#164465  by waldo041
 Mon Jan 28, 2019 6:35 pm
what is the output capacitance of the twin preamp you are using and also what is the input impedance of the Citation?

~waldo
 #164466  by Pointclear
 Mon Jan 28, 2019 6:57 pm
waldo041 wrote:
Mon Jan 28, 2019 6:35 pm
what is the output capacitance of the twin preamp you are using and also what is the input impedance of the Citation?

~waldo
This is a good question. I don’t know and, unfortunately, I’m not quite sure how to find out!
Please help if you think this is an important issue. I tapped my preamp right before the phase inverter input capacitor if that helps.
 #164468  by Pointclear
 Mon Jan 28, 2019 7:18 pm
Here’s a few specs I found on a quick google search. It says input sensitivity is 1.25v volts. I’m not sure if that means anything or not.


Specifications
Power output: 150 watts per channel into 8Ω (stereo), 300W into 16Ω (mono)

Frequency response: 4Hz to 40kHz

Total harmonic distortion: 0.05%

Damping factor: 300

Input sensitivity: 1.25V

Signal to noise ratio: 100dB

Dimensions: 483 x 356 x 235mm

Weight: 24.9kg
 #164469  by waldo041
 Mon Jan 28, 2019 7:20 pm
Pointclear wrote:
Mon Jan 28, 2019 6:57 pm
waldo041 wrote:
Mon Jan 28, 2019 6:35 pm
what is the output capacitance of the twin preamp you are using and also what is the input impedance of the Citation?

~waldo
This is a good question. I don’t know and, unfortunately, I’m not quite sure how to find out!
Please help if you think this is an important issue. I tapped my preamp right before the phase inverter input capacitor if that helps.
It is important, but i am no longer in the business of telling the "secrets" which actually are not really secrets but is actual science and the RC filter circuit in the audio world is as basic as it gets. This stuff was taught to me as well! The filters are in each stage of the amp at some point. Normally you would just choose a nice audiophile output cap and use a big one so there is no need to worry about "dialing" in an actual knee. Thus stuff goes right over the majorities headz but pay attention to your filters!

The mating of the twin preamp and the citation have these numbers in there specs or someplace, find them and do the calculations then return with your result which will tell us if there is a knee or not.

And for those smart ones who know what the values are for a Jerry type modified twin preamp's then you can use it with the known Mcintosh input impedance and find the knee, if there is one, that you should try and dial in. You can also do the caluctions with the known stock twin values as well.

~waldo
tntawney liked this
 #164470  by TeeJay
 Mon Jan 28, 2019 7:48 pm
Match your output cap to your power amp impedance to shoot for the 40hz mark. For Jerry tone it shaves off some of that low woofyness.
 #164472  by waldo041
 Mon Jan 28, 2019 8:20 pm
great, now plug in the 10k and the 40hZ Teejay answered for you and that will tell you where your output capacitance should reside in. If not, try and get it there.

~mike
 #164473  by Pointclear
 Mon Jan 28, 2019 8:32 pm
waldo041 wrote:
Mon Jan 28, 2019 8:20 pm
great, now plug in the 10k and the 40hZ Teejay answered for you and that will tell you where your output capacitance should reside in. If not, try and get it there.

~mike
Thanks mike and thanks teejay! I got a uf value of .398. Please excuse my ignorance, so does that mean I add capacitor in that uf range inline to the output jack, like a coupling cap?

I’m trying my best to grasp this, but I am sadly lacking in my electrical background knowledge. I’m still not sure how to find or determine what my output capacitance is right now with just the straight wire leading to the output jack. Thanks again for your guidance.
Last edited by Pointclear on Mon Jan 28, 2019 9:57 pm, edited 1 time in total.
 #164475  by TeeJay
 Mon Jan 28, 2019 9:46 pm
Thanks mike and thanks teejay!


Mike deserves all the thanks. I have just been paying attention in class.
Pointclear liked this
 #164484  by Pointclear
 Tue Jan 29, 2019 12:26 pm
Pointclear wrote:
Mon Jan 28, 2019 7:58 pm
The citation 16 has a 10k ohm input impedance....
..... which I have come to understand is way low compared to a mc2300 (200k ohm).
I’d really like to find someone who knows a ball park twin preamp output impedance.
I’m going to try some output capacitors and report back.
I wonder if it’d be reasonable to put a “pad” pot on my preamp tap.
 #164486  by Pointclear
 Tue Jan 29, 2019 1:15 pm
Geeeeez!!! I just popped in a .47uf 225p orange drop that I had lying around and tested it.
NOW I KNOW! .... it sounds like the snappiest thing I’ve ever heard - very 80’s, very 80’s.
It’s almost too stiff and and snappy for my ears. I’m going to dial down to a .1 and try it next.
I still don’t know about the impedance of the preamp, but what a huge difference that cap made.
Now I know exactly what you weren’t hearing in that clip I posted, mike. :shock:
 #164491  by waldo041
 Tue Jan 29, 2019 3:09 pm
The preamp output impedance is not what we are looking for, only the preamp output capacitance and the power amps input impedance. Those 2 numbers will get you your knee. For Jerry we want it around 40hz give or take, it is a 3 or 6 db step down from there so it is not like it is just cut off, it is a gradual drop but all those low sub harmonic frequencies are gone. that mud is gone.

The preamp is really where all the tone shaping is, the power amplifier should have the power to amplify it cleanly and the speaker to handle that amplification. Each junction from guitar to preamp to amp to speakers each have filters at those junction points. This is just one important one most don't heed the advice given and implement.

plug in a preamp output impedance of .02mfd and the citation 10k input impedance in to that rc calculator. It equals 796.2hz for a High pass knee. The fundamental E frequency is 80hz, and people who just turn knobs and recommend this amp or that do it without doing this simple math to see how to mate them correctly. Want an Ice Picky rig, do just this and add any JBL with aluminum dome and you are guaranteed it.

You should leave that .47 cap in there and work on the deficiencies you now hear in your preamp!

~waldo