Bijou All Tube Futterman Headphone Amplifier - Page 235

Hey, finally somebody else wants to combine the capacitance multiplier mod with amphead mod. Check out this post by adamus though, it elevates the CT and put it away from the heater cathode limit.

In his diagram, he has two 64k resisters, and two 10u caps, shouldn't the set off one leg of the heater power be removed, because the set off the two 100 resisters replaces them?

I can see what he is trying to do with the regal mod, however the way the diagram is posted it is a bit confusing.Amphead's mod removed them, however in the diagram then seem to return.

I guess my new question becomes, can the adamus mod of amphead's mod be done with the capacitance multiplier mod?

What would it look like the following diagram?

Or would the R9 resister need to be a 348k resister as per adamus original mod?

I don't have a lot of time right now, so I can't look at the values on your revised schematic, but as far as my understanding goes, yes you can add the adamus mod as well.

The cap multiplier is really only effecting the way B+ is being produced.

The goal of adamus' mod was to elevate the ac signal the heaters are seeing with a fixed dc offset. The reason for this is to ensure that the cathode to heater differential of the chosen tubes are not exceeded. The values for the max voltage differential can be found on the tube data sheets.
 

Quote:

Originally Posted by clifwst 

 

In his diagram, he has two 64k resisters, and two 10u caps, shouldn't the set off one leg of the heater power be removed, because the set off the two 100 resisters replaces them?

 

I can see what he is trying to do with the regal mod, however the way the diagram is posted it is a bit confusing.Amphead's mod removed them, however in the diagram then seem to return.

 

I guess my new question becomes, can the adamus mod of amphead's mod be done with the capacitance multiplier mod?

 

What would it look like the following diagram?

 

 

 

Or would the R9 resister need to be a 348k resister as per adamus original mod?

My original sketch up was indeed a little rushed, and the revised diagram above is correct (cap and resistor layout).

question is though, can that be done on the boards... probably but i havent looked yet. It may require a trace to be cut.

All we are doing is elevating the heater supply to 40ish voltages. 30 / 40 / 50 iit doesnt really matter. The 390k and 64k form a divider and having the high values reduced  current draw to something negligable.

.... juts needs someone to test.

I just have to recommend the bijou as a preamp.. It´s sounds wonderfull together with my audio research d250 mkII (2*250w tube). Since the input impedance of a power amp is way higher than the headphones you can get away with a small filmcap for the output. Right now Im using 120uf filmcaps (http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=260627749981) for both headphone and line output, but Im thinking about trying some fancy small filmcaps for line output.

How do I calculate the -3db freq? I know I have read it somewhere in this thread but I can´t find it.    

Thanks

Corner frequency is  f_c  = 1 / 2*pi*R*C

Thanks adamus, I am not real good at merging circuits with out smoke and flashes yet....  I am interested in building the kit with both mods and Regal's mod.  I plan on socketing R2, for more tube options.

I also had an idea for an option way to wire the amp for both ECC99 and 6N6Pi options using two DPDT switches to make the changes.  This would allow more options for tubes and tube combo's 

Two DPDT switches would be needed, and the throws should be ganged so they are thrown together.

Probably best put on the rear away from signal paths also.

I getting ready to start this build and have a few basic questions that I was hoping someone might be able to shed a little light onto.

• I've found a chassis I'd like to use and it comes in two sizes, 13W x 10D x 3H and 17W x 10D x 3H. I measured out the boards and it appears the 13W x 10D x 3H would fit, but it may be a little cramped. Anyone have a recommendation one way or the other? The transformer is going to be mounted on the top of the chassis FWIW.
• I saw that a few people here soldered the tube sockets upside-down on the PCBs and mounted the PCBs to the bottom of the top plate on the chassis. What size standoffs were you gents using? 1/2"?
• I'm ordering the Rubycons for the power supply at the moment. Newark has the HXC for high ripple current, MXC for standard purpose and MXG which is a miniaturized version, apparently for both. Any opinions on which would be ideal?

TIA.

Quote:

Originally Posted by HiGHFLYiN9 

• I saw that a few people here soldered the tube sockets upside-down on the PCBs and mounted the PCBs to the bottom of the top plate on the chassis. What size standoffs were you gents using? 1/2"?

If you want to do this, you MUST solder the sockets to the right side of the board, and all components to the wrong side. The pinouts will be wrong if you flip it.

You're absolutely right.

Quote:

Originally Posted by adamus 

My original sketch up was indeed a little rushed, and the revised diagram above is correct (cap and resistor layout).

 

question is though, can that be done on the boards... probably but i havent looked yet. It may require a trace to be cut.

 

All we are doing is elevating the heater supply to 40ish voltages. 30 / 40 / 50 iit doesnt really matter. The 390k and 64k form a divider and having the high values reduced  current draw to something negligable.

 

.... juts needs someone to test.

You know gents, the original Bijou PS already elevates the heaters to about 40V if you use the components in the BoM. Amphead's mod puts the heaters at 0VDC and this puts the ECC99s under some HK stress but not beyond their maximums.

Or maybe I have missed something important to the conversation. In which case I apologize for the useless information.

Quote:

Originally Posted by HiGHFLYiN9 

I getting ready to start this build and have a few basic questions that I was hoping someone might be able to shed a little light onto.

 

• I've found a chassis I'd like to use and it comes in two sizes, 13W x 10D x 3H and 17W x 10D x 3H. I measured out the boards and it appears the 13W x 10D x 3H would fit, but it may be a little cramped. Anyone have a recommendation one way or the other? The transformer is going to be mounted on the top of the chassis FWIW.

Looks like I'm going to go with the larger chassis as I'll be mounting the large-ish 70uf Obbligato Film Oil caps in combination with Rubycon 410uf photoflashes on C5.

Would anyone be willing to give their opinion on how this amp and the DT990 600 sound together. I understand that tubes will have a great influence on this symmetry. I am looking toward an amp for these cans and would prefer diy, also looking at the SOHA II, as I would prefer a tube amp.

Hi,

Here are a few pics of a Bijou I’ve just finished building today.

Only stock parts recommended by cavalliaudio site were used and no mods. I do not know if any of the mods will dramatically improve the sound, but as it is, this amp rocks. My HD650 never sounded so good, simply spectacular. I can't hear hiss or hum of any kind, the amp is dead quiet. 

Credit goes to www.vt4c.com for providing the chassis, transformer and misc. at a very reasonable price. Also to Jeff R. from www.glassjaraudio.com for offering the bijou and many other kits. It makes life easy for lazy people like me.

Finally many thanks to Mr. Cavalli for offering such a beautiful and high performance design.

Very nice work gabriel!