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24.114.104.182
Hey everyone.
I wonder if I can get some feedback on a weird issue that manifested itself while listening to the pre. I accidently turned the gain and level at high instead of low one day while listening to music When mute came off it blasted for a split second until I turned mute back on.
Since then when I play my denon 103 or my dynavector 10x5 I can only use my 100 ohm setting instead of 47 k like before. Unbelievable that they sound better to me at 47k.
What happens is everytime I switch to 47 there is a knocking distortion on the left channel that gets louder the longer I stay on 47. It's actually a scary noise. When I switch it back to 100 the whole system mutes for about 10 to 15 seconds until it starts playing again at 100 setting.
It sounds good at this setting but sounded better at 47k.
Any help will be appreciated. It could be something stupid or I might have to take it to a tech but until I do its driving me crazy. Could it be tubes which were pretty fresh whenI bought pre. I even switched tubes around and the distortion changed to a kind of static. Different from before but caused my system to mute again after switching back.
Why would it work on other settings and not on 47 anymore is my question All my mm carts actually work on 47. That's the other kicker. It only seems to happen with mc and not mm.
Thanks in advance.
Follow Ups:
Hi SOR,
It looks like you have blown the input FET. There is a weird feedback op-amp that is some sort of filter. My guess is that the blown input FET has a really high gate leakage current that makes it OK with a 100 ohm load, but that raising it to 49.9k (as shown in the schematic) causes everything to go haywire. It's not a tube problem and I wouldn't let anybody touch it other than Audio Research as they keep the identity of all of their transistors secret.
Hope this helps,
Charles Hansen
Thanks Charles. Very kind of you to go to the trouble for this info. Will try cleaning to switch first. You never know.
You say you would not let anyone touch it besides arc. Very expensive proposition. I was thinking of taking it to my arc dealer. They repair older units which were sold at their location. I'm sure arc will send them the part once they identify it. I know they order tubes from Arc to retube their units, hopefully they have access to all parts. Let me know if you've heard otherwise.
Will let you know what happens and thanks again for your analasys. You and the other gentleman have been great
You can try cleaning the switch first but I would go with Charles on this - left channel input FET. It looks like the switch is not in use on the 47K setting (bypassed), and MM cartridge has a higher drive than MC so it works on 47K setting.
The scenario you present is expensive.
Perhaps more than the op paid for the whole unit?
Would one way to IMO test your theory be to add a pair of 47K resistors. (or 49K? 50K added to the cartridge on the phono input, with the switch set to the 100 ohm setting.
SO running the op cartridge with an added 47K through the 100 ohm level of the switch.
Would this be enough to cause the same problem to show itself?
I am all about being cheap.
IMO if the op can use the preamp at 100ohms instead of spending as much or more than he paid.. I certainly would just use it at 100 ohms! The cost to fix it would be at least $700 to send it in.. plus shipping...
I have to assume he bought it used..And the final cost could be much more than that.
(I paid $600 for a SP-10. $1,500 for an Sp-15
The boxes alone would be at least $100 to replace. (ARC never sends stuff back unless it is in the original type boxes. So no original boxes when one sends the items in (two chassis set for SP-10 Sp-11 Sp-15, 40th anniversary), the extra cost is passed on for new boxes. At least $100 like I wrote.
I know Charles Hanson is a smart guy.. I just am hoping he is wrong!
I would still try cleaning the switch..
And if that fails, and the 47ohm added to the 100 ohm fails.. I would just live with the 100 ohm.. unless the op is rich enough to pay the $700 to $1200 a ARC repair would cost?
I will certainly start with the cleaning and see where that goes.
I would love to send it to arc but there is a big arc dealer here in Montreal with their own techs who work on these old units. I would hope they would use the same transistors from Arc but would have to ask them
If you look at the schematic, the 49.9kohm resistor is *soldered* to the PCB. It is the other values that are connected in via the switch.
It is 99.9% chance that the input JFETs have gone bad. As long as the local dealer can get the correct part from Audio Research, this will be the way to go. I would guess this will cost around $200, as most shops are aroun $100 per hour. Good luck!
Very kind of you. Thank you for your help.
Many audio companies do have other facilities for outside the USA.
Same for Bryston. They have a facility in USA. so not cross border duty confusion.
SO hopefully the dealer in Montreal can work on it if the cleaning does not fix it.
Thanks a lot for your input. Will let you know how it goes.
Hi...i am a new user here. As per my knowledge Switching tubes around changing the sound is just normal tube oddness.The failure is in the switch itself. Most likely some sort of fault to ground at the 47K position.Replace the switch and I bet all will be well.
Edits: 11/10/17
I own a ARC Sp-15 which is also a two box ARC of similar type.
The AC SP-10, SP-11 and SP-15)
Anyway, SO I have the same separate front panel phono impedance switch.That switch is in the phono low level circuit. Before any amplification.
I would think it is a Damaged SWITCH. or less likely blown/damaged 47k resistor.
Switching tubes around changing the sound is just normal tube oddness.
The failure is in the switch itself. Most likely some sort of fault to ground at the 47K position.
Replace the switch and I bet all will be well.ADDED: even cleaning the switch may clear up the issue. IMO. Try a contact cleaner sprayed into the switch.. moving the knob around back and forth. (with the pre turned off of course)
Edits: 09/25/17
That sounds like a plan! Thanks alot I will try it and get back with the results.
How do you like your sp 15? What do you run it with?
I love the sp 11 with my arc cl 120 amps. Before even with a Bryson 4 b st it was great
If it sounds better at 47k why would you want any other setting?
Maybe I didn't express myself clearly. That's the problem. Its the 47 k loading that's stopped working and making noise with my DL 103 and Dynanavector10x5. These carts sounded better on 47 k. On the other hand every mm cart I have works on 47. Has anyonre have any idea?
Since accidently blasting the volume it created this issue.
.
Meaning that the high frequencies become more extended at higher loading? Excuse my ignorance
At 47 the Soundstage is bigger and deeper in my set up. At least for the DL 103
I agree that 47k loading gives the best soundstage. I find that "loading down" an MC to tame its treble is something of a band-aid.
As far as the problem you are having with your SP-11, it sounds to me as though the cartridge loading is not with a physical switch but perhaps instead with a FET switch. FET switches can be damaged by overvoltage, and perhaps that is what happened with your "high volume blast".
Have you contacted Audio Research yet? They should be your best source of help and likely the only place that can fix it. I don't think they include schematics like they did in the old days, and whey they do they usually don't have the part numbers for the "proprietary" solid-state parts they use.
Hope this helps,
Charles Hansen
But if you're looking for a technical answer, you probably should have posted this in Tube/DIY, or at the very least, the Tubes Asylum. The tech minded guys may find it here eventually , but the header for this Asylum reads, "Looking for a new Amp or Preamp? If you're after tubes, post over here." , and the "over here" link takes you to the Tube Asylum.
Good luck with it!
"Suddenly, I'm not half the man I used to be. 'Cause now I'm an amputee" J. Lennon
Tanks for the info! Still getting used to the rules.
Thanks I will try it.
Appreciate the advice
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