Has anyone tried to put a DSP between PRE and Power amps?

Hi-Fi Corner
1

The questionis in the title.

it would be a room adjustment solution and also a frequency adjustment for people with particular hering issues.

I have a couple of Ideas but require some cabling reconfiguration

What are your toughts?

2

Assuming that your Preamp has a Tape Loop that’s where it should go.

3

I am talking about NAC552/NAP500

4

Are you thinking about the Accuphase DG-78?

5

There is absolutely no reason why it shouldn’t work as long as input/output impedances are appropriate and no abnormal signal current demand, nor excess ultrasonic output to upset the power amp. With old classic Naim you would of course have to connect differently from the normal Burndy via power amp.

I have used a(n upgraded) Behringer DCX2496 between my DAC’s volume controlled analog output (which I otherwise fed direct to power amp with no preamp between), or when I wanted to use an analog source a preamp, and Bryston power amps for triamping. In addition to the fully customisable AXO function, there was spare DSP capacity for some limited room correction (reducing a few room peaks). It worked fine, and sounded as good as an ATC EC23 analog AXO I also tried, though latter less flexible. As is common with devices having their own inbuilt ADCs and DACs, including some of Naim’s products, when ADC and DAC are matched they have little if any audible effect being in the signal path.

Depending what you are trying to do, if you use a digital source then may would theoretically be better to feed the digital signal into a DSC box, and the DSC digital output into your favourite DAC, doing the DSP in the original digital domain. There are a variety of potential devices depending of course on intent and requirements. I plan to follow through on this in due course for some degree of room correction (I have a different system now), while allowing potential ‘tone controls’ for poor recordings and possobly properly tailored ‘loudness compensation’ for low level listening.

6

Thanks, that’s very helpful — especially the point about ultrasonic output, which I hadn’t considered.

My system is a NAC 552 / 552PS into a NAP 500. The idea is to insert a miniDSP Flex between the 552PS signal output and the NAP 500 inputs, to compensate a hearing loss of mine centred around 3–4 kHz. I already use the Flex on the headphone branch, fed from the 552’s record out, and the result there has been remarkable — so I’d like to get the same correction onto the speakers, for all sources including vinyl and tape.

On your first two criteria I think I’m fine, from the Naim manuals:

  • 552PS main output is 0.775 V into less than 50 Ω; the NAP 500 input is 18 kΩ. So no impedance mismatch and essentially no current demand.
  • The Flex drives that load easily.

The one I can’t settle is the third. The NAP 500 is specified −3 dB at 100 kHz, so it’s wide open above the audio band, and I don’t know how much out-of-band noise a sigma-delta DAC like the Flex’s puts out up there. Two questions, if you don’t mind:

  1. With your DCX2496 into the Brystons, did you ever notice the amplifiers running warmer than with a direct connection?
  2. Would you bother with any passive filtering at the power amp input, or is this a theoretical worry more than a practical one?

I did think of your suggestion about doing the correction in the digital domain, and for my CD and streamer it would clearly be the cleaner route. The problem is that half of what I listen to is vinyl and tape, so a conversion has to happen somewhere regardless.

7

Hi Salvo,
No to 1 & 2. I flagged up ultrasonics not because I think it would be an issue, but that has sometimes been argued by others as a risk using other brands of preamp with Naim power amps, though I am not convinced myself that in reality there are many instances when it occurs.

In case it helps, some DSP boxes do have analogue inputs, which I would find useful myself for occasional other sources (I know that is the case for at least one MiniDSP product I looked at).

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8

Thanks, that settles it for me — those were the two things I couldn’t rule out from the manuals alone.

And yes, the Flex is one of the ones with analogue inputs: that’s exactly why I chose it. It’s been running on my headphone branch for a few weeks now, fed from the 552’s record out, with turntable and tape going through it as well as the digital sources. That part has worked beautifully — hence wanting the same thing on the speakers.

I’ll report back once I’ve built the cables, in case it’s useful to anyone else facing the same problem.

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