Hello, I am looking to build a balanced Bijou and I was wondering what does everyone use for their balanced volume control?
I'm thinking the joshua tree attenuator. Does anyone have any insights to which I should really use?
Personally I used an alps attenuator which also has a motor on it. there is also a more audiophile grade model without the motor. Dact is also another choice. This attenuator from part connexion can be taken into consideration. The reason I used the alps one was because it was easier to source and I consider Alps products to be trusted.
Now it's finished! The case is a rather large CO-meter previously used in a power plant. Almost the size of a regular computer case. The buttons on the front panel are pretty and still funcional (they do nothing) and the two displays are just for show.
The transformer still resonates but it doesn't get mixed into the signal anymore. For some reason I get a hum when connected to the phono pre-amp but not when there's a Nuforce Icon HDP in between.
I did a left-handed solder work to a Regal's mod after the pictures were taken and the change from Chinese tubes to 6DJ8 Bugle boys is quite remarkable! So impactful and not shrouded like it used to be.
Twice when powering it off it's messed up the Nuforce dac for some reason. They share the power socket so maybe there's a spike of some sort that messes up the circuits, dunno.
Now to get some sort of a router or switch to control all the sources and outputs so I don't have to change cables every time I use the Bijou instead of my monitors. Cheers!
No need, it's quiet:] There is a bit of extra on the black signal wires but I'm too lazy to even consider opening it again since it's very operational as it is.
Im finaly getting around to learn more about tube amplification :) Im tying to analyze my bijou but there is one thing (so far) I don´t understand.
How does the value of c1 affect the amp?
In a "proper" Futterman C1 is part of the positive feedback loop around the cathodyne and output stage. It allows ac at the output to go back into the junction of R5&R6 to create the loop while blocking the DC present at the output of the amp from getting back to the junction.
In the Bijou R6 and R5 are not sized properly to allow positive feedback to happen (in any meaningful amount anyways) so C1 does basically nothing except block DC. Since the cap does basically nothing, its size is not critical with the part values on the Cavalli site.
For proper "futterman action" R6 should be much smaller than it is and the global negative feedback resistors should be soldered to the PCB and never removed. No, I don't know how much smaller R6 should be. Yes, there is the very real possibility that you blow up your gear if you go mucking about with R6 and do it wrong BUT this possibility of failure is balanced against the possibility of finding something interesting.
If the amp had R5&R6 sized properly the cap would need to be large enough (enough capacitance) to pass the lowest frequency you cared about into what may be a lowish impedance. My gut instinct is that 10uF is large enough for preliminary experimentation by anyone inclined to experiment with different values of R6. Since you should not even think about tweaking R6 without measurement tools to verify stability you can very easily measure frequency response and figure out if 10uF is in fact large enough in the end.
Can you post a few pics? That might help rule some things out.
I'd vote that some ground connection on your left channel has a cold soldered joint somewhere, but it could easily be something else.
the tubes sit on top of the board that's why the extension wires. Also just tried the J1 connection and it didnt work. after the amp is left to complete cool down also the right channel experiences hum, 1-2 minutes powered up and the right channel hum dissapears
Are you using a toroidal, and is it located under the left channel?
Also is your amp chassis grounded to safety ground (earth)?