[dsavitsk]

The issue is that some of the tube types are picking up more noise than we like. So, we are working on a shielding solution. It is taking a while as we are both really really busy these days, and we just have not had the time to think about it. We figure we'd rather make everyone mad by delaying things, than make everyone really mad by shipping you an amp that is too noisy. But, rest assured, we are sitting on thousands of dollars worth of cases, transformers, circuit boards, tubes, and various other parts, so we have every incentive to get this thing done. Sometimes it just takes longer than hoped.

In the meantime, here's a little primer I wrote a while back on the ins and outs of designing a simple parafeed headphone amp. http://www.ecpaudio.com/pdf/parafeed_basics.pdf

 

[vvs_75]

Any good news? Wish you good luck guys to crack the problem!!!

 

[tomb]

Quote:

Any good news? Wish you good luck guys to crack the problem!!!

We're playing tag-team right now (kind of appropriate, given his avatar).  I ran some tests and then shipped it over to Dsavitsk.

 

 

[vvs_75]

Is it just nicely brushed raw aluminum  or some kind of coating also on your Torpedo enclosure?
Just trying figure out what to do with my build.  thanks

 

[tomb]

Quote:

Is it just nicely brushed raw aluminum  or some kind of coating also on your Torpedo enclosure?
Just trying figure out what to do with my build.  thanks

Yes.
 
 

 

[vvs_75]

Quote:

We're playing tag-team right now (kind of appropriate, given his avatar).  I ran some tests and then shipped it over to Dsavitsk.

 

Any good news on testing? I really can't wait to get this kit!  
 

 

[tomb]

 
Quote:

Any good news on testing? I really can't wait to get this kit!  
 

Like a lot of us from time-to-time, other things get in the way.  I don't think Dsavitsk has had much time to check out the noise issue, unfortunately.  The noise is a highly-variable phenomenon.  It's completely inaudible with some headphones and some tubes, but will manifest itself with others.  Either way, it's never anything that you hear with the music.  I still listen to mine (the older proto) as my primary amp.  I've never been one for soundstage comments, but this amp has it in spades.  IOW, even if I know there's a slight noise issue, I prefer the musicality and imaging of the Torpedo, anyway.  This is just my opinion, of course, but there's stuff there that you will never hear with a solid-state or hybrid amp.
 
KSC-75's with 6J6 tubes seem the worst for the noise.  5964 tubes seem the least noisy, whereas with some headphones such as Sennheiser HD25-II's - even with the 6J6 tubes - the noise is completely inaudible.  That's very odd, because one would think that with completely closed in phones like the HD25's, you'd be able to hear every flaw.  With the lid off, Dsavitsk reports that he can't hear any noise.  With the lid on, he can, which is another really odd thing, because the case is completely aluminum and shouldn't have any effect unless it's RF noise.  So,the problem is definitely that the tubes are picking up the noise through the air.  In my testing, the addition of the choke helped and we will recommend that now instead of the resistor - but it may have had more to do with providing more shielding to the tubes than anything in the circuit.  It's all in the tubes.  I guess you get what you pay for when using $2 tubes.  I think the 5964's are $4 ea, so they're a bit better, IMHO.

 
Some of you who have built a Starving Student and remember the structure of the 19J6 tubes may be able to remember that the grid in this tube family is somewhat exposed outside of the plates.  The grid is actually stretched between copper posts that are on the outside of the plates, so the grid wiring connecting to those posts is exposed.  There have been issues, too, of the Starving Student picking up noise through the tubes, whether cell phone, computer, etc.  The 5964 tubes seem a bit more conventional in construction and have plates that completely enclose the grid structure.  This may explain what's going on.
 
In any event, we may decide to go ahead with the kits anyway - with full disclosure of the noise issue.  As I said, it's my preferred amp regardless - and I'm using 6J6W tubes right now and the resistor instead of the choke.  Hopefully, Dsavitsk will have something to add soon.  
 
 

 

[digger945]

I have the later prototype, with choke. It is my main amp now.
As you said, it has some hum with certain tubes or headphones, and others it is not noticeable. Regardless, it does not interfere with my listening, even at low levels. 
Listening to the new PS500 now, and this amp really shines. Very enjoyable. 

 

[vvs_75]

 
To find a better tubes that do not hum at this price should be not a problem. Any infor on the kit price?

 

[HiGHFLYiN9]

Did you guys try experimenting with some grounded tube shields? I wonder if that would help at all. 

 

[tomb]

Quote:

Did you guys try experimenting with some grounded tube shields? I wonder if that would help at all. 

It's a good thought - and one that Dsavitsk had almost immediately.  I tried some great shields that were not grounded without much success.  Unfortunately, I was not very good at grounding them.  I couldn't get the solder to stick and was quite afraid to have bare wire leads bouncing in and around all that high voltage.

  I'm hoping Dsavitsk will have a bit better luck at it and maybe have different results.
 
 

 

[dsavitsk]

OK, here's where things stand -- As has been noted, the hum is very low. Using the amp with Grados, the hum is nearly drowned out by the fan noise from my laptop. It is very non-intrusive. I won't put a number on it as I don't have anything well enough calibrated to tell. Some prototypers didn't notice it until we told them it was there. However, it is there, and if you are someone who needs absolute silence, this is not the amp for you.

I have tried a number of different shielding techniques, and none of them seem to do much of anything. Additionally, there are not "expensive" tubes that will solve the problem. So, unfortunately, at least for now, it is what it is.

That said, we still think it is a good way for someone to be introduced to tubes and transformers. It is a fun amp that sounds good and does not cost too much, and we think most people will be pleased with it. So, I think the plan is to put the first batch up for sale, but at a discounted rate in light of the noise. We'll continue to work on finding a solution for when/if we do a second batch, and perhaps the collective wisdom of a few dozen builders will find something we missed.

Depending on Tomb's schedule, we should post the details sooner than later.

 

[Magedark]

Sounds like exciting stuff here.

 

[FrankCooter]

Having incorporated a number of Doug's designs into my own builds over the years, I have nothing but the highest respect for his work and very extensive contributions to the DIY audio scene. He is one of main reasons I read this forum. If he says the noise/hum is non-intrusive, I really doubt an average user would know it's there at all. Doug is a perfectionist.
 
Although simple in concept, it can be extraordinarily difficult to build a totally quiet tube based headphone amp incorporating both power transformers and output transformers on the same chassis. If you listen closely with sensitive headphones like Grados, even the most expensive commercial amps of this type are not totally quiet. Doug of course, is trying to bring this level of performance to a previously unattainable price point. This is a very worthwhile goal.
 
If your hum/noise is indeed caused by transformer interaction, your options, short of redesigning the amp for an external power supply, are at least in my experience pretty limited.
You've already got the maximum possible physical distance between the power and the output transformers. You've already got the transformer cores at 90 degrees from each other.
Next step would be to order transformers with appropriate shielding. If I had to choose, I would start by shielding the output transformers first. Ideally, the power transformer AND the choke should also be shielded (the choke may be causing more problems than it solves).  Sometimes rotating the power transformer to something other than a 90 degree core orientation can help, as can putting the transformers on a different mounting plane. Ultimately, you might want to think about replacing the EI core power transformer with a toroid or "R" core type.
 
Another possible approach would be to change your tube type to something that is less sensitive to externally induced hum. Everybody loves the high mu/high gm types in this sort of application, but they're almost all rf types and love to act like little antennas. If you can spare the gain, a paralleled 12AU7 should work with your output transformer. An EL84 type in this position would be something different and might be very interesting.
 
You've probably  been through all the above and more already. I'll bet you're being too picky! Best of luck in this very worthwhile project!

 

[JamesMcProgger]

Quote:

OK, here's where things stand -- As has been noted, the hum is very low. Using the amp with Grados, the hum is nearly drowned out by the fan noise from my laptop. It is very non-intrusive. I won't put a number on it as I don't have anything well enough calibrated to tell. Some prototypers didn't notice it until we told them it was there. However, it is there, and if you are someone who needs absolute silence, this is not the amp for you.
I have tried a number of different shielding techniques, and none of them seem to do much of anything. Additionally, there are not "expensive" tubes that will solve the problem. So, unfortunately, at least for now, it is what it is.
That said, we still think it is a good way for someone to be introduced to tubes and transformers. It is a fun amp that sounds good and does not cost too much, and we think most people will be pleased with it. So, I think the plan is to put the first batch up for sale, but at a discounted rate in light of the noise. We'll continue to work on finding a solution for when/if we do a second batch, and perhaps the collective wisdom of a few dozen builders will find something we missed.
Depending on Tomb's schedule, we should post the details sooner than later.

I like the idea. just waiting for the price now, this might be something to keep me busy on the xmas break.
 
what other headphones did you guys tried it with? AKG K series by any chance?