3 preamps with transformer hum, DC on the line?

Jea48, thanks again for the info. Here are the preamp's specs:

Output imp: < 20
Power consumption: 6.5 watts
Max output voltage: 3.8 v

With the above specs, is there a cheaper EI power supply I can try? Or maybe I can put my amp on the same EI supply. The power amp consumes 850 watts. Would the one you found be powerful enough for both the preamp and amp?

Yesterday I tried exactly what you stated by ONLY having the preamp plugged in to the dedicated 20 amp AV line with no other AV equipment powered up on the same line and all the other breakers off in the main fuse box. So, power was cut off to every breaker except the dedicated AV line and the only thing powered up in my entire house was the preamp. Still hums.

The power amp consumes 850 watts. Would the one you found be powerful enough for both the preamp and amp?
04-05-12: Sbrownnw

No...... For a power amp that consumes 850 watts I would not want to use an xfmr rated any smaller than 2.5KVA, 2500Va / watts....

Yesterday I tried exactly what you stated by ONLY having the preamp plugged in to the dedicated 20 amp AV line with no other AV equipment powered up on the same line and all the other breakers off in the main fuse box. So, power was cut off to every breaker except the dedicated AV line and the only thing powered up in my entire house was the preamp. Still hums
04-05-12: Sbrownnw

Searched the first couple of pages around transformer hum but did not find any specific answer around this. I have had the 3 following preamps in my main system with transformer hum, most of them on a dedicated 20 amp line:

- NAD T163 A/V preamp
- Audio Refinement Pre-DSP 2
- Audio Refinement Pre5 (current preamp)

If not for your original post I would say the Audio Refinement Pre5 is the problem.....

Take the preamp to someone else's house, not in your neighborhood, and check for the mechanical hum...

If the hum is the same, try one more persons house. Hum still the same it is the preamp......

http://www.audiorefinement.com/handbook/Pre-5-Manual.pdf

So I am going to try an isolation transformer. I found one of the two new (returnable if it does not solve my problem):

- Tripp Lite IS1000 in black (1000W) for preamp only
- Tripp Lite IS1800HG (1800W hospital grade in off-white) looks like it is just under the 2000W rating Jea48 recommends for preamp and amp

I am going to check around Seattle today to see if someone has the IS1000 in stock. Hopefully this works and gives me some more evidence to use if I can ever get the power company to come out and test my line.

If the IS1000 does not work for eliminating the hum in my preamp, it looks like it will have to go in for repair. Does anyone have any good repair shops besides Audio Plus Services?

Again, TIA everyone,

Scott

Found the following locally:

Tenma 450 VA Isolation Transformer, Isolated Outlet (2): 450 VA Continuous, 550 VA Intermittent, Direct Outlets (2): 900 VA, Isolation Leakage: <0.1 mA, Dimensions: (W x H x D) 6 x 5 x 9 , Weight: 16 lbs, Power Requirements: 120 VAC, 60 Hz

Going to give it a try for just the preamp. Fingers crossed.

Scott

Yesterday I tried exactly what you stated by ONLY having the preamp plugged in to the dedicated 20 amp AV line with no other AV equipment powered up on the same line and all the other breakers off in the main fuse box. So, power was cut off to every breaker except the dedicated AV line and the only thing powered up in my entire house was the preamp. Still hums.

I still see two ways DC offset can still infiltrate your system ... even with all the breakers off except the dedicated line ...

First you can be picking it up from your neighbor who is producing it and sending to the transformer you share ... his flat screen .. dvr/cable box .. computer .. hair dryer and anything else in his house that has a switching power supply with a half wave bridge rectifier will produce DC offset by drawing current in un-even pulses

I also not sure if a Isolation transformer or regenerator will help ... an isolation transformer will block common mode noise riding on the line ... DC offset is not like noise riding on the line ... it is a distorting of the sine wave .. so I would think that the Iso Tranfo will not remove or straight the distorted sine wave but just passes it through

My proof is your neighbors are creating plenty of DC offset and it is ending up in your home after it passes through the transformer on the pole on the street ...

The way to dissipate the DC offset is to pass it through a capacitor bank ... capacitors can not pass DC and the action of the capacitor merely straightens the sine way as the current passes through it

DC offset vs DC

Just for clarity (I hope) .. DC offset is when the sine wave doesn’t cross correctly at the zero crossing point were the wave turns from positive to negative phase ...

Here the half wave bridge rectifier in the switching power supply lops off half the wave and creates some DC from the AC wave form ... this created DC rides on the current and can only be dissipated by a capacitor bank which will not pass DC and this is what straightens the wave back out to its symmetrical wave form

Regenerator won’t help either ... I’ve been using a Exact Power EP15 since 02 and it’s no benefit .. here is why

The humming of the transformer you are hearing is the “Symptom” and not the “Real Disease” ... the Real Disease and silent killer as you can’t hear it is ... the reduction of the transformer’s efficiency

By the Offset shifting the Zero crossing point ... it reduces the transformer’s efficiency and this silently reduces dynamics and head room ... unlike the presence of RF that you clearly can hear ... the reduction in dynamics and headroom are not realized until the Offset is eliminated and dynamics are restored

Simply put DC Offset created by switch power supplies has a profound effect on dynamics and headroom

So now you add a regenerator and I don’t care what brand ... the DC Offset will hit the regenerators transformer first reducing it’s efficiency long before it hits the regenerating circuit ... so the generating circuit is now running down on power provided from it’s compromised transformer

Again IMO it is the reduced efficiency that is the perpetrator and not the sound of the transformer humming which I view as the symptom

When I unplugged my 500w Phase Linear amp and Arye D1xe player for the EP15 and put them into a PS HumbusterIII ... the improvement in slam and authority was immediate and profound ... wanna buy an EP15 cheap

I also didn’t experience the roll off in the highs as you did ... but that’s not the issue at this point or of this thread

Second point of entry ... with all the breakers off and only using your dedicated AV line ... I realize that you have shut off your video equipment also and you would think that you were safe but ...

All that video equipment .. Flat Screen .. cable box and or DVR have switching power supplies ... you would think by turning them off you’ve eliminated the effects of the switching power supplies ... but you haven’t

All these components work by remote and are in a constant stand by “ON” mode state waiting for a signal to turn them on ... in the stand by mode guess what ... the switching power supplies are still working to keep component in an ready state .. while waiting for a signal to turn on and thus creating the DC offset that continues to hammer your preamp even with those components turned off

Try UNPLUGGING your flat screen and cable box/dvr with all the breakers off and see if this stops the humming ... if it does and you still have the HBIII try re-plugging the flat screen and cable boxes into the HBIII ... this should eliminate the DC Offset from the video equipment and not roll the highs off to your stereo as the stereo is not plugged into the HBIII