This unit has three levels of gain. Have you tried it on the lowest setting, 0db in SE mode. I have owned several ARC preamps that use the 6H30 and they have all been dead quiet. I currently drive an ARC VS110 amp with no noise issues. I respectfully disagree with Analog SA on the ARC pre amps. I think they sound fantastic. But they are not everyone's cup of tea. To each his own.
John
John
Hi John,
The noise I am experiencing is not dependent on any setting on the LS25 mkII except that it is turned on and the mute is off.
The volume or gain setting or any other switch makes any difference on the noise (hum, hiss, and buzz).
Again, this noise is low level. It is not something I can hear above the music. I need to put my face in the speaker to hear it. However, I hear from owners of this preamp that it is dead quiet. Also, it is much noisier than my solid state preamp.
I feel there is something wrong with this preamp. So I am asking for help troubleshooting from the knowledgeable amp gurus here on DIY Audio.
In your opinion, what can be causing the noise? Power filter caps? Can you tell by looking at the schematic what areas I should check?
I have measured voltage points and they are all correct if not exact to the schematic. But my bench is 117 volts instead of 120 volts.
The spec of 14 micro volts hum and noise tells me it should be dead silent for this preamp...
well - in first place - you should wrote that fact in first post - that you need to stick your nose deep in cone , to hear noise ........
considering fact that power amp is 1V/full throttle sens , my opinion is that you promptly need to shut off that PC , relax about this "issue" , and enjoy in music .
you can also burn phone No. of ARC service
considering fact that power amp is 1V/full throttle sens , my opinion is that you promptly need to shut off that PC , relax about this "issue" , and enjoy in music .
you can also burn phone No. of ARC service
Seeing that you also have a problem with hum in your power amp i would suggest that your expectations may be unreasonable. Is there any hiss or hum you can hear a meter away from the speakers in a quiet room? Does it really matter that there is some noise with your ear glued to the tweeter? What are the chances that both units are defective?
As for comparing this preamp to a good solid state unit, it is not so straightforward.
Chances are the SS unit will employ a more sophisticated circuit, probably with some global NFB as well which will result a higher PSRR than a simple common source FET. ARC do not disclose the type of FET but it is the main noise contributor in the circuit, not the tube. Apart from its inherent (and unknown) noise this circuit is also very sensitive to PS noise. Although B+ is regulated, the regulator is not a particularly low noise type.
As far as components go, forget about the caps and try to source a pair of known good 6H30, maybe even the DR version. It is possible you have a dud pair.
In a dead quiet room, I can hear the noise from about 3 meters away. By muting and unmuting the preamp.
I did order a pair of 6h30s. I'll see if that helps. I heard from several other LS25 owners and they tell me it is dead silent in their system.
well - in first place - you should wrote that fact in first post - that you need to stick your nose deep in cone , to hear noise ........
considering fact that power amp is 1V/full throttle sens , my opinion is that you promptly need to shut off that PC , relax about this "issue" , and enjoy in music .
you can also burn phone No. of ARC service
I didn't mean the noise was THAT low. I can hear it from about 3 meters away at my listening seat. The power amp with the inputs shorted have a very quiet hum in the speaker. That, I can live with as it is very low. But with the preamp in the chain and on, the noise is considerably higher.
Can dirty pcb board do this? I noticed strange powdery dust covering it slightly. I wiped it off the best I could.
From where? I have stopped trusting most US sources for these tubes. There seem to be too many rejects on the market. Getting tubes from any of the ex - Soviet Union countries seems much safer.
in THAT case - contact ARC
have you any possibility to directly compare your LS25 with anyone else's , or do you have ARC dealer near you ?
I don't know anyone personally to do a swap test. I've only heard from owners of this preamp that it is dead quiet in their setup.
I'll get to the bottom of this sooner or later. I will contact ARC this coming week. Thanks for your help.
Ebay.
I may be a bit paranoid but what do you think happens to all those tubes which do not meet the matching/noise/microphony requirements of ARC and BAT? I doubt they crush them with hammers. The tubes i bought from Parts Connexion were 80% duds. Sent them back and from the matched replacements they sent only half were duds. Some worked normally for a while at very modest dissipation and then developed problems. The ones from Russian Ebay sellers were slightly more expensive but absolutely perfect.
This might make me run back to solid state... 80% failure rate? c'mon.
ARC LS3 is looking quite good now. I don't mind tweaking and fussing over things but if the tubes are that prone to misfire, I think I'll pass.
I'll check Ebay... sigh....
You have certainly misread me. I wasn't talking of tubes in general but merely of the leftover 6H30 offered to diyers. I have hundreds, if not thousands of other tubes, mostly NOS and failure rates are indeed very low. It could certainly be a bad batch, but rejects make a lot more sense. The tubes supplied by ARC should be first rate and work for tens of thousands of hours without fail.
Thousands of tubes?
Who are you?? Will bad 6h30s make noise in this LS25 MKII preamps? I understand the tubes are not used for gain purposes.After consulting with ARC, I'll figure out what to do. Perhaps have them take a look at it and have them install their 6h30s while they are at it.
Thanks for your help, by the way. I am learning quite a bit.
I spoke with Ben Jacoby. He's got a good reputation and also services ARC units here in NYC. He thinks it could be the fact that Focal 1027 be speakers are quite sensitve. Rated at 91db but more like 94db.
And the tubes are not ARC tested but just run of the mill 6h30s. However, you never know and he wants me to bring it in which I will.
In the mean time, I am really enjoying my music without the preamp going from my source to the VS60 poweramp. No noise, just music.
If I can find a way to connect all my sources and have a tape loop with a passive set up, that might be the ticket. Anyone know of such a passive preamp?
And the tubes are not ARC tested but just run of the mill 6h30s. However, you never know and he wants me to bring it in which I will.
In the mean time, I am really enjoying my music without the preamp going from my source to the VS60 poweramp. No noise, just music.
If I can find a way to connect all my sources and have a tape loop with a passive set up, that might be the ticket. Anyone know of such a passive preamp?
I suppose I can but am not really inclined to. I usually deal with electronics as a necessity to great music. But if no one already did the work to make such passive preamp, I guess I might have to... I am a full time musician and don't have too much time away from music.
By the way, on the +20v points on the LS25, I just set the trimmer so both points are at 20v? I can't make both exactly 20v. More like one point is at 20.3v and the other 20.01v. Is this okay?
fair enough
sorry - I can't help you with any particular finished product ;
perfect .
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