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-   -   Insertion Loss with CR1? (https://www.audioaficionado.org/showthread.php?t=41735)

Pampero 01-04-2018 12:36 AM

Insertion Loss with CR1?
 
I recently recalibrated/re-tuned my system and discovered about 4dB of insertion loss between my C52 preamp, CR1 X-over and my MC452 power amp. I'd been vaguely aware of it from the last tuning I did, but in retuning my rig I decided to try and set up the whole system to achieve unity gain. To do that, I used the main/sub balance controls as I couldn't think of another way to make up the gain from the CR1's output.

BTW, I am connected using balanced cables between all the components. Anybody else find this to be the case....that is that they had to do some make up in the crossover to obtain unity gain through their system?

crwilli 01-05-2018 03:27 PM

I just received a CR-1 and am reading the manual.

Have done all the easy things again?

- Recheck connections and all switches on the CR-1?

Pampero 01-07-2018 02:28 PM

Yeah, did that. 4dB makeup gain required input to output. Easy to see because MC gives you meters on the preamp and amp. If you get the same (unity) gain through yours, let me know. I suppose it could be there's an internal trim pot that is miscalibrated or needs to be set for my rig (more a question than statement). There's no obvious place to adjust gain externally so maybe there's some way to trim it inside, but I ain't goin' in there! Maybe I should call them.

crwilli 01-07-2018 02:46 PM

While I know what unity gain is, I am not at all clear how you ‘see’ that you don’t have it.

Can you tell me more about how you are measuring your ‘volts in and volts out’?

Pampero 01-07-2018 04:07 PM

Simple. Don't need a voltmeter if you have VU meters.

so:

If a system is set for unity gain throughput, any place you measure it (from the first meter's reading to the last meter's reading) should be the same. Unity gain examples: 0dBu in 0dBu out or -10 dB in, -10 out, +4 in, +4 out. Insertion loss can be measured in dBu (displayed on the meter) as well as dBv (references voltage). On either scale, the readings need to match for good gain structure.

If I feed a 1K signal into my preamp and set the preamp to output a level of -10dB(u, as I'm taking it off the meter), I should read -10dBu on the power amp's meter if I have my gain structured for unity. That's the result I get when the CR1 is not inserted in the circuit. However, when doing the the same thing with the CR1 inserted, (even before employing the filters) I read about 4dB less at the power amp.

I'm losing 4dB when the crossover is inserted in the system. 4dB insertion loss. Measured as dBu.

dBv, dBu, etc.

crwilli 01-07-2018 04:25 PM

Insertion Loss with CR1?
 
What happens if you set the xovers to 30 and set the sub/sat balance to all sat? Does it ‘recover’? Eg, keep the cr1 inline but have all/most of the signal go to your MC452 and fronts.

I don’t want to screw with my hard-to-find settings or I would try it.

crwilli 01-07-2018 05:45 PM

2 Attachment(s)
Here are pics of my C2300 PreAmp and one MC2301 Amp playing a 1KHz signal.

From this, it appears I am gaining about 4dB...?

Attachment 53416

Attachment 53417

Pampero 01-07-2018 09:20 PM

Quote:

Originally Posted by crwilli (Post 891087)
What happens if you set the xovers to 30 and set the sub/sat balance to all sat? Does it ‘recover’? Eg, keep the cr1 inline but have all/most of the signal go to your MC452 and fronts.

I don’t want to screw with my hard-to-find settings or I would try it.

My setup, that is level matching and phase alignment are done just as you did yours if you tuned phase to the null using Ober's approach. To achieve unity gain (for best S/N, headroom and for everything to clip at the same time) I have to add an apparent 4 dB of gain (as measured by the amp's VU meter). As you'll understand since you have one, I do this via the sub/sat level control. Once I've achieved unity gain, I just go ahead and do the level and phase adjustments the same way you do.

I ended up settling on 110Hz (at least temporarily) as my crossover point as well, although I'm going to experiment some more with that. I've gotten pretty fast at getting it dialed in. It takes more time too reverse polarity and power down the alternate side than it does for me to find the null by setting level and phase so I'm not afraid of playing around. The only real issue is when to run tone (Barry's CD)....my wife hates it! :D.

I was just wondering if anybody else had found this issue or if it's unique to my rig. To be honest, the noise floor hasn't been audibly disturbed by this so as a practical matter it's not a big deal but it has puzzled me as I'd assume the CR1 wouldn't have a noticeable insertion loss (or as in your case, gain). And maybe it shouldn't. It's puzzling.

Pampero 01-07-2018 09:26 PM

Quote:

Originally Posted by crwilli (Post 891112)
Here are pics of my C2300 PreAmp and one MC2301 Amp playing a 1KHz signal.

From this, it appears I am gaining about 4dB...?

Attachment 53416

Attachment 53417

Isn't that strange? :D.

What is going on? Just as odd.....I have to add gain, you'd have to back it down 5dB or so, we're both using Macs that are well matched for gain on their lonesome.

Maybe I'm not crazy after all but I'll call them and see what gives. I suspect they'll say "don't worry: they all do that!" I will report back.

Added...I should mention that to get the actual reading (if you've got the filters set and operating), you'd want to measure at the Xover frequency. It's A LOT easier to just bypass the filters in the crossover though. In theory, gain should be the same on both legs of the crossover at the center frequency. It might be easier to just use broadband noise rather than a sine wave. Set meters to slow if you have the ability, (which the 452 does give me) should you want to measure gain with the filters active. But I think it's easier to bypass the filters for this measurement. Make sense?

crwilli 01-07-2018 09:58 PM

My quick test was done with the CR-1 on and all my settings active.

If I can use the CR-1 bypass button, I will try again tomorrow.


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