ImPasse Preamplifier

[luvdunhill]

SY, what cutoff frequency would you shoot for when choosing a capacitor before the 10K input impedance of the Impasse?

I should add the source is a phono preamp that has a rumble filter (simple RC).

[luvdunhill]

quick question for SY and the others that frequent this thread.

I recently built some small subs to add to my full range speakers. My chain at the moment a digital source with 4V RMS output from its balanced output (238 output impedance on the balanced outputs), to my Impasse preamp to a pair of balanced bridged F4 (0dB gain) set to 200K input impedance per leg. This is connected to my full range speakers. For analog I have a .24mV MC cartridge, 76dB gain balanced output phono with 300 ohm output impedance. My second amp that I have to use as a bass amp, is balanced input as well, 100K input impedance with 20dB gain.

My plans are to construct a active crossover that would live after the Impasse, have the ability to attenuate the signal, with an appropriate buffer. I have it all drawn up and am playing with a discrete opamp to use in the circuit and getting that ready to go. The issue is, my time is disappearing for the year and I'd love to enjoy adding the subs sooner than later.

So, suggestions? Would something like a Behringer CX2310 fit the bill? or a single box with a PLLXO in it? Quick and dirty would be great.

[luvdunhill]

I think the only question is what is the maximum input the CX2310 can take. Otherwise, I could put it before my Impasse, but then the volume control there doesn't scale both speakers...

[SY]

Marc, sorry I didn't see this before.

I'd aim for a 2Hz rolloff (one decade below lowest frequency of interest). Quick and dirty, I'd throw together a diff input opamp circuit with adjustable gain for the subs, run it off the output of the ImPasse, use the opamp circuit's level to balance bass and treble, then leave it alone and use the ImPasse for a master volume control. Don't know the CX2310, but I've done something like that with a DCX2496, which ran into a 4 or 6 channel balanced pre.

[luvdunhill]

ok. thanks! i found a used CX2310 on Ebay for $60 shipped so I'll try that first.

Other than clipping the input of the CX2310 (which I'm not sure will be a problem anyways), the input impedance is 50K and I have 0.47uF capacitors in the Impasse (as I set my F4 to 200K input impedance).

[SY]

That gives you an f3 something under 7 Hz, which is probably fine.

[luvdunhill]

oh boy, this CX2310 looks like it will work. I need to fix up some more XLR cables in order to get both the bass and treble amp working.

One thing I'd like that I cannot get with this, is the high pass to not be crossed over, and only crossover the bass amp. I could do something strange, like use an XLR splitter on the input and connect that straight to the full range amp though, but I'm not sure what the consequences of that would be. For now though, I'll be happy just to play with this setup.

Oh and I also got a JAN-CHY-5692 to play with as well

[6L6]

A couple of questions, good sirs,

Can the inputs be both balanced and single ended, or do you have to choose one or the other?

Is the gain the same when using the output single-ended? (I'm only building one F4 to begin...)

[6L6]

Ordered the PCBs and Transformers from Jack, still rummaging through my
junk box, ahem, collection of various parts, to see what I can use.

Is there anything particularly important other than the CCS adjust resistor and the resistors in the split-load inverter?

[jackinnj]

I can provide the following components for the Impasse -- if there's enough interest I can also get the input transformers (although they often take weeks.)

C1 2 Not used See Text
C2,5 4 100nF 630V Polypropylene
C3,C4 4 470nF 400V Polypropylene
D1,D2 4 Red LED, 1.7V Drop
NE1 2 NE2 Neon Lamp
P1 1 100K ALPS Dual Audio Taper
PCB 1 Printed Circuit Board
Q1,2 4 DN2540N5 Depletion MOSFET
R1 2 18K 1/4W Metal Film See Text
R11,12 4 15K 1W Matched to 0.1% 2 pairs
R2,9,13,14 8 1M 1/4W CMF55 Metal Film
R3,10 4 1K 1/4W CMF55 Metal Film
R4 2 12k5 2W Wirewound or Film
R5 2 300R 1/4W CMF55
R5a 2 2.7K 1/4W CMF55 Metal Film
R6,7 4 120R 1/4W Metal Film
R8 2 680K 1W Metal Film
S1 1 2 Pole, 5 Position Selector Switch
Misc 6 Molex 0.100 Inch Pin Headers
Misc 4 Nylon Spacers with nuts
Misc 2 Tube Sockets


And the following for the Impasse Maida Power Supply:
C1 1uF/600V PP
C2,3 100uF/450V
C4 47uF/450V
C9 10uF/100V
D101,102 UF4007
D103 12V 1W Zener
IC1 LM317 Regulator
PCB Printed Ckt Board
R1,2 47R 1/2W
R3 470R 1W
R4 1K 1W
R5 20K 1/4W
R6 100R 1W
R7 47R
R8/13 28K/1W
R9 200R 1/2W
R10 4.7R/0.25W
R11 270K/0.5W
R12 47K
U2 TIP50 Transistor