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Old 15th April 2012, 07:16 PM   #1851
dhtrob is offline dhtrob  Netherlands
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Great! Thanks Ale..
Rob
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Old 16th April 2012, 10:35 AM   #1852
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I've been doing some extended listening to the new 26 preamp with my 300b and 2a3 amps, and I'm now coming back to preferring the 300b with 46 driver and Lundahl LL1620/80mA. With the new operating point the 26 preamp is sounding more detailed and the overall level of detail into the 300b SET is stunning. All of which means I'll have to go back and revise my previous 26 preamp. More experiments! But making some serious progress. As they say - necessity is the mother of invention. If I hadn't had the hair-brained idea of using cheap 12v DC power supplies none of this would have happened.

andy
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Old 16th April 2012, 01:43 PM   #1853
jamesdb is offline jamesdb  United States
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Andy, what is your HV supply like? SS or tube rectified? Single shared or dual LC supply?
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Old 16th April 2012, 05:47 PM   #1854
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The power supply for the new 26 preamp is very simple. It has a small mains transformer secondary 120v, rated 50mA, and an EZ80. Then a 2uf input cap to a 15H choke rated 30mA. After that a 50uf cap, 2.4K dropper resistor and another 50uF cap. All capacitors are polypropylene - I never use electrolytics.
My usual HT supply has an AZ1 mesh and is a bit more elaborate.

I'm building another 26 preamp exactly the same! Need to clone this. I'm out of Hammond 156c chokes so next one will be Lundahl LL1667/10mA. Otherwise the same. Will be interesting to compare plate chokes.

Andy
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Old 16th April 2012, 06:39 PM   #1855
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Quote:
Originally Posted by andyjevans View Post
The power supply for the new 26 preamp is very simple. It has a small mains transformer secondary 120v, rated 50mA, and an EZ80. Then a 2uf input cap to a 15H choke rated 30mA. After that a 50uf cap, 2.4K dropper resistor and another 50uF cap. All capacitors are polypropylene - I never use electrolytics.
My usual HT supply has an AZ1 mesh and is a bit more elaborate.

I'm building another 26 preamp exactly the same! Need to clone this. I'm out of Hammond 156c chokes so next one will be Lundahl LL1667/10mA. Otherwise the same. Will be interesting to compare plate chokes.

Andy
Hello,
Can you provide a link to a schematic of your 26 preamp? If it's been mentioned before, please forgive me, but this is an extremely long thread. Also, what phono preamp are you using?
Regards.
David
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Old 16th April 2012, 07:18 PM   #1856
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I don't play records - just CDs and most of my archive is now on a Mac Mini in AIFF on iTunes. I'll write out a schematic and post it.

andy
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Old 16th April 2012, 09:40 PM   #1857
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Well, I tried out a clone of the 26 preamp that has me transfixed. You're not going to believe this, guys, but the original two Hammond 156C plate chokes in series sound better than the Lundahl LL1667/10mA. May be inductance - Hammonds are 300H while the LL1667/15mA is rated at 270H. So the 10ma version should be similar to the Hammonds. The static resistance is different - 7K for the Hammonds and 2.3K for the Lundahls. Maybe the capacitance is a factor - two chokes in series may mean the Hammonds are lower? Haven't tried to measure. I think I've pretty much cloned everything else - only small differences. Now this surprises me, but it's good news economically!

I will have to do some extended listening, but with the Lundahls some of the magic has gone - slightly thicker sound. The Hammonds are very transparent. I'll have to check the filament regs to see if the current is exactly the same in starved filament - that may be a factor.

Andy

Last edited by andyjevans; 16th April 2012 at 09:57 PM.
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Old 16th April 2012, 09:59 PM   #1858
Magz is offline Magz  United States
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Progress report: I received my autoformer volume controls, front panel display board, rear input board and remote from Bent Audio today. Excellent quality, very substantial parts. Six remote-selectable relay activated inputs, two outputs plus a tape output, 1dB steps on the VC, with a range of -51dB to +7dB. I've rearranged my preamp-on-a-board to fit them in and shorten the signal path, and measured to determine the box size I'll need. I have a snapshot below with the preamp, the display and input boards, and the PS parts in back (still waiting on the power transformer).

Front Panel Express can make the boxes I'll need, I just have to set up the front and rear panels on their CAD software.
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File Type: jpg 26 preamp with TAP-X Parts.jpg (42.0 KB, 471 views)

Last edited by Magz; 16th April 2012 at 10:03 PM.
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Old 17th April 2012, 06:51 AM   #1859
dhtrob is offline dhtrob  Netherlands
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Quote:
May be inductance - Hammonds are 300H while the LL1667/15mA is rated at 270H. So the 10ma version should be similar to the Hammonds. The static resistance is different - 7K for the Hammonds and 2.3K for the Lundahls.
I use a Tribute 1:2 interstage in reverse. It has 160He on the (now) primary, very good results.
Imho the static resistance is VERY important here. If you want to try out something interesting: Just put a 100150ohm resistor between anode and choke in series. You will hear a noticeable difference..
Another thing: When playing at approx 97Volt on the plate, even a 0.4Volt difference on the cathode will sound different (and using other brands '26 as well? ..)

Rob
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Old 17th April 2012, 09:56 AM   #1860
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Hi Rob,

I tried out the LL1667 with an added 4.7K anode resistor to make it equivalent to the 2x Hammond 156Cs in static resistance. The sound was better - cleaner. But still not as good as the Hammonds.

I'm intrigued by all this. The next step is using the Hammonds for the driver stage in my 300b amp. Currently that's 46s into Hammond 126Cs. Its good as it is but I'm wondering if I can now sneak in a 10Y with 2x 156Cs as a driver at lower voltage and current with starved filaments....... Not sure if it would like the 8mA limit on the Hammonds but worth a whirl. Could be direct coupled from the 26 also.

Andy
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