Bi-amp by MC2505 and MC2205 with C2200

[ken8168]

I am using MC 2505 for tweeters and mid, woofers by MC2205.

According to spec, input sensitivity of MC2505 is 0.5v whereas MC2205 can be 0.75v or 2.5v (by switch). Thus,

I switched MC2205 as 0.75v so that it can match to MC2505.

Now, both amp (MC2505 and MC2205) are adjusted to mid position (12:00 o clock), I found that the bass (by MC2205) is a bit less than tweeters/mid (MC2505). Should I adjust MC2505 to around 11:00 position so that both amp's out are balanced?

Thanks.

 

[cnolanh]

Sure, although it might be better to instead turn up the gain on the MC2205. What speakers are you using? And internal or external crossover?

 

[ken8168]

Sure, although it might be better to instead turn up the gain on the MC2205. What speakers are you using? And internal or external crossover?

Thanks. I tried to gain on MC2205 a bit but I found that the noise become greater if over 12:00 o clock position, thus I adjusted gain control of M2505 to around 11:00 poistion. Is this symptom normal? According to sensitivity of spec, it seems correct, MC2505 is 0.5v whereas MC2205 is 0.75, this means MC2205 expect the input level is a bit higher, this concept is correct?

My speaker is JBL4312A with modified input terminals to separate tweeters/mid and woofer. BTW, I changed the tweeters from 035ti to LE20, 104H3 to LE5-2, 2213H to 123A3. Modify the crossover according to the spec of JBL4310 (tweeters: 3uf, mid: 13.5uf).

 

[Mike Gibson]

Nice setup you have. On my Altecs I run either a 275 or 2125 on the horns and a 2205 on the woofers. I use a SPL meter to get them close and adjust for my taste by ear after that. I have used my 2505 on horns once or twice with good results.

 

[Wadester999]

Nice setup you have. On my Altecs I run either a 275 or 2125 on the horns and a 2205 on the woofers. I use a SPL meter to get them close and adjust for my taste by ear after that. I have used my 2505 on horns once or twice with good results.

Hi Mike, I just picked up a 2205 and am planning to use it along with my MC-60s to biamp my Altec Valencias. Are you using an external crossover? If so, what are you using. If not, how is it done?
Thanks in advance.

 

[62caddy]

I am using MC 2505 for tweeters and mid, woofers by MC2205.

According to spec, input sensitivity of MC2505 is 0.5v whereas MC2205 can be 0.75v or 2.5v (by switch). Thus,

I switched MC2205 as 0.75v so that it can match to MC2505.

Now, both amp (MC2505 and MC2205) are adjusted to mid position (12:00 o clock), I found that the bass (by MC2205) is a bit less than tweeters/mid (MC2505). Should I adjust MC2505 to around 11:00 position so that both amp's out are balanced?

Thanks.

I believe 0.5V sensitivity is with the GAINs set at maximum on the MC2505 and 2.5V is around 12:00. You're going to have to play around a bit to achieve the right tonal balance. The relative physical settings between the two amplifiers should not be taken as an indication that something is wrong. Simply a fact of the differing gain structures between the two units.

 

[whoaru99]

According to sensitivity of spec, it seems correct, MC2505 is 0.5v whereas MC2205 is 0.75, this means MC2205 expect the input level is a bit higher, this concept is correct?

The answer is input sensitivity is not really the underlying point of concern. The factor at play here is gain. If two amps had the same input sensitivity and the same rated output power then one could go by input sensitivity alone. However, in this case, the amps have quite dissimilar output rating so we have to look beyond just input sensitivity and understand the gain, and how that guides for initial settings.

MC2505: input sensitivity = 0.5V, rated output = 50wpc @ 8 ohms = 20V. 0.5V in to get 20V out means gain = 32dB

MC2205: input sensitivity = 0.75, rated output = 200wpc @ 8 ohms = 40V. 0.75V in to get 40V out means gain = 34.5dB

So, in order to get matched output from each amp, the gain of the MC2205 needs to be reduced by about 2.5dB, to equal the gain of the MC2505.

If we set both amps with gain/level controls to max (with 2205 at the 0.75V setting), the equivalent input sensitivity for equal output would be;

MC2505: 0.5V
MC2205: 0.375V

Make sense, or just added confusion?

Since it sounds like you have neither unit set with the gain/level knobs at max, the actual net gain of either one is unknown. So, as some have suggested, balance the sound by ear to your preference, unless you are inclined to make it much more of a technical event than that.

 

[ken8168]

The answer is input sensitivity is not really the underlying point of concern. The factor at play here is gain. If two amps had the same input sensitivity and the same rated output power then one could go by input sensitivity alone. However, in this case, the amps have quite dissimilar output rating so we have to look beyond just input sensitivity and understand the gain, and how that guides for initial settings.

MC2505: input sensitivity = 0.5V, rated output = 50wpc @ 8 ohms = 20V. 0.5V in to get 20V out means gain = 32dB

MC2205: input sensitivity = 0.75, rated output = 200wpc @ 8 ohms = 40V. 0.75V in to get 40V out means gain = 34.5dB

So, in order to get matched output from each amp, the gain of the MC2205 needs to be reduced by about 2.5dB, to equal the gain of the MC2505.

If we set both amps with gain/level controls to max (with 2205 at the 0.75V setting), the equivalent input sensitivity for equal output would be;

MC2505: 0.5V
MC2205: 0.375V

Make sense, or just added confusion?

Thanks for your detail explanation.

However, I found that MC2505 needs to be reduced a bit gain control so that it can be balanced (verified by my ears) with the output of MC2205. What's wrong in my setting?

 

[62caddy]

I had the same experience when trying to match the output from an MC2505 with an MC2125 - the controls on the MC2505 always had to be set lower than the MC2125.

 

[whoaru99]

Thanks for your detail explanation.

However, I found that MC2505 needs to be reduced a bit gain control so that it can be balanced (verified by my ears) with the output of MC2205. What's wrong in my setting?

There are several possible reasons, no particular order -

• You prefer the mid/high output a bit less
• With the gain/level knobs set at arbitrary positions the net gains are a bit of a guess.
• The modifications to the speaker perhaps changed the voltage sensitivity of the mid/high section.
• The specs of the amps aren't actually as they are written.

There might be others but those came off the top of my head.

The only way to know for sure is to measure, but again that's largely an unnecessary technical exercise if you achieved the desired balance by ear. Anyway, even if you measured, and found the actual outputs same or different, would you leave it either way and just accept the sound or would you use what you preferred, regardless of a technical measurement?

 

[Mike Gibson]

Hi Mike, I just picked up a 2205 and am planning to use it along with my MC-60s to biamp my Altec Valencias. Are you using an external crossover? If so, what are you using. If not, how is it done?
Thanks in advance.

I use the ART CX 311 and am happy with it. You can use more expensive crossovers if you like. Such as Marchand offers. I started with a Rane 22 and would still be using it if it had not gone south on me. Both the ART & Rane allow switching crossover frequencies on the fly. The Marchand is a modular setup so for each frequency you want to try you need a module for that specific frequency last I read. I have tried several frequencies with the Vals. From 800-1200Hz. I settled on 1000Hz. I use a SPL meter to set the left/right balance and to get close on output. From there I put on music I'm really familiar with and adjust to suit my taste. If you do end up with an adjustable unit be sure and write down the settings you like so when you switch you can easily come back to where you started from. Good luck and PM me if you have any questions. I'll help if I can.

I'm not endorsing either of these this is just for information only. The choices are many so check them all out.
Here is info for the ART crossover.
http://artproaudio.com/crossovers_processors/product/cx311/

This is for the Marchand unit.
http://www.marchandelec.com/

 

[kevzep]

when the gain is at 12 o'clock and set to 0.75V on a MC2205, it makes the input sensitivity 1.4V.

When balancing a bi-amp situation, you do not necessarily want the bass set the same level as the top end, you need to take into account, the Fetcher Munson curve for human hearing.

Best to use you hearing, and adjust it until it sounds correct, if you do not have enough experience to do this, or want a guide, then use a spectrum analyzer, an app on a smart phone is good enough to set this sort of thing up...

 

[whoaru99]

When balancing a bi-amp situation, you do not necessarily want the bass set the same level as the top end, you need to take into account, the Fetcher Munson curve for human hearing.

It really depends on the type of biamp. If one has a "true biamp" with frequencies split before the amps and no or minimal crossovers (LF blocking caps, for example) in the speaker there is likely more to it than simply matching voltages.

If the biamp system is a biwire/biamp capable speaker with the jumper straps removed, being fed full range signals to each of the inputs, simply by implication of the normally strapped parallel inputs it's expected both sections receive the same voltage input when the straps are removed ( that is, to achieve the same tonal balance).

 

[kevzep]

It really depends on the type of biamp. If one has a "true biamp" with frequencies split before the amps and no or minimal crossovers (LF blocking caps, for example) in the speaker there is likely more to it than simply matching voltages.

If the biamp system is a biwire/biamp capable speaker with the jumper straps removed, being fed full range signals to each of the inputs, simply by implication of the normally strapped parallel inputs it's expected both sections receive the same voltage input when the straps are removed ( that is, to achieve the same tonal balance).

Yes good point!! I forget people are doing that sort of bi-amping... Active all the way in my world.

 

[ken8168]

when the gain is at 12 o'clock and set to 0.75V on a MC2205, it makes the input sensitivity 1.4V.

When balancing a bi-amp situation, you do not necessarily want the bass set the same level as the top end, you need to take into account, the Fetcher Munson curve for human hearing.

Best to use you hearing, and adjust it until it sounds correct, if you do not have enough experience to do this, or want a guide, then use a spectrum analyzer, an app on a smart phone is good enough to set this sort of thing up...

Hi Kevzep,

Good to know using spectrum analyser app can assist me to measure, I will try it.

BTW, I followed your modification guideline on AU999 several months ago, it is fantistic! The bass is incredibly improved.

 

[TSmith8605]

. . . If the biamp system is a biwire/biamp capable speaker with the jumper straps removed, being fed full range signals to each of the inputs, simply by implication of the normally strapped parallel inputs it's expected both sections receive the same voltage input when the straps are removed ( that is, to achieve the same tonal balance).

And I believe OP is set up with this type of bi-amp (as am I) and so the two amps need to be gain matched (per your post #7).

In my system, I do the gain matching by ear. This assumes your speakers are arranged symmetrically such that when a mono signal is on, you hear all the sound coming directly from the center (between speakers) with one stereo mono-amp. This also assumes that your pre-amp is feeding both amps with the same signal level.

With the speakers temporaliy strapped for normal mono-amping, connect the left channel of one amp (say the 2505) to the left speaker and the right channel of the other amp (2205) to the right speaker. Feed both amps the same (mono) signal (any music or voice will do) and start with the gain controls to 12 O'clock. Then adjust the gain on one amp or the other until the image is centered between the speakers. You will likely have to adjust, go get centered between the speakers and listen, go back adjust and go listen again until you get it. Repeat this process with the other channels of the two amplifiers (although the gain controls positions should match L - R in each amp). If your speaker arrangement is symmetrical, you should now have the amps very closely gain matched by ear.

Take a picture of the gain control setting on both amps so you don't forget in case you change something inadvertently or on purpose.

If your speaker set up or ears are not symmetrical, this may not work. It works really well if you point the speakers directly at each other and make sure you're exactly halfway between them. (You can use any pair speakers to get things matched.)

Now wire everything backup for bi-amping and you should get the same tonal balance as with one stereo amp. You can do a final check with everything wired up to insure a mono signal image is still centered.

These matched gain settings are a baseline from which you can, if you want, make minor adjustments to the relative levels to alter the tonal balance. You can always return quickly the matched settings.

 

[jdcarlson]

My solution may be a little more cost, but it will guarantee success.
Get an MEN220. Set theMC2205 for lower registers, and the MC2505 for upper registers.
Call the speaker manufacturer for what the proper crossover should be and what slope for the crossover.
Then, go through the setup procedure with the MEN220 calibrated mic.
I do not think you will be disappointed.
I have two MEN220's (one at home and one at office). For a while at the office, I ran two MC2500's (500 WPC, 1,000 Watts mono) for lower register, and twoMC2255's (250WPC, 500 Watts mono) for the upper register driving a pair of Legacy Signature III's (three 10 inch woofers each channel), and the sound was wonderful!
The surprise was not the increased bass I expected, but "cleaning up" the upper midrange (possibly due to eliminating "booming" from the mid-bass???).
My home speakers are not wired for bi-amping, so the MEN 220 just has to make do with balancing out the "single input" speakers. It still is nothing less than amazing in what it does.
The MEN220 will automatically adjust for different output sensitivities between channels and between different amps driving upper and lower registers. Looking at my signature, one can see I have a fair amount of MC equipment - but the MEN220 is ABSOLUTELY the best investment I have made in improving the system.

 

[SaturationPt]

<<snip>>With the speakers temporaliy strapped for normal mono-amping, connect the left channel of one amp (say the 2505) to the left speaker and the right channel of the other amp (2205) to the right speaker. Feed both amps the same (mono) signal (any music or voice will do) and start with the gain controls to 12 O'clock. Then adjust the gain on one amp or the other until the image is centered between the speakers. You will likely have to adjust, go get centered between the speakers and listen, go back adjust and go listen again until you get it. Repeat this process with the other channels of the two amplifiers (although the gain controls positions should match L - R in each amp). If your speaker arrangement is symmetrical, you should now have the amps very closely gain matched by ear.<<snip>>

I don't believe that you should run the outputs open as this method implies, you should have a speaker connected or a dummy load.

 

[SaturationPt]

My suggestion would be to first spectrum analyze the speakers mono-amped on a single amplifier (L to L speaker full-range, R to R speaker full-range) to see what your response curve looks like with your home-built speaker and crossover arrangement. Next hook all up bi-amped as you want it to be, tune by ear to get the amp gains close, then run your spectrum analysis again to tweak the gains until your response curve matches that of the mono-amped setup.

 

[TSmith8605]

I don't believe that you should run the outputs open as this method implies, you should have a speaker connected or a dummy load.

Amp outputs would only be open for a minute or two during the set up and with no signal needed on the open outputs. Why is that a problem?

As these amps have autoformers, I don't think you would not want to run these amps very long at high power without a load but with no signal for a short duration, I can't see any issues. I've done it a few times with ARC and Mc tube amps.

Edit: running a tube amp at power without a load is not good as power may be dissipated by the output transformers. I assume, but don't know for sure, that the same applies to Mc transistor amps with autoformers. (Running a non-autoformer transistor amp without a load, OTOH, should not be a problem as no current can flow anywhere and so no real power is generated anywhere.)

Given that running open-circuit without a load is a problem for autoformer amplifiers, then the OP's set up itself (but not my gain-matching procedure) has a problem because in the frequency range below the speakers' crossover point the crossover impedance is very high (since the bass part of the speaker has been disconnected) and so the MC2505 will be running essentially open circuit in that frequency range.

The MC2205 will have the same issue, but it will be open circuit in the treble region where less power is used and so is probably OK.

So, the OP might want to put a simple high-pass filter in-between the pre-amp MC2505 to keep the bass frequencies out of the MC2505 at its input.