5K opts in a Sex amp

xcortes · 19435

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Offline xcortes

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on: October 21, 2009, 12:26:44 PM
By PJ when asked about using a 5k output transformer (Tl-404 specifically but it applies to Exo-045 too) and a plate choke recommendation:

"The BCP-15, as used in the Paramour upgrade, is quite suitable. It has a bit less inductance than the BH-2, but fortunately it doesn't need as much inductance since it's operating into 5k instead of 8k impedance. Should work just fine.
No guarantees for the following, as I have not tried this myself. But the spreadsheet tells me the following changes should adapt the SEX amp for a 5k load. Change two resistors on each channel as follows:

Replace Rpsu (680 ohm, 3 watt) with 1600 ohms 10 watts. You'll have to mount it outside the T-strips instead of between them, and it will get hot(!). It's T6 to T11, and T26 to T31, bottom holes. This will drop the power supply voltage by about 45 volts.

Replace Rbias (620 ohm 2 watt) with 430 ohm 2 watt at T12U to T15U, and T32U to T35U. This will increase the quiescent current by about 4mA"

Xavier Cortes

Offline Capt.Z

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Reply #1 on: October 21, 2009, 04:21:31 PM
'xcuse my ignorance, but what benefit does this change got?


Offline Paul Birkeland

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Reply #2 on: October 21, 2009, 04:37:51 PM
Quote from: Capt.Z on October 21, 2009, 04:21:31 PM
'xcuse my ignorance, but what benefit does this change got?


The TL404 is the finest headphone autoformer available, and if an individual possessed the abilities and the currency, it is a really nice piece of iron to integrate into the SEX amp (which has been specially designed to run autoformers).

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Jim R.

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Reply #3 on: October 22, 2009, 06:44:49 AM
Will the BCP-15 and EXO 45 fit in the same space as the stock iron, and will the output power be significantly lower?

Anybody done this yet?

Thanks,

Jim

Jim Rebman -- recovering audiophile

Equitech balanced power; uRendu, USB processor -> Musette DAC -> 5670 tube buffer -> Finale Audio F138 FFX -> Cain and Cain Abbys near-field).

s.e.x. 2.1 under construction.  Want list: Stereomour II

All ICs homemade (speaker and power next)

Offline Skip Pack

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Reply #4 on: October 23, 2009, 06:25:41 AM
Quote from: jrebman on October 22, 2009, 06:44:49 AM
Will the BCP-15 and EXO 45 fit in the same space as the stock iron, and will the output power be significantly lower?

Anybody done this yet?

Thanks,

Jim


I have been running my S.E.X. amp this way for about three years. I wired the
EXO 45 as an autoformer per PJ's advice. Most of the time I used it with Lowthers
having 15 ohm specs, so the reflected impedence was close to the design spec
for the amp. Still sounds good on 8 ohm speakers. In that case, the power should
be slightly higher than stock and the same for the distortion, if I understand
correctly.

Skip


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