Cavalli EHHA

Figured I'd share my latest project

• Dual-mono with 160VA toroids
• Pair of sigma22's at +/-27V
• Gain adjustable with socketed resistors
• 2 inputs with rear input selection
• Separate power switch for heater circuit
  
• Rear speaker terminals + 4-pin XLR

 

Finally!

What's your ol and cl gain?

 

VAS stage resistor is 75k, feedback resistor is 10k

CL should be 11 (20dB) and OL should be 500-600 (55dB)

 

What tubes are you using? I had telefunkens and they paired really nice. I've also had 2 different builds with toroidal and R core transformers respectively. The R core version sounded cleaner and blacker.

 

Amperex (?) 6GM8 is my favorite so far. Better to use the tubes spec'd for the low plate voltage methinks.

I might want to add an input transformer for balanced inputs. Looking at Jensen stuff.

 

So, how does it sound?

 

I changed gain with R11 in mine, which is 1.2k default. I liked ~ 1.0k there the most, leaving rest as is.
Did you try original psu-s before sigmas?

 

Yes, tried the LM317/337 supplies. sigma22's are cleaner in the treble and more spacious. The bigger toroids (as opposed to the itty bitty Avel's) are pretty awesome with bass performance. Still forming my opinion on the amp's sound.

 

I preferred the 70's dimpled getter, A frame 6GM8 from Holland over Telefunkens myself. The good thing about 6GM8 is that it isn't quite as expensive as some of the other audiophile tubes. Even the Telefunkens, which are the most expensive of the lot can be easily had for less than $25.

 

Cool build, OJ!

Couple of points - don't leave wires hanging around like that. Try making braided or just twisted lines and zip tie them together. The perforated bottom plate is super handy for tying loose wires down. Make sure that no wires are pushing on heatsinks and other sharp edges, you're building for decades of operation and vibration can make these edges cut through isolation.

I'd also try avoiding leaving naked primary side AC lines near the IEC socket.

 

https://www.dropbox.com/sh/su8yapwkv5927pb/AAC5uEOvz9A1bdEzMohz4lb2a?dl=0

Here is mine! Made by SBAF user Priidik...

The PSU part is totally different, Priidik can comment more about this.




How much power it will give to speakers?

 

All these pretty builds tend to give me a complex but here's the eye sore that used to be mine :

 

Great work!

@gurubhai & @OJneg - both former Crack owners, right? what would the learning curve be like going from building a modded Crack to undertaking something like this? huge? I mean the bottlehead manuals pretty much hold your hand the whole way through - I'm guessing with builds like the Cavalli you really need to understand more of the what and the why of what's going on?

 

Grabbed a great deal on a pair of vintage Jensen input transformers. Despite my lack of planning I lucked out and they do mount nicely enough within a standard D sized cutout

 

Dat alignment >_<

Also @Jeb its a pretty big step in large part because the hardest part is doing your own casework, as OJ aptly demonstrates.

 

Great to see build variations of this fantastic amp.

@OJ 2 comments
- for speakers you might find the heatsinks lacking (and you may want to parallel another set of output devices = your psu will easily manage this)
- i might not be seeing it but i would generally try to build with a central or star grounding scheme. It appears that there are several ground points and you will be amazed at how easily you get weird current flow patterns. If it is dead quiet and sounds great you might want to ignore me.

When i first saw the picture, i assumed you had 6H30 tubes in there

And just for sharing old memories, this is what mine looked like

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..dB

 

Well, your transistors are definitely not going to overheat in that thing. You also get bonus points for the Fallout theme, I really like it.

 

Somehow I managed to forget to reply on this one. @Jeb : I actually went the other way round, EHHA was the first thing I ever built. I had never even held a soldering iron prior to this project and still I personally didn't find it too difficult especially stuffing the boards. Like others said, the difficult part is the chassis work and the wiring/ layout which is something you don't have to worry about in a kit like crack.

 

No actually, the sigma22's board is in fact used as the star ground. Channel grounds are separate, dual mono as a specified. All ground points (spkr grd, headphone gnd, circuit gnd) come directly back to its respective sigma22 port. I am letting the heater float, which actually seems to be the best configuration to my ear.

6H30's were in there when I took the picture but they just aren't as good as the 6GM8's in this circuit.

Biased at 200mA for the output stage. My cooking IR thermometer measured 60C on the heatsink surfaces. So far no problems at all driving the 81dB/W OSMT with all sorts of music. Am listening nearfield though.

 

Sounds perfect. Let us know how the transformers work out..dB