[Mullet]

Hey guys...

What volume level would you say this buzz (hum) is at? Is this just a low level hum or a really loud hum that over powers the music? My hum is at a super low level on my 332C. It's nearly inaudible with larger cans and slightly audible only when no music is playing with IEMs.

 

[BigTony]

The hum is audible without having to hunt for it, its quite noticeable during quiet passages in the music as well as between tracks. There seem to be no problems with hum on the 332c.

 

[Audict123]

Yes the hum is very clear with Senns. Like you are sitting to close to a PC. The hum is loudest in the left channel and a bit different in character (not truly constant, but more like a purring sound a cat makes). And if you put in low impedance phones instead, the hum is so loud it really ruins soft pasages in the music.

I replaced the wire that connect the ouput cap to the headphone socket board. That wire is parallel to two 130V wires for centimeters, so I decided to reroute that. Alas, that gives no reduction of hum. I'm starting to lose my patience with this problem.

 

[ogygia]

Quote:

Originally Posted by arie123 /img/forum/go_quote.gif I replaced the wire that connect the ouput cap to the headphone socket board. That wire is parallel to two 130V wires for centimeters, so I decided to reroute that. Alas, that gives no reduction of hum. I'm starting to lose my patience with this problem.

If the hum can be heard, no matter how high is the vol level...I suggest to rewire the coupling capacitor output wire as well.

They are from high power resistors to cap and from cap to headphone out. If you can weld the wire the wire directly to the headphone socket, instead of PCB. I do promise the sound will be better.

The 4 wires which have to be rewired, was pointed with yellow arrow as pic below.......The problem should be totally solved after this mod.

 

[Audict123]

Thank you very much for the suggestions Ogygia. I did not yet replace the wire between high power resistor and cap, will do that later today. Fingers crossed...
What puzzles me is the large difference between hum in the left channel (where it is by far the loudest) and right. Most asymmetry in the design is around the sockets, because the sockets are of course not mirror images (whilst the amp as a whole is). So some wires are closer to some pins and each other on the left channel than right... Could it also be because of poor socket quality?. Ho, stop, first try your suggestion regarding the high power resistor to bypass cap wire.

 

[yuking09]

We did some test , because these Soviet Union NOS tubes were produced before 70 years ago, they are difficult to burn-in.Total 27 tubes consecutive 8-day aging, and only 3 tubes qualified,without the hum.So If you want to achieve antihum,that need a longer time. However, there is no any hum when we replacing Chinese 6J1, indicating our headphone amp is no problem. In a few days we'll submit four Chinese 6J1 tubes free of charge to the users whom purchase 332S,and we regret any inconvenience caused to our users.

 

[Mullet]

It appears that Yuking09 is saying the issue is with the Soviet signal tubes and the amount of time it takes to burn them in. I'm assuming arie123 and BigTony are using different tubes at this current time. Can you guys confirm? If they are not using the stock tubes I would say their units are defective. At that point they should be able to swap out their units. The only issue in this is who pays for return shipping.

Like I said earlier in the thread... I had a problem with a Tung Sol tube that produced this loud buzz and then created this loud pop noise. I think DeltaSpirit had the same issue. I deduced it to the tube. In addition to that, I've also had a degree of low hum with my RCA 6AK5s. I think it was only with IEMs though. I've tried the Valve Electronic CV4010s with no hum and also the WE403Bs with no hum. I think Godkin also mentions this in a post basically saying that some tubes are noisier than others. Could this be the issue?

 

[Audict123]

Quote:

Originally Posted by ogygia /img/forum/go_quote.gif If the hum can be heard, no matter how high is the vol level...I suggest to rewire the coupling capacitor output wire as well. They are from high power resistors to cap and from cap to headphone out. If you can weld the wire the wire directly to the headphone socket, instead of PCB. I do promise the sound will be better. The 4 wires which have to be rewired, was pointed with yellow arrow as pic below.......The problem should be totally solved after this mod.

I replaced all wires indicated by the yellow arrows in Ogygia's picture of the amp by copper/silver teflon coated flexible wire. Unfortunately: no effect. Moving around the wires at various places does nothing to the hum level. It was worth the try, but it must arise somewhere else.

 

[BigTony]

I will have a test today with my box of tubes. I have swapped them around before and the hum remained, but I'll have a concerted effort to see if any combination will reduce/remove the hum.

 

[Audict123]

Quote:

Originally Posted by Mullet /img/forum/go_quote.gif It appears that Yuking09 is saying the issue is with the Soviet signal tubes and the amount of time it takes to burn them in. I'm assuming arie123 and BigTony are using different tubes at this current time. Can you guys confirm? If they are not using the stock tubes I would say their units are defective. At that point they should be able to swap out their units. The only issue in this is who pays for return shipping. Like I said earlier in the thread... I had a problem with a Tung Sol tube that produced this loud buzz and then created this loud pop noise. I think DeltaSpirit had the same issue. I deduced it to the tube. In addition to that, I've also had a degree of low hum with my RCA 6AK5s. I think it was only with IEMs though. I've tried the Valve Electronic CV4010s with no hum and also the WE403Bs with no hum. I think Godkin also mentions this in a post basically saying that some tubes are noisier than others. Could this be the issue?

Your analysis is right, it's definately not in these particular tubes. I had four different tubes in so far: stock, a long life/rugidized variant of stock, Mullard CV4010 and Ericsson LM 403B. The hum is clearly present on all (with sometimes an added distortion signal thay may be due to the tubes themselves). If this amp is only hum free with the chinese 6J1, I'm sure it will be a commercial failure: amps like these are bought by audiophiles that all sooner or later want to install better and/or NOS tubes. If it doesn't work with that, there is no market for this amp.

Yuking: you really will have to come up with a better solution. For starters, identify the true origin of the problem yourself and then contact the present buyers with a real solution. If a simple mod will do it, some (like me) may prefer to do that themselves, if not, you should come up with a trade in or even return option. This is a killer looking amp with (I think) very good commercial potential, but if you don't tackle this problem at the source, it will fail commercially. You will get my praise if you DO solve the problem, so take this chance ......

 

[yuking09]

Basically, all NOS tubes exist cathode-oxidation problem as production age-old, Phenomenon is the hum when they work, because of the different vacuum, this phenomenon has light or heavy. Therefore, burn-in is something we have to do, of course, burn-in time has long or short, precondition tube is normal. So please Plug in your Mullard CV4010 and Ericsson LM 403B etc. respectively for continuous 5~6 hours, then you can compare whether the changes in re-listen to hum.
Welcome sincerely to continue to discuss the issue of hum.

 

[BigTony]

Dear Yuking,
I've had a bunch of different NOS tube variants in the amp and all have hummed, I have left them to burn in for days on end. The hum reduced (the expected tube hum) but the amp has never exhibited a quiet background. I have Russian, Chinese, UK, USA tubes and they have all had the same end result. The Chinese tubes I have are new build tubes.

I would dearly love to have some hum free tubes. Here is a simple but effective test: Test a set of tubes in an amp at your factory, ensure they are hum free. Post those tubes to me and I'll see if I get the same result. One point for clarification; have you run the amps at 230VAC? Is it possible that the PSU differences are causing this problem (Its something I've come across before - USA amps were silent, UK amps hummed, and vice-versa).

Cheers
Tony

 

[Audict123]

Quote:

Originally Posted by BigTony /img/forum/go_quote.gif I would dearly love to have some hum free tubes. Here is a simple but effective test: Test a set of tubes in an amp at your factory, ensure they are hum free. Post those tubes to me and I'll see if I get the same result.

This test is a good idea Tony. But my hopes are not high: together we had close to a dozen tubes in and all hummed. Compare that to the 3322. And I wouldn't like to restrict use of the amp with 6J1's. There must be an underlying problem which brings me to ...

Quote:

Originally Posted by BigTony /img/forum/go_quote.gif One point for clarification; have you run the amps at 230VAC? Is it possible that the PSU differences are causing this problem (Its something I've come across before - USA amps were silent, UK amps hummed, and vice-versa)

But the voltage in China is 220, in my country it's 220 too. I'd expect this risk would be bigger for USA amps in this case. Could it be the sockets? Any other ideas anyone...?

 

[Godkin]

I agree - sounds like there is an underlying design flaw with this amp. You should be able to run western tubes - which are constructed to higher standards than the Chinese tubes - without any problems.

 

[Audict123]

Yuking: I appreciate you take part in this discussion - in fact you ARE part of this discussion.

I tested all tubes I used with an (impeccable) L3-3 tube tester. None of the tubes I used shows any leakage that could cause the hum and all tubes measure in the new range on both mA ('emission') and mA/V (i.e. 'transconductance', 'mutual conductance', Steilheit' 'Gm'). I have other tubed gear running on NOS tubes dating back to 1959 NOT showing any hum problems.

I really feel we (including you, representing the Figaro brand!) should be looking elsewhere to identify the source of the hum. I'm ready and willing to try sensible options, including rerouting of wiring (already did some), exchanging parts, etc. It's a hobby so I don't mind as long as it's within my technical ability. Doing some modifications may actually be fun!, but only if the end result is an amp with negligible hum.