[WireNut]

Since I’m planning on several Felix conditioner builds and also while I've been reading about how to build DC blockers, and if I really need them, I did an
experiment to try and measure DC Offset on some of my 1980’s equipment.

Not owning an oscilloscope I’m trying to measure with a DMM.
If the procedure below isn’t correct please chime in.

Equipment:
Pioneer SA 8500-MK2 integrated amp.
2-Adcom GFA-555mk1 amps.

Procedure:
With everything disconnected from the equipment, volume at zero, balance control at center, all filter switches off on the integrated amp,
Power up all equipment for 15 minutes.

DMM set to DC millivolts, Auto measuring, and I also measured manually.

All readings were taken from the loudspeaker binding post outputs on each component.

Pioneer SA 8500 MK2 integrated amp:
Left Ch:   000.4mv
Right Ch: 002.5mv

Adcom GFA-555mk1 amp:
Left Ch:   010.3mv
Right Ch: 073.8mv

2nd Adcom GFA-555mk1 amp:
Left Ch:   043.6mv
Right Ch: 027.6mv

If I did this correctly, it looks like the measurements are low and these components don't need a DC blocker.
I’d still like to know how to build a DC blocker, some of my other components may benefit from one with a Felix.

Thanks to Anand, TomS, Richidoo, Occam, and everyone involved with the “MANY” Felix threads on AC. 

Steve.


Pioneer SA-8500 mk2 integrated amp:





Adcom GFA 555mk1 amp:





2nd ADCOM GFA 555mk1 amp:

[ZAKski288]

Here is the DC Blocker Build info:    Good Luck Zak

http://www.audiocircle.com/index.php?topic=25757.440     PAGE #23 REPLY #447 Read down from there.

[WireNut]

Here is the DC Blocker Build info:    Good Luck Zak

http://www.audiocircle.com/index.php?topic=25757.440     PAGE #23 REPLY #447

Thanks, I forgot about the Last Page  .

[*Scotty*]

If the amplifiers were thoroughly warmed up and had reached their normal operating temperature then it looks like you are good to go. Cold amplifiers generally have more DC offset until they warm up.
Scotty

[WireNut]

If the amplifiers were thoroughly warmed up and had reached their normal operating temperature then it looks like you are good to go. Cold amplifiers generally have more DC offset until they warm up.

Scotty

They were  . I had them powered up for at least 15 minutes before testing.

Thanks Scotty.

[*Scotty*]

You might have measured lower DC offset if the amps had a half hour to cook, all of the semi-conducters in the circuit have to reach thermal equilibrium before you will see the lowest DC offset. It is also critical for the differential input pair to thermally track one another or you will have higher DC offset as well as drift over time.
 In any case your numbers look good enough.
 Scotty

[WireNut]

Hi Scotty,

 My first temporary Felix installment has been positive for my 80’s vintage equipment.
The 3 amp Felix with my Pioneer Integrated amp and JVC QL-7 turntable is a success. 
System is dead quite. No hum / buzz.

Anand, you were right. No blocker needed  .

Keep in mind that the caps in the Felix need to be broken in just as any other cap.

1 hour of listening:
Smoother, others have mentioned less detail, I notice the same detail with less grain.
Overall system after 1 hour is more enjoyable and I’m now able to listen at higher volume without fatigue.

So far so good.



I will be installing in a metal case with a fuse.

              More to come.
           

[poseidonsvoice]

Look at you WireNut you've got your big boy undies on! Well done!

Just be safe.

Best,
Anand.

[Speedskater]

Well DC blocking isn't really about blocking DC. It's about asymmetry in the AC power waveform (harmonic distortion) which causes a DC offset in the waveform. This makes some power transformers unhappy and they saturate.
So what you want to measure at the speaker terminals is AC. But it requires a DMM with a 200 millivolt scale.

[andyr]

Since I’m planning on several Felix conditioner builds and also while I've been reading about how to build DC blockers, and if I really need them, I did an
experiment to try and measure DC Offset on some of my 1980’s equipment.

I think you are confusing 2 completely separate things:
1.  DC on the mains - which a 'DC blocker' (a circuit consisting of caps and diodes) or an isolating transformer prevents getting into the power transformer.
2.  And DC offset on the output of an amp.

#1 can cause your power transformer to buzz - which is annoying.  It can also cause your power transformer to heat up more than if no DC was present on the mains.
#2 is a bad thing!     Too much DC offset can cause problems with speaker drivers.

Note that #1 does not cause #2!   

Andy
 

[poseidonsvoice]

I think you are confusing 2 completely separate things:
1.  DC on the mains - which a 'DC blocker' (a circuit consisting of caps and diodes) or an isolating transformer prevents getting into the power transformer.
2.  And DC offset on the output of an amp.

#1 can cause your power transformer to buzz - which is annoying.  It can also cause your power transformer to heat up more than if no DC was present on the mains.
#2 is a bad thing!     Too much DC offset can cause problems with speaker drivers.

Note that #1 does not cause #2!   

Andy

Andy is absolutely right.

DC offset as is dealt with many solid state designs using servos, etc...is an intrinsic problem to the main amplifier circuit (such as linestages, output stages of dacs, AVP's, DSP's and amplifiers in general). Of course it is something I measure for in tube designs as well but many are cap coupled or use output transformers, the only ones where you need to be careful are OTL's. Similarly, they have servos and other circuits to null out DC.

Nothing to do with your AC outlet.

Best,
Anand.

[WireNut]

     I think you are confusing 2 completely separate things:
1.  DC on the mains - which a 'DC blocker' (a circuit consisting of caps and diodes) or an isolating transformer prevents getting into the power transformer.
2.  And DC offset on the output of an amp.

#1 can cause your power transformer to buzz - which is annoying.  It can also cause your power transformer to heat up more than if no DC was present on the mains.
#2 is a bad thing!     Too much DC offset can cause problems with speaker drivers.

Note that #1 does not cause #2!   

Andy

Good point. Thank you Andy.

I'll most likely be adding a DC blocker on the Negative line before the Felix PCB. Fuses will be on the positive line before the Felix.
I might as well add the blocker while I'm building it. I understand there are debates on adding the blocker to the Negative or Positive line.   

The plan is to use, one 35A bridge rectifier, 2 Nichicon UHE 3300uF 35v caps or 4700uf 25volt.

If I'm wrong let me know. I haven't purchased the bridge or caps at this time.

[andyr]

I'll most likely be adding a DC blocker on the Negative line before the Felix PCB. Fuses will be on the positive line before the Felix.
I might as well add the blocker while I'm building it. I understand there are debates on adding the blocker to the Negative or Positive line.   

The plan is to use, one 35A bridge rectifier, 2 Nichicon UHE 3300uF 35v caps or 4700uf 25volt.

If I'm wrong let me know. I haven't purchased the bridge or caps at this time.

Certainly use a 35a bridge rectifier - an aluminium cased one, to guard against it exploding.  It will get hot so bolt it to the base of your case using some white transistor paste.

Re. caps: the design I based mine on (from Rod Elliott's site):
* uses 2x 4700uF caps.  When put in series, this drops to half - so 2350uF.
* which doesn't provide much smoothing - so I would suggest using 4x 6800uF at the very least.

I use 100v rated Nichicons on the active line (even though the caps are in-line).  If you're going to put them on the neutral line, possibly only a 35v rating is OK?  I don't know the relative merit of putting them on the active vs. the neutral line - one commercial unit here in Oz puts them on both lines!   


Andy

[WireNut]

Lots of time on my hands being recently retired to learn and experiment.
After cutting grass today and killing weeds I sat down and drew this up.

Take a look at my wiring. I see one thing I don't like and could use AC's input.

Notice the ground conductor. I'm using 2 receptacles with the tabs broken.
Since im going to break the tab between out-1 and out-2 the ground conductor for out-1 is not directly connected to mains earth.

How can I fix this?

The fourth output will not be used.

The case is all aluminum, electrically conductive.

This is a learning process for me, be gentle. 

Here's my cad drawing.


Damn, It's to dark, Gotta do it in all white.

[Speedskater]

If I were to build 3 Felix's (which right now I'm not) I would place each in it's own box with a very short cord to the hi-fi component (maybe a captive cord with IEC connector). The longer the cord from filter to component the poorer the filtering.
The best filters are attached to the component chassis, but in the real world that's hard to do.

[WireNut]

If I were to build 3 Felix's (which right now I'm not) I would place each in it's own box with a very short cord to the hi-fi component (maybe a captive cord with IEC connector). The longer the cord from filter to component the poorer the filtering.
The best filters are attached to the component chassis, but in the real world that's hard to do.

I wanted to build each Felix in it's own box but ruled it out due to cost having several Felix's projects to build. No room to build them and the blockers into the components.

One other thing Im wondering about is since I use bulk power cable with 3 wires + shield + drain wire Im not sure how Im going to hook up the shield/drain.
Connect the ground and shield drain wire to the case and receptacles or let it float.

[Speedskater]

Does the filter chassis have input & output receptacles or captive cords?

Either way, the Safety Ground/Protective Earth is required to be connected to the filter chassis.
I would connect all the shields & drains to the filter chassis, where each cord enters the chassis.
At the distant end of each cord, I would let the shield & drain float.

[WireNut]

Does the filter chassis have input & output receptacles or captive cords?

Either way, the Safety Ground/Protective Earth is required to be connected to the filter chassis.
I would connect all the shields & drains to the filter chassis, where each cord enters the chassis.
At the distant end of each cord, I would let the shield & drain float.

Hi Speedskater,

I think I’ll remove the output receptacles shown in the Felix pic above and just use bulk Belden power cable #19364 for the in/out.
This way will remove several connections.
The 19364 cable is a 3 wire cord with shield and drain wire. 

Below is a draft of the wiring plan.

Outlet from wall:
Male plug, Belden cable, hot, neutral, ground and shield/drain wire connected to the male plug.

Input to Felix / metal case:
1- Belden cable, connect both the ground wire and shield using the shields drain wire to Felix metal chassis.

Outputs:
3 - separate 19364 cables.
From the metal case, connect all ground wires / shield drain wires to chassis.

From there the hot, neutral, ground, shield, and drain wires from 3- Belden cords will pass thru the rear of the Felix case until reaching
the 3- IEC’s ( for components) where the shield and drain wires will be disconnected / floating.
Only the hot, neutral and grounds will be connected at each IEC.

I hope I’ve explained this right and mostly that its correct.



New drawing. Something like this.

[Bob2]

Wirenut,
Did you adjust the DC offset on the SA 8500? I take it you know about the error in the manual: says to adjust variable resistors VR1 & VR2 for the idle current, and to adjust VR3 & VR4 for the voltage? Apparently that info is backwards.
Bob

[WireNut]

Wirenut,
Did you adjust the DC offset on the SA 8500? I take it you know about the error in the manual: says to adjust variable resistors VR1 & VR2 for the idle current, and to adjust VR3 & VR4 for the voltage? Apparently that info is backwards.
Bob

Hi Bob,

 No, I sure didn't. Thanks for this info .  I don't have the manual. I'll head over to HIFI Engine and see if they have it.