I just bought an Audio Research SP-6 preamp. It takes about ten minutes after powering on for the power lamp to stop blinking and the unit to start passing signals. Other than that it sounds perfect on all inputs. Is this at all normal? Does it indicate something is about to fail? Ten minutes to warm up is more than annoying.
I enjoyed my SP-6b for 14 years. The power light stopped blinking after about 3 minutes. I normally let it warm up for an hour before listening. I suggest checking the bias voltage of V2 and V5 (The two middle tubes in each series of three). Unless your preamp has been modified, the bias voltage must be adjusted manually. If it is too far off, the unit will go into automatic mute mode (blinking light)at times. If you are not handy with an electronics screwdriver and a voltmeter, have someone do it for you. It has been a few years, but as I recall, I set V2 at 155 Volts and V5 at 150 Volts. There are adjustment potentiometers next to each of those tubes. Check voltage from the capactitor next to each of those tubes to ground. It is shown in the schematics. Be careful. Don't go poking around in there too much. Voltages are very high. One time I put my voltmeter lead on a transistor case and measureed 550 Volts! I still have an old analog voltmeter that I used for calibrating bias voltage. A digital DMM should be fine as well. Just that I prefer analog :)
One other thing... The tubes could be worn, which would also cause the bias voltage to be off. Try some new tubes- especially if you do not want to poke around in there with a voltmeter. I recommend trying some NOS tubes. Search the web for some ideas and places to buy and which brand/vintage to get. I bought some on the bay for a very reasonable price and was blown away at how good they sound.
My backup SP-6B preamp takes about a minute to stop blinking. A call to ARC service will give you good information. ARC has a great service crew with quick turn around. Keep in mind your preamp is over thirty years old. The 6B I bought in the mid eighties has been serviced 3 times by ARC...All the best..
Not familiar with that unit but 10 minutes does seem excessive. My cj premier 16 took less than a minute or so. Currently my Herron phono stage goes through the same start up sequence and takes less than a minute as well.
Which version of SP-6 do you have? The power LED on the SP-6 and SP-6A don't blink.
Starting from SP-6B ARC introduced a timer circuitry which auto mutes output on power on. If yours is AP-6B and later, I think that is what you are seeing. It is normal. Nothing to worry about.
All the SP-6's sound great. I like the 6A the best.
I owned a couple different versions of this preamp. The 6B and later did have a "timer mute" circuit, but I remember it only took a minute or two at most to unmute. It was a long time ago,so maybe I've forgotten.
Nope, it's not normal. I would recommend calling Audio Research. It sounds like you will be sending it in for repair. I hope you didn't pay too much for it. This is why a 9/10 rating on these older units is not accurate. The faceplate may be free of scratches, however, the electronics is 30 years old and failing. Also, if you want your preamp restored to original and sound the way it's supposed do not send it to anyone except Audio Research. It may cost a little more, but it is well worth it.
The mute time should not be more then 3.25 minutes. After that the LED should glow bright and the signal should be un-muted. If this is a B, or C version its usually caused by a leaky capacitor in the timer circuit and or a bad opto-coupler. If the unit hasn't been in for service, now would be a good time to do it. The B/C versions has multiple regulated supplies. A bad cap in any of them could cause a domino effect and take out the other regulators.
Why not call ARC? They were always very helpful when I would call them about the ARC amps and preamps I owned, and they have supported their older products admirably.
Jeffrey, the circuit diagram says longer and can cause a thump if the mute releases early. The B and C preamp versions have a very long DC time constant and so it takes a while for it to stabilize. If your preamp is releasing after one minute, the cap in the timer circuit is the wrong value and releasing too early.
I've had the SP9, SP11 & SP14 and none of them ever needed more than 30-60 seconds to end mute mode. Agrre with others that you should call ARC and send it in.
I own a modded 6-B which never took more than a minute or so. When I first glanced at the topic, I thought No the tone of my ARC 6-B was always on the colder, analytic side, and couldn't be warmed up by my usual tube rolls LOL!
Yes, as I said earlier and I guess it never made it to this thread; Because the SP-6B/C have long DC time constants, in order for the circuit to stabilize, the timer should not release after one minute or you might hear a thump and watch your woofers move in and out for a few cycles. It would be especially dangerous if you were using a DC coupled solid state amp. Usually the cause if the timer releasing early is the wrong value cap in the circuit. The circuit diagram I believe shows 2mins. 35 secs. with the right value capacitor. Minor changes to that time are strictly a function of the tolerance of the cap.
Just try some new tubes before doing anything else. High quality vintage gear is good stuff and can have many more years of service. The things to watch out for are corrosion and dried out electrolytic capacitors. I think it can be particularly rewarding updating vintage gear with modern high quality components. I bought my ARC SP-6b preamp in 1989. A few months later I had it modified by a buddy who was skilled in audio, a hobbyist and in the business of upgrading gear. Circuits weren't changed, just upgraded internal wiring with Litz, gold plated RCA jacks with teflon dielectrics, Wonder Caps and wire wound resistors in place of the carbon filled ones. My buddy also added better quality trim pots in the bias circuits. These were many of the things ARC incorporated into their later models. I used that preamp for the next 14 years. It sounded great. I only changed models eventually, because I wanted to get into the low output MC cartridges. I discovered NOS tubes too late in life. I'd love to go back and hear my old SP-6b again with NOS tubes.
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