[Ferrari]

Quote:

Originally Posted by runeight /img/forum/go_quote.gif ... Now Ferrari, when are you going to case up your amp???

It has high priority on my “To do list”, but due to lacking of free time my amp is still uncased. Also what I’m doing (transformer, large PS / MKP-output capacitors and tubes are going to be placed on top of the case) needs a bit more work than just put all the things in the case. As usual, I will take the time and get it done my way.
Hopefully I will get the case work done before X-mas.

My β22 was playing naked for more than 4 months before cased up. It seems to be that the same is happened now with my Bijou.

 

[Von Soundcard]

How much would the components alone cost for this ?
This is an interesting choice considering it has been favourably compared to other amps including the Doge. I wonder how it would fare against 'more serious' competition like say a heavily rolled / upgraded Woo6 or Doge.
Is anyone trustworthy offering to build these ?

 

[Clutz]

I imagine that fierce_freak might be able to build one for you, but that's just my guess.

The components cost for this alone, including case is probably in the range of $250 at a minimum- not includng the cost of shipping. I would guess you are looking at around $500 to get one built for you.

 

[Von Soundcard]

Mneaah, I would't need a case or esthetical finishes, I'd only ask for the components wired and assembled (allright, maybe some old dump of a case

). It would be interesting however to choose custom components and perhaps even some upgrades over the original scheme.
If this is such a good amp and it can stand up to serious competition (like a well rolled Doge / Woo6) than I'd be definitely interested.

 

[Clutz]

Quite often I build things and don't bother casing them. For example, I had my Dynalo cased up in a cardboard box for almost a year before I cased it up properly. My dsavitsk TDA1541A designed NOS USB DAC has been used for nearly two years and it's still not properly cased.

The Bijou is an amp you want cased. It uses high voltages that could hurt you. I considered building it without a case, but runeight convinced me that it was a bad idea.

 

[Von Soundcard]

It's not that. I'd case it myself

Would look like an 2000 $ amp too

It's just that I don't wand to pay extra for secondary aspects on a best-bang-for-the-buck amp, especially as I think the DIY'er (

) would have trouble himself with it if he doesn't build them frequently.
Well, I have to know more about how it sounds anyway before I make any decision.

 

[Skylab]

I don't know anyone offering to build them, but you could try asking in the DIY forum...

 

[Roam]

Quote:

Originally Posted by Mazuki /img/forum/go_quote.gif For this amp, the best thing to do is probably what Huskydawg did and socket the cathode resistor so that different tubes can be used. The more tube options, the better. There's no arguing against that.

Or use an LED to set the bias, allowing the removal of both the cathode resistor and its bypass capacitor. The bias sets itself to forward bias voltage of the LED, though the plate load may have to be adjusted for the various tube types.

Or for the ultimate in plug & play, LED bias in conjunction with a voltage referenced CCS plate load, change tube types without having to change anything else. Gets a little complicated though.

 

[runeight]

Roam, I'm not sure how to put a CCS on the plate and an LED on the cathode. I think that this will allow too much plate current variation when you swap out the tubes. At least my first simple thought about it.

However, there is a way to handle this on the cathode side which is what can really control the plate voltage.

I know that you guys want to get rid of the bypass cap (and I don't blame you), but if you can stand to leave it in, this arrangement will auto adjust the cathode bias for 100V on the plate of the input triode(which will set the phase splitter) at a plate current of about 1.5mA. The cathode bypass cap has to be included now for obvious reasons.

The servo is a simple current mirror servo and the other big cap prevents the servo from responding at audio freqs. In fact, to do its job it may need to be bigger. But the cap will be small because it can be a 10V jobbie.

The drawback here is that the plate load goes down because there are other resistors now attached to the plate.

With this arrangement you can swap almost any reasonable triode into the front end and the servo will compensate. It's not too many extra parts, but you can see why I didn't include it in the original where I was trying to keep things simple and the cost as low as possible.

If anybody decides to build this please let me know how it turns out.

 

[Clutz]

runeight: Would it be possible to replace the resistor + cap in parallel with a LED if I was happy not to bother with tube rolling- thereby getting rid of the cap?

 

[runeight]

Yes, no problem with the this in principle. The difficult part will be finding an LED with the right voltage.

The cathode of the 6922 wants to at about 2.9V. So maybe a 3V LED will come close. What you can do is adjust the plate resistor until you get around 100V on the plate. Then you can swap tubes and they will all hover around this operating point.

 

[Clutz]

Okay, you're talking to a toob noob here.

As it currently stands, if I'm happy (at least for now) with just running the 6922 as the tube then I can just switch out the resistor in parallel with the capacitor with a 3V LED (how much current should I aim for?) and I'll be good. if I wanted to be able to tube roll a bit, I would want to play with the plate resistor (and since it's a triode, we have the cathode, the grid, and the plate (the part that goes to the B+?)).

Maybe this is being naive, but I don't think I'm going to do a lot of tube rolling, which is why I just want to optimize this amp for this tube - and eliminating a cap from the signal path seems like a good idea to me (though I know there will still be that giant 470uF 250V cap at the output).

Cheers to a great design! Since my parts for my Beta and Mini haven't come in yet, it looks increasingly like I will be building the Bijou this weekend!

 

[runeight]

Easiest thing to do is to put in the 3V LED to see what happens.

 

[Roam]

Quote:

Originally Posted by runeight /img/forum/go_quote.gif Yes, no problem with the this in principle. The difficult part will be finding an LED with the right voltage. The cathode of the 6922 wants to at about 2.9V. So maybe a 3V LED will come close. What you can do is adjust the plate resistor until you get around 100V on the plate. Then you can swap tubes and they will all hover around this operating point.

It shouldn't be too hard, an infrared LED in series with a red or orange LED will be pretty close to that figure. Use low current LEDs for best results, something in the 5-10mA range should be more than sufficient.

 

[Ferrari]

As promised, I succeed to case my Bijou proto up before X-mas.

I don’t have the talent to write an extended review as others did here, but I can confirm that this -technically very well designed- amp is a really good sounding DIY tubes amp at a very attractive price point.