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Bijou All Tube Futterman Headphone Amplifier - Page 120

post #1786 of 3981
11/4/08 at 8:24pm
Thanks. I can't wait to see everyone's amps when they're done.
Ferrari's is spectacular.
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post #1787 of 3981
11/4/08 at 8:48pm
Quote:
Originally Posted by fishski13 View Post
amp boards connected, with 10 min. or so, here's what i get:

R8 point = 332V
R7 point = 308V
Q2 = 68 C
Q1 = 40 C
TIP50 = 30 C

so if my maths are correct, the Q2 mosfet is dissipating around 1.7 W

my mosfets are not isolated with pads from heatsinks - only a thin layer of thermal grease.
Wow, your R8 voltage is very high. Were you having problems getting to 250V before you added the BJT filter section?

In any case, 332V is quite high. And, as a consequence, there is still 58V on the mosfet.

If you have any EZ80s lying around try one of those in one of the PSs and see what the voltages are.
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post #1788 of 3981
11/4/08 at 8:48pm
Quote:
Originally Posted by funch View Post
Here are some new pix of my 'Blue' Bijou...
Looks good . Hammond case with custom front plate?

btw fishski13 if you were still interested, I put in that capacitor switch. It doesn't spark or do anything crazy if I flip the switch with the amp on. However, it can take up to 2 full minutes for the DC on the output to drop below 400mv (which I think is the acceptable range?) In my impatience however, I typically plug in a cheap headset after about 30 sec which drops the DC to 0v almost instantly. Anyway, it works and I'm happy.
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post #1789 of 3981
11/4/08 at 8:50pm
Quote:
Originally Posted by funch View Post
Here are some new pix of my 'Blue' Bijou showing all the updates/mod's that
I've made since it was built.

snip

Here's what I've done so far:
Added a separate heater tranny for the PS.
Regal's mod's.
Amphead's mod's.
Choke PS mod, variation 2.
6H30 gold pin input tubes.
ECC99 gold pin output tubes.
EZ81 PS rectifier.
Auricaps in C3, C4 and C6.
Changed signal wiring to cryo'ed Vampire (buried under all that shielding).
Stepped attenuator (50K) from ebay (Taiwan).

I just installed the stepper yesterday, and now understand the enthusiasm for them. The sum total of all the mod's has produced one fantastic listening experience. It's very detailed and dynamic, yet not at all fatiguing.

Thanks, Alex, for all your hard work on this design, and your continued efforts
in this thread. Thanks, also, to all of you who continue to tweak this great
design. I finally think I'm done (yah, right!). Now I gotta stop reading this
forum so I can just enjoy the music.
That's one heck of a lot of changes funch, but it looks great. But most of all I'm delighted that after all of your work it sounds so good.
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post #1790 of 3981
11/4/08 at 9:20pm
Quote:
Originally Posted by runeight View Post
Wow, your R8 voltage is very high. Were you having problems getting to 250V before you added the BJT filter section?

In any case, 332V is quite high. And, as a consequence, there is still 58V on the mosfet.

If you have any EZ80s lying around try one of those in one of the PSs and see what the voltages are.
no EZ80s lying around.

no problems dialing in 250V before or after inserting the BJT filter section.
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post #1791 of 3981
11/4/08 at 9:44pm
OH. OK. You probably didn't need to make this mod. But now that you did, thanks for testing it out. Others can now make the mod if they are having B+ problems. I assume that your amp is still quiet?

I think you might grab some EZ80s to lower that 332V. Don't want to change the resistor on the BJTs because they are now burning about 1W each and this is enough for your heatsinks.

I can pretty well guarantee that your B+ will never drop below 250V.
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post #1792 of 3981
11/4/08 at 9:51pm
Quote:
Originally Posted by runeight View Post
OH. OK. You probably didn't need to make this mod. But now that you did, thanks for testing it out. Others can now make the mod if they are having B+ problems. I assume that your amp is still quiet?

I think you might grab some EZ80s to lower that 332V. Don't want to change the resistor on the BJTs because they are now burning about 1W each and this is enough for your heatsinks.

I can pretty well guarantee that your B+ will never drop below 250V.
thanks. i think i will just go back to bog standard and remove the add-on.
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post #1793 of 3981
11/4/08 at 9:52pm
I can't remember, did you ever get around to doing regal's mod fishski? (trying to entertain the necesity of the mod in conjunction with regal's, etc)
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post #1794 of 3981
11/4/08 at 10:08pm
Quote:
Originally Posted by chobint View Post
I can't remember, did you ever get around to doing regal's mod fishski? (trying to entertain the necesity of the mod in conjunction with regal's, etc)
nope...excellent food for thought.

runeright,
can i just add some more heatsink to Q2 and call it good? i understand the error of my maths - the mosfet is still dissipating 4 W.
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post #1795 of 3981
11/4/08 at 10:59pm
Quote:
Originally Posted by fishski13 View Post
nope...excellent food for thought.

runeright,
can i just add some more heatsink to Q2 and call it good? i understand the error of my maths - the mosfet is still dissipating 4 W.
Yes, you can do that. But, if you're going to make the regal mod you may want to keep your BJT filter section because it will draw quite a bit more current per channel.
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post #1796 of 3981
11/5/08 at 3:43am
Pabbi, you have me worried man. Are you alright?
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post #1797 of 3981
11/5/08 at 5:39am
Quote:
Originally Posted by amphead View Post
Pabbi, you have me worried man. Are you alright?
hopefully he's stoned out on the fresh tunes.


performed 10K surgery on the other BJT filter. i think i will order up some resistors for regal's mod in addition to more heat sinks. i'm going to stack another Standard Products Found on top of each existing Q2 heatsink, doubling the size of each - thermal grease in between where they meet.
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post #1798 of 3981
11/5/08 at 12:00pm
Quote:
Originally Posted by amphead View Post
Pabbi, you have me worried man. Are you alright?
You know, sometimes electronics takes a wierd turn - to wit, my wife bought a new ceiling light fixture that i had to put up last night - a snappy 2.5 hours. Worse than casework.

So, I haven't looked any further, trying to think through the current dliemna. The Goldpoint site gives me one hope of how to knock down the gain, but I also simply need more steps in the volume control, so, to drag this out a bit more, I am pondering a combination of the Goldpoint solution (as also recommended ad nauseum by dsavtisk) along with the new Joshua Tree 128 step(per). The other oddities still need looking at (perhaps something shook loose in shipping), but I need a clear head for that.

Now, since there is plenty of room in the case, JT makes sense.

Yeah, yeah, going all the way around the mountain to justify a poor initial decision, but, the outcome will still be rather unique.

Fishki, mayhaps you will have a better outcome, and, solution.

Edit: And Ron, you did everything you could - this is on me, but what's the fun in no challenges? :-)
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post #1799 of 3981
11/5/08 at 1:45pm
Quote:
Originally Posted by pabbi1 View Post
You know, sometimes electronics takes a wierd turn - to wit, my wife bought a new ceiling light fixture that i had to put up last night - a snappy 2.5 hours. Worse than casework.

So, I haven't looked any further, trying to think through the current dliemna. The Goldpoint site gives me one hope of how to knock down the gain, but I also simply need more steps in the volume control, so, to drag this out a bit more, I am pondering a combination of the Goldpoint solution (as also recommended ad nauseum by dsavtisk) along with the new Joshua Tree 128 step(per). The other oddities still need looking at (perhaps something shook loose in shipping), but I need a clear head for that.

Now, since there is plenty of room in the case, JT makes sense.

Yeah, yeah, going all the way around the mountain to justify a poor initial decision, but, the outcome will still be rather unique.

Fishki, mayhaps you will have a better outcome, and, solution.

Edit: And Ron, you did everything you could - this is on me, but what's the fun in no challenges? :-)
i'm going to tackle the attenuators tonight or tomorrow night. i have 2 two deck make-before-break rotaries from Electroswitch http://www.electro-nc.com/rotaryus/d9.pdf.

i'm going to try a shunt type. i found this schematic which looks pretty simple - and only 2 resistors in the path. diyAudio Forums the downside is that your source will not see the same impedance from click to click on the switch.

i'm anticipating only needing a total of 20 dB of gain. the trick is, what value should R2 start out at, and how much gain do i want at each step - first couple of positions could have 3-4 dB of gain, and the rest 1-2 dB. i have a bunch of resistor values that i think will work, but experimentation will be necessary. i'm going to try a boutique 100K Caddock or Kiwami for the R I/O, and populate the rest with Vishay RN60 after i get the resistor values worked out.

here's a cool calculator for determining the amount of attenuation you want.
Stepped Attenuator Resistor String Calculator - Neville Roberts

this may also be of some interest to you as well.
S5 Attenuator with Sweet Whispers Advise
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post #1800 of 3981
11/5/08 at 3:48pm
pabbi1, perhaps you can turn up the NFB? You can also remove the cathode bypass cap. I can't recall what you've got on your amp right now.

Another thing you can do, as a temp, till you get your attenuator is to build a cable with an inline cap and take the + line and reference it to ground instead of - . You effectively become single ended, but it's only temporary and should allow you to use your amp.

Another little thing to try till you get your JT going.

Shunt mod - How to? - World-Designs-Forum
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