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  #1  
Old 08-31-2014, 06:43 PM
vinyl_junkie vinyl_junkie is offline
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Bozak phono input capacitance

So the big question on my mind is... What is the Bozak's CMA 10-2DL's capacitive load on the phono input?

We all know for a MM cart to operate correctly as the manufacturer intended it to it needs to be correctly loaded but the mixer doesn't state the load it presents at the input.

Buzzy stated that...
"The phono card that is in the DL series mixers came from the 919 stereo home Hi Fi mixer. The original front end of the card was designed to accept a wide variety of cartridges with different capacitive ranges and the second stage adapts it to broadcast flat response. A couple resistor changes can be played with but you will not end up with a very much better response than the original card is capable of. I may have an old chart I can dig up showing the resistor/capacitor combination changes and some of the carts we experimented with and their values. The final tailoring of the front end of the card was aimed at the most popular Stanton Disco series at the time and those specifications still generally work well with most cartridges."

Now I could be barking at the wrong tree here but the Bozak being discrete and transistor based could it be that the design of the card generally can accept a wide range of loads and still perform correctly? i.e. I think j-fets in some designs are used for this reason?

Some one with more technical knowledge can explain this perhaps

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Old 09-05-2014, 12:01 AM
Reticuli Reticuli is offline
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1) It's inductance on the cart end. The phono preamp and cabling end is the capacitance.

2) It's really difficult to get broadcast flat without matching capacitance to inductance properly unless you're using something like maybe HOMC carts. Preamp and cart manufacturers love to talk about how they've done something super special that has improved compatibility, but it's B.S. This issue mostly affects the high frequency electrical resonance and the roll-off. There are also mechanical resonances that can cause peaks that are totally independent of the electrical considerations.

Apparent phono imbalances in the lower frequencies are often the result of inherent cartridge design and "voicing", as well as things like poorly-sourced parts matching for the mixer's EQ stage, and not necessarily the phono stage's fault.

And of course, always test your mixer's balanced outputs' individual + and - signals to ensure they're functioning well. If you can avoid them and use a short unbalanced run, go that route. Balanced is a remedy for going very long runs around lights. Its complexity and difficulty in getting right makes it easy to cause fidelity degradation.

There's usually a (sort of) simple way to find out what the phono stage capacitance itself is by either looking at the circuit diagram or by opening the unit up and seeing what loading caps are installed. For instance, it might be two 100pF caps per RCA connector, which would mean it's 200pF or so. That's a pretty common happy medium.

If it's discrete, it just means that the ICs have been substituted by discrete part arrangement-equivalents. The ICs were of course substituting for earlier discrete designs. You'll probably still have dedicated loading caps in a discrete MM preamp stage. Both my discrete and IC-based ones do.

By the way, the type of loading caps you use actually make a damn difference. Really disturbingly. I personally preferred polypropylene caps to ceramics for that purpose. I can't tell you why it makes a difference, but it does.

One last thing: Obviously we all know that TT isolation is HUGE... direct acoustic, surface/material vibration feedback, etc. But also make sure the interconnects, the TT rcas (if it has them), the wiring, everything is metering properly, not intermittent, not weird resistance or capacitance from one channel to another, etc. Phono is outrageously susceptible to otherwise inconsequential differences caused by bad soldering jobs or damaged interconnect ends, for instance. If one TT sounds slightly different than the other even after you account for everything else, that's probably what's going on. Save yourself the headache and test those connectors and cables first rather than later when you're trying to figure out why everything you've done is still producing strange results.
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Last edited by Reticuli : 09-05-2014 at 12:05 AM.
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