Old school stereo & New school technology issue

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JZM

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#198456 9-Jul-2016 19:06

I have a Sony LBT-a37 with Video and Phono inputs. I have connected a standard RCA Audio cable to the Phono and then to my Behringer Ultra-Compact Phono Preamp PP400 with muffled sound however I have had better luck with plugging it into video. However the base and beats are awesome but I think that the audio could be a bit more louder.

From the Preamp I have it plugged into a 3.5mm to RCA cable and this works find via my laptop - not plugged into charger I need to get a ground loop but when I plug it into my iMac it sounds very far away and like its 3 blocks away and nothing via my iPhone.

My final goal is to plug a bluetooth transmitter into the pre amp.

Regards,

Jess McKenzie

JZM Web Development

richms

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#1588950 9-Jul-2016 19:32

That's the problem with analog audio unfortunatly. To defeat ground loops get an isolator made for car use, it will need to go on the line level side of the pre-amp.

The phono input of the reciever will have a preamp in it, usually a pretty dire low quality noisy one made for the lowest price possible. Avoid that input.

Nothing follows standard levels for audio in consumer gear, so too loud or quiet is very common. Worse with phono since there is a huge variance between cartridge output levels. If there is no output level control on the pre-amp then you may have to upgrade to one that has it if you cant get enough gain from the volume control of the receiever to be loud enough.

I had 2 standalone pre-amps before giving up and just using the old DJ mixer I bought ages ago. Worked well enough and let me mix PC audio with music.

Richard rich.ms

wally22

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#1588983 9-Jul-2016 20:30

The Phono preamp "Converts your phono signal to a line level signal" so would need to go into the video input. What happens if you connect direct to the phono input, bypassing the preamp?

Sideface

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#1588995 9-Jul-2016 21:19

wally22:

The Phono preamp "Converts your phono signal to a line level signal" so would need to go into the video input. What happens if you connect direct to the phono input, bypassing the preamp?

The Sony STR-A37 is a 1993-vintage Stereo AM/FM Receiver

Input sensitivity: 1mV (mic), 3mV (MM), 300mV (line)

... where "MM" = moving magnet type phono cartridge.

So if the Sony is still working well, you should be able to plug the turntable directly into the phono input.

You can download the manual from here.

Sideface

Fred99

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#1589090 10-Jul-2016 10:19

A phono preamp should apply RIAA equalisation - it's not just boosting signal.

Possible results from doing it wrong:

If the turntable cartridge has high enough output and the line-in enough gain so that it "works" without running through a dedicated phono input, then it's going to sound tinny/distant and lacking bass.

If the turntable is plugged in to a separate phono pre-amp, then plugged in to a phono input, apart from the fact that the signal level will probably be way too high, it will also have RIAA equalisation applied twice, so high frequencies will be attenuated and bass accentuated. It should sound terrible.

The RIAA equalisation curves aren't necessarily standardised/accurate.

Even high-end audio these days may not have a suitable phono input - but that old Sony amp is probably fine. I helped set up a $1500 phono pre-amp to get a turntable with low output MC set up on a Krell/B&W system a few weeks ago. The preamp had two switchable RIAA curves, I could hear some subtle difference - but it was negligible and I'd struggle to say which might have been "better". It also had variable input impedance, continuously variable via a potentiometer, the theory being that this had an effect on needle damping characteristics. Turning the knob from one end of the range to the other, I'm certain that I could hear absolutely no difference at all. That phono preamp had both RCA and balanced (XLR) outputs, the Krell preamp also had balanced inputs, so we used those. Still some noise though - that's what you get with analogue input devices / transducers.

Inspired by this to get my old record collection out, I had the same problem with no MC phono input, though the Dynavector MC cartridge was a high output (2.5mv) variant. The rest of the system uses pro audio balanced XLR, so is practically noise-free. I just grabbed an old amp with phono input, then took line out via RCA through the mixer I use to the rest of the system. Perfect. I'd be very surprised if a separate "high end" phono preamp would makes any real difference compared to the preamp stage on any reasonable old stereo amp.