| New Preamp on the bench [message #9902] |
Fri, 02 February 2007 10:54  |
SteveBrown
Messages: 330
Registered: May 2009
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Grand Master |
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Just wanted to mention that I have a new preamp on the bench, well it has actually moved beyond the bench and into my system for a listen. Initial impressions are very good. This design uses a 5687 (1/2 per channel). The 5687 is biased (82ohm AN Tant) for 18ma and the plate load is a CCS. Pretty ordinary, but then the fun begins. This goes to a 3.3uf Obligato parafeed cap (cool looking copper jacket) and then to a Lundall LL1676 4:1 step down transformer. This gives me single ended or balanced output, lower output impedance, and loads of isolation from the rest of the system. The power supply is tube rectified (6CA4) and choke loaded and will soon be shunt regulated using a CCS on top of gas regulators. For volume control I'm using a step attenuator and the pre is silver wired throughout. If anyone is looking for a nice project, this has been pretty rewarding so far. As it cooks in, I'll add any meaningful comments about the sound. One thing I did notice right off is that there is great focus and depth. The bass is a bit different than before, it isn't as "thick" as my prior 6SN7 pre, but seems to have more punch. Strange. I'll investigate further.
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| Re: New Preamp on the bench [message #9906 is a reply to message #9905] |
Mon, 05 February 2007 06:32  |
SteveBrown
Messages: 330
Registered: May 2009
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Grand Master |
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Thanks for the offer, Wayne, but after more listening, I don't think she's ready for the dance just yet. After trying a number of combinations I just couldn't get "tone". Sounded lean - and I've exprienced that with these transformers before. There's no indication of this if you look at the frequency response, it's very extended. But on actual listening, my simple 6SN7 plate loaded line stage sounds much better (about 150v on the plate, 7 -8ma I, Rk=600, B+ = 300, Rp = 20k Mills 5w). And I was lucky enough to have Bill E confirm my feelings on the differences. Once I get the phono stage worked out, I'll see about posting photos and schematic. Wish I had some good schematic drawing software!
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| Re: New Preamp on the bench [message #9907 is a reply to message #9906] |
Mon, 05 February 2007 12:13 |
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Wayne Parham
Messages: 18674
Registered: January 2001
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Illuminati (33rd Degree) |
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Sounds good, thanks!About schematic software, you might download the demo version of OrCAD. There are tube models available for it, and you can model the circuit with PSpice, which is a built-in module. To distribute a schematic, you can make a GIF file of the CAD drawing.
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| Re: New Preamp on the bench [message #9948 is a reply to message #9902] |
Wed, 11 April 2007 10:16 |
randle
Messages: 179
Registered: May 2009
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Master |
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I wanted to know what a preamped bench was. Is this what you would consider to be what the speakers go in when you stick them into your car. I think they call it a pre made box that supports for speakers bass.
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