Pending Paramour Build

[porcupunctis]

If my Fluke 112 is accurate at this level, I still have about 7mv of hum on each amp.  This is after the C4S upgrade. 

My speakers have a sensitivity of 94db.  I can clearly hear the hum with my ear near the speaker but barely when I'm at the listening point (and only when all other ambient noises are quiet).  It's not really affecting the listening experience but I'm concerned that maybe I have a problem that I need to track down like a bad solder joint or something. 

Both amps are measuring the exact same, so whatever I've done to one side has been faithfully duplicated on the other (in reflection). 

Dang, they do sound good, though!

[Grainger49]

Randall,

My speakers are 94dBW sensitive too.  I have not trimmed the hum pots after a recent tube swap and have about the same hum you have.  I haven't moved my hum pots to the top plate, yet.  I assume you did. 

The thing is I can hear the hum at my speakers but not at my seat so it isn't a pressing problem.  I'm surprised you have hum at or above mine.

[Doc B.]

If that is an RMS reading it is high, if it is peak to peak it is about average. It's most likely RMS on a Fluke I think, but you really need a scope to see what exactly the noise is that is being added together to create that number. All the hum pot nulls is 120Hz, if there is other than 120Hz noise present it won't affect it, and that can throw off the measurement.

[porcupunctis]

This one shows the two Paramours.  You can see the mirror finish and the mirror build.  Wardsweb is awesome and I stole his ideas shamelessly.

I still plan to do some finish work on the transformers but I'm waiting to see which ones I end up with.  I may upgrade in a few months.

[porcupunctis]

I think I located the hum problem and confirmed something that I suspected all along.  I took Doc's suggestion and put it under the oscilloscope.  Nothing too interesting at first.  It told me the hum was 60Hz and it's RMS was 5-6 mV.  This is very close to what I had measured with the Fluke.

After taking the measurements, I shut the amp off.  That's when I noticed something really odd.  The 60 Hz RMS reading on the scope actually went up.  UP?  to about double what I had when the amp was on.  I finally had to unplug the amp from the wall before the reading fell down to the 1-2 range.

The power cords that I received with the kits looked suspicious from the start but I went ahead and used them anyway.  After all, I plan on mounting an IEC connector on the back and will go to something else in the near future anyway.  So the wire colors on the power cord didn't match the instructions.  No big deal.  I know which is which.  The power cords have zero shielding.  Nothing.  I think they were designed to attach to a buzz saw or something.  They are long and massive and nothing like the manual describes. 

I will try an experiment sometime this week with a properly shielded cable and see what happens.  Right now, this is my prime suspect.

[porcupunctis]

Doc warns everyone about buying second-hand kits.  If the power cords and the 15K resistors are the only issues, I think I'll be OK.

[porcupunctis]

Here is a close up showing the fuse holder and the hum pot mounting.

It also shows the odd mounting of the hole shrinker.  I mounted it on top to hide the regularities of the hole punching operation.  An unintended side effect is that it give the driver a little pedestal so it doesn't look so small up against the 2A3. 

[porcupunctis]

There is some challenge to the mirror build, but it really wasn't that bad.  Once the hardware build was done, I labeled all the connection points just like the manual says.  On the mirrored Paramour I only had to reverse two of the terminal strips.  That was 16 - 20 and 21 - 25.  These ended up being labeled right to left instead of left to right.  The two tube sockets just have to be labeled what they are, you can't transpose the tubes.

I actually built both amps at the same time.  I would solder one wire or part on the "correct" amp and then make the same connection and solder on the "mirror".  At each step, I stopped, pondered, considered, reconsidered, and re-read the manual until I was certain that it was perfect. 

The C4S upgrade actually simplified most of the build and I wish I had just put it in to begin with. 

Since there is at least one other Paramour I kit out there in the wild maybe this will help someone who is giving the mirror look a consideration.  Since I had purchased my kit second-hand, I wasn't too worried about voiding the warranty.  I knew it was up to me to get these babies running.

This experience has gotten me studying the Paramount underbelly.  These would mirror along the short edge and not the long edge like the Paramours.  Somebody has surely tried this already. No?

[Paul Joppa]

... It told me the hum was 60Hz and it's RMS was 5-6 mV.  This is very close to what I had measured with the Fluke....

If it's actually 60Hz then the hum pot will adjust it out. Also if it's 60Hz, consider the possibility of nearby transformers which might have a magnetic hum field around them.

Also, make sure the 12AT7 heater pin 9 is grounded to the chassis at T14. In the original build the heater power floated; I don't think this grounding made it into the manual. And while I am reminiscing about this amp, make sure the 499 ohm grid stopper at the 2A3 pin 3 goes to T17, and so does the 270K grid resistor and the 0.1uF coupling cap. Only the stopper goes to tube pin 3, nothing else. The instructions as printed were wrong - I had forgotten these until I checked my ancient marked-up schematic. They came up on the old forum but that's a lot to wade through. Here's a link to the old forum, archived on Audio Asylum:

http://www.audioasylum.com/forums/bottlehead/bbs.html

You can do a search on "Paramour" and get the 200 posts thought by the search algorithm to be most relevant. The algorithm is not very smart though.  :^)

[porcupunctis]

I added the ground wire from pin 9 to T14  Then moved the 270K resistor off A3 to T17.  Everything else was as you described.

The scope doesn't report any 60Hz signal.  The RMS is hard to read because it wanders too much but I see some 1, 2, and 3 readings now and then.

What is most important is that when I hooked them back up I had to get my ear right on top of the cone before I could hear anything.  When I step back to my listening position, I hear nothing from the speakers. 

I think I got it now.

Thanks Paul.

[2wo]

Congrats, The mirrors do look nice . I think your "stop and ponder" approach has you well set for this game.

 Are those arrowheads?...John 

[porcupunctis]

Thanks John.  Yes, those are arrowheads.  Wal-mart specials.  I think I was able to buy enough of those to handle five boxes (4 feet each) for about 5 or 6 bucks.  I got the suggestion from Wardsweb.  I have to give credit where credit is due.  I left the black anodize on, though. 

[porcupunctis]

At this point I probably have 20 to 25 hours of listening in on the Paramours.  Impression?  They are wonderful.  I had been listening to a S.E.X. amp with full nickel output TFs so when I switched to what is basically a stock Paramour I didn't expect to be blown away.  At least not until I get around to some upgrades.  The thing is, they are really holding their own in the starting position.

The upgraded S.E.X. and the stock Paramours are both great but in different ways that I'm not sure I can describe.  The full-nickel S.E.X. I think wins on clarity and low (none) background noise.  The Paramours have some noise if you go listening for it and they seem to win on the low end with what seems like a little more bass extension and I think they present a better "stage". 

I haven't even broken in the stock caps yet and the Obbligatos have finally arrived.  I'm still waiting on some resistors to come in that were missing from the C4S upgrade.  I don't even want to mention how I worked around that one.  I will probably try Grainger's cap break-in technique before I go back under the hood.

There is also work to be done adding the IEC connector or maybe just running the power cord through a hole in the chassis.  Finally, there is the potential Iron upgrade and driver tube change. 

At this rate, I will never get around to the Crack and Seduction builds that are waiting in the garage.