Rebuilt Quickie: "The Bonze"

[aragorn723]

Sounds like that might be the answer!  How about placing another box below the Quickie to make room for the teflons?
 

Dave

[mcandmar]

If were talking Russian Teflons the K72's are fairly compact and should be easy to fit.  e.g. here is a 2.2uf K75-10 with a .022 K72-6 i used in one of my amps.   I found with the K75's on their own to be dark sounding, adding the K72's brought back the high end detail.  I'm usually not a fan of bypassing caps but in this case it worked rather well.

[aragorn723]

i'm curious to see if the teflons would change the bass too..  That's the main thing i'd like to see come back a little more.  The black gate bypass caps aren't burnt in yet (I feel funny about using up battery power to burn in caps; they only have 30 hours on them out of ~400)..  Probably should let those burn in !

Dave

[mcandmar]

Going to say no. The small capacity .022uf will only pass high frequencies and do little to nothing for the low end.  To me the K75's roll off both ends of the spectrum, their strong point being the rich mid range tone. It was because of that lack of low end i removed them.

I would suspect a basic Mundorf or Solen MKP would perform better overall.  I tried a bunch of 2.2uf caps in my Quickie and ended up staying with the ClarityCap ESA, and for $8 each they are reasonably priced too. Then again the Mundorfs and Solens are half that price and almost as good. Any of them will have better low end than the K75's IMO.

[Bonzo]

Going to say no. The small capacity .022uf will only pass high frequencies and do little to nothing for the low end. 

Just a question: the resistance across the output rca of the quickie (if I remember correctly) is 220kohm, so with a 0.022uf cap the cutoff frequency of the rc filter would be 33hz. It seems, by my calculation, that the teflon bypass cap could pass also some bass frequencies, or did I completely miss the point?
I haven't considered amp's input impedance, assuming it was pretty high like all Bottlehead's kit (with a low input impedance amp, the cutoff frequency would rise a lot).

Ciao!

 

[Paul Birkeland]

I haven't considered amp's input impedance

That is certainly worth considering.  It isn't uncommon to see an amp with a 10K input impedance.

[Bonzo]

That is certainly worth considering.  It isn't uncommon to see an amp with a 10K input impedance.

Yes,
you're right, but I assumed we're speaking about Bottlehead's amp, so with a minimum of 60k.
When paired with low input impedance amp (for example a DIY SIT L'amp  ) bigger caps are needed!
Thank you!

[Paul Joppa]

Just a question: the resistance across the output rca of the quickie (if I remember correctly) is 220kohm, so with a 0.022uf cap the cutoff frequency of the rc filter would be 33hz. It seems, by my calculation, that the teflon bypass cap could pass also some bass frequencies, or did I completely miss the point?...

That is technically true, assuming a similarly high input impedance for the following amplifier. However, the impedance to ground of the "hot" lead is very high, making it sensitive to electric and electromagnetic fields - also known as hum and noise.

[Bonzo]

That is technically true, assuming a similarly high input impedance for the following amplifier. However, the impedance to ground of the "hot" lead is very high, making it sensitive to electric and electromagnetic fields - also known as hum and noise.

Now I lost the track! 
Paul, do you mean the design of the quickie is likely to be sensitive to hum, period, or that is better to use a low impedance amp with it to reduce hum (and so is better to use bigger teflon caps to hear their contribution even to bass frequencies)?

Sorry for the dumb question! 

[mkane]

   I modded the Quickie with Clarity MR Series .022 caps. The Stereomour, running wide open, using a Mallard 12AT7, has a slight amount of hum. Much more so with the JJ's or the Psvane.

[aragorn723]

That is certainly worth considering.  It isn't uncommon to see an amp with a 10K input impedance.

Interestingly, I have an amp with 10k input impedance.. So does that mean the rolloff frequency would be lower with that?  The bass isn't bad, I just wish there was a little more sometimes.. Maybe a subwoofer would fix this (got a few laying around).

Dave

[Paul Joppa]

Now I lost the track! 
Paul, do you mean the design of the quickie is likely to be sensitive to hum, period, or that is better to use a low impedance amp with it to reduce hum (and so is better to use bigger teflon caps to hear their contribution even to bass frequencies)?

Sorry for the dumb question! 

Hah - I'm sorry for the unclear post, so we're even  :^)

For the best noise sensitivity, the coupling cap impedance should be less than the source impedance of the preamp (about 2K ohms for the stock Quickie, 4K with the PJCCS), at the lowest frequency of interest for noises. That places the "hot" interconnect line at the lowest possible impedance to ground, enabling it to minimize electric field (capacitive) coupling.

My usual rule is to make the cap impedance less than the source resistance at 120Hz. I also check that the response corner for the lowest rated load impedance is 5Hz or lower. These are two different and independent criteria, and are occasionally over-ridden by listening tests - I love science but it is not everything.

[Paul Birkeland]

Interestingly, I have an amp with 10k input impedance.. So does that mean the rolloff frequency would be lower with that?  The bass isn't bad, I just wish there was a little more sometimes.. Maybe a subwoofer would fix this (got a few laying around).

Dave

If you have a tiny cap at the output of the Quickie and a 10K input impedance on your power amp, you'll get bass rolloff. 

The output impedance of the Quickie is also a tad high for a 10K load, but this is more about distortion rather than frequency response.

[Bonzo]

Hah - I'm sorry for the unclear post, so we're even  :^)

For the best noise sensitivity, the coupling cap impedance should be less than the source impedance of the preamp (about 2K ohms for the stock Quickie, 4K with the PJCCS), at the lowest frequency of interest for noises. That places the "hot" interconnect line at the lowest possible impedance to ground, enabling it to minimize electric field (capacitive) coupling.

My usual rule is to make the cap impedance less than the source resistance at 120Hz. I also check that the response corner for the lowest rated load impedance is 5Hz or lower. These are two different and independent criteria, and are occasionally over-ridden by listening tests - I love science but it is not everything.

OK, now I got it, thank you very much Paul! Now I have a way to calculate the output cap value by myself! 

[aragorn723]

If you have a tiny cap at the output of the Quickie and a 10K input impedance on your power amp, you'll get bass rolloff. 

The output impedance of the Quickie is also a tad high for a 10K load, but this is more about distortion rather than frequency response.

The output caps are 2uf Russian K75-10s, shouldn't be an issue with rolloff, right?  (Except the inherent k75 bass rolloff).

Dave