I finally got Khorns and ARC and I have a big problem

[Ld1955]

After many years I finally assembed the system I always wanted. Khorns, a LS7 preamp and I just hooked up a D70 MkII I got on Agon.

As soon as I power up, I have way too much gain. I just barely touch the volume control, set on 0, and hear it through the speakers. I know the horns are efficient but I did not expect this. The LS7 manual says that there may be problems with certain speakers. Yeah right.

I obviously need a different preamp. I have searched the forum for recommendations, but I would like to stick with a vintage ARC. Maybe someone can help. What's the issue here? What specs should I be looking at? Gain? Output Impedance? Rated Output?

Puzzled

[Edgar]

Line Level Attenuators

[russ69]

I believe ARC can modify the pre-amp for you. I think that's one of the basic design features.

Thanx, Russ

[LarryC]

I just barely touch the volume control, set on 0, and hear it through the speakers.

I'm puzzled that this should be so extreme. This site says it should only have about 13 dB gain, which ain't much compared with most line stages' 20 dB. I suggest you get in touch with ARC before adding anything to your pre. It might also be something in the gain of your amplifier.

Maybe the previous owner had some changes made to either the pre or amp to push up the gain. The factory might have some information about that.

[Ld1955]

Thanks for the help. I will follow up with ARC and maybe check out the attenuators. I have had the preamp since 2000, but I bought it used. It could have been modified I suppose, but I will check.

[tube fanatic]

Another solution is to go with a passive line stage (basically, a single resistor and a potentiometer) between your source component and the power amplifier. With extremely efficient speakers, like K-horns, it allows them to be driven to ear shattering levels; and many consider the sound quality to surpass that of any preamp since you are eliminating all of the noise generated by another power supply and numerous resistors, capacitors, switches, etc. If you are handy, one can be made for around 20 bucks!

[artto]

Some (many?) ARC preamps have a gain switch on the back to adjust total gain for certain high sensitivity speakers like Khorns. There is usually a protective cover over the sliding switch to prevent accidentally moving the switch while the unit is on. The amp should be turned off and disconnected from the amplifer when switching gain settings.

[Ld1955]

I checked the LS7 but there is no such switch. I called ARC and there is a fix but it requires adding four resistors to the circuit board.

I think I am going to go the passive attenuator route since I only have a Marantz SACD player as a source for my 2 Ch system.

Again thanks for all your thoughts.

[LarryC]

there is a fix but it requires adding four resistors to the circuit board.

Did they explain what the problem was to begin with, i.e., were the 4 resistors supposed to be there and are just missing?

It's hard for me to understand how a mere 13-dB line stage could produce such overwhelming gain, but whatever works --

[George Roland]

Hi,

I had the same problem with my ARC SP-8 preamp and a pair of Klipschorns. Have you phoned Leonard at Audio Research? I believe they had a provision for lowering the gain on at least some of their preamps for situations like yours. Maybe they can offer you a fix if you want to keep your preamp.

My ARC SP-8s had *WAY* too much gain for K-horns. I was using a VT-100 Mk I for power. I ended up using a Juicy Music Blueberry Xtreme and some 300B SETS (Welbornes) that produced some great sounds with my K-horns, but to be honest, I've never heard another preamp as clean and detailed as my SP-8. ARC makes good stuff!

Let us know how it all works out.

George

[Ld1955]

The LS7 owners manual saysthat there may be too much gain with some sources, if so call. I did. The tech said the solution was to add 4 100k resistors, 2 on each channel and they could mail me the resistors and a diagram. It is not something that was omitted. I know it is not something I want to tackle and i do not have a repair shop I trust nearby. I don't want to send the preamp to ARC and really not be certain of the results.

I did have a friend lend me a Luminious Audio Axiom passive preamp. All it is a volume control with one set of inputs and outputs, no switching.

It totally solves the problem! The D70 really is a definite improvement!

Any other suggestions for a passive preamp? I have read about the Lightspeed attenuator and the Creek OBH11 from Stereophile (Sam Tellig).

[LarryC]

I don't want to send the preamp to ARC and really not be certain of the results.

I'm glad your problem is solved. If it wasn't, sending it to the factory to have it done would be an alternative IMO. Did you get the factory carton with the ARC? It's usually a good thing to keep around for selling it or if you decide to ship it.

[fini]

Late to the party here, but I thought I'd throw out that some CD/SACD players have a variable output. Yours may be cranked way up?

[Ld1955]

Its working out well. The advantage of the Axiom is that they customize it to your setup. They ask for the efficiency of your speakers in db at 1w/1m, the input impedance of your power amp, the input sensitivity of your power amp in mV and the output voltage of your cd player: I have ordered one for myself at $162.00, as a stopgap, but I will probably look elsewhere for a permanent solution.

[Ld1955]

A good question. I have a Marantz SA-8260 and I don't think it has variable outputs but I will check the owners manual. Still, I have not tried a different CD player. That is worth a shot.