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December 08, 2019, 07:01:44 PM

Author Topic: Less gain than SEX?  (Read 177 times)

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Offline oguinn

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Less gain than SEX?
« on: May 21, 2019, 01:28:38 PM »
I finished the Stereomour II today and started testing it (very limited tests so far). With everything the same, it seems to have a good amount less gain than the SEX with C4S. Is that to be expected or is there a possible issue?
Jameson O’Guinn

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Main System: Schiit Bifrost MB, U-Turn Orbit, Reduction w/ Integration, Smash w/ Smashup & SmashQuiet (replacing w/ BeePre), Stereomour II w/ DC Filament & Shunt Regulator (replacing w/ Kaiju), SEX 3.0 w/ C4S, Blumenstein Orcas, HD6XX

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Offline oguinn

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Re: Less gain than SEX?
« Reply #1 on: May 21, 2019, 01:40:11 PM »
It seems like the SEX has a gain of 15 and the Stereomour has a gain of 8, so that seems to track with what I’m seeing (as long as I’m reading that right and understanding it).
Jameson O’Guinn

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Main System: Schiit Bifrost MB, U-Turn Orbit, Reduction w/ Integration, Smash w/ Smashup & SmashQuiet (replacing w/ BeePre), Stereomour II w/ DC Filament & Shunt Regulator (replacing w/ Kaiju), SEX 3.0 w/ C4S, Blumenstein Orcas, HD6XX

Desktop System: Crack with Speedball

Offline Paul Birkeland

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Re: Less gain than SEX?
« Reply #2 on: May 21, 2019, 01:42:01 PM »
Are the impedance taps set the same between both?

I see 15dB of gain for the SEX on the 8 ohm OT configuration, which IIRC doesn't go up a whole ton with the C4S upgrade.  I roughly calculate that the Stereomour would be a few dB below that.  If you'd like to increase the gain of the Stereomour a bit, you can install cathode bypass caps on the driver cathode bias resistors.  2200uF at 6.3V would be my recommended starting point.
Paul "PB" Birkeland

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Offline oguinn

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Re: Less gain than SEX?
« Reply #3 on: May 21, 2019, 01:46:09 PM »
I believe I had them both wired for 8 ohms. I’ll double check when I get home.

I might do the cathode bypass caps after some listening time. If I do I’ll 100% need some help understanding what that means and how to do it.
Jameson O’Guinn

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Main System: Schiit Bifrost MB, U-Turn Orbit, Reduction w/ Integration, Smash w/ Smashup & SmashQuiet (replacing w/ BeePre), Stereomour II w/ DC Filament & Shunt Regulator (replacing w/ Kaiju), SEX 3.0 w/ C4S, Blumenstein Orcas, HD6XX

Desktop System: Crack with Speedball

Offline oguinn

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Re: Less gain than SEX?
« Reply #4 on: May 21, 2019, 01:53:06 PM »
If I go that route, I assume these caps are sufficient. Any concerns?

https://www.mouser.com/ProductDetail/647-UKL0J222KHD
Jameson O’Guinn

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Main System: Schiit Bifrost MB, U-Turn Orbit, Reduction w/ Integration, Smash w/ Smashup & SmashQuiet (replacing w/ BeePre), Stereomour II w/ DC Filament & Shunt Regulator (replacing w/ Kaiju), SEX 3.0 w/ C4S, Blumenstein Orcas, HD6XX

Desktop System: Crack with Speedball

Offline Paul Joppa

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Re: Less gain than SEX?
« Reply #5 on: May 21, 2019, 02:33:02 PM »
The cathode bypass caps will make a very small difference - I calculate 0.7dB.

My calculations show a gain of 7.08 (17dB) for SEX with C4S, and 4.5  (13.1 dB) for Stereomour II, both set for 8 ohms. Note that they use the same output transformer, but at different impedance levels, so the 8-ohm wiring is different between them.
Paul Joppa

Offline oguinn

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Re: Less gain than SEX?
« Reply #6 on: May 21, 2019, 02:39:17 PM »
I think it’ll be loud enough for my current room. I’ll revisit in the future if it becomes an issue.

I have a handful of those caps on the way just in case, although it sounds like they won’t make much difference.
Jameson O’Guinn

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Main System: Schiit Bifrost MB, U-Turn Orbit, Reduction w/ Integration, Smash w/ Smashup & SmashQuiet (replacing w/ BeePre), Stereomour II w/ DC Filament & Shunt Regulator (replacing w/ Kaiju), SEX 3.0 w/ C4S, Blumenstein Orcas, HD6XX

Desktop System: Crack with Speedball