[dsavitsk]

Don't know what it is about my build that may be different, but I can't detect any hum.

Interesting. Could you post details and perhaps some closeup pics of the tubes you are using?

even though it could use a bit more gain (for quiet recordings).

Unofficially, if you jumper pins 1 and 2 on the OPT, you can eek out a tiny bit more gain -- the transformer has a 10K primary, but I had them wind them such that pin 2 is a 7.5K. tap. The difference is pretty small - changing from a 18:1 voltage stepdown to a 15:1, and it does it at the expense of perhaps a little more distortion. But, if you just need a tiny bit of gain, it might make enough difference. Anyhow, I've never tried this, so do it at your own risk.

 

[looser101]

The only way I deviated from Tom's build is the physically smaller coupling caps and the volume pot is ungrounded.  C7/C8 not populated.
 

 

 

 
Neither of these tubes hum.  Rogers (Mullard) 6J6 on the left and RCA 5964 on the right.  They're the only two pairs I have.
 

 

 

 

 
Thanks for the tip on the output transformer taps, Doug.  May be useful in the future.
 

 

[tomb]

Quote:

Don't know what it is about my build that may be different, but I can't detect any hum.  Had it out to a mini meet last night and no one could hear any either.  Sounds great with Grados, and can drive a K340 even though it could use a bit more gain (for quiet recordings).  Thanks to Tom and Doug for making it easy to build, by providing us with a kit.

As Dsavitsk has also remarked, this is very interesting.  I don't think it's the tubes by looking at your pics.  I've half suspected whether there was some variance in the PTs (Power Transformer) from Edcor.  The extent of the hum seemed to vary among my 3 prototypes, for instance.  One of the things Dsavitsk tested was swapping the PT in my production prototype for one of the earlier PT's that was slightly different.  It made no difference as far as I can tell.
 
Yet - maybe you got a quiet PT, while crappyjones got a noisy one (although it sounds like the tubes might be the culprit), and the rest of us somewhere in the middle.  Then DingoSmuggler gets one that doesn't work at all.  Interesting ... maybe ...   I've asked Dsavitsk if he's had more talks with Edcor - it may be warranted in light of some of this feedback.
 
We appreciate all the work from you guys and the many comments.  My hopes are high that we can lick this eventually.  As several of you have noted, the amp sounds pretty dang good in spite of it.
 
 

 

[HiGHFLYiN9]

Curious... I wonder if raising the tubes up out of the chassis would alleviate any noise. It would require cutting a piece of aluminum to a suitable size rectangle, putting a pair of holes in it to accept two chassis mount 7 pin tube sockets, mounting it on a pair of standoffs that are drilled to the PCB, and running the corresponding wires from the PCB to the sockets. Might take an hour or two and about $10 in parts... any thoughts? 

 

[DingoSmuggler]

I've decided to hack together a basic magnetometer for measuring magnetic fields around my torpedo (once it gets its new transformer).
I'm just going to hook a linear hall effect sensor (powered from a 9V battery -> 5V reg) to my multimeter and measure AC voltage which should give an indication of the strength of the AC magnetic field at the sensor.
Not sure if it's going to work that well for this purpose - but at a parts cost of under $5, i figured its worth a shot.
If it gives any useful info, i will share it on here.

 

[dsavitsk]

Curious... I wonder if raising the tubes up out of the chassis would alleviate any noise.

Interesting thought. Something like this perhaps.



The tube sockets are rotated slightly to make the pins line up. Only thing to think about is that you might want to remove the grid stoppers on the PCB, but put stoppers on the socket. Email me if you want the FPE file. I may give this a try at some point if no one else does.

I've decided to hack together a basic magnetometer for measuring magnetic fields around my torpedo (once it gets its new transformer).

Interesting. I look forward to see what you find. The crude way to test this is to build the whole amp except for the OPTs. Then, hook up an OPT to some phones and move the transformers around and listen for hum.

 

[HiGHFLYiN9]

I think I'll give it a shot. I modified the FPE file a little bit in the interest of making it a permanent install (3mm thick and extra mounting holes for rigidity). Even if it doesn't make a difference with the noise, I like to see the tubes. 
 

 

 

[Rescue Toaster]

From my experience with Edcors, the output transformers (XSM's in my case) are quite magnetically 'active' if you will. They are VERY susceptible to external magnetic fields (was seriously affecting my dynamic range/SNR in RMAA until I moved the power supply 2-3 feet away). Also mine 'sing' like crazy when playing test tones. I need to get some rubber grommets in place to try to isolate them from the chassis, see if that helps. I don't remember them doing that in the past, but I did have them on a wood breadboard, rather than bolted to an aluminum chassis, so maybe that is making the difference now.
 
 
 
 

 

[jdkJake]

Quote:

Also mine 'sing' like crazy when playing test tones.
 
 
 

Funny, I noticed that as well.
 

 

[DingoSmuggler]

Thanks Dsavitsk for the desoldering advice, i had been using flux when i was struggling, but it was a no-clean flux and didn't seem to work the best with the braid i had - which already had rosin flux in it.
I got some liquid rosin flux and some fresh braid, followed your advice and was all done in 5 minutes. Orders of magnitude easier than the struggle before. 

 

Replacement transformer for the faulty one was received today, thanks Tom.
 
Another torpedo complete and ready for launch...
 

 
In case someone was going to ask, the little blue parafeed caps there are 4.7uF jantzen standard z-cap (about $3.70 from partsexpress)
otherwise a pretty much standard bom.
 
A point that other builders might find useful is that all hardware I used is M3-0.5, so those from countries where metric is more readily available that's a good option - it will have about 5% less wiggling room that #4 screws, but all the holes line up good so that extra leeway didn't seem to be needed. If tapping the front/rear panel holes for M3 though you will need to enlarge the holes with the correct pilot drill.
 
The tubes in the pic are GE 6J6s, the left one though had a bad case of electron tubicus microphonicus 

change the volume, piiiiiiing! click my mouse, piiiiiing! tap my foot on the ground, piiiiing! tap the case, piiiiiiiiiiiiiiiiiiiiing!
And Tom, don't worry about it mate, got plenty of others.
 
So swapped in my 5844s. Man this amp sounds epic with MSpros. Sounds good with other cans too
Not going to try and say too much without spending more time with it.
I'll try to get some good pics next week.

 

[HiGHFLYiN9]

I made a cool little logo for an engraved plate for my build. Feel free to swipe it. 

 

[tomb]

Wow!  That's very cool!

 

[DingoSmuggler]

 
Here's a pic of my torpedo after i gave the top a coat of wrinkle paint(VHT wrinkle plus).
It's a nice effect, good looks and feel, will do the bottom the same when i get a chance.
 
also, loving the sound of the amp

 

[tomb]

Wow - very nice!

 

[HiGHFLYiN9]

Finished up yesterday:
 

 
As you can see, the tubes were mounted on the plate mentioned above so they would stick outside of the chassis. There is a smidge of audible noise that sounds like it's from flux interaction, but it's barely audible and hardly worth mentioning; this was tested with a headphone with 32ohm impedance. I'd definitely consider it a non-issue. 
 
I strayed from the BOM just a little bit with Kiwame resistors, gold plated Neutrik jack, standard RCAs and ClarityCap ESAs for parafeed duty. 
 
Sounds great so far! Looking forward to some more critical listening this weekend.