Hissing sound when Tone Control is turned on

Hello all,

Wonder if any one of you experienced the same issue with your Mcintosh preamp ? If you did and what was the solution to it?
I have noticed that apparently audible hissing sound can be heard from my speakers during idle while the "tone control" is enabled on my Mcintosh C49 preamp. As soon as i toggled the tone contol switch off from the front panel the hissing sound is completely gone and the background is dead silent like it supposed to. 

Is this considered normal ? Any advises will be appreciated.



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Hi guys,

Thanks for your replies. The hissing tone remained the same level even when the preamp was set at zero volume. No other tone controls or EQ were in the chains. I have tried unplugging each sources one by one made no differences. And i have also tuned down the treble or made no gains from the power amp, the result was the same. But as soon as the tone control button is turned off on the front panel the hissing goes away completely. That was why i was wondering if this is considered normal for Mcintosh preamp’s. Thanks

Hi oldhvymec,

May i ask which Mcintosh preamp you are using ? This preamp performs very nicely and i love it. But this is my 1st time using Mcintosh product and i have no friends using some brand so i can compare with. Maybe i bought a slightly defective unit or perhaps it is normal. I have tried to ask Mcintosh technical support by email but not heard back from them yet. I will just wait and see how they reply to me.

C11, C20s, C2500, Mx110z, Mx120.  A few.. When they are tuned up and running they are quiet..

Did you buy it new? Did it just start making noise or out of the box. it made noise?

They make music, not noise..:-) This summer 50 years with Mac.. YUP I'm a Mac guy.. I like their older valve gear.. MC225, 240, 275, 30 and 60s. I don't currently own ANY SS Mac Power amps.. Just valve.. I have a Cary V12R I really like with a Mac front end... Just perfect for me.

I use class Ds to do all the bass duty.. Actually I'll be swapping over within a month or so.. See how the weather act.. Class D, for the main monitors in the summer too. Valves are just to hot.. It gets to be 110 + here where I live..

I bought a 1.5 year old pre-owned C49 preamp from my Mcintosh dealer. So i had no idea about how this preamp functioned when new. That was why i was hoping to get some guides from Mcintosh users first.

After some time-consuming tweaks on settings of preamp and power amp, I was finally able to track down the problem, The hissing sound during idle can no longer be audible if the output gain on my Parasound A21+ power amp is set to appropriate matching level. I had to turn the gain level down to almost minimum to get rid of the hissing when Tone Control is enabled on my Mcintosh C49 preamp (of course turning off the Tone control is another less preferred option). My previous setup was pairing my Parasound A21+ power amp with Parasound P6 preamp and Parasound official recommended the output power gain for both channels to be set to maximum all the times. And the parasound P6 and A21+ combo were working beautifully as well. I guess i should have done this equipment output matching practice before i raised my concern, especially when i pair the Pre & Power amps designed and manufactured by different brands. I am still new to hi-fi world so i learned an important lesson today.

Thank you for your valuable inputs anyway.

Happy Music Listening !

Juicy good my friend, you found an answer.. Parasound, that is another under appreciated amp.. I have a ZPre3 I use with a C20 to add a remote control and all the goodies of an OK DAC via a tape loop.. Just needed to do a little matching.. Even added a sub out option, still sounds like my C20 100%, serious little preamp.. GREAT phono stage MM MI and an MC with 56 db of gain.. (52?) It has a wonderful bass contour for the phono/tape section.. attenuated bass step baffle. 

I hate noise.. LOL 

Overall i have to patiently tweak and find the best matching gain levels between my MAC C49 preamp and Parasound A21+ amp.

Here is a thread found in AVS Forum, members were also discussing the similar topic : https://www.avsforum.com/threads/parasound-owners-thread.1122095/page-332

Crack me up.. Of course there is a reason for tone control. That's why the OP opted to have it just like me for the last 50+ years.. You don't need it until you do.. LOL One a month or so always ask "I need a bass boost, or they are a little boomy on certain albums"  It really doesn't matter.. When you need it.. You need it.

AND no I don't want to know what it sounds like live.. That's usually REAL bad... so... Tone control...  You get in your car you don't adjust the tone control? BS yes you do and or you did or it auto sets the tones to some preset EQ.... No Tone Control is just a CHEAP way to make a piece of distribution equipment, nothing more.. Not because it sounds better. The purpose of a preamp is to color the sound...

I don't care what anyone else thinks, that is what they use to be made for and what I still use them for.  Somethings just never change..

Ha! I haven't used a tone control since 1987. Never found a need to "color" the sound. Each to his own.
Well, there is certainly a purpose for a tone control.  Unless your listening room is an anechoic chamber and your system is perfectly tuned to deliver 144dB SNR and perfectly balanced signal from 20Hz-24kHz, you're going to find situations where you need/want to correct for something. 
Never had a pre with tone controls but will likely try in the future.   You guys make a good point.