2. amps-preamps
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ARC ls 25 mkii cd/dac input too hot?

I have an Audio Research ls25 mk2 preamp and pass x250.5 amplifier. I have a Bryston bda-1 dac and Acurus acd11 CD player. When I listen to CDs and the recorded music gets louder, it sounds like the signal going into the preamp gets too hot creating a little distortion. I’ve tried a few different CD players, both connected directly to the preamp, as well as using them as transports through the dac. Both created the same issue. I don’t think I’ve noticed it when using the iMac as a source for the dac.... I’ll have to check that again.
I’ve had no problems when listening to records. The signal is definitely lower.

It seems like the output of the digital sources is too loud for the preamp. Does that make sense?
tripg
9 responses Add your response
andirocks
28 posts
 
Have you tried adjusting the gain on your preamp? There are 3 different settings per input.
Post removed 
tripg OP
21 posts
 
Andirocks, yes. I have them at the lowest setting. 
adg101
1,063 posts
 
Are you running balance from your Bryston to the ARC? If you are, try a single ended cable to see if that helps. You mentioned running  a couple CDP’s directly to the ARC so this probably isn’t the issue as I’m guessing they don’t have balanced outputs. If you are using balance on the Bryston try single ended.

Also if you’re running balance to your Pass, try single ended as well.

I had a ARC LS25 MKII at home for a short time on my Pass X250 and had no issues whatsoever and the older X250 has a higher gain output than the .5 series I believe. Have you had your tubes checked lately?
monoogan
55 posts
 
According to the schematic the LOW/MED/HIGH gain setting is applied between the selection relays and the volume control chips. If it's still too loud on LOW that's a weird combination of levels.

Is the BAL/SE switch in the right position? It's for setting input configuration, not output.

Good luck. With a 2 volt source MED or LOW usually work fine.
tripg OP
21 posts
 
Adg101,
the Bryston is connected with balanced cables and, as you mentioned the CD players, when connected directly, were single ended cables.
I’ll try your suggestions about trying single ended cables on both the Bryston and the amplifier. 
I should have thought to mention I got the same distortion through the headphone amplifier. Supports the theory the issue is the preamp, and/or it’s relationship to the digital sources.
The tubes are fairly new but I do wonder if they might be the problem.
thanks for your advice!
tripg OP
21 posts
 
Monoogan,
I’m pretty sure the balanced/se switch is in the correct position, but I’ll double check. I’ve made that mistake before. 
Thanks!
lowrider57's avatar
lowrider57
5,417 posts
 
The Acurus has 2V output gain, so it shouldn't be overdriving the preamp.

Do CDs sound at all harsh, or is the problem only at high volume? If so, there could be a ground loop between CDP and preamp traveling thru the unbalanced interconnect. Try using a cheater-plug on the CD, then crank up the volume.

tripg OP
21 posts
 
Lowrider57, CDs don’t sound harsh. It’s just during dynamic peaks in the music. I’ll try the cheater plug and see if it changes anything. Thanks for the suggestion!
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