S.E.X. 3.0 Completion with S.E.Xy Speakers

[jtreynol]

I recently completed a system based on the S.E.X. 3.0 amplifier, and figured I’d pass on a few notes about my attempt at a “S.E.Xy speaker” setup.

I decided to build a frame for the amp out of leftover walnut from a previous project. I had the chassis plate powder-coated in silver-vein by a local shop. I finished the power transformer and plate chokes with engine enamel (baked in an oven to cure).

As far as the speakers go, I went with the Bottlehead “S.E.Xy Speakers” idea, using Fostex FE166En 6.5" full range drivers installed in Dayton Audio TWC-0.25BK cabinets. (Unfortunately the cabinets no longer seem to be available.) Because I was shooting for a small system for my office, I went with Fostex SubMini2 powered subs for the woofers.

The u-turn Audio turntable goes through a Schiit audio Mani phono preamp via a SYS input audio switch (to switch between a digital source and the turntable). Coincidentally, the preamp and switch are made in my town.

The system sounds great, and while not room-shaking, provides enough volume to achieve uncomfortable listening levels.

[oguinn]

Huh. I steered away from doing anything requiring heat on the plate chokes because I wasn't sure about their tolerance. How hot can you get those before you damage anything?

Nice build, by the way!

[Paul Birkeland]

That's a handsome looking office system!

[jtreynol]

Thanks oguinn and Paul for the complements!

oguinn:

The engine enamel called for a 200 degrees F cure for one hour. I consulted with an electrical engineer on this, and he thought it was a fairly low risk of damaging the plate choke. I accepted that risk, but monitored the temperature of the oven during the cure cycle very carefully. (My oven apparently has a fairly loose control system..).  I’ve had no issues to date with the amp. Standard caveat: YMMV.

John

[Doc B.]

Nice!

[Karl5150]

Wow. I'd say the whole system is pretty S.E.Xy.

[jtreynol]

Thanks Doc and Karl for the kind words!

Unfortunately this may have been a "gateway" project leading to a more ridiculous project in the future for my living room.. 

John

[Natural Sound]

I know this an old post but I was very much interested in using your idea. I even went so far as to drop a pair of the subs in my shopping cart. Then I realized that this sub won't connect in the traditional S.E.Xy way. The SubMini2 doesn't have speaker level inputs on the plate amp. How did you cable this up?
 

[Paul Joppa]

As shown in the owner's manual, preamp to sub input, [thru] terminals to power amp.

[Natural Sound]

As shown in the owner's manual, preamp to sub input, [thru] terminals to power amp.

But in the S.E.Xy configuration there is no pre-amp, Just speaker outputs from a S.E.X. integrated power amp. A plate amp with speaker level inputs is required but this one only has line level inputs. What am I missing?

[Paul Joppa]

You are right, the sub you are looking at is not designed for use with integrated amps - it seems to be designed for use with a phone or computer.

But you can get an adapter to feed the speaker outputs to the sub, in parallel with the speaker. Here's an example:

https://www.allaboutadapters.com/sp2ba.html?viewfullsite=1

[jtreynol]

I’ve been off the forum for a bit, but will respond to Natural Sound’s question regarding wiring of the SubMini2 "subwoofers" from last June (for the record!).

The Fostex SubMini2 subwoofers claim to accept a maximum 15 dBV input signal (I’m guessing 0 to peak), though the typical use case they show in the manual is connection of a consumer audio line-level output (which I understand to be typically ~0.5 V). The subwoofer input impedance is 10 kOhm. I measured the tube amp output (while connected to the passive speakers) at about +- 3 V peak to peak when cranked.

I was originally planning on making a high-impedance, line-level output voltage divider to connect the amp’s speaker outputs to the subwoofer input. However, since the input can handle 15 dBV (around 5.6 V by my calcs), and already has a high input impedance, I figured I could just connect the tube amp speaker output directly to the subwoofer input.

So, my final solution was to run a shielded cable from the speaker connections (at each speaker) to the RCA input of each respective subwoofer unit. Note that the subwoofers each have an internal crossover and a volume knob. The idea is that once these are set appropriately, the master volume on the tube amp will be all that’s necessary for normal use.

As described in my original post, the system sounds great! (There do not appear to be any odd distortions or other anomalies coming from the SubMini2 speakers.)

John

[mcandmar]

That is a S.E.X.Y build, nice work!

[jtreynol]

That is a S.E.X.Y build, nice work!

Thanks, mcandmar!