[vlb]

My dual mono bijou have been running for a while now and it´s the best headphone amp I´ve ever heard. But it needs just a little more bottom end and dynamics before Im satisfied. It should also function as a preamp so it has to match the sq of an arc d250.  
Im going to:
 
Amp
Replace c1 with 2x20uf film (done)
Replace c3, c4 with 0.68uf film
 
Ps
Paralell c1 with another 470uf and a 20uf film.
 
Im a newbie so please tell me if Im about to do something stupid.

 

[runeight]

This is not an unreasonable plan, although the extra electrolytics might be detrimental to the SQ. Hard to say.
 
You might try changing in stages as you've already done with C1. Try C3/C4 next, then C5.

 

[vlb]

Im doing it step by step to se the improvements. C5 is already replaced with 120uf film and right now and I think it sounds best without the cathode bypas cap. So the amplifier is free of electrolytics.
 
Could an extra electrolytic in the ps realy decrease the sq? I thought 2 in paralell would cut the esr in half. 

 

[nikongod]

 
Quote:

 
Could an extra electrolytic in the ps realy decrease the sq? I thought 2 in paralell would cut the esr in half. 

When you look at signal current loops, which almost always go through a fat electrolytic cap, absolutely.
 
From what I have read on the interweb The issue is seldom ESR in audio-frequency applications. The issue is that capacitors have their own funky distortions which get into the signal through signal current loops. Lynn Olson OR Thorsten Loesch (I cant remember who! More than likely Thorsten, Lynn's style leans more towards push-pull amps to break signal current loops. Read as much as you can written by both of these guys anyways) briefly touched on the subject in his article on designing a SET 300B amp, and the hidden challenges that are easy to overlook and make your amp have "beautiful tone". 
 
ESR is critical in digital applications, and switching power supplies, but is not really a significant factor at low frequencies. The difference in ESR of 2 different caps at 100khz will make a world of difference in a switchmode power supply, but means nothing at 1khz smack in the middle of the audio band.
 
On the other hand, the output stage of the Bijou has some PSR, so the inclusion of the caps in the signal current loops is probably not as bad as on a SET amp.

 

[SBoy]

I don't know if this is the best way to post this but I didn't want to create a thread on this.

I was wondering if anybody has heard LCD-2 on this amp? I am about to purchase a LCD-2 but i wonder if its gonna work wonders with the bijou.

 

[vlb]

2x 20uf film for C1 in the amp and 20uf paralell with C1 in the power supply right now.
 
It´s a big improvement. The sound is more detailed and dynamic, but never get´s harsh. The bass has improved a little, but I gues it get´s better when i change c3 and c4.
How do i calculate -3db for c3 and c4?
 
Thanks

 

[nikongod]

 
Quote:

How do i calculate -3db for c3 and c4?
 
Thanks

This is harder than it looks. 
 
Most people will observe that the 2 caps, and their bleeder resistors are equally sized and apply the basic equation for a high pass filter without more thought.
 
C3 (to the bottom triode) is calculated in the normal fashion with the -3db point given by the equation:
f=1/(2piRC) 
where R is the 470K resistor in this case, and C is the 100nf cap.
 
However this is not 100% correct! It will get us close enough for most purposes, but dosnt tell the whole story....
 
C4 is harder. Let me tell you a little story.
You see that 470Kohm resistor there. yea, thats the one R9 sexxy little bit of DCR. m'hmmm. you look at her and say "hello MS. 470Kohms I would like to put you, my cousin the capacitor, and my buddy pi into a room and let them put their AC signals into you while I take pics to post on the web." but there is a problem with this. Not only are you being very disrespectful to the 470Kohm resistor by even thinking she would entertain an idea such as this but she is doing the deed with the triode brothers (you can see this by looking at the center of the output stage - the diodes are there because the top brother dosnt trust her and wants protection in case she tries to strip his cathode {OK, so these are not actually protection diodes, and I dont think cathode stripping will EVER be an issue with a circuit like this, nor would protection diodes do anything to help that but this would not be as fun of a story otherwise}) and trust me when I say that these guys will put up a fight with sparks and electricity to protect her. Since you are trying to apply signal into what ammounts to being another signal that is in the same phase the impedance of this resistor is actually several meg ohms. OOH SNAP! You were all ready to go and tell this resistor who is boss, and the resistor is like "I can resist much more than you initially thought you limp-leaded capacitor!"
 
link to article that actually explains this
 
In the end it probably dosnt matter, and I'm just a little bit bored. As long as the high pass filter created by C3/R11 checks out you dont have much to worry about. Use the same cap for C4 so that the circuit looks pretty.

 

[vlb]

I tried swtiching + and - on my speakers and headphones so the sound wouldn´t be phase-inverted. Before I thougt that the soundsstage could become messy in some songs, especialy when preamping my magnepans. The instruments posiotions ar much clearer now and the bass is punchier .
 
Nikongod:
Thanks! I appreciate when people take their time to explain things. Now i have some reading to do.
 
My pretty test setup:
http://img413.imageshack.us/img413/148/201009041036.jpg

 

[Coupe]

So I am about 130 pages into this post.   Very interesting indeed and also very confusing to follow! 

 
However, I am starting to get the idea.  Unfortunately, I ordered the kit from GJA on September 1st.  I have yet to receive it.  I e-mail this past Sunday and have yet to get a response.  Is Jeff ok? 
 
Also, I have built a Millet MiniMax and done a lot of wiring in my life.  I am a mechanic and I've done work around the house.
 
This will be the first time I am working on a HV complex circuit.  I have been reading about how the caps hold charge for long after, and the recommended waiting time is 15 minutes.  Is there anyway to discharge the entire circuit of stored energy after it has been unplugged?
 
I also am curious about the acronyms and terms used.  It is making it difficult to understand some of the posts.  I'm assuming that O/P means output, but some of the others I am not understanding.  Would anyone mind breaking down some of the acronyms or giving a resource where I can learn them?
 
I am also trying to understand what the whole nature of bypassing is.  After reading it seems that people use Caps to bypass.  Why?  What is this for?  What does the UF rating actually mean for audio?
 
If there is any great resource to where I can study audio circuits and have them explained that would be greatly appreciated.  I would really like to understand AND enjoy rather than just the latter.
 
Thank you so much for all your responses and thanks to Mr. Cavalli for this great schematic.
 
-Steve

 

[HiGHFLYiN9]

Quote:

...Unfortunately, I ordered the kit from GJA on September 1st.  I have yet to receive it.  I e-mail this past Sunday and have yet to get a response.  Is Jeff ok? 
 
Also, I have built a Millet MiniMax and done a lot of wiring in my life.  I am a mechanic and I've done work around the house.
 
This will be the first time I am working on a HV complex circuit.  I have been reading about how the caps hold charge for long after, and the recommended waiting time is 15 minutes.  Is there anyway to discharge the entire circuit of stored energy after it has been unplugged?
 
I also am curious about the acronyms and terms used.  It is making it difficult to understand some of the posts.  I'm assuming that O/P means output, but some of the others I am not understanding.  Would anyone mind breaking down some of the acronyms or giving a resource where I can learn them?
 
I am also trying to understand what the whole nature of bypassing is.  After reading it seems that people use Caps to bypass.  Why?  What is this for?  What does the UF rating actually mean for audio?
 
If there is any great resource to where I can study audio circuits and have them explained that would be greatly appreciated.  I would really like to understand AND enjoy rather than just the latter.
 
Thank you so much for all your responses and thanks to Mr. Cavalli for this great schematic.
 
-Steve

 
Jeff can take a few weeks to get your kit together, nothing to worry about. I found a nice easy tool for myself (a non-engineer) was the MAKEzine series (MAKE:Electronics). It's not as dry as a textbook. μF is a microfarad, μ meaning micro or 10^-6 and farad is a unit of capacitance. 99% of capacitors I've seen use μF, occasionally you'll see nF or nanoFarad. There's some great articles online regarding bypassing so I recommend a google search rather than trying to explain it myself. Also for lots of info on audio circuits, check out http://www.pmillett.com/
 
As I know it, bypassing an electrolytic with a film cap can have sonic benefits, and bypassing a large cheap film cap (e.g. Solen) with a nicer quality film cap can also be beneficial. Most people recommend 1% or less for a bypass cap value. I've seen bypassing in both coupling and power applications.
 

 

[fishski13]

Quote:

This will be the first time I am working on a HV complex circuit.  I have been reading about how the caps hold charge for long after, and the recommended waiting time is 15 minutes.  Is there anyway to discharge the entire circuit of stored energy after it has been unplugged?
 
 
-Steve

i would not dick around inside the Bijou without using a means to discharge the caps.  just get a 10K-30K 5W wirewound resistor and solder/insulate wire leads on the ends and terminate with insulated alligator clips.  i usually just keep one end clipped to safety/chassis ground and touch the other end to the caps i need to discharge.    

 

[funch]

 
I just had an interesting experience with one of my Bijou boards. I had disassembled my amp a few days ago in order to replace the
chassis. I was picking up several items, and placed one of the amp boards on top of my hand to hold it. I felt a slight stinging and
thought it was probably a clipped lead on the bottom of the board, but it persisted. Turned out that it was the C5 cap, so I measured
the voltage, and even after several days it still read 42 volts. I measured the other board, and C5 on that one read 52 volts. Guess next
time I'll make sure to discharge things.

 

[fishski13]

Quote:

 
I just had an interesting experience with one of my Bijou boards. I had disassembled my amp a few days ago in order to replace the
chassis. I was picking up several items, and placed one of the amp boards on top of my hand to hold it. I felt a slight stinging and
thought it was probably a clipped lead on the bottom of the board, but it persisted. Turned out that it was the C5 cap, so I measured
the voltage, and even after several days it still read 42 volts. I measured the other board, and C5 on that one read 52 volts. Guess next
time I'll make sure to discharge things.

i had sparks fly when my crescent wrench touched C5 and chassis while trying to remount one of my boards.

 

[yiancar]

Hey guys, just a quick question on the Rcore transformer (r80-36). It has a 6.3v secondary with a CT. Each of the CT is equal to 3A right? so connecting only the gray wires(without the CT) will give me 6A or still 3 A?. If the above is not correct, parallel connection with the 2 6.3v secondaries will give me 6 A ?

 

[PoulE]

Hi 
I new, and i have just got the Bijou from Jeff, and I'm gonna go for both Regals's and Ampheads Mod's
I guess it will be good to do that in the  beginning.
 
Im going for Ecc99 goldpins , ..... AND ,  >>>is it importend that these 2 tubes are matched balanced and so on ,
or shall i just order 2 ?????
 
Thanx
 
Poul from 
Danmark