Hi Guys,
I wired up my LL1676 input transformer for application in a new amp, and the initial tests on it came out horrible. It rang like crazy on a 1kHz square wave, and only cleaned up when I lowered the load across each seconday to a measley 1k ohms.
I have it wired in the "1:1" setup that's been discussed here before.INPUT POS: pin #9 + #7
INPUT NEG: pin #10 + #8 + #6
OUTPUT POS: pin #2
OUTPUT NEG: pin #5
OUTPUT GND: pin #4 + #1I also tried seperating Pin #8 and grounding that, which didn't help. The input negative side has to be grounded also, otherwise I get what looks like oscillation. I thought that was optional?
The source I'm using is a Protek signal generator with a 600 ohm output impedance (measured at 580 ohms), and output is measured with my Philips scope, 1M/20pF input.
Did I wire it wrong, measure it wrong, or is this the type of performance to expect?
Joel
Follow Ups:
- Re: Help! LL1676 - what did I do wrong??? - Gary P 06:43:05 04/26/04
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- In Reply to: Help! LL1676 - what did I do wrong??? posted by Joelt on April 25, 2004 at 10:11:27:
Hi Joel,
The only difference in connection between yours and mine is I have pin 8 connected to the output ground. This allows the input to be driven differentially without coupling the negative signal into the output stage via the shield.
I'm pretty sure that the standard is to connect the shield to the signal ground and have the primary floating.
You may be getting some form of feedback via coupling between the shield and the output driving the - input.
There is a schematic of the transformer wiring in the 47 P-P section in my web page, most of the way down the page.
Gary
- thanks guys. It wasn't me... - Joelt 06:36:40 04/26/04
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- In Reply to: Help! LL1676 - what did I do wrong??? posted by Joelt on April 25, 2004 at 10:11:27:
Well, after looking at the o-scope photos on Gary Pimm's website (thanks for the link Kevin) and reading arend-jan's posted results, I can easily see that we have the exact same behavior. The 1k squarewave has quite a large amount of ringing. The 10k squarewave is highly distorted.
Yes, the phase shift is very low, and the balance is excellent - but I guess I expected better performance from a $90 transformer.Joel
- I hear with my ears, not with my oscilloscope - KevinC 08:03:12 04/26/04
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- In Reply to: thanks guys. It wasn't me... posted by Joelt on April 26, 2004 at 06:36:40:
First of all, sorry for the brash title; it wasn't meant to be offensive, but to underline a point. In my opinion if you haven't listened to the result, you haven't done the crucial test. I can build an amplifier that has great square wave transmission performance that sounds bad and one that has terrible square wave performance that sounds really good. Now I have a dilemma: do I believe my ears or do I just dismiss the good sounding amplifier as fatally flawed because it has bad square wave performance?
I have come to the point of view that because music reproduction is about enjoyment, I choose my ears over my oscilloscope. If there are response peaks outside of the audio band, it is not offensive to me so long as I enjoy what I am hearing. Many audiophiles decry the lack of "objectivity" that this attitude conveys, but enjoyment is not about "objectivity". Where can one find the "absolute sound"? If this seems to you like sloppy engineering disguised as listening enjoyment, then so be it. Many users have been very happy with the technical and sonic perfomance that they have observed with the LL1676. Perhaps you aren't happy with the square wave performance, but listen, too, and see if this makes you think twice.
Second, some might not consider the 5-10% high frequency overshoot (far removed from the audio band) shown in one of Gary's oscillograms "quite a lot of ringing". If you desire only transformers with "perfect" square wave performance, then you will have to choose the transformers, driving conditions and loading conditions very carefully, indeed. Good luck in your quest!
- Amen! (nt) - AnandR 19:49:50 04/26/04
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- In Reply to: I hear with my ears, not with my oscilloscope posted by KevinC on April 26, 2004 at 08:03:12:
nt
- Amen! (nt) - AnandR 19:49:50 04/26/04
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- I hear with my ears, not with my oscilloscope - KevinC 08:03:12 04/26/04
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- Re: Help! LL1676 - what did I do wrong??? - arend-jan 03:30:14 04/26/04
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- In Reply to: Help! LL1676 - what did I do wrong??? posted by Joelt on April 25, 2004 at 10:11:27:
You might also want to check this thread.
Additionally, I have to agree with Kevin. It might not measure particulary well on square waves, but it sounds good.
- Re: Help! LL1676 - what did I do wrong??? - arend-jan 00:52:20 04/26/04
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- In Reply to: Help! LL1676 - what did I do wrong??? posted by Joelt on April 25, 2004 at 10:11:27:
You might also want to check this thread.
Additionally, I have to agree with Kevin. It might not measure particulary well on square waves, but it sounds good.
- Re: Help! LL1676 - what did I do wrong??? - KevinC 18:46:45 04/25/04
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- In Reply to: Help! LL1676 - what did I do wrong??? posted by Joelt on April 25, 2004 at 10:11:27:
Well, I suspect that you have the test system set up wrong. Others have tested the same connection you are measuring (with pin 8 grounded) and seen little or no overshoot. Check out Gary Dahl's comments at http://www.audioasylum.com/forums/KandK/messages/890.html and Gary Pimm's at http://www.pacifier.com/~gpimm/1676_1684.htm.
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