: .655V. 

Looking at my post now, I realize you might’ve been confused by the “+”—I wasn’t arriving at that number by adding the two numbers together. That was just the way I typed it. I measured between pins 2 and 3.

Thanks Jakob.
« Last Edit: June 08, 2020, 10:02:27 AM by groselicain »

groselicain

Re: G-PULTEC problems, please help!
« Reply #767 on: June 12, 2020, 08:08:42 PM »
So, no suggestions from anyone?  Is there really a way to damage the Lundahl transformer? That’s where things seem to go wrong, but I don’t see how. I mean, you can’t put it on the board incorrectly, but I can’t see another issue. Could someone help?

Thank you.


 

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