Cavalli Compact Tube Hybrid (CTH) Tube & Tweak thread.
Mar 30, 2009 at 2:50 PM Thread Starter Post #1 of 691


1000+ Head-Fier
May 1, 2007
OK, I've been trying to pawn off the starting of this thread but one can't always pass the buck

And since I've the first working proto PCB CTH (by a few days?) guess it should be me.

Surely much of what may be posted here will be based on opinion, listening tastes, headphone synergies, source attributes, etc. But some observations could/should carry across these. I'll get this rolling (ha ha) with a few bits that come to mind & that I think transcends the variables above.

  1. Amperex 6dj8 white label Holland - Lower end & upper ends a bit enhanced, perhaps at some expense of mids. Bugle Boy variant perhaps a bit "better" presentation of these characteristics. Is/was a personal favorite (w/BoM, Sonicap Gen II or Wima coupling caps & D2000s)
  2. Siemens "chrome plate" ECC82/12AU7 (1963) - Bit more refined/balanced presentation, vocals/mids performer. As many tubes do, lends an interesting personality to music... Hard to pin down but enjoyable. Not particularly a bass or top end champ - but this can be a good thing.
  3. Mullard Mullard 6922/E88CC Gold Pin, Sylvania 12BH7A, RCA 12au7a "clear top", Raytheon 5814a - All fine candidates that I need to come back to. My enjoyment of the above 2 or 3 has kept me from rolling these back in. BUT see below WRT coupling caps - I WILL be giving these another shot.
    You certainly don't need expensive tubes in this amp for it to sound good. Tube trading amongst those w/CTHs would be a fun & inexpensive way to go.
Coupling Caps
  1. General - Thinking this design, like some other Cavalli designs, do not need boutique parts to sound good/great. The BoM couplers (@ 75 cents USD?) & minor Wima upgrade caps are fine in this design. Some builders prefer these to alternatives below, perhaps most will.
  2. Sonicap Gen IIs - These, which fit reasonably well tombstoned on PCB, I found slighly "sweeter" in the amp. But not enough to go to great lengths to acquire or install them (e.g. only as part of mini GB or other larger order).
  3. Mundorf Supreme Silver/Oil - These huge & expensive caps (Sonic Craft - 20% off) require larger-than-target enclosure. Have only had these in for a couple days but can say most noticeable is the bass enhancement & softening of the highs. Shift is enough that my DT-880s become a better match than the Denon D2000s I primarily use & I'll have to cycle through my tubes to ID a more "balanced" one than those Amperex 6dj8s.
    If $$ is no object, you've the room, want more bass/softening of highs & want to play around you could try this. Doubt anyone could want more bass out of a tube hybrid than this design w/S+O & those Amperexs... My bet is they would want less. Edit: Take away shouldn't be that I'm disappointed w/the S+Os.. They do more to the sound than enhance bass & soften treble. They lend a different character to the amp though that I'm interpreting as less crisp/darker than before. Perhaps more like some would like from an amp w/a tube in it

O.K. I've started this. There's a huge world of tubes for this amp... My last search of the bay yielded 600+ listings AFAIR. My gut says this design lets tubes "come into their own" by running them closer to spec, using better/lighter loading, etc. than some other designs.
Mar 31, 2009 at 5:28 AM Post #4 of 691

Originally Posted by rds /img/forum/go_quote.gif
I remember something about stability issues when using the Sonicaps tombstoned. Has that issue been solved?

yes it has..certain BOM changes have been made for that.
Mar 31, 2009 at 5:40 AM Post #6 of 691

Originally Posted by rds /img/forum/go_quote.gif
I see, so other component values have been adjusted to maintain stability with the tombstoned Sonicaps?
I'm probably being really lazy, but could you tell me which parts were adjusted?

Looks like Chris managed to tweak the E12 R4E resistor to work with the boutique capacitors..But I will let the guys who are using such capacitors to chime in. My amp uses BOM components and is not in my hands at the moment. SO I haven't been able to try such tweaks..
Mar 31, 2009 at 11:54 AM Post #7 of 691

Originally Posted by rds /img/forum/go_quote.gif
I see, so other component values have been adjusted to maintain stability with the tombstoned Sonicaps?
I'm probably being really lazy, but could you tell me which parts were adjusted?

Yes, in my build (w/100k R14s + R15s, 1.8k R13s) raising R4E to SOHA II's 2k value addressed things. And if this proved not to, raising R1E+R2E toward SOHA II values would in all likelihood do the trick.

BUT wiatrob & runeight are on the leading edge of this AND think maybe core CTH value adjustments should go in "A Very.." thread.
BTW See wiatrob recent post there for pics of the gorgeous black kit build up - I feel offerings are great service to this project & DIY community.

Want to try to keep this thread to things changing sound, stuff like tubes + caps + perhaps output resistors.

Will be rolling tubes over the next few days to find better mate for S/Os... But they sure make the amp sound much "heavier" than it is
Mar 31, 2009 at 5:39 PM Post #8 of 691
Just as a point of reference, my prototype build uses VitQ's as the interstage coupling caps mounted underneath the board, and it has worked w/o changes to other components...

I have no doubt things would continue to work making the latest change, but I'm sticking to Alex's sage advice - "Don't mess with anything that is working."

I can say that the VitQ's sound really good - although I have nothing to compare them against, in order to say how they affect the sound. If I build a second CTH, I'd go ahead and use WIMA's just to be able to do a comparison using the same tube, and see what I think...

~ One thing to note though for those not familiar with the build yet - VitQ's under the board mean you are not using the 'standard' configuration in the small Hammond case. ~

I decided to try a different approach with all of the taller components under the board, and the tube fully exposed outside of the case. This raised the difficulty of the build a bit, but I'm quite happy with the results.

Anyway, I'll be posting a list of tubes I've rolled so far, with some impressions of how they sound with my DT880's. As I go through them again, I'll make sure to plug in my AKG 701's as well...
Apr 1, 2009 at 3:43 AM Post #9 of 691
some brief tube impressions.

Sony DVP-S7000 -> Tributaries Silver Coax ->
Zapfiltered Zhoulo 2.5C -> Wired Direct w/ Neotech UPCCC -> CTH Amp w/ stepped pot / wima mk4.

Tubes (all 12au7 variants)

Siemens E82CC - very balanced, neutral, good sound stage, alittle sweet with touch of sprinkled highs. Im finding this to be my favorite again. Feeling like the music is much more alive with this tube. Going to get the triple mica version either the ECC802S or the 5814A.

Amperex 7316 - delicate yet precise. Has really great separation between notes and can almost visual where the instrument are coming from.

Telefunken smooth plates - very involving, works great with the amp.

GE 6680 - notes hit with clarity and has upfront vocal sound but background sounds are distinct. The highs still simmer and twinkle. Has my toes tapping.

GE 5814A Triple mica 1960's - hint of sweet mids, highs have abit of grain but may go away after more use, has a more enveloping sound stage, like notes have reverb and good decay. Great tube with k501 & classical.

Brimmar 13D5 - very warm, abit muddy compared to above tubes. Every note seems to have emphasis on the lower end. The bass has depth but lost some punch. May clear up with more hours. Vocals are lovely with this tube very intimate.

RCA 5814 Gray plates - lots of air, decent transparency. Missing the full bodied sound as the tubes above. This used to be pretty good on soha.

Mullard 4003 - great separation between notes, layered and each has its own place. Good mids but highs seem to be grainy though it may clear up as I havent used this tube in a while.

RCA 12au7a clear plates - detailed but not sharp. Bass hits hard but quick. Notes seems to be all on a similar level.

CBS 12au7 black plates - notes ring with good decay, sounds spacious. Mids are little thick but getting sweeter. Bass reaches down but seems to stay there.

Mullard (12au7? writings gone) - has alot and sounds lively more energy then CBS or RCA clear plates, sounds like it has higher gain.

tubes I hated with my soha sounds so much better on this amp.

default polyester - hard, fast, good space, and detailed (want more smoothness)
Wima mk10 - too soft lost alot of some pace/detail from above
Wima mk4 - soft/smooth but more detailed then above, good middle ground.
Sonicap Gen IIs - initially sounds too slow, then it got more exquisite and also sweeter. But still darker/slower then caps above.
PIO caps (russian/vitaminq)- too slow and dark, didnt burn them in yet.
To come: russian teflon ft3 and sprague orange drops.
Apr 1, 2009 at 7:31 AM Post #10 of 691

Originally Posted by cfcubed /img/forum/go_quote.gif
BTW See wiatrob recent post there for pics of the gorgeous black kit build up - I feel offerings are great service to this project & DIY community.

Absolutely, it is a great service and convinced me that I can't pass on building a CTH. It really looks amazing in that little case with the perforated top.

Thanks for the info on the caps. I'll back out of this discussion and leave it to people who actually have experience with the amp to comment on tweaks.
Apr 1, 2009 at 2:14 PM Post #11 of 691

Originally Posted by keyid /img/forum/go_quote.gif
some brief tube impressions.

Holy cow! You've been busy there keyid. Thanks!
Reads like pretty much everything you've rolled tube-wise sounds good

Obvious I think, but will say it anyway, presentation differences likely/mostly persist across headphone choice but synergies/favorite pairings may emerge on an individual level. E.g. I'll try to stick to one set of cans for comparisons across tubes & coupling caps.

BTW I was somewhat of a skeptic of boutique cap use but am no longer, at least for those in direct signal path. $30 caps may have advantages over $0.30 ones
BUT think w/this amp one can be extremely happy w/o having to go there. At the same time tho, some could find fancy pants couplers may propel this amp to an even higher level.
But please, recommendation is to get your CTHs built & confirmed working w/BoM/kit parts before rolling things other than tubes
Apr 1, 2009 at 2:45 PM Post #12 of 691

Originally Posted by keyid /img/forum/go_quote.gif
Mullard (12au7? writings gone) - has alot and sounds lively more energy then CBS or RCA clear plates, sounds like it has higher gain.

What Mullard? Short Plate. Long plate?

Longplate Mullards - Boxes on the anode (plates) are taller than they are wide.

Shortplate Mullards - Boxes on the anode (Plates) are wider than they are tall.
Apr 1, 2009 at 7:55 PM Post #14 of 691

Originally Posted by keyid /img/forum/go_quote.gif
I believe short plate with o getter, had yellow writing, and I should have few more mullards long and short in same condition.

Short plates are nice, they are IMO the very definition of "Tubey" sounding. Thick bass and beautiful mids and slightly rolled off highs. The Long plates will be more like a 7316 with lots of color, not so rolled off at the top and not so heavy at the bottom as compared to the short version.

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