Bottlehead SEX, now what ???

[Capt.Z]

I do have a Bottlehead SEX with the C4S boards, stock iron, driving a pair of Hornsoppe Horns. I recently had the Cathode Follower amp by Transcendent on loan, and it did sounded more detailed and refined and probably a little leaner than the SEX. Also, the Transcendent sounded just right with the Horns. Had 3 Watts instead of the 1.8 Watt of the Bottlehead.

Well, yesterday I returned the Transcendent and I am wondering what upgrade path I should take in the future.
Wondering if 'just' the iron upgrade in the SEX would do, or if another SET amp is lurking somewhere in the future. I believe the SEX with the stock iron produces a somewhat warm sound. Would the pinstripe Iron give a more neutral frequency response? (speak a little leaner, better bass extension and better higher frequency extension)

Nice thing on the SEX amp is it's low profile and it fits well on my Audio rack. Spacing between shelves is 8 inches in heights. So the SEX fits well with it's short bottles. The Transcendent was just a little too tall to fit and even if it fit I would not have felt too good having the hot tubes so close to the next shelve.

Also, if I ever upgrade I could never go over $ 1000 new, used or kit. I know that is not much for SET.

Looking for great detail, great holographic, good soundstaging. AND CLEAN SOUNDING. Needs to sound good at lower volume settings too.

What is your take on this???

[Paul Joppa]

"more detailed and refined and probably a little leaner" - that's a pretty good description of what a bit of negative feedback brings to the party, and of course a cathode follower does have negative feedback. (It's the best kind - local to a single stage, and not too much of it.)

PB is right, the MQ upgrade iron will make a big difference. Technically, the higher inductance of the plate choke and output transformer will reduce tube distortion introduced when there is bass energy, and the superior core materials will reduce transformer hysteresis distortion - overall, similar benefits to those of negative feedback. Whether it goes far enough in that direction for you is not easily predicted, of course! For the leanest and cleanest midrange, I'd spring for at least some nickel in the core - but that's my preference showing through.

Better coupling capacitors will make a difference as well. Not a big a difference (to my ears) as the magnetics, but you won't have any trouble hearing it. Remember in both cases to allow for at least 50 hours of playing music before making judgements. You can substitute an 8-ohm power resistor for the speakers if you don't want to listen while the components break in, or look up Grainger's fast break in technique for caps.

[Doc B.]

Yeah, I would say the iron upgrade would get you going in the right direction. It will allow the bass to go deeper, more cleanly and give the amp better resolution. However the other issue is that you are putting nearly twice the power into the speakers with the OTL amp. If the S.E.X. amp is being pushed it might sound a little more "soggy". The upgrade transformers would definitely help this, but the amp will never make more than a couple of watts.  Is that the issue with the speakers? I don't know, never having heard them.So while the trans upgrade definitely makes the amp sound better it's a little difficult to say for certain that it would get you all the way in the direction you want to go.

Beyond that it may be time to consider directly heated triodes. The upcoming Stereomour 2A3 amp just might be the ticket. With its similar power output level a 2A3 amp might end up sounding better than the 3W OTL amp. That said, OTL amps tend to have a more lean and "detailed" sound. I would not say that the typical use of the word detailed translates to high resolution, to me it represents more the tonal emphasis of being a bit laid back in the lower mids and a bit more emphasis on the highs, giving an impression of "coolness". SE amps typically give a better midrange presentation which can be perceived as warm. It may be that your speakers benefit from that more detailed, cooler tonal balance.

No definitive answers, but hopefully some food for thought. If you can get a handle on whether the S.E.X. amp sounds like it's being pushed a little past its limits or not - does it sound better playing softly then it does playing loudly? - we might be able to help refine the decision for you.

[Capt.Z]

Thanks Doc for the input.

The Transcendent amp I borrowed was NOT OTL, but transformer coupled.

Power wise, I guess I can life with the SEX for most of the time. I do have a PP EL34 amp in my other system close by that I can use if I need more power.

[Doc B.]

Ah, OK, the CF single ended kit. If the power of the SEX kit seems adequate I think the iron upgrade would be a pleasant improvement in the direction you want to go.

[Capt.Z]

Guess the iron upgrade is the 'cheapest' step up.
Other options would be to sell the SEX and save the money from the iron and buy something else.
Can the Stereomour run 300B tubes?

[Paul Joppa]

....Can the Stereomour run 300B tubes?

Only the 2.5v filament versions. It won't change the power capability though, still 3.5 watts. It will also run 45's, but only produce 2 watts. The 45 is especially linear, as well as having a directly heated cathode, so many really like the sound of that tube.

[Capt.Z]

Like I mentioned above, I did not build this amp, but bought it used. So don't blame me for the looks. I only assemble and installed the C4S boards, changed the volume pot later and now acctually have the volume pot disabled, since I use a pre-amp, that sounds a lot better than the volume pot.

Paul Joppa mentioned better caps may help too.
Have no idea what caps the original builder used, so I attached a picture I took this morning.

Any idea what kind of caps these are and how they my sound in comparison to others.

If I needed to change the caps, what caps would you all recommend to get better detail, soundstaging and great holographic?

[Doc B.]

Couple suggestions:

Bend that blue electrolytic capacitor farther away from the power switch. That close to the AC terminals it is an accident waiting to happen.

When you bypassed the wiper of the volume control, did you leave it in the circuit as the grid load, or did you install a 100K ohm resistor in place of the pot? I can't quite make out the image on my dinky notebook screen. If you did the former, using a metal film resistor instead of the resistive track of the pot as the grid resistor might make a subtle difference in the sound. Or it might not. But it only costs a few pennies a couple minutes time to find out.

[Capt.Z]

Will bend that cap over when I get home.

On the volume pot we just soldered the incoming and outgoing leads to the post on the pot. No resistor used.

Pre-amp has no gain, so would adding a resistor lower the output?

[Paul Joppa]

Looks to me like the caps have already been upgraded. That would be the fat orange cap - looks like a 716P Orange Drop film/foil for the 0.1uF coupling cap - and the dual white caps in the parafeed position. Since they are paralleled, you have 2uF per side, which is the right value for the upgrade (and twice the normal stock value). I don't recognize the type, maybe someone else will?

[Paul Birkeland]

Tell me about the black electrolytic on the left side of that photo that looks out of place... (capacitance and voltage). 

[Capt.Z]

The last owner told me that when the original builder put the amp together, he found one of the power caps to be faulty. So he replaced it with another (larger one) that he had on hand.

One cool think this builder did was to add a switch to the headphone jack so you can switch between low and high impedance phones. Setting is for 32 ohm, off, and 600 ohm cans.

[Doc B.]

In 16 years I have never heard of an electrolytic arriving in faulty condition from our vendors. Tubes, yes. Switches, sometimes. Transformers, very occasionally. 'Lytics, never. I have seen quite a few that were faulty after the builder installed them backwards and then just turned them around instead of replacing them once he heard funny noises when he first turned on the amp.

[Grainger49]

Tell me about the black electrolytic on the left side of that photo that looks out of place... (capacitance and voltage). 

Paul, Caucasian Blackplate, is asking if the larger capacitor is a different value and voltage than the other 5 in the power supply.