[fishmalt]

Can somebody tell me what I'm messing with as far as risk . . . 

I built an AKSA 100 Nirvana plus amp a few years ago.  I forgot (really  ) that I had disconnected star earth from chassis ground due to hum  . . . I joyfully used my amps for years without any issues . . .

 . . . as I started to build again, Hugh recommended I could upgrade my AKSA N+ with a Lifeforce power supply as an upgrade.  I did and it sounds great, except . . .

. . .  if I connect star earth to chassis ground  . . . via a resistor and two diodes (facing opposite directions) all in parallel as recommended by Hugh I get hum (relatively low levels) but disconnecting the star earth from the chassis gave me a dead quiet amp . . . connecting star earth to the chassis gives me hum . . .

I know hum can be a bugger to resolve but could some one give me:
1) the risk I'm taking by disconnecting star earth from the chassis; and
2) any other strategies to resolve the issue that are undoubtedly safer. . .

 . . . the hum still occurs with the amp connected to the speakers without interconnects connected . . . it increases slightly when connected to my preamp . . .

Thanks in advance,

M-
Anchorage, Alaska

[AKSA]

Hi Mike,

Welcome to our forum!

As long as your transformers are AC tested to 4000V, and the standard in Oz, dunno about the States, says they all are, and as long as the chassis of your amp is connected to IEC power earth, then no connection between star earth and chassis is cool bananas.

You do not require this connection for electrical safety.  The option is included only to ensure that you can choose between connected and unconnected, giving lowest hum.

Question:  If the amp is not connected to a source, do the speakers hum when the star IS connected to chassis via the back to back diodes/10R resistor?

Cheers,

Hugh

[fishmalt]

Thanks for the response Hugh,

I made the assumption that if I disconnected the star to chassis ground connection that I would have the same result I had with the previous Nirvana PS but after reading your response I did disconnect the star/chassis connection and the hum increased slightly . . . so to answer your question below: I do get a slight hum with no source connected and the star IS connected to chassis via the back to back diodes/10R resistor. . . it however, increases slightly when disconnected . . . as opposed to decreasing which is what occurred with the old Nirvana PS . . .

The hum (with star/chassis connected) is slight but it would be nice to get rid of it completely as I suspect it is possible. . . whether or not I can figure it out is another question . . .

Regards,
Mike

[stvnharr]

Mike,
Why do you want to connect star earth to chassis ground?  There is generally no need to do this unless your amp boards are totally isolated from the chassis.  By connecting chassis ground to star earth you are connecting the ground system in your whole house, as the ground wire is connected to the neutral buss bar in the house service box.
You only need to connect the ground wire in the 3 wire romex to the chassis.  Looking at the pic of your amp in your gallery, it looks like you have the heatsinks on the chassis, so therefore any catastrophic fault in the amp will go to the chassis and safely routed away by the ground wire.

Granted, these diy efforts are not UL approved, but it doesn't seem you have anything to worry about.

Steve

[fishmalt]

Thanks for the response Steve,

I don't necessarily "wan't" to connect it but I originally thought I was supposed to by design. . . Hugh's response above makes it sound like it can go either way . . .

the bottom line is I have a low level hum issue and I'm trying to figure out how to fix it . . . my original hypothesis above was incorrect in which I thought by disconnecting the star/chassis ground as described it would reduce the hum which is was happened with my old power supply but in fact the opposite occurred, the hum got slightly louder . . . so I'm back where I started . . . I've got a hum issue and I'm not sure how to proceed. . .

Are there steps that can be taken to logically eliminate possible contributers to the problem?

Thanks,

Mike

I added a new pic of the updated power supply and other mods to the Gallery . . .

[AKSA]

Hi Mike,

To find the hum, short the hot inputs to ground with a shorting RCA plug, and switch on with speakers connected.

Do you have hum?  If yes, jigger wires and trafos around until it disappears;  usually it's interference between the AC transformer and the input circuits. Wire trim and trafo shielding will normally remove it.

How efficient are your speakers?

Anything higher than 95dB/watt/meter can be quite difficult to banish hum.  Speaker sensitivity is a big factor too.

Hope this helps,

Hugh

[stvnharr]

Thanks for the response Steve,

the bottom line is I have a low level hum issue and I'm trying to figure out how to fix it . . .
Are there steps that can be taken to logically eliminate possible contributers to the problem?

Thanks,
Mike

I added a new pic of the updated power supply and other mods to the Gallery . . .

Okay I understand.

[fishmalt]

For any one who has made it this far in the thread . . .by using the shorting RCAs, I realized the hum level is very low and actually resides with my new pre-amp project.  I connected the amp up to my CAT SL-1 Ultimate pre-amp and there is virtually no hum but with my new DIY Audio Note L3 there is a bit of hum which I am now working to resolve . . .

Bottom line: my AKSA 100 is a combo of the Life Force power supply with the Nirvana plus upgrades and a few "upgraded" components of my own choosing and taste . . . the amp continues to deliver the emotional goods (ie I envision my limbic system lighting up under fMRI studies . . . ).

Thanks for bearing with me on this journey.  Hugh even contacted me directly to ensure my problem was resolved after not hearing from me on the forum. . . you don't get that kind of support in any other forum! . . .at least not any that I've been involved with. . .

Thanks Hugh and Steve for your help!

Mike

[AKSA]

Fantastic, Mike!!

I love a happy ending, though now you have to chase down hum in your preamp circuit.  What design are you using, care to discuss it?

Hugh

[fishmalt]

I recently built the tube based Audio Note Dac 3.1 transformer coupled DAC and it really opened up my system . . . I have been very pleased with the emotional engagement of this addition so I am now using my modded Audio Research CD player as my transport. 

At this point my system was bi-amped with a pair of WAD 300B PSE monoblocks and the AKSA 100 N+ (now with Life Force PS), a DIY pair of speakers with x-overs designed by Rick Craig with Selah Audio and my own enclosure design, and all DIY interconnects and power cables mostly of the Chris VenHaus (VH Audio) design amongst others, so the only remaining factory component was my CAT SL-1 preamp. 

So I clearly needed to build a preamp and I have been intrigued by the transformer coupled approach used by Audio Note.  The L3 preamp kit (while relatively expensive for a kit) sounds fantastic (very "musical") and both Audio Note kits I own include upgraded components and their c-core output transformers.  I built a Gold Point shunt attenuator with Audio Note Tantalum input resistors and Takman Carbon Film resistors to sue with my preamp. . . .so far so good (in fact I'm thrilled with my system) except. . .I have a relatively low level of hum (but still too high for this design) that I haven't been able to track down yet . . . I'm confident it will eventually be resolved but so far it has alluded me . . .

I can listen to my system which I would describe as very musical and emotionally engaging which are exactly my priority criteria for a system but of course I need to resolve this residual hum issue before I will be completely satisfied . . .

That is the current status . . . (sorry you asked?)

Mike
Anchorage, Alaska

[AKSA]

Mike,

Tube pres can be susceptible to hum, no doubt about it, and usually the issue comes back to earthing, EM screening at the tube grids, or power supply noise.

My knowledge of Audio Note is sketchy, but generally transformers can help greatly in eliminating hum as they break earth loops very nicely.  I'm pretty sure that design has a highly adequate power supply (Andy Grove design, IIRC, he's VERY good), and very likely includes an inductor, so here are my suggestions:

1. Hum is either 60Hz, mains, in which case it emanates from magnetic coupling of the mains primary circuit, OR 120Hz, when it is coming off the rectified AC on the secondary side of the trafo and just before the filtering.  You need to isolate which it is;  hum (60), or buzz (120)
2.  Place a shorted RCA into the input of the preamp, with all interconnects and the speakers in place, amps on.  If the hum disappears, then the issue is further back in the chain, presumably the DAC.  Otherwise, if it persists, then it's very likely the preamp, just as you suspect.
3.  The input to the first tube in the preamp will be via the grid, naturally, and if you can isolate this connection, short it with a croc clip to the braid connection of the input RCA.  This shorts out the input grid without affecting the bias providing, and this is important, the preamp has appreciable gain.  We can verify this if you could send me a picture of the schematic, so I can analyse the circuit more effectively.  If hum disappears at this point when input tube grid is grounded, then we are talking very likely EMI - induced hum - into the high impedance input point of the tube.  This can normally be eliminated by reducing the value of the grid resistor and taking some shielding precautions.  Otherwise, keep moving on, and I will talk later about this stuff after you can get back to me (preferably by email, to keep this process private, not boring the others here!!)

Cheers,

Hugh