Dynacord Powermate questions

[Violinista]

Hi guys!

My band owns a Dynacord Powermate 1000/2. We play on PM for years but we're still ignorant about electronics and the way it works, so I would be really gratefull for some tips and explanations.
Recently our guitar player found some small gig and he wants to connect just one speaker on PM1000 (doesn't want to carry other speaker). I think that's not a good idea but I don't have a real argument since we both don't know anything about how it works - and his argument is - that can work, so why not.

1. Can connecting of just one speaker to PM1000/2 damage the mixer and how? (can't find the explanation on google or dynacord manual since everyone connect even number of speakers.)

2. Other thing that I dont understand - relation between number of speakers and impedance and power - since we usually connect 4 or 6 speakers on powermate (i guess that's called serial connection - from output of 1st speaker to input of 2nd speaker...). How do we calculate the Ohms, output power per speaker (what does it really mean/changes).

I know that for most of you these are amateur questions, but my life would be much easier if I could understand the basics of the equipment that I'm working with... so, thanks in advance for your time in answering this.

[soundguruman]

When you connect one speaker into another, and so on, it's a parallel connection. Not serial.
Two 8 ohm speakers in parallel is 4 ohms. Two 4 ohm speakers in parallel is 2 ohms.

Now look at the powermate...I cannot find the manual for the 1000/2, BUT we can safely assume that the minimum load allowed on each channel is 4 ohms.
And there are two channels, right and left, that will drive 4 ohms each.

And it just so happens that a solid state amp does not have to be loaded, so you can plug speakers into one channel and leave the other channel unused. That's OK.

But now we have to look at your speakers. List each speaker and list how many ohms it is. Is each speaker labeled?
If the impedance is not listed on the speaker, you will need to find out from the manufacturer, or look in the manufacturers manual...

[soundguruman]

When you connect one speaker into another, and so on, it's a parallel connection. Not serial.
Two 8 ohm speakers in parallel is 4 ohms. Two 4 ohm speakers in parallel is 2 ohms.

Now look at the powermate...I cannot find the manual for the 1000/2, BUT we can safely assume that the minimum load allowed on each channel is 4 ohms.
And there are two channels, right and left, that will drive 4 ohms each.

And it just so happens that a solid state amp does not have to be loaded, so you can plug speakers into one channel and leave the other channel unused. That's OK.

But now we have to look at your speakers. List each speaker and list how many ohms it is. Is each speaker labeled?
If the impedance is not listed on the speaker, you will need to find out from the manufacturer, or look in the manufacturers manual...

[Violinista]

1. Thank you for such a fast answer.

2. Speakers are labeled - 15" - 8 Ohms

3. The thing I don't understand -
when I put one speaker on channel - we have resistance of 8 Ohms
when I put two 8 Ohms speakers on that same channel - we have 4 Ohm resistance.

Why is resistance lower when we added more resistors?
Is there some universal formula that I can use to calculate this?

Powermate manual says this
Maximum Midband Output Power, 1 kHz, THD=1%
into 2.66 Ohms 2 x 870 W
into 4 Ohms 2 x 700 W
into 8 Ohms 2 x 430 W

and I understand that - less resistance - greater power... but I dont understand how is resistance smaller when we add an extra resistor?

I apologize if my questions are stupid and if I'm blind for the obvious, but I really dont understand how this works. Thanks again.

[soundguruman]

1. Thank you for such a fast answer.

2. Speakers are labeled - 15" - 8 Ohms

3. The thing I don't understand -
when I put one speaker on channel - we have resistance of 8 Ohms
when I put two 8 Ohms speakers on that same channel - we have 4 Ohm resistance.

Why is resistance lower when we added more resistors?
Is there some universal formula that I can use to calculate this?

Powermate manual says this
Maximum Midband Output Power, 1 kHz, THD=1%
into 2.66 Ohms 2 x 870 W
into 4 Ohms 2 x 700 W
into 8 Ohms 2 x 430 W

and I understand that - less resistance - greater power... but I dont understand how is resistance smaller when we add an extra resistor?

I apologize if my questions are stupid and if I'm blind for the obvious, but I really dont understand how this works. Thanks again.

The first speaker times the second speaker, (RESULT) divided by
the RESULT OF first speaker plus the second speaker......OR

R1 X R2
-------- =
R1 + R2

LOAD 1 X LOAD 2 DIVIDED BY
LOAD 1 + LOAD 2 =

8 OHMS X 8 OHMS = 64, DIVIDED BY
(8 OHMS + 8 OHMS)= 16 OHMS
TWO 8 OHM SPEAKERS IN PARALLEL= 64 DIVIDE BY 16 = 4 OHMS

Now let's suppose you want to add the third speaker to the output.
You have already calculated that two 8 ohm speakers in parallel = 4 ohms
AND NOW you now want to add an additional 4 ohm speaker.....

Your first two speakers are four ohms total, your third speaker is 4 ohms.

R1 X R2 = 4 ohms X 4 ohms = 16, divide by
(R1 + R2 = 4 + 4)= 8
16 divide by 8 = 2 ohms

Two 8 ohm loads in parallel with one 4 ohm = 2 ohms.

BUT the two ohm load may cause the amp to run much hotter, and are you really sure you wanna do that

[soundguruman]

Now do one more example, three 8 ohm speakers in parallel

Just do the first two speakers first

8 X 8
------ = 4 ohms
8 + 8

OR 8 X 8 = 64
8+8 = 16
64 divided by 16 is 4 0hms

Now that you have calculated two 8 ohm speakers in parallel = 4 ohms
take that four ohm result and add the additional 8 ohm speaker...

4 ohms X 8 ohms = 32, divided that by
4 ohms plus 8 ohms = 12
32 divided by 12 = 2.6 ohms

The next step to understand is that the lower the impedance, the more power is in the speaker(s)
If the amp puts 100 watts into 8 ohms
It may put 200 watts into 4 ohms.
Check the manufacturers specification sheet. It will quote the power output into 4 or 8 ohms, usually...

Then if you go down into 2 ohms the output may be 400 watts, are you following this?
BUT at 400 watts the amp may start to get rather hot. Maybe a little too hot to operate constantly. This is why most amps are rated to a 4 ohm load, and not 2 ohm.

[Violinista]

Well ok, that was helpfull!

Since we have six 8 Ohm speakers, with your formula, I get 2,67 Ohms per channel and it fits to the minimum declared on Dynacord manual... and now I understand how to calculate it myself. Thanks Soundguruman!

The other thing that still bothers me - I found at some forums that if channells doesnt have well calculated impedance or unequal impedance - it can hurt the amplifier... why is that (it fits the situation that my guitar player wants to do - 8 Ohms at one channel, no impedance at the other channel). That was my last question I promise )

[soundguruman]

You did it! Bloody good show.
No it usually does not hurt the (transistor) amp to have no load--only unless it's a tube amp.
The tube amp MUST have a load. The transistor amp don't care.
So using one side of the transistor amp is fine.
If it's a stereo tube amp both sides MUST have a load.

Now there have been rare occasions where transistor amps MUST be loaded. But we are not talking about 99% of modern amps. Most modern amps have a self shorting input jack.
In this case, the unused channel volume control is turned down to Zero. At times, it is necessary to short the unused input jack to ground, especially when it's RCA. This is called a shorting plug in hi fi terms, and it is jumped from tip to sleeve on the rca or phone plug. On these particular amplifiers, again rarer, the amp will oscillate if the input jack is not shorted, or if the output is not loaded and the volume is turned up above zero.
The shorting plug (or factory shorting phone input jack) is used to prevent this from happening, in hi fi, but again in prosound too.
The oscillation can overheat the unloaded output section, but keep in mind as above, most well designed amps would not do this...

2.67 ohms is pushing the outskirts of infinity, it's gonna be hot.
The music is not continuous, you see, and that's how they get away with doing it..
the amp is not pushed 100% all the time, and it gets to rest in between music notes.
when the music plays it gets hot, during a rest, it cools off, and that strikes a balance to prevent overheating.
The fans help too.

[soundguruman]

And one more thing...and that's important

ALWAYS use real speaker cables. DO NOT use guitar cables to hook up speakers. Meltdown can occur.
The shielded wire used in guitar cables can upset your amplifier. The two wire cable (lamp cord) is the correct speaker wire.

[Violinista]

Well, this was a valuable lesson for me. Thanks for the tips also (I never tried to connect it with guitar cables, but it's good to know what can happen)!
Thanks a lot Guru!

[Steve Conner]

Soundguruman is right, the only thing that can hurt a transistor amp is a load impedance lower than the stated minimum. It should work fine with one channel disconnected.

At these high powers and low impedances, it is indeed a good idea to use speaker cables made of thick wire and good quality connectors. A short circuit caused by a cheap jack plug falling apart (or a guitar lead melting ) is one way to trash your amp.

[Gtr_tech]

I wouldn't take it below 4 ohms if it were me. Sure the amp's rated for 2 ohms, but sound quality and reliability can take a hit. The amp will run cooler and with less distortion with a 4 ohm load. If you need more speakers, use another amp to drive them via the line outputs on the mixer.

Another note....if this thing is class D...and I'm thinking it is...it closely resembles a similar Behringer product...I'd really keep it at 4 ohms. Its common for the switching pwr supply to get taken out with the output section in the event of pwr amp failure. This adds to the cost of repair.