Bottlehead S.E.X 3.0 DIY tube amp - review and measurements

[Philipp Paul Klose]

This is a quick review of the Bottlehead S.E.X. 3.0

The cheeky name stands for single-ended experimenters kit, version 3. It is ordered directly through https://bottlehead.com/product/single-ended-experimenters-kit-3-0-for-headphones-sensitive-speakers/ (~785USD w/o tax and shipping). Input is via RCA jack, output through binding posts or 1/4" TRS headphone jack.

Bottlehead gives no specs on the amp. The only spec I could find on their page was low output impedance (which makes sense with tubes) and 2W of power.

The internals of the DIY kit are not on a PCB, it is point to point wiring - very old school. Most of the build is easy and the description is easy to grasp. There was only one point where four components came together. A bit finicky, but not too hard to solve. It took me three days in total to build it.

Regarding the tube sound... Either you like it or you hate it. My preference for it switches on a daily basis. Sometimes it is cool, sometimes not.

At unity gain (0dBV in, 0dBV out), 123mW into 8R are no problem. Noise is fine but THD is already 1,23%, giving us a SINAD of 38,2dB.

At the specified 2W output power (into 8R), the THD is at 5,46%, giving us a SINAD of just 25,25dB.

At max power, the 4W are battered with quite some THD.

Overall, it does not sound bad, but it is far from clean.

 

[kemmler3D]

Let me say something snarky and mean just to get it out of the way.

For $800 shipped, you can get a lot of guitar pedals with similar amounts of distortion without having to build them yourself.

OK, it's out of my system.

I really appreciate you taking the time and posting these measurements. Frankly I'm interested in a bit more subjective description of how it sounds at different levels. This is more of an FX box than an amp in my view, (not saying that pejoratively, just 2W with (at best) <40 SINAD isn't what you buy to get hi-fi) so the subjective experience of this amount of distortion is important to understanding its value.

Or let me put it another way. Having heard it and having measured it- would you buy it again, and would you seek out other gear with a similar type of performance?

 

[Jim Taylor]

Tube aficionados claim that "the first watt is the most important", and "If you can't get the first watt right, what's the use of the rest of the power".

With well over 1% THD at only 123 mW, (roughly one-eighth watt output) I'd say that the first watt is in serious trouble.

Jim

 

[MaxwellsEq]

Fascinating review, thank you! This is the kind of engineering research I love!

My immediate reaction to the product itself is: "why?".

 

[restorer-john]

That thing is a deathtrap. I don't think I've ever seen less safe mains wiring on anything, ever.

You have used some scavenged two core shielded DC cable for mains? WTF. Did they send you that in the "kit"? Completely exposed switch and IEC socket wiring and the most extreme rat's nest of unsecured and floating components in the entire history of rat's nests.

In fact, actual rats would be deeply hurt for even insinuating this was remotely reminiscent of their work.

And this is the example they give you?

Going forward, let's use DPDT mains rated switches and switch the active and the neutral. Let's use mains rated cable for primary side wiring and if using a three pin IEC, use a proper earthing technique, not a bit of tinned copper wire. Let's insulate with two layers of distinct insulation- every mains wire. Perhaps consider not using single piece of CAT5 for all the inputs and outputs. Let's secure any component (caps etc) that can move if the unit is shaken/dropped etc.

The "design" is a mess of earth points and loops (look at the RCA gnd loops...), all over the aluminium chassis plate.

You need to take electrical safety seriously. After all, somebody, someday, may plug this in, buy it at a yard sale, or give it someone.

 

[Philipp Paul Klose]

I would not say it is tro

Let me say something snarky and mean just to get it out of the way.

For $800 shipped, you can get a lot of guitar pedals with similar amounts of distortion without having to build them yourself.

OK, it's out of my system.

I really appreciate you taking the time and posting these measurements. Frankly I'm interested in a bit more subjective description of how it sounds at different levels. This is more of an FX box than an amp in my view, (not saying that pejoratively, just 2W with (at best) <40 SINAD isn't what you buy to get hi-fi) so the subjective experience of this amount of distortion is important to understanding its value.

Or let me put it another way. Having heard it and having measured it- would you buy it again, and would you seek out other gear with a similar type of performance?

Yes and no. It sounds different than guitar pedals. More open, mature. Less narrow minded. If you understand. The THD value gives a completely false impression of the sound.
I use the thing as a sound effect in my mixing studio. On drums and bass, keys and other subgroups it glues stuff nicely together and gives an impression of polished, but in a good and more rough way. Room sounds and spill are more natural, some instruments gain body and more intimacy. I cannot discern if that comes from the tubes or the transformers.
Would I buy it again? Maybe. Most loudspeaker bring this thing to its knees, but the sheer power it provides to drive headphones is pure fun.

 

[Philipp Paul Klose]

That thing is a deathtrap. I don't think I've ever seen less safe mains wiring on anything, ever.

You have used some scavenged two core shielded DC cable for mains? WTF. Did they send you that in the "kit"? Completely exposed switch and IEC socket wiring and the most extreme rat's nest of unsecured and floating components in the entire history of rat's nests.

In fact, actual rats would be deeply hurt for even insinuating this was remotely reminiscent of their work.

View attachment 375261

And this is the example they give you?

View attachment 375265

Going forward, let's use DPDT mains rated switches and switch the active and the neutral. Let's use mains rated cable for primary side wiring and if using a three pin IEC, use a proper earthing technique, not a bit of tinned copper wire. Let's insulate with two layers of distinct insulation- every mains wire. Perhaps consider not using single piece of CAT5 for all the inputs and outputs. Let's secure any component (caps etc) that can move if the unit is shaken/dropped etc.

The "design" is a mess of earth points and loops (look at the RCA gnd loops...), all over the aluminium chassis plate.

You need to take electrical safety seriously. After all, somebody, someday, may plug this in, buy it at a yard sale, or give it someone.

Completely agreed. It used stored safely away. When it is live, I only touch it with electrician gloves, ESD shoes and goggles on. It will never be sold.

 

[Philipp Paul Klose]

Fascinating review, thank you! This is the kind of engineering research I love!

My immediate reaction to the product itself is: "why?".

As an engineer, I was just interested in seeing and doing something different.

 

[kemmler3D]

I would not say it is tro

Yes and no. It sounds different than guitar pedals. More open, mature. Less narrow minded. If you understand. The THD value gives a completely false impression of the sound.
I use the thing as a sound effect in my mixing studio. On drums and bass, keys and other subgroups it glues stuff nicely together and gives an impression of polished, but in a good and more rough way. Room sounds and spill are more natural, some instruments gain body and more intimacy. I cannot discern if that comes from the tubes or the transformers.
Would I buy it again? Maybe. Most loudspeaker bring this thing to its knees, but the sheer power it provides to drive headphones is pure fun.

I was just comparing it to a guitar pedal to be snotty, I know it wouldn't sound quite like that. If you are using it as an effect I actually think that's totally appropriate. I'm an ITB guy so I just turn to Variety of Sound plugins if I want to warm something up in a clean/open way, but using this for processing tracks seems totally reasonable and appealing to me. As a playback device, questionable to the same extent that it's useful as an effect, of course.

 

[jdjung]

That thing is a deathtrap. I don't think I've ever seen less safe mains wiring on anything, ever.

You have used some scavenged two core shielded DC cable for mains? WTF. Did they send you that in the "kit"? Completely exposed switch and IEC socket wiring and the most extreme rat's nest of unsecured and floating components in the entire history of rat's nests.

In fact, actual rats would be deeply hurt for even insinuating this was remotely reminiscent of their work.

View attachment 375261

And this is the example they give you?

View attachment 375265

Going forward, let's use DPDT mains rated switches and switch the active and the neutral. Let's use mains rated cable for primary side wiring and if using a three pin IEC, use a proper earthing technique, not a bit of tinned copper wire. Let's insulate with two layers of distinct insulation- every mains wire. Perhaps consider not using single piece of CAT5 for all the inputs and outputs. Let's secure any component (caps etc) that can move if the unit is shaken/dropped etc.

The "design" is a mess of earth points and loops (look at the RCA gnd loops...), all over the aluminium chassis plate.

You need to take electrical safety seriously. After all, somebody, someday, may plug this in, buy it at a yard sale, or give it someone.

How dangerous we talking about here? I've had mine for years and used it all the time with no issues but your comment have me wondering if I should just sell it?

 

[Philipp Paul Klose]

I haven’t died, yet.

 

[DVDdoug]

It shouldn't be dangerous unless you touch the circuitry inside. For safety, there should be a bottom cover. And I assume the metal plate/chassis is grounded (through the power connector).

...I'm just thinking $100 per Watt!!! WOW! And you have to build it yourself! Or, you get to build it yourself.

 

[Ruhled]

I used to have their preamp. The channel balance was always off, well, because negative feedback is evil, right? But volume pots and triode sections are not equal by nature. Sold it on years ago. It was fun to build though and back then I want to say it was only like $100 for the kit. So it was the gateway drug it was supposed to be and for that I am grateful. I've built much better stuff since. I do still have a pair of the original s.e.x. output transformers I picked up a while back. I think they were just small autoformers iirc.

 

[mhardy6647]

There's an unbuilt Bottlehead Foreplay preamp (original morph, with no 'upgrades') a-sittin' in the basement. There's a story connected with it.

I do happily keep a pair of very early Bottlehead Paramour single-ended 2A3 'monoblocks', which my kids & I built together here as spares in case my SE 2A3 amp has a mishap. Perfectly listenable little amplifiers despite their laughable OPTs made from line matching transformers wired in reverse (i.e., primaries and secondaries swapped).