Ripping vinyl

I tried taking the pre out feed from my integrated amp to the Behringer thingy, but to get the recording level high enough the Spendors were playing louder than ever. Is it safe to disconnect the speakers?
I'm now connected up direct from the Reflex to the line in of the MacBook Pro (how good/bad is its ADC) and am trying VinylStudio, which looks really good.

I've not yet played with the setup of the G1042 so I'm recording from my Technics SL-7.

Edited by ICL1P - 25 Jan 2016 at 8:15pm

Do you understand the voltage supply to computer devices and understand the implications?

Analogue isn't digital. Analogue derived signals exceed 0dBfs where digitally derived signals cannot.

Computer peripherals (built-in cards or external) typically run from 5V supplies. The op-amp (they always use them) on the input before the A to D runs on the 5V supply. Unless it's a rail to rail device it can only swing to 1.5V below the 5V and to 1.5V above 0V. This means it can only swing 2 volts.

That 2 volts is peak to peak. Half of peak to peak is 1 volt - and r.m.s. is 0.707 times that which is 707mV.

So, let's take a 3.5 mV nominal output cartridge and amplify it 120 times (like most of my designs do). We get 420mV. OK, that will fit!

But will it? Remember I said "Analogue isn't digital. Analogue derived signals exceed 0dBfs where digitally derived signals cannot."

Not a lot of people know this, but peak recorded level on vinyl at mid frequencies can reach +14dB - that's 5 x rated cartridge output.

So the 3.5mV on peak recorded level can be as high as 17.5mV. Multiply by the phono amp's 120x gain and you have 2,100 mV ... ouch!

So now we'll use a 6.5mV output Goldring 1000 series cartridge. We can get up to 3.9 volts!

That is gross overload.

How much attenuation do we need? 10dB? 20dB? It all depends on the cartridge output, the recorded level of the vinyl, what type of op-amp the ADC is using, and its voltage supply.

Some ADCs use the computer's 12 volt supply - that will be better because it can take around 3V input, and maybe you'd need a 10dB attenuator for "hot" vinyl - or no attenuator for quieter recordings.

But to get 3.9 volts down to 707mV we need 3.9/0.707 = 5.5, which in dB language is 15dB, so we may have to choose a 20dB attenuator.

Wouldn't it be better if ADCs had a physical level control on their inputs?

Well yes, of course! But the vast majorioty don't, and that's why I decided to fit the Accession phono stage with one. It's also buffered so it works with low impedance input ADCs too.

Paul H wrote: How are you getting on with this? I'm having the same input loudness problem with my own (completely different) set up. I'd be interested to know if you find a solution.

No, I've given up. I chatted with Bob via email and looked at the Lexicon and couple of others, but in the end decided not to do anything for the time being. I decided the most sensible solution would be to swap out my Reflex M for an Accession, but that'll have to wait a while. In my mind it's queued behind, Cyrus CD promo upgrade (going for the Xt Signature), Majestic and then a pair of Proprii. It'll take a while to get all that past my wife!

A computer USB port will provide 5VDC power.