HiZ input for any preamp

[12Bass]

[quote author="clintrubber"]Source impedance won't be 1M (assuming a passive bass or guitar), but 6 nF is indeed a lot more than the typ input capacitance of a 'Hi-Z' kind of input. Usually the capacitance of a 6 meter guitar-cable is the dominant capacitance 'at the input-node', but even for bad cable (200pF/meter) it's still far from that 6. So the PU-resonance will shift even lower, a task usually not desirable for a DI-kind of input.

Regards,

Peter[/quote]

Sorry to interrupt this thread.... But I'm wondering if 1M is sufficiently high for a passive electric guitar or bass? My Eden WT-500 bass amp appears to have a 1M input impedance, and I'm wondering if it might be worthwhile to increase it? Is there any advantage for use with magnetic pickups?

 

[clintrubber]

[quote author="12Bass"][quote author="clintrubber"]Source impedance won't be 1M (assuming a passive bass or guitar), but 6 nF is indeed a lot more than the typ input capacitance of a 'Hi-Z' kind of input. Usually the capacitance of a 6 meter guitar-cable is the dominant capacitance 'at the input-node', but even for bad cable (200pF/meter) it's still far from that 6. So the PU-resonance will shift even lower, a task usually not desirable for a DI-kind of input.

Regards,

Peter[/quote]

Sorry to interrupt this thread.... But I'm wondering if 1M is sufficiently high for a passive electric guitar or bass? My Eden WT-500 bass amp appears to have a 1M input impedance, and I'm wondering if it might be worthwhile to increase it? Is there any advantage for use with magnetic pickups?[/quote]
I guess 1M is fine, but further increasing it above that value won't give very noticable differences for most pickups.

FWIW, when building own stuff I settle for a bit more, say ~2M35 (as resulting from a 4M7-biasing-resistor and the anti-pop-resistor preceeding the AC-coupling cap).
IIRIC the SVT-preamp has 2M2.

Bye,

Peter

 

[lagoausente]

I need to re-questioning the question. what have better sense, a DI input to a Mic pre input, or a DI input to line level? Gived the situation of that doesn´t matter that if its in or out the box/preamp...

And in relation with this, is any of the circuits mentioned suitable for giving the line level if the answer to the question above would be "line level"?

 

[SonsOfThunder]

>>> Could you explain where are switched the J4 when pluging the jack, and how works Q7?

IIRC, J4 is a TRS jack as follows:
3 = Tip
2 = Ring
1= Sleeve

So when you insert a TS plug into J4, pins 2 and 1 short bringing the base of Q7 to ground which then actuates the relay coil connected in parallel with D2. That relay switches the input of the mic transformer from the XLR connector (and the phantom power resistor/cap network) to the output of the DI circuit.

Pretty clever, Dan is. As I understand the story, Fletcher played a part in the development of the MP2NV and he insisted that the input trafo needed to be in line on the DI input so Dan devised this scheme to make that possible..so now you can too!

HTH!
Charlie

 

[lagoausente]

Pretty clever, Dan is. As I understand the story, Fletcher played a part in the development of the MP2NV and he insisted that the input trafo needed to be in line on the DI input so Dan devised this scheme to make that possible..so now you can too!

Mine has no Trafo. So, will no get any colour from that. So the question I have now is:
DI to Mic input circuit? or
DI to Line level circuit?

Doesn´t make the DI to Mic ones a step down in gain? to go to Mic level?
Seems not much sense go down first, to go up then again..

 

[BYacey]

Doesn´t make the DI to Mic ones a step down in gain? to go to Mic level?
Seems not much sense go down first, to go up then again..

Right you are - If you are driving a mic preamp after this you are just adding noise with the gain loss and re-amplification. If you can drive a line level input you would be further ahead. Keep in mind a preamps signal to noise is highest at low gain settings, so if you can skip the mic preamp stage so much the better.

 

[lagoausente]

Keep in mind a preamps signal to noise is highest at low gain settings, so if you can skip the mic preamp stage so much the better.

I can skip the preamp.

 

[lagoausente]

Can someone explain me, why the DI inputs, usually go to the mic pre input, instead of going directly to the line output of the preamp?

I mean, they usually go from instrument level to Mic level, while they could be directly to line level. Why is the reason?