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Old 29th May 2009, 12:46 AM   #1
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Question Brother can you spare a preamp design?

I'm back again. I am wanting to build an SE amp with a 6SL7 pre, 7408 output, and probably the obligatory 5Y3 rectifier. Anyone know of ant SE amps with a 6SL7 preamp whose design I can purloin ?
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Old 29th May 2009, 01:20 AM   #2
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There are lots of 6SL7 designs out there, from simple cathode followers to SRPP to Aikido

The 7408 is a 6V6 equivalent and there's a thread here in the forum you might be interested in - http://www.diyaudio.com/forums/showthread/t-74176.html
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Old 29th May 2009, 09:58 AM   #3
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If I read you right you're actually asking for a two stage SE amp design with 6SL7 in the first stage. So not a preamp as such - that would be in a different box.

you could do a search on "two stage amp". you would then find that there are alternatives to the 6SL7 for the first stage. I haven't personally gone that way, but I know that oscillation is your problem with these high transconductance jobbies - the 6SL7 is OK because it's transconductance is lower due to its plate resistance being high.

andy
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Old 29th May 2009, 11:10 AM   #4
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hey-Hey!!!,
Look at the JE Labs 2A3 design on Angela Instruments website. I've seen this one do very well, and with some careful attention to construction, it can have some interesting options.
cheers,
Douglas
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Old 29th May 2009, 06:37 PM   #5
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Default Re: Brother can you spare a preamp design?

Quote:
Originally posted by bereanbill
I'm back again. I am wanting to build an SE amp with a 6SL7 pre, 7408 output, and probably the obligatory 5Y3 rectifier. Anyone know of ant SE amps with a 6SL7 preamp whose design I can purloin ?
The 6SL7 is a high gain triode. If you want to use one of these in a preamp (unless you need lots of gain) your only viable choice would be to connect the 6SL7 as a differential, use the 7408 as a cathode follower, set the gain by gNFB, and basically make a glass op-amp.

That'll work quite well, but some folks out there don't like the idea of using gNFB in a pre.
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Old 29th May 2009, 08:51 PM   #6
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Default Re: Re: Brother can you spare a preamp design?

I also think we must first confirm whether Berianbill wants a pre-amplifier, or is just talking about the input part of an S.E. power amplifier.

Quote:
Originally posted by Miles Prower

That'll work quite well, but some folks out there don't like the idea of using gNFB in a pre.
Some folks don't like the idea of using any NFB. "Like" to me denotes a taste, not showed performance improvement. Good luck to them; it is a free country and their money..
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Old 29th May 2009, 08:58 PM   #7
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Aah...thank you my good friend, Johan...I was about to clarify that as it seemed some were confused with my question. It is the preamp stage of an SE amp. Basically a 5C1 Champ, but with a 6SL7 in place of the 6SJ7, and cathode biased. I am also adding a single tone control. I will attach a schematic of the 5C1 circut I am starting with. Sorry for the confusion.
Attached Files
File Type: pdf champ_5c1_schem.pdf (75.5 KB, 26 views)
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Old 29th May 2009, 10:42 PM   #8
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Hi - it would help if you don't call parts of an amplifier a "preamp".

What you are describing is the input stage of an amp, not a preamp. I suggest you drop that word unless you are literally talking about a preamp in a seperate box.

andy
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Old 29th May 2009, 10:52 PM   #9
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Sorry Andy, I thought I did a good job of clarifying that and apologizing in my last post. In actuality, the first half of the dual triode will input the signal and the second half will pre-amp it... sorry if our nomenclature doesn't match.
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