Can ZV9 get by with a passive pre??

[cadaverdog]

I have an Adcom gcd-750 that outputs 3V p-p. Would this voltage be adequate for this amplifier??

[Nelson Pass]

Short answer, no.

You can raise the gain of ZV9, but I think you're better off
with a preamp stage. 3V p-p isn't a lot.

[cadaverdog]

Great, thank you sir.......................

[Vix]

I run my ZV9 with a "passive" pre (ok. a cathode follower), but my ZV9 isn't really a ZV9, because I run it without feedback, hence its a transconductance amp with a higher gain than "stock" ZV9. With Visaton B200's in an OB, it gets loud enough.

The sound? It's a cross between an F2 and ZV9, just what I like

Regards,

Vix

[Nelson Pass]

In that case you can just keep increasing the value of the
feedback (47K) resistor until you're happy.

[lordvader]

Originally posted by Vix
I run my ZV9 with a "passive" pre (ok. a cathode follower), but my ZV9 isn't really a ZV9, because I run it without feedback, hence its a transconductance amp with a higher gain than "stock" ZV9. With Visaton B200's in an OB, it gets loud enough.

The sound? It's a cross between an F2 and ZV9, just what I like

Regards,

Vix

I'm currently building a feedback-less F3 amp. How much more gain did your feedback-less ZV9 have ? Did you change much more, besides removing the feedback cap and resistor, and replace the input resistor with a resistor to ground ?

[Vix]

Originally posted by lordvader


I'm currently building a feedback-less F3 amp. How much more gain did your feedback-less ZV9 have ? Did you change much more, besides removing the feedback cap and resistor, and replace the input resistor with a resistor to ground ?

I don't know how much more, but looking at the ZV8 article, I guess that it should have around 18 dB of gain, which is enough if you have efficient speakers.

Basically it's a schematic from Fig.4 at ZV9 article. No Aleph CCS and no feedback.
While you are at it, I could recommend lowering supply voltage and increasing bias (at 3 amp if you can). In that case you'll also have to adjust the Jfet source resistors to get lowest distortion. It will sound better, unless you need many watts (5 are enough).

Also, load the output with the resistor. Anything between 5 and 50 ohm will most probably work, it depends on the speakers/cabinet you have. I've tried various values, and settled with 10 ohms.

Regards,

Vix

[lordvader]

How would a feedback-less F3 behave with the Aleph CCS (seems like I'm chopping this thing up with a hacksaw !)?

Dunno about lowering the supply voltage, as I've already ordered the transformers, and don't want to use resistors to drop the voltage. The tranny has 2x18V secondaries though ... Would wiring them up in parallel be OK, or would that be too low (25V DC) ?

And how would one go about determing the new source resistance given the new voltages (currently hovers at less than 1ohm), or can values calculated for the higher supply voltage work on the lower voltage ?

Sorry if it's a lot of questions, but I want to get this right the first time

[Vix]

If that makes you feel more comfortable, just use "normal" power supply, as is on a schematic. Adjust everything as described in a ZV9 article. Just follow schematic on fig.4, that's it.

I guess that Nelson can better answer your questions. In the worst case, you can always have the "stock" ZV9 with feedback and Aleph CCS. It's a good amp that remained under the shadow of F4.

Add a Jfet Boz and you're happy!

Btw, Best wishes for the new year 2008!

Regards,

Vix

[MikeW]

Originally posted by Nelson Pass
In that case you can just keep increasing the value of the
feedback (47K) resistor until you're happy.

I am running mine with an 80k for the feedback and it sounds great. This may be the best sounding Pass amp I have made.
Nelson, did you try any power jfets in a preamp?