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PostPosted: 13 Jun 2018, 03:39 
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Suncalc designed a two stage cathode follower preamp. Previously I married a 4SU premp with a Pass BoZ jFet stage to drive SS amps. Now an all tube preamp.

http://retro-thermionic.blogspot.com/2018/06/lagoon-two-stge-tube-preamp-with.html
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PostPosted: 18 Jun 2018, 19:14 
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This preamp was a commission job do gone now. Back to old faithful. Fortunately another tube preamp.


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PostPosted: 04 Sep 2019, 23:19 
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The preamp had some issues which I have only just come to realise was due to excessive gain. By dropping Rp to 15k and Rk to 390ohms (thanks Bruce) gain and associated hiss can be tamed. In this new build I use a Hammond wood cheek chassis painted (Epoxy paint and etch primer) hammertone blue. Two selectable inputs, external PS, Alps blue velvet pot and 4oz solid brass gold plated knob. Russian PIO caps for interstage and output. Tubes are Mullard re-issue with a heavy tube ring.

Sound is very fast, snappy with tones of bass. Good solid sound. Now called “Lagoon 3”.
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PostPosted: 07 Sep 2019, 23:58 
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Had hiss and gain problems with the cathode follower so now Bruce’s SRPP. Still some hiss and too much gain but I have the 12AX7s in because I don’t have any good U7s which is what Bruce has suggested. Sounds good though.

I’ll order some and try.
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PostPosted: 20 Sep 2019, 22:21 
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Had more noise and hiss issues so converted the preamp to Bruce’s SRPP. Still had noise problems until I purchased some JJ 12AU7s to replace my new Mullard 12AX7s. Now the preamp is dead quiet. I though the JJ weren’t the best (definitely the cheapest I can buy locally) but Bruce commented he thought they weren’t so bad. Listening to them now and though only a few hours on them all sounds very good.

Finally I have finished this build which has been carried over for years and now put to rest. Worth it in the end. The preamp always sounded very good just when up close to the speakers there was always a hiss. The snake catching JJs fixed that. I have used JJs in a few phono tube preamps and they have always performed well and very quietly. Anyhow good result. Persistence has paid off.

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PostPosted: 17 Oct 2019, 07:18 
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Schematic?


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PostPosted: 17 Oct 2019, 16:49 
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PostPosted: 18 Oct 2019, 18:13 
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Joined: 13 Jan 2018, 21:33
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Mark, there was also this suncalc circuit with the cathode follower setup Gio built viewtopic.php?f=9&t=5186&hilit=cathode+follower+gio#p43845

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PostPosted: 18 Oct 2019, 18:27 
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Woodo wrote:
Mark, there was also this suncalc circuit with the cathode follower setup Gio built viewtopic.php?f=9&t=5186&hilit=cathode+follower+gio#p43845

I had noise issues with the common cathode design so I rewired for Bruce’s SRPP. In the end it wasn’t the design at all but two noisey tubes. So it could have stayed with a common cathode.

Regardless going with SRPP and now new JJ 12AU7 the preamp is dead quiet and sounds excellent. Other SRPP preamps I have built (4 of) using 6SN7s have also worked extremely well and been dead quiet. The design seems very sound (pun intended) and works into high loads without problems.

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PostPosted: 18 Oct 2019, 23:03 
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which version do you favour 6sn7 or 12a#7? Any particular strengths and weaknesses? I use new JJ and older RCA 6sn7 of course for the 300b set and both are quite good. Hard to gauge any difference. good ears may be able to. i have a couple of 12 au7 for a prospective 6as7 amp but have not heard any amp using them yet.

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