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REVIEW – Cavalli Audio Bijou DIY tube headphone amp

post #1 of 52
Thread Starter 
Another Head-fier asked me if I would be interested in reviewing the Bijou, a DIY amp design from Alex Cavalli. Of course, I said yes . Extensive information on the design can be found here: The Bijou Stereo Headphone Amplifier and as such, I am not going to describe the design in any detail. For those who can’t be bothered, the Cliff Notes is that the Bijou is derivative of the Futterman output transformerless tube amp design. In the version here, the amp uses 6DJ8/6922 for the driver tube, Russian 6N6P’s for the output tubes, and a EZ80 rectifier tube. I auditioned the amp with Amperex EZ80’s and 6DJ8’s.

Pics:




This is the first amp I have ever heard with a variable negative feedback control. This will allow the greatest flexibility in use with headphones of widely varying impedance. My preference was to use as little feedback as possible, and since the lowest impedance can I tried with the Bijou was the 80 ohm Darth Beyers, this was not a problem. With the 600 ohm DT990s I used the minimum amount of feedback possible, with good result. And the sonic signature of the Bijou made it a better choice for the DT990’s (see below).

The amp was totally free of any sort of hum or noise, which is always nice from a tube amp, and certainly not always the case in my experience. This gives the amp a very black background, which helped contribute to the excellent dynamic swing the amp has. And it sounds terrific overall. Some of what I will say below will sound like I am picking on the Bijou. I am really just trying to describe its sound, which it does have, but it was, throughout my audition, incredibly fun to listen to, and it’s an amp I would recommend to anyone who has a desire (and the skills) to tackle a DIY project like this, or can find someone to talk into building one for them. It is also important to note that I’m sure the sound can be altered even further by using different 6DJ8s. All my 6DJ8s were Amperex made (I have some branded RCA but they also were made in Holland by Amperex – RCA never actually manufactured 6DJ8s), but there are clearly lots of other options that might change the sound further.

I initially used the Bijou with 6N6Ps as both driver and output tubes (meaning 4 total). This produced a meaty and dynamic sound, but it lacked a little detail and nuance. This has often been my experience with Russian tubes. Using Amperex 6DJ8’s as the driver tube improved this significantly. Used with the latter tubes, the Bijou sounded truly excellent. Still plenty of dynamics and a robust sound, but also good detail. It isn’t the world’s airiest tube amp, and it has a more “tubey” sound than my Singlepower Extreme (which is of course a very different amp). Using more negative feedback makes the sound a little leaner, but doesn’t make it any more extended in the treble. Still, this really isn’t a complaint – the Bijou sounds lovely, and is a very, very musical sounding amp. It was very easy to enjoy a very wide variety of music using the Bijou – the mids were so lush and pretty that it was addicting to listen to it.

Bass is quite good with the Bijou – there is a healthy amount of it, and it’s reasonably deep and tight, especially for a tube amp. The bass was not overly ripe or fat, and had good punch. No one will mistake it for a solid state amp in any aspect of its performance, and this is true for the bass as well – my Blue Circle SBH has noticeably tighter and deeper bass. Of course, the SBH is a $1200 SS headphone amp, so it’s a different breed. The SBH also has a more extended treble. But while the SBH has a very nice midrange for a SS amp, the Bijou’s midrange is purer and prettier than the SBH’s.

That is really true about the SP Extreme, too. The Extreme sounds much more like the Blue Circle amp than the Bijou does. The Bijou sounds more like my Ming-Da EL84-based tube amp – its got that more classic tube sound, which of course I think is incredibly fun to listen to, depending on the headphone. The Bijou is TERRIFIC with the Beyer DT990/600. It brings out the mids, and the 990’s supreme treble extension mates well with the slight roll-off of the Bijou’s treble.

So what we have here is a terrific DIY OTL tube headphone amp that gives full measure of what tube amps are about. I confess that occasionally I wish the Singlepower Extreme sounded a little "tubier" than it does, and the same with the Darkvoice 337. As such, it’s really nice to have amps like the Bijou available that sound like we all think a tube amp sounds, and has that breathtakingly beautiful, lush midrange which is what keeps us lovers of the thermionic valve so deeply in love

So all you skilled DIY’ers, have at it!
post #2 of 52
Nice review Rob!

If you could get over your tube love I'd have you review the β22.
post #3 of 52
Thread Starter 
Quote:
Originally Posted by swt61 View Post
Nice review Rob!

If you could get over your tube love I'd have you review the β22.
LOL! Yeah, I am having my "tube renaissance". My first real hi-fi was a Van-Alstine modified Dynaco PAS-3 preamp Stereo 70 power amp. Oh how I loved those things. I then went through a LONG stretch with all solid state, until I bought a tube preamp about 8 years ago. While I am again all solid-state in my speaker hi-fi, I have been really enjoying tube headphone amps, to the point where I am thinking of going back to a tubed preamp for my speaker stereo...
post #4 of 52
What case is that and where did you get it?

Same ? about the transformer.

How does it compare to the darkvoice?

Also you may want to try the 6H30 tubes for the input, lower gain = less required NFB.
post #5 of 52
Nice review as always. Thanks!
post #6 of 52
Thread Starter 
Quote:
Originally Posted by regal View Post
What case is that and where did you get it?

Same ? about the transformer.

How does it compare to the darkvoice?

Also you may want to try the 6H30 tubes for the input, lower gain = less required NFB.
I am not sure, as stated in the review, I personally did not build the amp. I also did talk about how it compares to the Darkvoice (337) in the review
post #7 of 52
Thanks for the review. I was hoping for it to be more SS like as I'm not really a fan of tubes. I'm still building it though.
post #8 of 52
Quote:
Originally Posted by holland View Post
Thanks for the review. I was hoping for it to be more SS like as I'm not really a fan of tubes. I'm still building it though.
the tube sound is highly likely to be from the large electrolytics on the output.
There are 330uF Auricaps that will reduce the syrup. This has been discussed before that a large electrolytic on the output of an amp magnifies the tubiness. I haven't tried this yet but others have and reported increased clarity. I would not do this with low impedance phones due to the -3db point.
post #9 of 52
Thanks, I'll note that down. I won't be building it for a few months at least. I'll do research just before I get ready to build.
post #10 of 52
Quote:
Same ? about the transformer.
Looks like the transformer is from LiTe. You can get them here: Audio Catalog
post #11 of 52
Is there any way to contact the builder to find out what case that is ?
post #12 of 52
Thread Starter 
Quote:
Originally Posted by regal View Post
Is there any way to contact the builder to find out what case that is ?
The case is just something the builder got off EBay.
post #13 of 52
Skylab, do you have a subjective ranking of the Blue Circle, Extreme, Darkvoice, and Bijou?
post #14 of 52
I am not sure how I missed your review - actually that is not hard to figure since I hardly ever wander away from the DIY forums ( a sad life indeed )

I really just wanted to second your thoughts. I have listened to the Bijou primarily through my AKG501s and as an addict of that phenomenal tube midrange, I have been smitten by the sound that this amp delivers. I was converted to tubes some 20 years ago by the sound of the classic Leak stereo 20 and for any who have heard the vocal reproduction of this amp will understand the seduction. To get to the point, I found that the Bijou reproduced this midrange and it really hadn't occurred to me why I liked the Bijou that much until putting it into context. I don't find the highs attenuated but that is perhaps a good partnership between the AKGs and my personal preference. ( I truly dislike the AT-SS sound ) The AKG501s have been described as bass shy but that is far from the truth when driven by a suitable amp and the Bijou reproduces bass with the best of them. Unfortunately my point of reference is other DIY amps which most have not had the opportunity to hear and they are hybrids which not all embrace openly.

Thanks for sharing mazuki and for the great review skylab..dB
post #15 of 52
Thread Starter 
Quote:
Originally Posted by fierce_freak View Post
Skylab, do you have a subjective ranking of the Blue Circle, Extreme, Darkvoice, and Bijou?
Somehow I missed this post, sorry. My ranking would be:

1. SP Extreme
2. Darkvoice 337
3. Blue Circle SBH
4. Bijou

BUT: please don't read into that that the Bijou is a bad amp. It's terrific. It's just that we have some pretty stiff competition here. And as bDel84 eloquently says, the mids of the Bijou are pure tube, and for anyone looking for seriously lush tube mids, the Bijou would be the way to go. The SP Extreme and the DV337 have wonderful mids, but they are not super-romantic sounding, they are more neutral.

The Bijou is also better than the (very good) WooAudio3, Darkvoice 336i, and EC LunchBox II.
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