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Bijou All Tube Futterman Headphone Amplifier - Page 146

post #2176 of 3981
1/20/09 at 4:15am
Thank you amphead for the pointers. Please excuse my ignorance but I have a few more questions. A post by Ferrari mentioned the 470uf output cap is theoretically adequate for low Z phones. I assume that is possible by significantly increasing the negative feedback and because the high frequencies are bypassed at the output caps. I have minimal experience with tube amps and how does one know the appropriate amount of feedback to apply?

Applying Ferrari's equation to compute the –3dB point I calculated ~1100 uF needed for the output caps. Should the output e'lytic cap be increased to this size? If so, do you know of a quality 250v e'lytic you could recommend (I did not find any Nichicon muse caps with sufficient voltage ratings)?

If the output cap size is increased, is there an equation for calculating the size of the cap for bypassing the output caps?

I apologize for the audio-101 questions . My expertise is in the digital domain not analog. Can anyone recommend any books/websites that would help me come up to speed. I do have a EE/CS background and I am a quick study!

Thank you.
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post #2177 of 3981
1/20/09 at 7:16am
You should be ok with the caps that I used 410uF 300v.

RUBYCON PHOTO FLASH / STROBE ELEC CAPACITOR 410UF 300SV - eBay (item 360080999665 end time Feb-15-09 18:13:28 PST)

I substituted 1/2" shaft for the 1/4" shaft on my knobs. It is mounted through 1/2" bronze bearing. Moves smoother with the teflon washers I installed.

Edit: Alex Cavalli is mentioned in the Jan. 2009 issue of HiFi News. On sale at Barnes and Noble. ;-)
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post #2178 of 3981
1/20/09 at 12:38pm
Quote:
Originally Posted by amphead View Post

Edit: Alex Cavalli is mentioned in the Jan. 2009 issue of HiFi News. On sale at Barnes and Noble. ;-)
Umm, are they talking about me? If so, what are they saying? I guess I'll have to go to B&N and buy a copy.
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post #2179 of 3981
1/20/09 at 2:27pm
Quote:
Originally Posted by amphead View Post
You should be ok with the caps that I used 410uF 300v.

RUBYCON PHOTO FLASH / STROBE ELEC CAPACITOR 410UF 300SV - eBay (item 360080999665 end time Feb-15-09 18:13:28 PST)

Edit: Alex Cavalli is mentioned in the Jan. 2009 issue of HiFi News. On sale at Barnes and Noble. ;-)
BTW, I still have PLENTY of those caps for Bijou builders... do not pay the ebay price. Search the thread for details. Basically, I will send you a cap for every $1 donated to Head-fi, and I pay shipping.
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post #2180 of 3981
1/20/09 at 11:35pm
Egads, I went to both B&N that are near my house. They carry Hi-Fi News but they don't have any copies!!!!
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post #2181 of 3981
1/21/09 at 12:11am
Thread Starter 
someone is going to have to post an excerpt, I am dead curious now ..dB
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post #2182 of 3981
1/21/09 at 12:24am
Quote:
Originally Posted by runeight View Post
Egads, I went to both B&N that are near my house. They carry Hi-Fi News but they don't have any copies!!!!
Same here, stopped at one on the way home and there were no copies left. The Cult of Cavalli must have wiped them out! Prepare for a rush of builds!
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post #2183 of 3981
1/21/09 at 12:32am
I simply have no idea what this is all about, but I hope they said something good.
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post #2184 of 3981
1/21/09 at 12:53am
Quote:
Originally Posted by pabbi1 View Post
BTW, I still have PLENTY of those caps for Bijou builders... do not pay the ebay price. Search the thread for details. Basically, I will send you a cap for every $1 donated to Head-fi, and I pay shipping.
If these things are a significant upgrade from the stock caps, sign me up. I've been wondering about that big electrolytic, and what I can do about it. Are there any other suitable options? I'm sure it's covered somewhere in this thread, but there's a few hundred pages now
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post #2185 of 3981
1/21/09 at 4:00am
Quote:
Originally Posted by V-DiV View Post
Amphead, how's the casework coming?

Thanks Pabbi, fishski, and Chobint. I put in an order to Mouser for resistors for Regal's Mod and for tube rolling, Wima's for C6, jacks, power inlet, and some odds and ends. Also ordered a pair of 6DJ8. Next up is wire, transformer, and decision on case.

I would like to build the amp boards upside down under the top plate and air wire the tube sockets. TimmyMac soldered straight to the boards for his air wire. It looks like Ferrari soldered sockets to the boards and wired from the sockets - does that make for a less positive contact?

If the PS board is upside down will the FETs get too hot? Can I air wire those too and mount them on top with the tubes (and tranny) like on my Starving Student Millett?




or will all of that air wiring likely result in hum or signal degradation problems regardless of how carefully routed? If it is a problem, would shielded wire fix it?

Thanks,
Vic
i'm not sure that there's any specific answers other than following the general rules about heater wiring and thermal management. in DIY, you have to suck it and see, and be prepared to be flexible to make layout/wiring changes if need be.

if mounting the PS FETs underneath, i would personally add a taller heatsink if you have the room - they get hot. i've posted my experiences dealing with heat and power dissipation with the multiplier mod i performed on my PS in this thread. i wouldn't be comfortable mounting the FETs to the chassis either.

i also played around a bit with running multiple LEDs over a distance for some trick lighting effects. since the LEDs carry heater AC, they will carry noise as well. with no attenuation, source connected but no signal, heater noise was audible and changed in volume depending where i moved the LED wire. the least offensive was with the wire going straight up, perpendicular and away from the PCB. but heater noise was inaudible with attenuation at sane volume settings, so not an issue. i'm not suggesting that you don't air wire an LED or tubes, but rather to illustrate a point.

i would do Amphead's Mod and add shielding to the air wired heaters if needed.
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post #2186 of 3981
1/21/09 at 5:56am
Quote:
Originally Posted by amphead View Post
If you decided to give it a go, welcome to the Bijou club!
Thanks! I have decided to join the club.
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post #2187 of 3981
1/21/09 at 6:25am
Quote:
Originally Posted by pabbi1 View Post
BTW, I still have PLENTY of those caps for Bijou builders... do not pay the ebay price. Search the thread for details. Basically, I will send you a cap for every $1 donated to Head-fi, and I pay shipping.
I did not follow all the discution.
Theses caps are intended to replace C5 ?
What changes this will introduce ?
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post #2188 of 3981
1/21/09 at 6:39am
Quote:
Originally Posted by balderon View Post
Thank you amphead for the pointers. Please excuse my ignorance but I have a few more questions. A post by Ferrari mentioned the 470uf output cap is theoretically adequate for low Z phones. I assume that is possible by significantly increasing the negative feedback and because the high frequencies are bypassed at the output caps. I have minimal experience with tube amps and how does one know the appropriate amount of feedback to apply?

Applying Ferrari's equation to compute the –3dB point I calculated ~1100 uF needed for the output caps. Should the output e'lytic cap be increased to this size? If so, do you know of a quality 250v e'lytic you could recommend (I did not find any Nichicon muse caps with sufficient voltage ratings)?

If the output cap size is increased, is there an equation for calculating the size of the cap for bypassing the output caps?

I apologize for the audio-101 questions . My expertise is in the digital domain not analog. Can anyone recommend any books/websites that would help me come up to speed. I do have a EE/CS background and I am a quick study!

Thank you.
Balderon, I have written that post by head and by looking at the actual output schematic of the Bijou, with headphone connected.

The bypass cap is intended to lower the ESR of the main output cap and has no (negligible) impact on the cut-off frequency (-3dB point). The amount of negative feedback is intended to reduce the effective gain of the amp when desired (not implemented in mine) and has also no impact on the cut-off frequency (-3dB point).

You didn’t say what kind of headphone you are going to use, but based on your descriptions I think that it’s probably 32Ω or lower and you have the cut off frequency of ~5Hz in mind (?).
An output capacitor of 470µF will indeed result in a higher cut-off frequency, but it can work.
Personally I’m using ~400µF MKP with AKG K701 and have not experienced any lack of bass.
As for output cap, I think that “quality” is ruling over “quantity” (with a reasonable value).

If you are interested in some readings you might try this link, and especially about passive filter, take a look here.

Btw, no need to apologize. Many (or may be most) of the DIY folks at this place don’t have much expertise in EE, no matter analog or digital (sometimes… even folks who has done 10 projects) .
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post #2189 of 3981
1/21/09 at 7:37am
Yes, good point Ferrari!

Alex, would you like me to get you a copy of HiFi News and send it? As I remember, Jeff Rossel brought his Bijou to Burning Amp and displayed it at Amb's table. The magazine reporter mentioned that it was your design in the article. Amb was also mentioned in the same article.

Well I have drilled a 1.25" hole in the front panel and installed a 1/2" precision bearing. That volume knob rotates as smooth as silk. I have to do that for the other volume knob now. This added another $25.00 to the cost of the chassis.
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post #2190 of 3981
1/21/09 at 11:37am
Quote:
Originally Posted by amphead View Post
Yes, good point Ferrari!

Alex, would you like me to get you a copy of HiFi News and send it? As I remember, Jeff Rossel brought his Bijou to Burning Amp and displayed it at Amb's table. The magazine reporter mentioned that it was your design in the article. Amb was also mentioned in the same article.

Well I have drilled a 1.25" hole in the front panel and installed a 1/2" precision bearing. That volume knob rotates as smooth as silk. I have to do that for the other volume knob now. This added another $25.00 to the cost of the chassis.
Thanks amphead. Let me try a few more place here in Austin. And then if I run out of sources I may take you up on your kind offer.
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