Modified RIAA Curve to DIN

[Craig Maier]

Here are two presets that you can use in the VPA to approximate the European DIN LP curve, which is very similar to the RIAA curve, except that the Rolloff time constant is 50 uSec rather than 75 uSec. There are two presets, one to be used with flat preamps and the other to be used to correct an RIAA preamp to the DIN response.

Craig

[ebrjvd]

Phono preamp

Attached is a picture of the excellent British "Front End" phono preamp made by Ted Kendall for restoration applications.
You can see the three switches to select the EQ time constants.

Jos

[Craig Maier]

Hi -

For precision EQ, it is best done in software not in analog hardware. The reason for this is that analog circuits have circuit tolerances and aging effects which degrade their accuracy, both short term and long term. Also, the matching of the response from the left channel to the right channel will always be inexact.

When this EQ function is done in software (as with the Diamond Cut Virtual Phono Preamplifier) and in conjunction with a flat preamplifier, your results will be as precise as they could possibly be.

Craig

[ebrjvd]

Parametric VPA

Dear Craig,

Would it be possible to have a "parametric" VPA, where one can select the three time constants (like on Ted Kendall's "Front End" phono preamp)?

Jos

[Craig Maier]

Hi,

It would be possible, but we do not offer that right now. If you look in the VPA, most of the common curves are covered. If you want to create other exact curves, use the Multifilter and cascade several "Integrators" (first order low pass filters) together and adjust them for the desired time constants. You will need to put a gain stage at the end of the chain, to compensate for the losses.

Craig

[Craig Maier]

Hi,

It would be possible, but we do not offer that right now. If you look in the VPA, most of the common curves are covered. You can create any frequency response that can be imagined with a combination of integrators and/or differentiators cascaded together in the Multifilter. An integrator is found in the IIR Low Pass Filter and a Differentiator is found under the IIR High Pass Filter. Just set these for a 1st order response and adjust the frequency values appropriately. You will need to put a gain stage at the end of the chain, to compensate for the signal losses. You will need to use the following relationship to convert time constant into frequency:

RC (time constant in seconds) = 1/2 x pi x f (in Hertz)

or

Expressed in another way -

f (in Hertz) = 1/2 x pi x RC (time constant in seconds)

Craig

ps - The LPF and HPF needs to be of the IIR type found under the Filter Menu (not FIR type found under the Forensics Menu)