GC SuperSymmetry

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#102
I attempted throwing away some gain this weekend, using voltage dividers after the differential pair to drop 6dB before the LM3875's. There is still a stability problem, although the amplitude and frequency of the oscillation seems to have decreased.

Nelson, any idea how much of a reduction in open loop gain will be required to stabilize these circuits? I need to place an order for resistors to continue and was wonderng if you had any insight as to a ballpark figure... :xeye:

Getting closer 😀
 
#104
OK, tried my last set of suitable resistors before I have to order in more. Have thrown away 15.5db of gain, and things have improved again, but not there yet. With no signal at the inputs, the outputs (positive and negative speaker outputs) are reading about 1V above ground. I can play music, but it just doesn't quite sound right, very hard sounding. Lastly, when I switch the volume (using a stepped attenuator) I get a bloody big pop each time. I think my next attempt will be -21dB.

Terry
 
#106
originally posted by gencard
I just changed two resisters as Metalman's suggestion. it's better.
Click to expand...

Actually that was a suggestion Nelson gave to me. I was just passing it along😀
I have been quite surprised by how much gain I have had to "throw out", much more than I expected. But then again, I was warned.

originally posted by Nelson Pass
One of the key issues is the enormous open loop gain of the
chips, which can give rise to some difficulty.
Click to expand...
 
#109
Eureka! It's alive.

At last a working circuit with no apparent problems. No hot chips, no clicks, pops, strange voltages, nothing that I can tell is wrong. Plays music quite well too, although I have only tested it with my portable CD player and el-cheapo bookshelf speakers. Is this circuit optimal? I have no idea, but it does work.

Terry
 

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#118
First, let me preface my descriptions with where I am so far with testing and listening. I have since moved the amp into my main system but I am still driving it from a single-ended source, and as Nelson has stated previously, supersymmetry really needs to be driven balanced to be truely effective. I almost have my X-BZLS completed and my balanced DAC should also arrive soon, so I hope to be driving the amp via a balanced signal before Christmas. Next, the amp has only seen about 12 hours of playing time so far, and GC's are notorious for their long break-in period.

That being said, this amp is dynamic and very detailed. Words that come to mind are clean, analytical and precise. No one will ever say this amp is warm sounding, however I personally don't find it to be so bright as to be harsh or unmusical. I also have BrianGT Basic GC Kit built that I can run off the same regulated powersupply, and in comparison the X'ed GC sounds more detailed and dynamic, definitely cleaner, but at the same time less bright. Also, the bass from the X'ed amp is deeper and better controlled, in fact I would say that the bass is the area of biggest improvement.

In comparison to my Rotel RA971 integrated, so far I prefer the X'ed GC. The X'ed GC again is cleaner, more detailed, with a better defined soundstage, and substantially better bass performance. The X'ed GC looses warmth and is drier sounding in direct comparison to the Rotel.

I'll post some more comments once I get it better broken in, and after I get a chance to drive it balanced.
 
#119
Thanks for the info. It’s very positive.

I think that getting all at once is uneasy. In my case, I always have to compromise it between warm and detailed analytical clean wide dynamic stage sounds. Anyhow, after having read your info, I wish to build one. 🙂
 
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