optimum output cap value

[kip.duff]

I've had significant improvement by cap replacement in my Paramount 1.1 monoblocs, so I want to do the same with my Eros 2.  I have already put V-Cap CuTFs in the RIAA section of my Eros 2.  But I'm confused about the value for the cap in position between the 7308 tube and the output RCA jacks.  I currently have Russian surplus MBGOs here @ 1.0uF- but want to try the ODAMs.  Manual diagram shows 1.0 uF- while in the manual assembly instructions, this cap is listed as 1.5uF.  I am ordering caps for this position.  For the Paramounts, the shipped Solen parafeed cap value is 3.3- but techs on Bottlehead forum said 5.3uF is "correct" value based on calculations.  I used that 5.3uF value in the Paramounts (V-Cal ODAM 2.2 plus ODAM 3.3, "low spec" in parallel)- and I am glad I did.  So I need to know what is optimum value for the Eros.

Thanks, Kip.....

BTW, the improvement with install of the V-Cap ODAMs in the Paramounts was not minor....

 

[Paul Joppa]

There is no "optimum" with Eros, there are only minimums. This is because there are no inductances for the cap to resonate with.

The primary guidance is that it must have enough capacitance to pass bass frequencies to the following preamp or integrated amp. I usually find that a -3dB point of around 5Hz is more than enough. If the Eros drives a 100K input resistance, then 0.33uF would be enough - but with a 25K load, you'd want 1.3uF. Into a 15K load, which is the minimum recommended load, you'd want 2.2uF. But at 1uF, it's still only 10Hz, and may not be audibly different depending on your system.

If I recall correctly, the original design called for 1.0uF but at some time that cap was on back order so we shipped the 1.5uF cap from the S.E.X. amp. It sounds equally good, and reduced the number of parts in inventory, so there has been little pressure to revert.

 

[Doc B]

I'd suggest considering subsonic frequencies in this. If you can avoid passing LF junk that comes from the cartridge going over a warp on the record by keeping that rolloff up closer to 20Hz it could help avoid over-excursion of your speaker drivers. 

 

[kip.duff]

So since I'm feeding signal to 56k Ohms impedance (BeePre), 1.0uF is where I'm supposed to be.

Thanks so much.....

 

[bosmaworks]

So since I'm feeding signal to 56k Ohms impedance (BeePre), 1.0uF is where I'm supposed to be.

Thanks so much.....

Hey Kip,

How are you liking those ODAM caps in the Eros?

Cheers,
Thijs

 

[sl-15]

Doc what cap value would this roughly translate to with the 40 kOhm load from the ExtendedFP3? Thanks

 

[Doc B]

I'm gonna make you work for it. Go to this page, scroll down halfway and use the RC high pass filter calculator. Solve for capacitance. Plug in 40K ohms for resistance and 20 Hz for cutoff frequency.

https://electronicbase.net/high-pass-filter-calculator/

I can't type the answer upside down at the page bottom like they used to in the text books.

 

[sl-15]

- I can't type the answer upside down at the page bottom like they used to in the text books.-

Ha, that made me laugh. Thanks Doc I will give this a try.