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Old 5th August 2012, 04:49 PM   #21
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I just bought a used and abused 5800 on Ebay. After fixing some problems with it, I played it through my Accoustat Spectra 2200 speakers. I have a homebuilt 6SN7 mu-follower tube preamp that I've used for a decade now.
I have heard a scratchiness to the treble on the 5800 with both my stats and my ancient ADS L810 speakers as well.
I read that a HiFi shop which upgrades Adcoms hard solders all the spade lug connections in the amp to eliminate crackles and scratchy sound resulting from the "diodic" action of oxidized connectors. It makes sense to me, the scratchiness does sound like a preamp with a bad selector switch that I fixed a while back. I plan to try cleaning my connections with De-oxit first as the poor amp was a dustbin when I got it.
I think Mr Pass and KBK both have valid points. CLS should definitely address all of Mr Pass' concerns about cabling and such. Mr Pass has 1uf mylar bypasses on the supply rails right next to the active circuits in the GFP-750 preamp but there are none on the GFA-5800 amplifier channel pcb supply rails. Perhaps adding some compact Panasonic 1uF 250V polypropylene caps from the supply rails to ground would be beneficial in the amplifier?
Thanks for the awesome design Nelson Pass!
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Old 19th September 2012, 10:08 AM   #22
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I was wondering if there is a passive preamp (DIY or not) that has the same design as the GFP-750 with XLR inputs/outputs and a remote control...
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Old 23rd September 2012, 04:02 PM   #23
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My Gen1 5800 is sounding smoother after its De-Oxit treatment. Also it's new Panasonic HF Polypropylene input-coupling caps have broken in. These were chosen mainly for compactness and economy. The amp occasionally has a bit of a "spitty" quality on some transients. I'm wondering if this is due to my using polarized Elna Sil-Mic electrolytics for input coupling. I've gotten some Bi-polar Nichicon Muse lytics to try in their place.
I couldn't recommend a totally passive preamp. Read Mr. Pass' DIY article on the B1 buffer. It wouldn't take much to make a balanced version. I just completed a B1 using mainly parts found on Ebay (matched Fets, etc.), and I'm quite impressed with the clarity and smoothness of the sound. It's lacks the warmth and soul of my tube preamp, but it's eminently listenable.
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Old 23rd September 2012, 08:09 PM   #24
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The Elna Silk caps are very good. I doubt that this is the source of
the spitty quality.

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Old 21st October 2012, 09:21 PM   #25
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Thanks for the reply, Mr. Pass!
The Silmics I got were from China, who knows if they were genuine? The casings were blue instead of the brown on the domestic Silmics I got. They fit in the amp without cobbling so I used them. The amp had huge bass with overblown dynamics and the aforementioned spitty quality occasionally.
The last time I opened the amplifier I double-checked the output Zobel capacitors and they were fine. After finding a negligible voltage difference across the input coupling capacitors, I went ahead and replaced the polarized Silmics with some Nichicon Muse nonpolarized caps. I bypassed these with a 0.47uF Dayton polypropylene film/foil unit and a 0.01uF RelCap theta. I had to hang the big Daytons under the pc board.
The amplifier now sounds much more refined and controlled. The bass and dynamics aren't larger than life anymore, but everything sounds more coherent. The spitty quality is gone. I'm not sure if the improvement is due to the NP electrolytics or that I'm using larger and better polypropylenes across them..
I replaced the 100uF 100V capacitors in the power supplies with Elna Silmic IIs and changed the film bypasses on the big main filter caps to 1uF Panasonic polypropylenes.
I have gotten some domestic Elna Silmic IIs from Mouser but I am reluctant to put them in the amp. I have always heard you need a few volts difference across a polarized electrolytic for them to sound their best.
If my preamps all have output capacitors to block DC, is there even a reason to keep the input coupling capacitors on the amplifier?
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