Are there any upgrade worthy parts on the SEX kit?

[jon_k]

Hi,

I'm new here. I got the kit with all the addons, it's on it's way (from massdrop). So, I've seen people on these forums replace capacitors, the volume knob, and various other components in these amps.

I was once told by another hardware hacker, if your manufacturer didn't have the inclination to select quality hardware, how can you believe they had worthy audio circuit design even worth upgrading?

Are there any parts on the SEX amp that would lead to the biggest change in quality to cost?

I got the SEX amp because close friends have assured me he honestly feels it is $2000 quality for $500 cost. I decided to experiment, and see if these claims are substantiated and am always willing to upgrade.

Any ideas?
Alps pot is a definite first order.
I plan on using my own power and signal wire as well.

 

[Paul Birkeland]

I was once told by another hardware hacker, if your manufacturer didn't have the inclination to select quality hardware, how can you believe they had worthy audio circuit design even worth upgrading?

This comes up sometimes.  We provide exceptionally high quality parts where such parts are hard to replace or replicate (mostly transformers).  Where one could spend a few dollars or a few hundred dollars for the same value of cap, we will leave that up to each individual customer.  Often times even something like an Alps Blue just isn't available in the quantities we need with sufficient regularity to include it in our kits. 

As far as what to replace, I would recommend replacing nothing, as this will often complicate troubleshooting if you have an issue, and you'll never know what improvement was gained by making the substitutions.

 

[jon_k]

As far as what to replace, I would recommend replacing nothing, as this will often complicate troubleshooting if you have an issue, and you'll never know what improvement was gained by making the substitutions.

Fair enough!

I will only add the Alps pot after testing the stock unit, and may get time to experiment later.
I am probably also going to install two phone jacks with a resistor on source for attenuated listening. Those aren't really significant mods though.

I'm sort of in line with a $500 capacitor is probably not going to change the world audibly. Though you know some people think they feel it.

I've heard the SEX isn't anything to underestimate, so I'm really excited to see what it's all about.
I'll probably be back to post pictures of how I finish mine.

 

[mcandmar]

Hi Jon,

I've spent the day reading this site looking for the same answers (i'm in the massdrop too),  and also couldn't help myself and added the C4S and Switch kit  :

My pre build parts list are a volume pot and headphone sockets, i.e. a better socket and adding an XLR socket too.  But i agree with the wisdom of building, testing, get used to it before making any more changes.  There are lots of interesting threads about "cap rolling" to make your head spin, but nothing really jumps out at me as being worth sourcing straight out of the box.

Also if you have a few hours to kill have a browse though the gallery section, some very nice builds in there.  I still cant decide on the cosmetic side of the build, i haven't done wood work since i was in school.

Cheers,

Mark

P.S. Fair warning to the moderators, there will be at least a dozen of us wide eyed eager tinkerers coming to disturb the peace!

 

[Grainger49]

Paul,

Very well said and good advice.

Jon,

I have been kit building for a long time, decades.  The Bottlehead circuits are simple, yet elegant.  There is noting there to get in the way of the music.

Here is my list, from most effective to least, of the tweaks most often used on Bottlehead equipment.  It is just my opinion, but it comes from experience:

C4S
Upgraded Iron
NOS tubes
Film output caps
Improved power supply, upgrade the final cap and a choke replacing the second resistor, maybe even both resistors
Upgraded volume control "device"
Improved, thick film, R1 resistors for the C4S
Fred Cree, ultra soft recovery, diodes replacing the UF4007 diodes
Improved signal path wire
Improved RCA Jacks
Improved headphone Jack/Speaker terminals

 

[mcandmar]

Improved, thick film, R1 resistors for the C4S
Fred, ultra soft recovery, diodes replacing the UF4007 diodes

Hi Grainger,

Can you help identify the values of those resistors, wattage and working voltages?

I assume for the diodes the UF4007 replaces regular IN4007?

Thank you,

Mark

 

[Doc B]

The UF4007s have pretty clean reverse recovery and seem to avoid RF hash. If I was going to improve upon them them I would install CREE high voltage schottky rectifiers, as FREDS sometimes add HF noise.

 

[Grainger49]

Mark,

I never built the SEX or SEX C4S.  So I can't supply the values.

Dan,

I'll change the recommendation.  I thought Freds and Crees were the same, just different names.

 

[Paul Joppa]

Cree is a manufacturer. It is almost impossible to get more than a 100v rating in silicon when making a Schottky diode, so they make high voltage ones from silicon carbide, up to 1200 volts. (It is possible in theory to make even higher voltage diodes from diamond crystals, but it's challenging!)

Schottky diodes have no reverse recovery at all; they are like tube rectifiers in that respect. The FREDs, fast recovery, ultra-fast recovery etc. designs reduce the magnitude of the reverse recovery spike, but cannot eliminate it.

 

[PassionForSound]

As a recent builder of a S.E.X. kit I can highly recommend leaving it stock to begin with just so you can be shocked at how good it sounds even without any upgrades!

 

[compassionator]

Hello, will adding a stereo mini jack output (rather than use an adapter) affect the performance of the amp?  If not, can it be wired from the standard jack?  Thanks.

 

[mcandmar]

Do you mean a 3.5mm socket instead of the stock 1/4"?  I don't see any reason why not.  Though as far as i know the supplied socket disconnects the speakers outputs when a headphone is inserted, so you will probably lose that functionality.

 

[compassionator]

Sorry, about my wording...

Yes, 3.5mm and the stock 1/4".  Is there a way to wire both and not lose the disconnect the speaker outputs feature?  Or is this the function of the 1/4" jack?  If I wire the 3.5mm jack from the 1/4" why wouldn't it work? 

 

[mcandmar]

I belive the supplied 1/4" jack is similar to this Neutrik model (http://www.neutrik.us/en-us/plugs-jacks/m-series/nmj6hc-s) which is a switched version.  Basically there are a set of input and output pins, outputs being wired to the speaker posts so when a headphone jack is inserted the contacts are lifted from the output pins, hence disconnecting the speakers.  I think that is how it works, but i have yet to receive my kit and confirm that.

You may be able to source 3.5mm socket with the same functionality, or just add a manual switch, or dont wire them up at all which is what i will be doing as i dont have any speakers to connect to it.  ...yet.

Diagram of switch contacts -> http://www.neutrik.us/zoolu-website/media/download/2804/Jack+Circuits

 

[2wo]

Yes, 3.5mm and the stock 1/4".  Is there a way to wire both and not lose the disconnect the speaker outputs feature?  Or is this the function of the 1/4" jack?

The actual sticking in, of the 1/4" plug, is what switches the speakers off.
Just like my wife, ba, dum, dumt. Sorry, channeling Rodney Dangerfield for a sec. ;D   

You could wire a 3.5, in parallel with the 1/4. When you want to listen to the 3.5, just plug in a empty 1/4 jack in to turn off the speakers. Just make sure your 3.5 isn't  switching as well...John 

 

[compassionator]

Thanks for the responses.  I think I'm inclined to add a manual switch for the speakers off function and just wire both the 1/4" and 3.5mm output jacks.  But if I can find a 3.5mm jack that is wired like the 1/4" that comes with the kit, that might be a more elegant solution

I seem to have thrice as many headphones with 3.5mm jacks, and just 2 headphones with the 1/4", which I listen to more often.

 

[mcandmar]

You know a 1/4" to 3.5mm adapter is the quick an easy solution 

I "think" i may have found you a solution, Switchcraft part number: EH35MMSNSC

http://www.switchcraft.com/productsummary.aspx?Parent=740
http://www.switchcraft.com/Drawings/EH35MM%20SERIES_CD.pdf

Its referred to as a "normaled" version and has fours pins, two for left, two for right, and a shield connection.  It either shorts the normaled pins to each other assuming they will be connected to ground, or it disconnects those pins when a jack is inserted.  Which one it is i am unsure, and i cant find any info to clarify it. You would just have to buy one and test...

To be honest, just go with a 1/4" adapter, i've found as i upgraded to better headphones the higher end ones are almost always 1/4".

 

[compassionator]

To be honest, just go with a 1/4" adapter, i've found as i upgraded to better headphones the higher end ones are almost always 1/4".

Yeah, I'm slowly coming to that conclusion.

 

[mcandmar]

Cree is a manufacturer. It is almost impossible to get more than a 100v rating in silicon when making a Schottky diode, so they make high voltage ones from silicon carbide, up to 1200 volts. (It is possible in theory to make even higher voltage diodes from diamond crystals, but it's challenging!)

Schottky diodes have no reverse recovery at all; they are like tube rectifiers in that respect. The FREDs, fast recovery, ultra-fast recovery etc. designs reduce the magnitude of the reverse recovery spike, but cannot eliminate it.

Hi Paul,

I got my hands on a pair of Cree CSD01060a as used in the Mainline kit and just want to be 100% i have a suitable part before installing them. Looking at the datasheets for the UF4007 vs CSD01060 a few differences jump out at me,

1) Max Reverse voltage of 1000v for the UF vs 600v for the CS.  I assume this only comes into play on powerdown when the transformer shuts down and the caps are still charged, or is my understanding of that totally off?    Are we still within the safe working range for these diodes? 

2) Average rectified forward current of ~10amp for the UF vs 1.4-2.2amp for the CSD.  Looking at the tube datasheets it lists the plate current for both sections being ~68ma and ~150ma so am i right in saying the total load of the four section will be well within 1amp, + whatever the startup current maybe will still be within that safe rating?

3) Forward voltages are pretty much identical so nothing to worry about there.

4) Heat sinks shouldn't be required assuming the current load is as low as above, however the metal tab is live to the output so covering in heat shrink would be a sensible idea.

Anything else i should be aware of?

Cheers,

Mark