[mazinguerbeta]

I do not have more tubes , the amplifier has approximately 20 hours of use. I have an amplifier corda meier and this problem don´t happens.thanks

 

[bdh]

The HD250 has two seperate driver tubes, not a single tube in dual-triode operation. If he changed tubes, he would have swapped both pairs of input and output tubes.

 

[Tonski]

Kevin,

Did you sort out your hum issue. looks like mine may have the same issue.

Thanks,

Tony

 

[kds5000]

Quote:

Originally Posted by Tonski /img/forum/go_quote.gif Kevin, Did you sort out your hum issue. looks like mine may have the same issue. Thanks, Tony

No, actually.

I left it as that since only Indydieselnut and I seemed to have the problem.

The problem is much more obvious with low impedence and/or high sensitivity cans. That may explain why the other owners who listen with the HD250SE through 300ohm Senns or low sensitivity K1000s don't hear the problem.

With a Grado RS-1 plugged into either of the jacks, here's further info after experimenting with the inputs:-

1. With all the inputs disconnected, the hum is very low. It does not get louder with the volume turned up.

2. As soon as I plug a source into the inputs (it's the same for both inputs), the hum comes back and it gets louder when I increase the volume. At first, I thought that it could be my CD player (Marantz SA8003). But I plugged in my friend's Audio Research CD-5 player into the amp and the hum is there with the same intensity. Did the same with my Maverick Audio D1 and the problem remained. Changing interconnects didn't help. I used my ipod with another interconnect and I got the same hum. Plug out all the inputs and the hum almost disappears (see point 1).

Now that you too have the same problem, perhaps the 3 of us should write to Lloyd to find a solution - 30% is not an insignificant number.

 

[mrarroyo]

Have you tried a cheater plug? The polarity may be the issue here.

 

[kds5000]

Quote:

Originally Posted by mrarroyo /img/forum/go_quote.gif Have you tried a cheater plug? The polarity may be the issue here.

I haven't tried the cheater plug yet, but I've brought it to a friend's place and tried it at a different location around my home - still the same result.

Could this still be a polarity issue? I'm not really keen on putting another device (cheater plug) in my rig. To me, less is better...

 

[rich1122]

I recently received my new HD250 (#9), and sad to say, I am having similar hum issues. It's barely audible when listening to music, but I can definitely hear it during quiet passages and when no music is playing. The strange thing I notice is that the hum doesn't change in volume when I turn the volume control all the way up or down.

I haven't had a chance to test the amp on other electrical circuits, so I'm not positive that the hum isn't caused by some kind of interference, but I let you know what I find as soon as I do.

 

[Parafeed]

Chaps, eliminate the ground loop as suggested earlier with a cheater plug. If this clears the hum then the signal earth can always be "lifted" from the mains (chassis) earth with the usual combo of a 10R resistor, paralleled with a 0.1uF cap for a more permanent and safe solution. If there is still residual hum with the cheater plug, it could be AC heaters, proximity of AC heater wiring to sensitive circuitry, HT smoothing (too much or too little), magnetic induction - those Hammond output transformers are hum magnets, very sensitive to placement relative to other iron on the chassis. Dead black backgrounds with low imp, high sensitivity, (especially closed back), phones is asking a lot from a tube amp, unless it is designed with that in mind from the get go.

 

[bdh]

It's dead black for me, even with the volume at 100% (no music of course). And no hum with music playing either.

And four months on I continue to make changes to my settings to get every last drop of goodness from this setup and I continue to be amazed at the sound and music at makes.

 

[indydieselnut]

I will try the cheater plug as an experiment but I haven't been distracted in my setup. I also use the RS1i, GS1000i, and 325is with the amp. If I have the 'phones on when I power it up it is clearly audible. After 60 seconds or so it starts "stepping down" in volume and by 90 seconds is BARELY audible. I've never had a musical selection where the residual hum interfered with the music. I don't feel I have golden ears but...well, they aren't tin either

I'm running mine from a dedicated 20A outlet that's only about 30 feet from the breaker. It is also plugged into a Furman power strip. I'm pretty content at the moment.

However, I don't want to leave a few HD250 owners out in the cold. If you end up contacting Lloyd for a solution I'm happy to chime in and share my experience with him.

 

[kds5000]

Quote:

Originally Posted by Parafeed /img/forum/go_quote.gif Chaps, eliminate the ground loop as suggested earlier with a cheater plug. If this clears the hum then the signal earth can always be "lifted" from the mains (chassis) earth with the usual combo of a 10R resistor, paralleled with a 0.1uF cap for a more permanent and safe solution. If there is still residual hum with the cheater plug, it could be AC heaters, proximity of AC heater wiring to sensitive circuitry, HT smoothing (too much or too little), magnetic induction - those Hammond output transformers are hum magnets, very sensitive to placement relative to other iron on the chassis. Dead black backgrounds with low imp, high sensitivity, (especially closed back), phones is asking a lot from a tube amp, unless it is designed with that in mind from the get go.

Thanks for your analysis.

I will try to get the cheater plug as suggested just to diagnose the problem. If any of you try the cheater plug first, please post your impressions.

The thing is, I listened with the humble EAR+ HD amp with my Grados for 2 weeks just before my purchase of the HD250SE, and the blackground was black as night. No hum or hiss at full volume whatsover - even at 3 in the morning...

I know it's a different architecture etc but I'd expected the top-of-the-line HD250SE to have a completely black background as well.

 

[Parafeed]

Quote:

Originally Posted by kds5000 /img/forum/go_quote.gif Thanks for your analysis.

I should have also added mains wiring (from the IEC to the switch on the front panel) to the list of possible hum sources and also poor tube heater->cathode insulation. For the later, if you do not have a tube tester, do you have a second set of tubes that you can try in place of the first? (A 12AX7 with poor H->K insulation when warm will cause hum for sure if the heaters are AC.)

Looking back at your previous posts, I see you tried another set of interconnects. Shielded interconnects I hope?

Assuming the iPod was running on battery and the only thing it was connected to was the amp, then I doubt that a cheater plug is going to help as it rules out a ground loop. I don't quite understand what Lloyd was talking about - the selector switch and the way it is wired to ground causing hum in the mute position, but would suggest that you select an input and ground the chosen inputs at the RCA jacks, which you can do with a pair of dummy RCA's - hot connected to ground, or just cut an old pair of interconnects and twist the hot and ground wires together. Do you hear hum? It would be usual to start debugging with this, rather than a cheater plug in any case. Inputs selected and grounded, phones plugged into the amp and amp plugged into the mains. No other equipment connected to the amp. ie. no other source connected to the second set of inputs, or anything connected to the pre-amp out RCA's.

 

[Parafeed]

I've just been chatting about about the EAR headphone amps with an owner who has read my comments. If I wasn't clear, I'm not suggesting anything negative about the EAR design or implementation. My "sources of hum" comments are generic - they could be applied to any tube amp, not necessarily the EAR. I don't own any Mapletree product, but have designed and built several very similar designs with a gain stage driving a cathode follower, transformer or autoformer parafeed coupled to phones. To also clarify my earlier comment about the Hammond 119A output transformers (used in the EAR design) being "hum magnets". This wasn't directed at the EAR amp, or meant to suggest that their placement in the EAR amp is less than optimal. This comment was based on my own experiences with their placement in an amp with a choke input PSU filter. Orientation was critical with the Hammonds (for lowest noise pick-up from the PSU choke), but not an issue using alternative iron - the Sowter 8665 or MQ TL-404's.

PS. One last comment, (and I should probably stop digging), but .... I'm told the SE uses a SRPP input stage. I'm also told the filament voltage is DC, with one leg tied to PSU ground after the rectifier. The cathode of the upper triode is going to be at half the B+. The filament is at 0 volts. While the 12AX7 H->K rating is 200V and I expect that this is not exceeded in the EAR design, I wouldn't be surprised (based on my own experiences with the 12AX7 in SRPP), because of the H->K differential, a) that the circuit is picky regarding the noise floor depending on the 12AX7 used - sample to sample, and that b) without a positive bias on the filament supply, 12AX7's will have a propensity for going noisy over time. Again, I'm stating an opinion, based on what I've been told, not that I have the circuit diagram in front of me.

 

[Afrikane]

I wish I could add something helpful to this but as I do not own any low impedance Grados and the like; all I can say is that my HD250 is dead quiet, one of the quietest tube amps I have owned.

 

[Tonski]

Ok guys. I have done a bit of experimenting and this is what I have found. I disconnected all interconnects and found that the hum dropped off in volume but didn't disappear. This shows that this amp is somewhat sensitive to a ground loop so I have made an unearthed cable for the short term to eliminate some of the hum. Another way (and safer way) to do it is to disconnect the earth on the interconnects.

However there is still a low level hum that can be heard through my Grados. I have notified Lloyd about the issues that some of us seem to be having. I'm not really keen to send the unit back and if Lloyd can work out a fix then I will try it at home and let everyone know what can be done. However if it gets too complicated I will be sending it back. I have had other tube amps which have a black background but no where near as musical. Just wish I could eliminate the hum and I will be a very happy man.