Which upgrade would be more beneficial? interstage vs parafeed caps

[arsun]

Hi,

I have the original SEX amp with MQ irons and c4s upgrade. If one would pick one capacitor to change, which position will be more beneficial? Interstage one (0.1uF) or the parafeed one (2.0uF)? Has anyone made a comparison regarding interstage vs parafeed with original and upgraded caps? I am thinking Duelund or Jupiter copper foil caps.

Thanks to everyone for their input.

[Paul Birkeland]

You may have a really tough time fitting caps from those brands into a SEX amp.  The S3X has a little more room and flexibility compared to the SEX 2.0 and 2.1, but still probably not enough for a lot of the huge parallel feed caps. 

I would recommend starting with the coupling cap.  IMO you could go with a 0.047uF cap if you increased the grid leak resistor to 500K on the second triode in each channel.  This would keep the physical size of the coupling cap down a bit.

[arsun]

Please do not worry about the size. My amp has another metal box under it, which has a larger volume than the amp itself. I have plenty of room underneath.

Will your recommendation "going first with the interstage coupling cap" change, if you do not take the size of the capacitors into account?

[Tom-s]

For interstage coupling, look at Russian FT-3 teflon capacitors 600V 0.1uf.
For output coupling, Audyn True Copper Max are a cheap and good alternative to your options.

[arsun]

For interstage coupling, look at Russian FT-3 teflon capacitors 600V 0.1uf.
For output coupling, Audyn True Copper Max are a cheap and good alternative to your options.

Thank you for the reply, but I am more or less set on the brand of capacitors, however I might go slowly and update one at a time. This is why I asked which cap is more important.

For now, please do not consider size or cost, which cap is more important sonically? Which one would you upgrade at first? Has anyone made a comparison about these two caps?

[kgoss]

Well if it were me and I wanted to hear the sonic differences of each capacitor upgrade i would start with the interstage cap.  The signal goes through it first so it makes sense to replace it first.  Let that cap break in and make your observations before replacing the output cap.

I upgraded both caps on mine at the same time I installed MQ full nickel iron so I can’t say which had the greater impact.  I just wanted to do all the work at once because I don’t enjoy doing rework on a working amp.

[arsun]

Well if it were me and I wanted to hear the sonic differences of each capacitor upgrade i would start with the interstage cap.  The signal goes through it first so it makes sense to replace it first.  Let that cap break in and make your observations before replacing the output cap.

I upgraded both caps on mine at the same time I installed MQ full nickel iron so I can’t say which had the greater impact.  I just wanted to do all the work at once because I don’t enjoy doing rework on a working amp.

Ok, thanks. That's a valid approach, if one did not know which upgrade would be more beneficial. If there isn't anyone who had a first hand experience, I will probably take that route. Still, if there is anyone, who made such a test, please speak now, or forever hold your peace .

[Tom-s]

From experience with both a S3X and Mainline (both with upgrades).
For the money spend on Duelund caps -> buy a Mainline. There's no better upgrade.

[arsun]

From experience with both a S3X and Mainline (both with upgrades).
For the money spend on Duelund caps -> buy a Mainline. There's no better upgrade.

Thank you for the feedback, but:

Buying a Mainline is out of question. I am not living in the US anymore and customs here is like hell. Also, my sex amp is already modified quite a bit and I am using its speaker taps for a pair of Audeze headphones and already like the sound I am getting. I got a bit of upgrade-itch and just wonder which location would be the best to go first with.