Answered Turntable Pre-AMP and Phono Hum

Big Simon

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Hi All,

I have just recently purchased an Audio Technica USB AP120 Professional turntable, (spec attached) which comes with a built in pre AMP.

https://www.audio-technica.com/cms/turntables/583f30b3a8662772/

I have this unit connected via RCA to a phono switch box (spec attached) but am using this in reverse as i need to connect to 2 x Phono Out sources. The turntable is thus connected into the 'Output to Amp' connection on this box--

https://www.amazon.co.uk/HQ-3-Way-S...8&qid=1527097074&sr=8-1&keywords=phono+switch

I am then connecting RCA cables from AUX 1 and Aux 2 on this switch box to my respective devices.
One is a Pioneer DDJ-RR controller which seems to work fine, the other is a Marantz PM6005 AMP which is were the problem comes in, (see attached spec).

Marantz UK | PM6005

The RCA connection to the AMP is connected into the 'Phono' Audio Out and when i switch the source from both the phono switch box to AUX 1 (Where it is connected) and also to the phono source on the AMP I am getting a bad hum.

When i play the vinyl from the turntable the audio quality is good and drowns out the hum but when it stops the annoying hum is still there.

As the turntable is fitted with a pre-AMP i was wondering is this causing a conflict and should therefore be removed, however.....

When the turntable is off the hum is still there when i have the phono source on the Marantz AMP selected and is connected through to the switching box. (The turntable power is still connected however its switched off on the deck through the circular on switch).

it's a bit like looking for a needle in a hay stack here. My first thought was pre-amp in turntable may be the issue but now im not so sure and dont want to have it removed for no benefit?

Turntable quality is poor when connected into the other sockets, CD, Tuner etc via RCA on the Marantz AMP although the hum is not there.

Would really appreciate the help of anyone on here who might be able to help get rid of this?

Thanks Folks

Simon.
 
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Hi Simon, firstly, you cannot use the Riaa EQ Pre Amp Circuitry (boosting low frequencies and attenuating high frequencies) on the Record Deck and the Marantz Amp (phono input) at the same time, otherwise it will sound awful as you will be EQ'ing twice.

Apparently the Record Deck has a Switchable Pre Amp, in which case, turn it on (possibly off at present) and go into the CD or Tuner input of the Marantz Amp and it should sound fine.

Your Pioneer DDJ-RR has no Riaa EQ so you will have to use the built in Record Deck EQ.

Once things sound correct with Record Deck and Marantz Amp alone via Cd/Tuner Input, then introduce the Pioneer DDJ-RR and switch box again.

Hope this helps.

Mike
 
Mike,

Firstly thank you so much for a detailed and prompt response, it is very much appreciated.

Excuse my lack of knowledge on this. The back of the turntable has a switch for Phono or Line. Should i switch this to line when connecting to the Phono output in the AMP, or the CD/Tuner for that matter? (Image attached)
Other than that i cant see another switch that might disable pre-amp.

Hope this helps

Simon.
 

Attachments

  • ATLP120.jpg
    ATLP120.jpg
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Switch to Line and go into the Marantz CD input, see how it sounds.

I suspect is is set to Phono at the moment.

This may not cure the hum, but at least we know where to start troubleshooting. :smashin:
 
Just tested, much better and working really well. Thank you so much for all your help. Just one query. Why use the CD port of the Marantz Amp as opposed to phono?
CD sounds great, just curious.
Thanks again for all your help
Simon
 
Because by using "Line" out on the TT you are utilising the preamp within the TT and therefore do not need to use the "phono" preamp section of the Marantz. Any line in connection on the Marantz amp (CD/Aux/Tuner etc) will accept the signal but not the "phono" as you will then be trying to double the EQ'ing.
 
Appreciate that.

So there is essentially no way to use the pre amp on the Marantz instead. Ie when phono is enabled on the TT and plugged into Phono or CD on the Amp, sound quality is poor.
 
Whilst it is many a year since I played with a TT, in theory and according to the specs there is no reason why your Marantz amp phono input shouldn't accept and amplify sufficiently a direct connection from the phono out on your Audio Technica TT. There is often a ground wire from TTs for connection to the amp to alleviate any hum.

Have you tried a direct connection without the switching box? If so, then sorry I can't help further but someone else maybe be along shortly to help......
 
Just tested, much better and working really well. Thank you so much for all your help. Just one query. Why use the CD port of the Marantz Amp as opposed to phono?
CD sounds great, just curious.
Thanks again for all your help
Simon
Hi Simon.

The Phono input on the Marantz Amp has EQ for the turntable and is different to the other inputs. So bearing in mind the EQ is being adjusted by the turntable, it would sound awful via the Phono input on the Amp. So you have to use a normal input, especially as you wish to go via the mixing desk.
 

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