[Russellc]

I have used 2 of these units since the mid 90's.  Everytime my "preamp" of the month (currently Counterpoint SA 1000) blows up I pull out the trusty Super Pas III.  I do notice some Hum, especially through the phono section.
This is not exessive and seems not to be noticable except between tracks or when no music is playing.  I do use High efficency speakers, currently much massaged Altec A7s, which do reveal a little more hum than < 90 db efficient speakers would.  I also get just a faint radio station in the background if no music is playing and it is VERY quiet.  Is this normal for the old beast or should it be sent in to Frank?  It does have the optional selector switch and Ground plane jacks.  Thanks in advance.

Russellc

[Dan Kolton]

My guess is that you need to do something different with chassis grounding for the hum (you might even switch polarity of the power cord by turning it over 180 degrees and that you also have a probllem with your interconnects picking up RF because of incorrect shielding.  Try another pair or try a "ground" wire from a chassis screw on the pre to one on the powe amp.

[Brett Buck]

I have used 2 of these units since the mid 90's.  Everytime my "preamp" of the month (currently Counterpoint SA 1000) blows up I pull out the trusty Super Pas III. 

    Perhaps this is a little off-topic,  but why do the preamps keep blowing up? I've been building, buying, or using various preamps for the last 40 years, but other than a bad tube (dead heater) about 25 years ago, I haven't ever blown anything. Preamps, in particular, ought to be essentially bulletproof, if correctly designed.

     Brett

[Russellc]

My counterpoint developed some problem letting a little dc through intermittently, I believe it is a problem with the timer/relay on it.  It didnt blow up.  I have been using tubes for decades and have never blown up a tube anything.  I have blown up a few solid state power amps however.  Trouble with tube pres is usually when they begin to get complicated, like audio research, Conrad Johnson, and then they dont blow up, just some ancillary circuitry like a regulator or something goes south.

russellc

[Russellc]

My guess is that you need to do something different with chassis grounding for the hum (you might even switch polarity of the power cord by turning it over 180 degrees and that you also have a probllem with your interconnects picking up RF because of incorrect shielding.  Try another pair or try a "ground" wire from a chassis screw on the pre to one on the powe amp.

Thanks for the ideas, but I was just wondering how much is normal on these things.   It hasnt been a problem with speakers of normal effiency, but when I use horns (over 100db )  I hear a little.  Have you used a super Pas III?

Russellc

[Zheeeem]

I have used 2 of these units since the mid 90's.  Everytime my "preamp" of the month (currently Counterpoint SA 1000) blows up I pull out the trusty Super Pas III.  I do notice some Hum, especially through the phono section.
This is not exessive and seems not to be noticable except between tracks or when no music is playing.  I do use High efficency speakers, currently much massaged Altec A7s, which do reveal a little more hum than < 90 db efficient speakers would.  I also get just a faint radio station in the background if no music is playing and it is VERY quiet.  Is this normal for the old beast or should it be sent in to Frank?  It does have the optional selector switch and Ground plane jacks.  Thanks in advance.

Russellc

Well.  You really shouldn't have much, if any, hum from the preamp itself.  Does it hum when the source is disconnected (at the preamp)?  Same with the radio reception?

I am guessing that the hum may be elsewhere - like the TT, arm and/or cartridge.  And especially the RF, which likely comes from the cables or arm wires.  You don't mention what your source gear is.  But I noticed when I tried Kimber PBJ ICs I got a tremendous hum.  Grado cartridges are also fairly notorious hummers.

If the hum continues with nothing connected, call Frank and have him walk you through troubleshooting.

[Wayner]

With high efficiency speakers, you have to expect a little residual noise, it's the nature of the beast. If I put my ears up to my Dynacos (92db efficient) I can hear a small amount of residual....back away 2 feet and it's gone.

Wayner

[Russellc]

I have used 2 of these units since the mid 90's.  Everytime my "preamp" of the month (currently Counterpoint SA 1000) blows up I pull out the trusty Super Pas III.  I do notice some Hum, especially through the phono section.
This is not exessive and seems not to be noticable except between tracks or when no music is playing.  I do use High efficency speakers, currently much massaged Altec A7s, which do reveal a little more hum than < 90 db efficient speakers would.  I also get just a faint radio station in the background if no music is playing and it is VERY quiet.  Is this normal for the old beast or should it be sent in to Frank?  It does have the optional selector switch and Ground plane jacks.  Thanks in advance.

Russellc

Well.  You really shouldn't have much, if any, hum from the preamp itself.  Does it hum when the source is disconnected (at the preamp)?  Same with the radio reception?

I am guessing that the hum may be elsewhere - like the TT, arm and/or cartridge.  And especially the RF, which likely comes from the cables or arm wires.  You don't mention what your source gear is.  But I noticed when I tried Kimber PBJ ICs I got a tremendous hum.  Grado cartridges are also fairly notorious hummers.

If the hum continues with nothing connected, call Frank and have him walk you through troubleshooting.

When I get home tonight, I will try your suggestions and report back the results.  Right now, the only components hooked up to the pre amp are my Rotel CD player and my AR " the AR turntable"  which has a full house of Merrill/Scillia mods.  Cartridge is the Shure V15Vxmr.  The Tone Arm on the Table is a Magnepan Unitrac, whose rca plugs were quite oxidized, cleaning them up helped a little.  Interconnects Are ones I made from Silver sonic cable and Cardas Rcas.  The cable is very well shielded, with shiel connected at the preamp end.

Russellc

[Russellc]

With high efficiency speakers, you have to expect a little residual noise, it's the nature of the beast. If I put my ears up to my Dynacos (92db efficient) I can hear a small amount of residual....back away 2 feet and it's gone.

Wayner

Yes, I agree and these speakers are OVER 100 db effiecient.  When my Counterpoint was in place, there was a lot less hum. With my Aria 5, 91 db, no problem, and Microns, 88 db, no problem. In the past I have been able to quiet down the Super Pas by playing with cable and power cord placement.  Reversing the plug on both the turntable or preamp seems to make little or no difference. Thanks.

Russellc

[martyo]

Is this a tube unit? If so, could it be the tubes?

[Brett Buck]

My counterpoint developed some problem letting a little dc through intermittently, I believe it is a problem with the timer/relay on it.  It didnt blow up.  I have been using tubes for decades and have never blown up a tube anything.  I have blown up a few solid state power amps however.  Trouble with tube pres is usually when they begin to get complicated, like audio research, Conrad Johnson, and then they dont blow up, just some ancillary circuitry like a regulator or something goes south.

    There should be nothing very complicated about the electronics in a preamp. The switching and the wiring to the switch is usually pretty imposing but the amplifier itself should be simple. There's no advantage to "complicated", if that's where the complication is, then it's probably poor design.

    As for the hum - I would be very surprised if there was anything much wrong with the amplifier. Many of the part failures that lead to hum are not going to cause a *slight* hum and certainly won't lead to picking up faint radio signals. It's not at all unusual to have a low-level hum that is audible on high-efficiency speakers with the volume turned up. If it's a "buzz" then maybe there's an issue with the power supply caps or rectifier.

     Hum is usually picked up from the inputs. The fact that its louder on the phono is pretty classic, since the overall gain through phono is obviously much higher than the line inputs. To see if this is true, put shorting plugs in the inputs (*not the outputs!*) and try again. If it goes away, it's being picked up by the input devices or improperly shielded cables. To test the cables, get the 79¢ RCA-brand cables from WalMart, Radio Shack, etc, and put those in place of the cables you have. If it still has hum, it's probably coming from the input device. If not, it's the "magic" cable,  leave the inexpensive cables in place since they are equal to or superior to audiophile cables in any case. You can get fancy about tracking it down by shorting the far end of the cables, instead of at the connector, but it should be obvious pretty quick without that.

   If the amp still hums with the inputs shorted, try moving the amplifier around, and reorienting it. I have a spot in my house where, for whatever reason, there's some magnetic field that creates a hum induced into the transformer. If I move it a foot to either side, or re-orient the offending device, it goes away.

     Brett

[avahifi]

It is possible that the external power transformer of the Super Pas Three is dumping hum into the cable set from the preamp to the amp, especially if the cable is poorly shielded.  We had that issue using Kimber Cables with the Super Pas Three.

The transformer was moved to the back panel to eliminate hum interaction with the unit's tubes when it was mounted inside the chassis.

Other causes can be AC cables and signal cables running in parallel, a dirty AC strip connector, a three wire ground unit in the setup somewhere, even RFI interference.

Note that regarding this issue, we are talking about the very very old Dyna PAS chassis with AVA circuits installed, not about any modern AVA designed chassis units.

Merry Christmas
 
Frank Van Alstine