Bijou All Tube Futterman Headphone Amplifier - Page 70

Yes, everything works fine. But I want to try changing resistors values on amp boards to implement Regal's mode. Then I'll see if PS needs any tweaking. And finally I'll try this input cable wiring that you mentioned to eliminate hum completely. But my Bijou currently works great, thank you! :-)

Recently I purchased e-mu 0404 and must say that it's internal SS headphone amp is not that bad either. 0404 may be just a perfect match for somebody who wants an inexpensive all-in-one solution. But Bijou's sound is more pleasant (smoother) when connected to e-mu's line-out.

The next Bijou that I build is going to use pillars and floors/levels for the chassis similar to yours Chobint. I can think of a couple of ideas for running wiring inside the pillars, using them as conduit/shielding. The amp would be oriented so that the legs are on the bottom. Square channel aluminum 2 inch, copper pipe 2 inch etc. Bottom floor transformer, second floor power supply board, 3rd floor amplifier boards L/R. Heater wires running up two legs from bottom floor to 2nd floor and third floor. Separating ez80 heater wires from amp board heater wires. Signal wiring running up/down the other two legs. Top of the amp/roof small rotating beacon. ;-) I might even create it as a prize to be won by some lucky Head-fier! Similar to what was done for the Beta22. Imagine the excitement, when our fellow Head-fiers realize that they might be struck by lightning too! ;-)

Edit: btw, keep source volume lower and amp volume higher for a little better resolution and less distortion. When running my source at mid volume and the amp compensating at lower volume I lose some fidelity and get a tinge of distortion on loudly recorded vocals or similar sound. Really enjoying high quality recorded material with the amp in this mode, taking on the load. It shouldn't provide more headroom, but it seems too. Runeight? Or maybe the source was overdriving the preamp.

Cool, I like your idea amphead. Sounds similar to the original, super-clean, mostly no-wire look I had imagined, but lacked the skills to make. I think you may find, even with only three layers, that the amp will be quite tall and will need a very wide base to remain stable.
I've been getting a fair bit of this with loud midrange vocals too, the sound is vibrant but choppy. It's audible at all amp volumes, but the source volume is fixed since it's a cheapo dvd player.

Edit: deleted previously posted question

You can over drive the input. So there is balance to be struck between source volume and Bijou volume. However, to get the best fidelity I think you want to come out of the source from line outputs.

You both may be hearing distortion in the source and you may not have heard it before. The Bijou is pretty good at revealing the quality of the source, either the electronics or the recording itself.

Runeight, I did Regal's mode yesterday and got some problems with an input stage at one channel.

I have a pair of new JJ e88c that replaced JAN Philips 6922 at the front.

With Regal mode I see 4.3 or 4.7 mA through the first stage of one channel and 5.8mA through the first stage of second channel. The plate voltages are 115V and 96V respectively. The second stage is also unbalanced as it's bias relies on the plate voltage of the first stage. And I can hear a permanent static (not hum or buzz) on the channel that draws less current at the front (where I have 115V on a plate). This static has a strong hearable level that has no reaction on volume pot. I tried swapping the tubes between channel and the voltages and static follow the tube. Just did that to check if something is wrong with my soldering.

B+ is at 243VDC, C6 is at 299VDC, heaters are 6.2-6.25 VAC, total current is about 76 mA. So, I definitely need to push 370DAX slightly beyond it's specs.

I guess one of the JJ e88c is defective? That's strange because they where tested to be pair matched. But maybe they where tested at 1mA and not at 5mA.

Then I tried to put my old 6922 back. Now I'm getting 88V and 94V on plates with no audible static. But unfortunately one of my 6922 is very sensitive to any vibrations (I can hear that when I slightly tap on the chassis or move the Volume POT). B+, total current and other voltages are pretty much the same as before.

I thing sound became slightly juicier :-)

Now I fully understand what Jeff Rossel meant when he told me that tubes are tricky :-) They really are!!! :-)

I would say the tube must be defective, 5 mA's is still pretty low for a 6922, its common to run them at 10 mA.

What is your voltage at the input of the regulator? Are you using the EZ81?

I agree with regal. The tube is not necessarily bad, but it is fairly far away from the norm. You could try letting it break in for a while to see if the emissivity of the cathode increases.

Tubes are not any trickier than BJTs or MOSFETS. They SEEM to be because they have nice sockets and you can swap them in and out.

But, nearly every circuit with an active device must be designed for the operating points of those devices. If you swap out active devices the circuit can go whacky.

You don't notice this much on SS amps because you don't swap out the devices. For example, if you have a mosfet output stage on an amp, you couldn't expect it to work if you swapped out the power mosfets with completely different devices. The reason the mosfets seem trouble free is because they are soldered in to the board and you can't swap them out.

Your results are pretty reasonable. Try running the transormer on the 110V taps. If you can pull the B+ up to 250V the rest of the voltages will be reasonable.

Yes I recently built a Jfet discrete DAC, the first Jfets I used gave a noise very similiar to tube noise, at first I thought it was the 6DJ8's in my Bijou. So yes solid state devices can hbe just as noisey as tubes

Regal, I'm having about 50V voltage drop across R7+R8, so it's about 250V at the input of the regulator which is low. That's running the primary winding of Hammond 370DAX at nominal voltage. The only solution I see here is to push 370DAX beyond it's rated voltage at the primary. That's why I'm trying to use 110V with some serial resistors with primary winding. I'm getting 117V to 122V on power line.

with your new op point have you tried the 110V operation without resistors?

I have ~20 hours on those JJs.

Runeight, I agree with what you're saying, although I see some differences :-)


I just tried to connect 110V winding taps directly to powerline (no resistors). I'm getting ~285VAC on loaded HV secondary, ~320-330VDC on C6, ~270VDC on C4, ~250VDC output, ~56V drop across R7+R8, ~6.75VAC on heaters. That's with 118.5VAC on powerline. I guess when powerline will go up to 122VAC I will be getting ~300VDC on HV secondary and ~7VAC or more on heaters. I guess that's high and above specs both for tubes and transformer.

Wow, I'm imagining a very warm xformer after a couple hours of use, not to mention some hot resistors. Are you using a separate transformer for heaters? That might be one way of reducing heat on the power tranny.

These numbers are not so bad and if it weren't for the heater voltages, things would run happily at 122VAC on the 110VAC windings.

An alternative is to go back to 120V operation and simple set the B+ to 240V. I think the amp will sound about the same.

Another alternative is to run at 110V and put a resistor in series with one of the heater leads. 0R13 would do the trick if you are pulling 3.5A. It will burn about 2W so a 5W resistor would be in order. I've done this myself on a few projects.

And, of course, there is the resistors in series with the primary. Perhaps this is the best solution.

Runeight, I have more results :-)

I added 12.6R resistor (two paralleled 5W resistors) in series with primary.
My tube configuration is JAN Philips 6922 + JJ ECC99 + JJ EZ81.
With 118VAC on powerline I was getting ~112VAC on transformer primary, 265-266VAC on HV secondary, 6.22-6.3VAC on heaters, 299VDC on C6, 251VDC on C4 and ~244VDC on B+. So, heaters are OK but B+ is low. I need more voltage at C6.

I could try smaller resistor - 10R or 8R in series with primary but decided to try my old 6n6p instead of ECC99 as my 6n6p-s draw less current both for heaters and plates.

So, here's what I'm getting at this moment (12.6R in primary circuit):

117.4 VAC - powerline
111.7 VAC - primary
~269 VAC - secondary HV
6.31 VAC - heaters
~310 VDC - C6
~264 VDC - C4
~250 VDC - B+

Everything looks pretty much normal :-) I guess I still be OK if the powerline will jump to 122VAC.

Now I'll try to burn in my e88c-s more but I'm skeptical that this static noise will go away.

The reason I wanted to try serial resistors for the primary instead of serial resistors for heaters is that's it's easier to "play" and connect 10R resistor than 0.2 Ohm one. But I may be mistaken here.

I'm attaching a few pictures.