2. amps-preamps
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CD signal into a phono stage?

I'm trying to sell an integrated amp. Although I have no real reason to believe that there is a problem with the phono stage (since I've never used it), I think it might be a good idea to check it to make sure. How can I do this? Is it OK to run my CD player through the phono stage? Would the signal be too strong and fry the circuit? How about a tuner? There are actually two phono stages - it's switchable between MM and MC. Can I check both stages with a CD player or tuner? If not, any other ideas?

Thanks
Don
hessong
7 responses Add your response
slipknot1
1,423 posts
 
1 word: OVERLOAD. This applys to MC and MM stages. Signal will be so overloaded you would have no way to verify its quality or its ability to pass the much lower voltage a cartridge has. I wouldn't risk it.
marakanetz's avatar
marakanetz
5,473 posts
 
Use pocket cd-player with adjustable volume control set to the very minimum(you may check the output level with voltmeter to make sure that you do not exceed 25mV) and adapter from headphone output to the line RCAs for the phono input. This way you can check out MM section. Otherwise to check an MC section, I'd assume it's working or I'd only recommend turntable record and cartridge.
buscis2's avatar
buscis2
468 posts
 
Hessong, you can in fact use a CD player to "test" your phono section providing you are using a player with a variable output. Many players, Levinson, Sony, Denon, Cary, Audio Aero, etc. do provide you with variable outs. Some actually attenuate in the digital domain which obviously would not apply in your application.

Of course, begin testing with the volume control at it's absolute minimum output level and you should have no problems. All of the above is assuming you are "testing" only.
sidssp
1,077 posts
 
You cannot do that. Beside overload problem, phono stage has RIAA equalization which increase the bass and reduce the high frequency. The difference of gains can be as much as 20db on each end comparing to the 1K point. It will not sound right if you feed it a CD signal.
buscis2's avatar
buscis2
468 posts
 
Sidssp, I have to assume Hessong is simply testing to assure that the phono circuits are passing signal. But, of course you know what happens when you assume. I am not in any way implying that this could be used for "listening" tests. Most CD players with variable outs will have an output level as low as 0.1v. which in no way will harm the actual phono circuit, although it will allow you to test for signal pass. But your correct, it won't sound great.
Post removed 
hessong OP
15 posts
 
Thanks for all the (rapid) responses. This confirms my suspiscions.

Don
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