New Kaiju Build and a Question

[ScottAstroNut]

Despite a promise to Queen Eileen that I would be patient in building the Kaiju that arrived on my doorstep on Monday, I haven't been able to help myself and am deep into the build. I've attached a photo showing the jig that I built to help me in assembling the Kaiju. The building jig is tall enough that I can test the circuit with the 300B's installed and the whole thing inverted without any risk to the tubes or the newly painted finish of the transformer bell. This photo was taken just after the kit successfully passed its high power voltage supply voltage test with the 300B tubes installed. Yay!

This build is going extremely smoothly. As always, the instructions are very detailed and complete and make building this "monster" a joy. Things are going quickly enough that I thought I had better ask a question that is on my mind...

I have both 4 ohm and 8 ohm speakers that I would like to try with this amp. What set of speakers I will actually end up using with the Kaiju is a bit of an unanswered question at this point. Am I better off wiring the output transformers for 4 ohms or 8 ohms? My strong suspicion is that I will end up with 8 ohm speakers when all is said and done, but my S.E.X. 3.0 has done surprisingly well with a pair of high quality speakers (Dynaudio Excite X38's) I own that are 4 ohm, despite only being 88 db efficient. They don't play excessively loud, but my room is small and I am not a loud kind of listener most of the time. The Dyns sound quite sweet with the S.E.X. As a final pairing with the Kaiju I am looking at much more efficient speakers such as models from Zu Audio, Tekton, or perhaps even something like Klipsch Forte III's, and most of these are 8 ohms nominal. My thinking is to wire the output transformers for 8 ohms. Am I correct in my thinking?

Thanks!

Scott Burgess

 

[Doc B]

The bass won't be quite as tight if the 4 ohm speaker runs on the 8 ohm setting, but you won't hurt anything.

 

[ScottAstroNut]

Hi Doc!

Glad to know that running 4 ohm speakers on an 8 ohm tap is OK. Just out of curiosity, what about running 8 ohm speakers off of OT's configured for 4 ohms?

Thanks,

Scott

 

[Paul Birkeland]

Glad to know that running 4 ohm speakers on an 8 ohm tap is OK. Just out of curiosity, what about running 8 ohm speakers off of OT's configured for 4 ohms?

You trade less power for more damping, lower distortion, and lower noise.

 

[ScottAstroNut]

Thanks for the reply, Paul.

Given that I am running in a small room, where power is not really an issue, might I not then be better off configuring the OT's for 4 ohms instead of 8? Also, aren't many "8 ohm nominal" speakers such that their impedance drops below 8 ohms over part of the frequency response anyway so? I know that with my higher-powered (36 watt) EL34 tube amp that has taps for both 4 ohms and 8 ohms, it is suggested to try 8 ohm speakers on the 4 ohm output just to see if it sounds better.

Scott

 

[Doc B]

You can't do any harm with any of this. The general gist of it is that an "exact" match gives some guarantee of what the distortion level will be at the rated output. Sonically what happens is that matching a higher impedance speaker to a lower impedance output tap might sound a bit more lean (and maybe a tiny bit more clean) than the exact match. Or it might sound just the same. Conversely, running a lower impedance speaker off a higher impedance output tap might sound a little more fat and loose in the bass. Or it might not. Your volume control will sit at a slightly different point for the same listening level for the two different configurations.

It takes a bit of soldering but not a huge deal to change from one output impedance configuration to another. I'd suggest simply reconfiguring it yourself to learn what the effect is.

 

[ScottAstroNut]

Inspired by photos from the Kaiju instruction manual, I had Godzilla help with the build! The rest of the build went very smoothly. Given how heavy the amp is, I decided to secure the wooden base to the chassis plate, so added some angle brackets and mounting bolts. Also reinforced the corners of the base, "just for good measure." This was a longer and more involved build than the other Bottlehead kits I've put together, but I enjoyed every second of it!

 

[ScottAstroNut]

Another Kaiju lives! The completed Kaiju sounds great! When used with 96 db Klipsch RP-600M speakers I did notice some hum. I didn't notice any, however, with my 88 db efficient Dynaudio Excite X38's. When adjusting the hum pots, I found that the lowest hum I could achieve was 8.8 mV, which was above the 5 mV target mentioned in the manual. However, the amp sounded just fine when actually playing a source, so I figured that the hum being a bit high was a non-issue and probably idiosyncratic to my tubes. After listening to the stock Kaiju for a day, I then added the DC filament upgrade. The hum completely disappeared, and the hum I measured as now being only 0.5 mV. Adjusting the hum pots after installing the filament upgrade seemed to have little actual effect. Is this normal?

Frankly, I am surprised at just how good this amp sounds! Superb! I am using a Schiit Saga S preamp, as it's what I had on hand, but wonder what would be gained by going to, say, a BeePre? I am using the Kaiju primarily with the Dynaudio Excite X38 speakers, as they are the best speakers I own and the Kaiju sounds very sweet with them. I have a small listening room, so the Excites are fine in terms of SPL, but am wondering if I would gain a little extra volume by going to a different preamp? The Saga S is a fantastic value, but only offers 1X gain.

In any case, thank you Doc, Eileen, and Paul for all your help from start to finish. This has been my best Bottlehead experience to date, and made all the more enjoyable by your tremendous support.

Scott

 

[Karl5150]

Nice work, I like your plate securing scheme. Your experience with the DC filament kit may be the impetus to do the same with my SII. Thanks for sharing the build pictures.
Karl

 

[Deke609]

She's a beauty! What did you finish the wood with? Danish teak oil? That's a really nice golden brown.

Adjusting the hum pots after installing the filament upgrade seemed to have little actual effect. Is this normal?

Same with my Kaiju. I was told that the hum balance pots usually don't do much, if anything, after the DC Filament upgrade.

  wonder what would be gained by going to, say, a BeePre?

If your ears are anything like my ears the answer is crazy goodness.

cheers, Derek

 

[Doc B]

Beautiful! Regarding the BeePre, Eileen and I actually took a listening break yesterday. This almost never happens any more, and it was a nice change. One of the things we were talking about was how putting the BeePre in the system takes the soundstage from being flat and wide to having a great sense of depth as well. This is the "holographic" thing that single ended DHT amps have been lauded for since they came back in the early 90s. IMO it's the DHT aspect that really influences this (along with no global negative feedback). And so one could infer that adding the BeePre to the Kaiju avoids "squashing" the sound stage before it gets to the Kaiju. IME BeePre also fleshes out the lower midrange a bit and adds a nice bass punch.

 

[ScottAstroNut]

Darn it, Doc! I was afraid that you would say something like that! Now I have to find a way to get a BeePre kit to go with the Kaiju!

As for the finish on my Kaiju, I applied six coats of wipe-on poly. Although I also very much like hand-rubbed oil finishes, I have become proficient enough with the wipe-on poly that it has become my finish of choice.

 

[ScottAstroNut]

BeePre has been ordered! The Kaiju just sounds so good, even with my very basic preamp, that I can't help but imagine the sonic bliss I will be in once I add a BeePre to the Kaiju!

I am really rocking with the Kaiju! I have a more expensive, higher-powered tube amp that also is a top performer, but the pure and transparent sound quality of a great circuit coupled coupled with the pleasure of listening  to a piece of gear you put together yourself makes for a very satisfying and enjoyable audio experience unlike any other. But I'm preaching to the choir here!

Count me a grateful and happy Bottlehead fan!