Questions for an upcoming Kaju build

[larcenasb]

Hello! Planning my next build, but just have a couple questions:

1) Are there any concerns about using a passive preamp with the Kaiju? I think I remember back in 2010 at a headphone meet, that the AKG K1000 was driven by Paramount monoblocks, which were fronted by a passive preamp….Am I remembering that right? It sounded glorious.

I plan to have this audio chain: DIY point-to-point passive preamp -> Bottlehead Kaiju -> Klipsch Heresy IV

2) Can 6SN7-to-5670 6.3V adapters be used safely in the Kaiju? Such as these:

https://www.ebay.com/itm/193445726979?hash=item2d0a438b03:g:EVkAAOSwiqNbtVLZ&amdata=enc%3AAQAIAAAAwAEoMwKaVxNexYlESXiWEMD9N26YTigyPYHoCo%2BqmiRnu%2F%2FaGgCxJB7KwPZqEB%2Bxwgd8JH14ZYPC7wZnQtkjf1hzemKlj0jfKYOSSruf8PuHy5jN7PaABA7Ym%2F89eB1r0ha6q76nvpAWn14Tvia1hVq2HSqYm2lbyNB1B9Zw3pMqGhtLtwnOuiZxk%2BYobccM3M0A0jzTQi5XaEfCMtP2woUxa3iqTEDYEG5CI2%2BZGJhVQmKBINiysh%2BQx41H2uYx%2BA%3D%3D%7Ctkp%3ABk9SR8r5vPfFYg

Thanks so much for any help, and I’m very excited to build this hopefully in the near future. Cheers!

[Paul Birkeland]

The question of using a passive preamp depends on the sources you're using (in particular the output impedance of each source), the impedance of the passive control, and the lengths of your cables (the capacitance per foot is important).  You can analyze all of these datapoints together and make some decisions based on the data, but keep in mind that once you want to add a new source, you need to go back and reanalyze that again. 

I do not see any issues with using those adapters.  The 6SN7 will have lower gain, but beyond that there shouldn't be any issues.

[larcenasb]

Thanks so much, Paul. Had no idea a passive preamp is a little finicky… Could you please point me in the right direction to get more info on how calculate this and how to understand the numbers/data? Thanks and have a great weekend!

[Paul Joppa]

The reduced gain with a 6SN7 is a potential problem.

Stock Kaiju needs 1.56 volts RMS to drive it to full power; with a 6SN7 it will need 2.70 volts.

The original standard for CD players is 2.00 volts, which is not enough for the 6SN7. Phono preamps are often lower in output voltage, and phones, iPads, etc can be even lower. Check the specs on your source devices!

Of course, you might never need full power with sufficiently sensitive speakers  like the Heresy.

[larcenasb]

Hi PJ! Thanks for making sure, just in case, that I’m informed about the drop in power. I appreciate it!

My room is 12’x15’ w/ 8’ ceilings. And my sources will be:

- VPI Cliffwood w/ Nagaoka MP-150 -> Pro-Ject Tube Box S2
- PS5 -> TV -> Schiit Bifrost 1

[Paul Joppa]

The  Pro-ject appears to have plenty of gain available but the Bifrost outputs a peak 2.0 volts, so you won't be able to get more than 4 watts out of the 8-watt Kaiju.

[Paul Birkeland]

and phones, iPads, etc can be even lower.

This is really enough of a reason to at least throw a Moreplay in there, as I think you'd get about 1W out of the Kaiju with 6SN7s substituted and a phone driving a passive preamp.

[larcenasb]

Okay, I’m leaning away from the passive preamp idea. I work weekends at Hawthorne Stereo now, and we have a bunch of solid state preamps in the warehouse, I’ll be sure to try some out to see how that fares. Eventually though, a BeePre2 would be perfect.

Thanks, PB & PJ, yet again for your great support. Hope to order mine within the next couple months. Expect another build log

BTW, on a family road trip en route to Lake Tahoe. Cheers and hope everyone reading has a great weekend.

[Natural Sound]

Okay, I’m leaning away from the passive preamp idea.

Might I recommend that you "lean away from" the idea of modifying the Kaiju from using the designed 5670 to 6SN7 before even hearing what the original design has to offer?

[larcenasb]

Hi there! I do have a pair of WE 396A that I will definitely try! But the 6SN7 will be used with adapters, so nothing permanent at all. I’ll definitely be tube rolling like a madman.

[Larpy]

I'll suspect you'll find that the Kaiju sounds much better with the 5670s. I'm a big 6SN7 fan myself, but the 5670 is the better tube in front of a 300B.

[larcenasb]

I’m very curious to compare and see!