[fishski13]

i like to buy locally when possible and picked up a pair of these:http://tctubes.com/6DJ8-ECC88-Amperex-A-frame-dimpled-disc-getter-pair.aspx
 
everything should be coming together by Thursday night!

 

[fishski13]

i got off work this am at 0730, had the tubes in my hands by 0900 and in situ by 0945

.  in addition to the Amperex white print, i picked up a pair of matched Sylvania 6DJ8.  since i socketed cathode bias resistor R2, i was able to just plug in 475R from the parts bin to bias at 5ma with Regal's Mod.  the sonic differences are apparent with the Sylvania, so much so i'm wondering if the former 6N1P with R2=180 was clipping with my K702 and K240 DF?  sometimes i felt there was a "hardness" in the mid-range that i just chalked up to the HPs preferring sand - i never had an issue with my K271 though.  i'm hearing better transients, more treble detail, natural tone and dynamic shadings with my K240 DF.
 
i took some readings with my DMM with the 6N1P last night and drew out a load line on the plate curves with B+ 253V.  i calculated and measured 0.9V on the cathode.  my y2 DAC puts out 1.4V rms.  my rectifier is EZ81 and i installed the cap multiplier mod (btw Alex, you should add this to the "Tweaks" on you site).  i'm measuring 2.4V on the cathode with 6DJ8 and R2=475.  any thoughts re: clipping?
 
  

 

[fishski13]

done...
 
 http://www.amb.org/forum/post3912.html#p3912

 

[HiGHFLYiN9]

I started putting together my kit last night and had a couple of questions.
 
There's a through hole under V1 that connects to pin 4 on the amplifier boards. What is that used for?
 
If I flip the MOSFETs and mount them to the bottom of the board, won't that mess up the pin configuration?
 
TIA

 

 

[balderon]

 
Quote:

I started putting together my kit last night and had a couple of questions.
 
There's a through hole under V1 that connects to pin 4 on the amplifier boards. What is that used for?

 
This trace is connected to the power LED and it happens to be routed via a through hole under V1.
 
Quote:

If I flip the MOSFETs and mount them to the bottom of the board, won't that mess up the pin configuration?
 
TIA

 
The pin configuration will be fine as long as you maintain the correct orientation. The easiest way I ensure the correct orientation is to note where pin 1 is on the silkscreen side and on the backside of the board and where pin 1 is on the transistor. When I place the component on the opposite side I ensure that pin 1 is inserted into the correct through hole.

 

[graematter]

I just finished my Bijou tonight and I have some serious humming. This is my first tube amp so I'm sure I have many areas to correct, but I was wondering if you guys could give me some idea as to how to locate the hum. It changes when I unplug my laptop power cord, when I unplug my M2Tech HiFace and sometimes when I touch my NFB pot. I can turn the NFB all the way up to reduce it, but not eliminate it. I have a star grounding system. I have some wires crossing that maybe shouldn't be crossed... maybe? I can post some pictures soon, but I was hoping to get on top of it sooner...
 
P.S. sounds GREAT besides!
 
...the hum is basically its own song though....
 
grae
 
 
EDIT: It also has a faint grinding sound when I use the trackpad on my computer....

 

[johnwmclean]

Graematter, I’d double check the input and output from you pot is not mixed.

 

[fishski13]

graematter,
try shorting the input to ground on the boards of each channel.  if you still have noise, it's probably the amp/grounding/wire management.  if no noise, it's the pot back to the source causing problems.  i'm guessing that if you get a reduction in noise with the NFB turned all the way up, it's the pot to the source.

 

[graematter]

Graematter, I’d double check the input and output from you pot is not mixed.

Mixed. As in I'm having shorts or I wired it incorrectly? And I used a jumper between 2 posts on my NFB pot... That's what I was supposed to do right?

Some other areas of question:

I have unshielded RCA input jacks... Problem?

I built it in a wood enclosure - with a piece of aluminum sheet metal on the bottom to mimic a metal chassis to try and pick up any interference... Stupid?

The only thing connected to that piece of aluminum is my star ground and the transformer body... And lines ground at the star ground post... Was this a dumb thing to do?

I have shielded wire running from my input jacks to my ALPS volume pot. I didn't connect the shield of the wire to star ground. The shield is only connected to the ground of the RCA jacks and thus whatever that's grounded to... Could this cause a "ground loop"?

When I unplug everything (laptop, HiFace) the hum becomes more "pure"... It gets messier when everything is setup.


I'm using the new Gigaworks DAC with Coax connection from my HiFace.

Blue Jeans Cables connecting it all.

P.S. I also get a buzzing when I move my NFB wires around... But is very manageable... Any advice to completely eliminate?

 

[fishski13]

i would not connect the shield of the chassis wiring to the ground of the RCA - you're adding RFI noise.  just tie the shield to chassis ground, anywhere. 

 

[graematter]

I'm at work - I'll try the shorting trick as soon as I get home.





Some other points of question and maybe concern:





I built it in a wood enclosure. I put an aluminum plate at the bottom. It's connected to star ground and transformer casing. Thought this would help reduce RF interference... Stupid?





I have unshielded RCA input jacks. I used shielded wire to connect those to my ALPS volume pot. I grounded the shielding of this wire to the jack ground, but not the star ground... Should I connect it to star? Tried connecting with no reduction at all to hum.





I'm using the new Gigaworks DAC (coax connect) with a HiFace. All hooked up with Blue Jeans Cables.





When I unplug everything from the amp, the hum becomes more "pure".





My star ground wires cross a bunch of other wires - nothing under any boards or anything. There is a lot of room, so they aren't truly that close. No effect to hum at all when I mess with then though... I think they're fine.





I'm thinking I will have results when I short the input. Is there a specific way that I have to do this? Can I damage anything by performing this?





P.S. I get some buzzing when I mess around with the NFB wires - they are my longest hookup wires by far... That ok? The buzz is VERY manageable, but I'd like the "blackness" that I know is acheivable with the Bijou.





Hum = Goliath


Buzz = David





Graematter





EDIT: sorry for the double post... Working with an iPhone and I thought my first post was lost... And now I can't delete my first one for some reason... And I like my second one. I'm eccentric - my apologies.

 

[balderon]

Ensure the frame of NFB pot is grounded to the chassis ground and none of the pins on the pot are touching the NFB frame. Also I found it helpful to use a ground loop breaker (simple R/C network) to connect earth ground to chassis ground. I used a 10 ohm 1W wirewound resistor in parallel with a 0.1uF 250VAC capacitor. For a test you could jumper earth and chassis ground but I wouldn't recommend making that permanent.

 

[johnwmclean]

Quote:

Mixed. As in I'm having shorts or I wired it incorrectly? And I used a jumper between 2 posts on my NFB pot... That's what I was supposed to do right?
 

Wired incorrectly, check that you haven’t mixed up the input and output wires of your ALPS volume pot, mixing these up causes a hum that reduces when the volume is turned all the way up.

 

[graematter]

Ensure the frame of NFB pot is grounded to the chassis ground and none of the pins on the pot are touching the NFB frame. Also I found it helpful to use a ground loop breaker (simple R/C network) to connect earth ground to chassis ground. I used a 10 ohm 1W wirewound resistor in parallel with a 0.1uF 250VAC capacitor. For a test you could jumper earth and chassis ground but I wouldn't recommend making that permanent.

Very helpful thank you. I had connected earth to chassis without a ground loop breaker - guessing that is causing some big problems.



So... Earth ground to Ground Loop Breaker to Star Ground (or somewhere other than star?)



I built it in wood remember... So almost every single ground I have is going to star. Any I should isolate?



And when I connect the NFB and volume pot casings to ground, should it be star ground or does it not matter where?





Still at work... Just wanted to pick up any materials I will need on the way home.

 

[chobint]

I'd wager you're using a USB source aren't you? It is typical for actions like typing or scrolling to cause audio noise when using a USB DAC. As others have mentioned, grounding the input and grounding the NFB pot are good places to start.
p.s. Take it easy on the spacing. It makes your post more difficult to read.