Another SEX amp!

[Todd R]

It's that time again, the urge to build another SEX amp has hit so I ordered a 3.0.

Any idea what to expect in sound differences between the 2.1 and 3?

Reviewing the instructions for the 3, I see there are only 4 & 8 ohm wiring options where the 2.1 had 4, 8, 16, & 32. Why is that?

BTW, the pictures are easier to see in the 2.1 manual.

 

[Paul Birkeland]

Any idea what to expect in sound differences between the 2.1 and 3?

They should sound nearly identical.  Through some testing during development for the S3X, we were able to lower the noise floor just a tad more, but this may not be noticeable.

Reviewing the instructions for the 3, I see there are only 4 & 8 ohm wiring options where the 2.1 had 4, 8, 16, & 32. Why is that?

We frequently ran into the situation where a Grado headphone user would wire the amp for 32 Ohms, which would deliver 2000mW for a headphone that maybe needed 50mW.  There would also occasionally be the 110dB sensitive 16 ohm horn speaker user who would also wire for 16 ohms.  In both instances, wiring the amp for 4 or 8 ohms was much more sensible.  Consequently we rewrote the instructions to recommend the 4 ohm setting for headphone use and the 8 ohm setting for speaker use. 

BTW, the pictures are easier to see in the 2.1 manual.

Try zooming in on a picture from the 2.1 manual, then the 3.0 manual.  I've attached a 650% zoom on a socket from each manual.

 

[Todd R]

They should sound nearly identical.  Through some testing during development for the S3X, we were able to lower the noise floor just a tad more, but this may not be noticeable.
We frequently ran into the situation where a Grado headphone user would wire the amp for 32 Ohms, which would deliver 2000mW for a headphone that maybe needed 50mW.  There would also occasionally be the 110dB sensitive 16 ohm horn speaker user who would also wire for 16 ohms.  In both instances, wiring the amp for 4 or 8 ohms was much more sensible.  Consequently we rewrote the instructions to recommend the 4 ohm setting for headphone use and the 8 ohm setting for speaker use. 
Try zooming in on a picture from the 2.1 manual, then the 3.0 manual.  I've attached a 650% zoom on a socket from each manual.

Thanks Paul.
I plan to use Hifiman HE1000V2 phones, 35ohm 90db sensitivity. Still wire it for 4 ohms?

Ah, zooming....who would have thought? 

 

[Paul Birkeland]

I believe those want about 100mW into 35 ohms.  The 4 ohm tap will give you more than twice that.

 

[Todd R]

Paul,
On another subject....
I'm rounding up premium parts for this next build, Goldpoint attenuator, Cardas hardware, premium resistors, etc.
I use Audience caps but they don't have a 1.5  µF 630v available. The have either a 1 µF or a 2  µF in 630v. is there a way to use either of those values?
The do have a 1.5  µF, but only at 200v.

 

[Paul Birkeland]

Either of those caps is going to work nicely. 

 

[Todd R]

Any reason to prefer one over the other?

 

[Paul Birkeland]

The 1uF caps will be easier to fit while the 2uF caps may give a little more bass extension than the 1uF.

 

[Todd R]

Thanks 

 

[Todd R]

Reading the SEX manual again...
I thought it was a misprint, but there is a "0: ohm resistor going to the speaker terminals. Puzzled by that.
Why not just a piece of wire?

 

[Paul Birkeland]

It can be a challenge to strip really short pieces of wire, so the jumpers we provide make the build a little easier.

 

[Todd R]

It's alive!
Still need to do the C4S later this week maybe.

 

[Todd R]

It sounds good, with one little thing....
Right channel will quickly blip out for a split second randomly. Thought it was dirty tube pins, so I took them out and cleaned with fine sandpaper and Deoxit, and swapped positions. Right channel still having random quick cut outs.

 

[Paul Birkeland]

It's looking good.  What you're describing is almost always a solder joint that is either missing or not all the way flowed. 

 

[Todd R]

Paul,
Exactly right again. Someone (I'm not saying who), neglected to solder the 220 ohm resistors at A&B 3!
Working much better now!