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Lundahl LL2765 Headphone Amp Project
Lundahl LL2765 Headphone Amp Project
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Old 18th December 2017, 07:36 PM   #1
Gungnir is online now Gungnir  United States
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Default Lundahl LL2765 Headphone Amp Project

I recently acquired a pair of nice SE Lundahl LL2765 (60 ma version) and have been trying to find a good headphone amp schematic to use with them. They are 5K primary and 32/300/600 ohm taps. I will be using these with 300 and 600 ohm headphones. I was originally thinking of 45 tubes or maybe even 112a.
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Old 18th December 2017, 10:23 PM   #2
audiowize is offline audiowize  United States
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6C45P, 6E5P as SPUD headphone amps.

60mA would cooperate with a 300B or 2A3 two stage amp.
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Old 18th December 2017, 10:49 PM   #3
sharpi31 is offline sharpi31  United Kingdom
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Lundahl LL2765 Headphone Amp Project
I’m planning to build a 6c45p spud headphone amp soon - slowly acquiring the parts. I like the idea of Brian Clark’s El Spuddo described here: Any good flea-watt SET designs?

The input transformer and cathode pot looks like a nice way of handling variations in tubes.
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Old 20th December 2017, 07:48 PM   #4
hpeter is offline hpeter  Slovakia
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Quote:
Originally Posted by Gungnir View Post
I recently acquired a pair of nice SE Lundahl LL2765 (60 ma version) and have been trying to find a good headphone amp schematic to use with them. They are 5K primary and 32/300/600 ohm taps. I will be using these with 300 and 600 ohm headphones. I was originally thinking of 45 tubes or maybe even 112a.
45 or 2a3 with those irons it will blow your socks off
(lets hope no low quality h-p will be hooked on)
5k with 2a3 will be well damped, id try even a no global fb
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BLOG. XMOS_U8/PCM5102A > LL1544A > 6H9C+gyrator > 2A3_SOV/JJ > LL1660 > STAX SR207 _ SR L300 _ SR007 # LL2748 > 394A > LC 12H/1000

Last edited by hpeter; 20th December 2017 at 07:52 PM.
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Old 20th December 2017, 08:01 PM   #5
Gungnir is online now Gungnir  United States
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Yeah 2a3 is out of the question. I'm thinking of 112a driving 71a.
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Old 25th December 2017, 05:05 PM   #6
hpeter is offline hpeter  Slovakia
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https://frank.pocnet.net/sheets/021/1/112A.pdf
https://frank.pocnet.net/sheets/021/7/71A.pdf
12a has ideally gain 8.5, when resistor loaded it will be less.
total ideal gain could be 25.5x; opt ratio like 3:1
best case gain will be 8.5x including opt.
line out is about 0.3vrms, output will be 2.55vrms
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BLOG. XMOS_U8/PCM5102A > LL1544A > 6H9C+gyrator > 2A3_SOV/JJ > LL1660 > STAX SR207 _ SR L300 _ SR007 # LL2748 > 394A > LC 12H/1000
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Old 25th December 2017, 05:14 PM   #7
Gungnir is online now Gungnir  United States
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What if I used the lundahl as an interstage and another transformer I have for the output?
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Old 25th December 2017, 05:22 PM   #8
Gungnir is online now Gungnir  United States
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I really want this amp to be all DHT if possible
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Old 20th February 2018, 09:21 AM   #9
Gungnir is online now Gungnir  United States
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So, I decided to go ahead with the 71a for the outputs, I just cant decide on the driver. So far I have 300v choke loaded into a salas shunt reg (K&K audio version, one for each channel), which will be adjusted for 220v at the plate of the 71a, then a dropper resistor for the voltage to my driver tube, which will be choke loaded with two Hammond 156c chokes. For filament I am using separate DC filament supplies for each 71a and the driver tube will also be DC, but will share one board (series connected). I am leaning toward the 112a due to the low filament current and I have a bunch of them. I also have 26,01a, and 27/56 globes. I will probably run my headphones off the 300 ohm tap (currently use HD650 and DT990 600 ohm version) since Lundahl only gives the option to use one tap at a time.


Also, I have the power supply in a separate chassis and all of the regulation is in the signal chassis.

Last edited by Gungnir; 20th February 2018 at 09:25 AM.
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Old 20th February 2018, 11:50 AM   #10
merlin el mago is offline merlin el mago
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Could you share your schematic?
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