The Canadian Guitar Forum banner
1 - 17 of 17 Posts

·
Registered
Joined
·
5 Posts
Discussion Starter · #1 ·
Greetings!!!

So I've decided to build a new rig and in the process...I remembered that I'm a dummy with ohms. I could use a little help

The amp is a 150w solid state Crate Powerblock. It pushes 150w @8 ohms mono, and 75w @4 ohms stereo.

Cab is 2x12. 200w @16 ohms mono, and 100w @8 ohms stereo.

What I'm wondering is, how to properly match ohms to get the most out of this amp and cab.

Any help would be appreciated.
 

·
Premium Member
Joined
·
18,789 Posts
I was hoping that someone with knowledge/experience would have commented on this by now. I am interested and enjoy learning about electronics.

Don't go by response, but I would choose 150W @8 ohms into 100w @ 8 ohms.
I'm just trying to match impedance...it is an old habit that I can't shake...LOL
 

·
Premium Member
Joined
·
2,641 Posts
the more complicated answer is to this:
Obviously, you mono connection is setup up in series to give the 16 ohms...
If you can rewire just the mono connection to parallel, you'll get 8 ohms mono and keep the 8 ohms Stereo.

The more simple solution is to forget the mono stereo / stuff for the cabinet.
Just wire the 2 speakers in parallel and your get a nice 8 ohm load suitable for most amplifiers.

thats my story and its not "fake news"
G.
 

·
Premium Member
Joined
·
12,980 Posts
the more complicated answer is to this:
Obviously, you mono connection is setup up in series to give the 16 ohms...
If you can rewire just the mono connection to parallel, you'll get 8 ohms mono and keep the 8 ohms Stereo.

The more simple solution is to forget the mono stereo / stuff for the cabinet.
Just wire the 2 speakers in parallel and your get a nice 8 ohm load suitable for most amplifiers.

thats my story and its not "fake news"
G.
No, if you rewire it, you will get 4 ohms mono (2X8 ohm speakers in parallel). This connected to the output (there are no taps on an SS amp, the output devices connect straight to the load) would see the amp driving the 4 ohm load and producing 75 watts.

But those specs seem suspicious to me. Usually power increases as you lower output impedance. For it to get smaller indicates the power supply is weak (edited: read again - 75W X2 @ 4 ohms - stereo output, so power remains the same 150w at 4 or 8 ohms).

Sadly, there is no way to wire two 8 ohm speakers into a single 8 ohm load. It's either going to be 4 or 16, unless you put a dummy 8 ohm resistor in there and piss away half your power as heat. Not to mention it changes the tone of the cab as well.

Bottom line is how loud do you need it. The amp will probably produce 75 watts into 16 ohms as well, and there is no sonic benefit to series or parallel wiring. So I'd start with that - just plug the cab in and see if it's loud enough. If not, try re-wiring for 4 ohms - the amp may put out more than 74w @ 4 ohms. But with those specs, there is no way I would run that amp below 4 ohms. You absolutely CAN NOT hurt an SS amp running into a higher impedance (like 16 ohms). In fact, SS amps love being run into open circuits as they don't have to produce any current at that load.
 

·
Premium Member
Joined
·
9,794 Posts
What he ^ said, usually as you go down in ohms you go up in power. I have a couple of solid state bass amps, that can run 8 or 4. One the power is [email protected] and [email protected], the other is something like [email protected] and [email protected]

Mostly but with exceptions you are safe mismatching ohms with a SS amp. Caveat, most SS bass amps don't like to be run with a 2ohm load, which is a fairly common 3-cabinet load (or 2.67 to be closer to the truth).
 

·
Premium Member
Joined
·
12,980 Posts
What he ^ said, usually as you go down in ohms you go up in power. I have a couple of solid state bass amps, that can run 8 or 4. One the power is [email protected] and [email protected], the other is something like [email protected] and [email protected]

Mostly but with exceptions you are safe mismatching ohms with a SS amp. Caveat, most SS bass amps don't like to be run with a 2ohm load, which is a fairly common 3-cabinet load (or 2.67 to be closer to the truth).
All true, except strictly speaking you can not mismatch an SS amp - no OT. You can load it down more and more until it fails or starts on fire - I suppose you could consider that a mismatch, but I tend to use the term when referring to matching two inductive devices (like old 600 ohm audio gear or an OT to the voicecoil of a speaker).

Think of an SS amp as a constant voltage device. It will try to produce a constant voltage into what ever load you strap onto it. If you give it a 16 ohm load, it will have to produce half the current / half the power of an 8 ohm load (Ohm's Law I=V/R). The more you lower the load impedance, the more current the output devices will try to deliver. Eventually the power supply won't be able to provide enough current to the output devices and power output flattens out. That is happening with this amp at 4 ohms. Some amps have such robust power supplies and output devices that it can work down to 2 or even 1 ohm. But if it isn't spec'd as such, I wouldn't try it.

This was often a problem when bridging power amps. You get four times the power at rated output (P=Vsqared/R; double V and P goes up by 4) but usually the output impedance is spec'd at twice the safe output unbridged. Bridge it and run it at half the output impedance and you are really working the power supply and output transistors, trying to produce 8 times the output power.
 

·
Premium Member
Joined
·
18,789 Posts
Clarification of my previous post. I understand about mismatching impedance in SS amps. I just didn't know which choice (of the ones offered) would be the best for volume and tone/sound. I then revert to "When in doubt, match the impedance".
 

·
Premium Member
Joined
·
1,297 Posts
What seems to be confusing is Crates power rating. This is a stereo amp with bridged capabilities. In a lot of cases a sold state amp will double it's power as impedance is halved (within the spec on the power supply and heatsinking). So I will make an assumption that the 8 ohm rating in stereo is half the 75 watts (37.5 into 8 ohms). As High/Deaf mentioned a bridged amp could in theory quadruple it's power into the same impedance (4x37.5=150), but the minimum load is doubled. That's why the bridged spec has a minimum of 8 and the stereo a minimum of 4 ohms.
What they don't take into account is just how hot an amp is going to get when running full tilt into its minimum load. Being a former Crate service tech, I've seen a number of similar models from them and I would play it safe and run the amp with the two 8 ohms in series for 16 ohms, or leave it stereo and run the 8 ohms. You cannot run this amp into a paralleled 8 ohm mono cabinet (4 ohms). It will overheat and self destruct.
 

·
Registered
Joined
·
5 Posts
Discussion Starter · #10 ·
the more complicated answer is to this:
Obviously, you mono connection is setup up in series to give the 16 ohms...
If you can rewire just the mono connection to parallel, you'll get 8 ohms mono and keep the 8 ohms Stereo.

The more simple solution is to forget the mono stereo / stuff for the cabinet.
Just wire the 2 speakers in parallel and your get a nice 8 ohm load suitable for most amplifiers.

thats my story and its not "fake news"
G.
Yeah I get what you're saying. Rewirering the cab is probably not gonna happen though. I just got it brand-new last week from Carvin...I just can't bring myself to tinker with it. The amp on the other hand I bought used on EBay for cheap. So I'll probably search for a more suitable amp to compliment the cabinet. It's my fault really...I should have done my homework.

Also, the overall "tone quality" of the amp isn't of big importance, I just need something with an effex loop to run my Atomic AmpliFire amp modeler through.
 

·
Registered
Joined
·
5 Posts
Discussion Starter · #11 ·
So with that being said, what should I be looking for (watts and ohms wise) in an amp that will allow the cab to live up to its full potential...volume and tone wise?

Cab is a Carvin 2x12. 200w @16 ohms mono, and 100w @8 ohms stereo. Something small, light and cheap. I won't be going through the front of the amp...just the return for an amp modeler.

Any suggestions?
 

·
Premium Member
Joined
·
12,980 Posts
Have you tried what you already have? Is it not loud enough?

If your amp modeler has stereo outputs, when not just get a stereo power amp with 100w/channel @ 8 ohms. Run the cab in stereo. Bryston 2B's are wonderful.

If not stereo, get a mono 200 watt amp @ 16 ohms (400 watts at 8 ohms). All your tone is generated in the modeler, you just need to amplify it accurately.
 

·
Registered
Joined
·
5 Posts
Discussion Starter · #13 ·
Have you tried what you already have? Is it not loud enough?

If your amp modeler has stereo outputs, when not just get a stereo power amp with 100w/channel @ 8 ohms. Run the cab in stereo. Bryston 2B's are wonderful.

If not stereo, get a mono 200 watt amp @ 16 ohms (400 watts at 8 ohms). All your tone is generated in the modeler, you just need to amplify it accurately.

Yeah I've tried what I have (to a certain degree) just in my apartment. Of course I wasn't able to crank it out of respect for my neighbors, but even at "apartment" volume...I can tell that when I get to a band rehearsal situation that it will lack the punch or "oomph" that I would get from a proper amp/cab ohm match. I dunno...maybe I'm wrong?
 

·
Premium Member
Joined
·
12,980 Posts
You are overthinking it. There is no such thing as an 'ohms match' with SS equipment. You can kill an SS amp with too low of an impedance (ohms) but other than that, there is no such thing as matching impedances or power ratings or anything.

You can not have too much power. No such animal, Dave. Do you buy car with just enough power to go 100km/hr? No, you make sure you have excess power - and then don't abuse it and get a bunch of tickets or crash. Same with audio - it's easy to kill a speaker if you don't pay attention. You can play a speaker too loud and kill it, but there's lots of warning first. And a '100 watt' speaker doesn't blow up at 101 watts or even a second of 150 watts.

Use the amp you have and follow the advice of @dtsaudio . He is technical and he has familiarity with that equipment. If it isn't loud enough, get more power. You can buy huge buckets of SS power for $200 or $300. Get a 400 watt / channel amp and drive the cab in stereo (for a total of 800 watts) or mono (probably around 800 watts if you bridge the amp, 200 if you don't). If your speakers aren't loud enough with that much power, you need more efficient (or more directional) speakers.
 

·
Premium Member
Joined
·
18,789 Posts
You are overthinking it. There is no such thing as an 'ohms match' with SS equipment.
@Gusto My apologies as it is quite likely/possible that my post misinformed, misguided and/or confused you. I must refrain from commenting in these threads as I am not sufficiently educated or experienced.

This specific issue arises quite frequently in many different scenarios. It is always very helpful to have threads like yours (this) as a reference.
 

·
Registered
Joined
·
5 Posts
Discussion Starter · #16 ·
Thanks for all the info guys, I believe I have a far better understanding now. I'm just so damn used to tube amps, it was always just a matter of plugging into a perfectly matched rig. The only SS amp I ever owned was a combo amp I purchased with my very first guitar. And I'm talkin' early 80's here, so yeah...I'm feeling old lol.

I feel especially old now that I'm messing with this amp/cab modeler from Atomic AmpliFire. I'm just on the cusp of feeling buyers remorse for getting this Carvin cab. Wondering if I should have gotten a powered fr/fr to get the true tone of these cabinet sims.
 

·
Premium Member
Joined
·
12,980 Posts
Cool. One bit of progress (I guess) is that solid state equipment is more forgiving (no more 600:600 matching on line level equipment, no more amp to load matching on power amp stuff).

But there's nothing like a hard working tube power stage IMO. You do have to be aware of impedance matching (not to say it has to be perfectly matched, some mismatches can be nice). I have tube amps of various outputs to work with different sized situations, so I can just about always have a hard working power amp. Transistor amps are horrible if you work them too hard (getting into distortion) so the more power, the better in that world.

As far as listening to IR's / cab sims, a pair of hi-fi speakers will give you a respectable idea of what they will sound like at lower volumes (good hi-fi speakers will absolutely annihilate any FRFR out there, if you really want to go down that rabbit hole LOL). A PA speaker or keyboard amp will get you close to a dedicated FRFR, so you may be able to try that side of things without going to heavy into a good FRFR. Depends on what you have available to you without having to buy anything extra.
 
1 - 17 of 17 Posts
Top