Help me understand please

[invertigo]

So, rather than looking at large combo amps, I'm looking at considering a head and cab pairing that gives me something I can use at home but also room to grow. Specifically, the TC BQ250 head in this case.

Now, I understand that the 250w power is based on a 4ohm output, and using an 8ohm cab is fine but power is reduced somewhere around 40-50%. My question is, specifically, if I were to need a bit more kick and, lets say, wanted to run both an 8ohm 2x10 and an 8ohm 1x15 off of this, does that work considering it has one speaker output and not 2 like larger heads? Can you use a splitter to break it into 2, or would it require a cab with in and out speaker connectors?

Also, another question. The above head has a dedicated headphone output. If I were to want home silent practice, would the amp still need to be connected to the speakers if the headphone output was in use, or does this effectively disable the power amp stage?

Edited December 5, 2019 by invertigo

[Teebs]

Not an expert, but I'd imagine a splitter from the amp's speaker out to the speakers would work, and make the load 4 Ohms, giving you full power to the speakers.

Not familiar with the amp - if it's Class D it should be fine using headphones and no speaker load.

I'm sure that someone will be along soon who will know for sure.

[Skinnyman]

55 minutes ago, invertigo said:

So, rather than looking at large combo amps, I'm looking at considering a head and cab pairing that gives me something I can use at home but also room to grow. Specifically, the TC BQ250 head in this case.

Now, I understand that the 250w power is based on a 4ohm output, and using an 8ohm cab is fine but power is reduced somewhere around 40-50%. My question is, specifically, if I were to need a bit more kick and, lets say, wanted to run both an 8ohm 2x10 and an 8ohm 1x15 off of this, does that work considering it has one speaker output and not 2 like larger heads? Can you use a splitter to break it into 2, or would it require a cab with in and out speaker connectors?

Also, another question. The above head has a dedicated headphone output. If I were to want home silent practice, would the amp still need to be connected to the speakers if the headphone output was in use, or does this effectively disable the power amp stage?

So long as the splitter is wired in parallel, not series then you'll be fine - two 8ohm speakers connected in parallel will present a 4 ohm load to the amp.

If there aren't two outputs on the amp or two sockets on one of the speakers then you'll need a splitter as you say - just make sure it's wired in parallel.

Edit: i just read your post again and it seems like the 2x10 has two sockets so you can use them quite happily - one in from the amp, one to feed the other cabinet.

Oh, and so long as it's not a valve output (which it isn't) you can run the amp without speakers and just headphones

Edited December 5, 2019 by Skinnyman

[invertigo]

Cheers folks! So for clarity, the comment about cabs having in and out was more hypothetical - I assume a speaker cable splitter would be parallel by default? And if the cab has an in and an out socket it effectively creates a parallel circuit for the second cab?

It is indeed a Class D solid state amp so no tubes to keep happy.

Cheers again, first time delving into the world of separate components and it's a bit daunting at first!

[Teebs]

1 minute ago, invertigo said:

... if the cab has an in and an out socket it effectively creates a parallel circuit for the second cab?

I think that would link the cabs in series, not parallel.

The 'Y' splitter would create a parallel circuit.

[Teebs]

One of these should do it:

https://www.amazon.co.uk/kenable-6-35mm-Socket-Splitter-Adapter/dp/B003OSTW9U/ref=sr_1_20?keywords=jack+y+splitter+mono&qid=1575562523&sr=8-20

 

[jrixn1]

21 minutes ago, Teebs said:

I think that would link the cabs in series, not parallel.

Using the two sockets on the back of a cab will create a parallel circuit.

 

18 minutes ago, Teebs said:

One of these should do it:

https://www.amazon.co.uk/kenable-6-35mm-Socket-Splitter-Adapter/dp/B003OSTW9U/ref=sr_1_20?keywords=jack+y+splitter+mono&qid=1575562523&sr=8-20

You'll want to use something designed specifically for speakers due to the higher currents involved.

[invertigo]

8 minutes ago, jrixn1 said:

Using the two sockets on the back of a cab will create a parallel circuit.

 

You'll want to use something designed specifically for speakers due to the higher currents involved.

Now that makes sense in my head a bit more, I imagine something like this: http://www.pulse-audio.co.uk/product/nl4-split/

Would be a product designed to split speaker outputs to 2 cabs parallel?

 

One final question, lets say you have a head with 300w at 4ohm, and two cabs that are rated 200w 8ohm, is the amp going to end up sending too much power to both cabs or will it be split?

[jrixn1]

10 minutes ago, invertigo said:

Now that makes sense in my head a bit more, I imagine something like this: http://www.pulse-audio.co.uk/product/nl4-split/

Would be a product designed to split speaker outputs to 2 cabs parallel?

Never used one myself but yes it looks like exactly what you need.

 

Quote

One final question, lets say you have a head with 300w at 4ohm, and two cabs that are rated 200w 8ohm, is the amp going to end up sending too much power to both cabs or will it be split?

The power will be split equally; so if 300W was coming out of the amp, each cab will get 150W. 

[Bill Fitzmaurice]

Amps don't send power, they send voltage. If two identical cabs are wired parallel to the amp each will receive the same voltage. Cabs consume power. When two identical cabs are wired parallel each will consume the same amount of power. A 300 watt amp can't provide two cabs with 300 watts each, it can only provide 150 watts to each without exceeding its rating at the given THD of the rating.

[invertigo]

Well, that pretty much sums up all my questions. Thank you all for the very quick responses and detailed answers, I feel like I have some idea of what I'm looking for now.

[BassBunny]

Personally I wouldn't bother with the splitter if the speakers have dual inputs. It's just introducing something you don't need and could go faulty. 

1 lead from Amp to Cab1, then a lead from Cab1 to Cab2.

[pete.young]

24 minutes ago, BassBunny said:

Personally I wouldn't bother with the splitter if the speakers have dual inputs. It's just introducing something you don't need and could go faulty. 

1 lead from Amp to Cab1, then a lead from Cab1 to Cab2.

This. You don't need to buy anything else.

[invertigo]

Cheers all. Ended up going for a bit of a compact rig with the tc electronic BAM200 head and 208 cab, it has dual inputs so nice and easy to expand with another 8ohm cab if required in future.

On a side note, quite impressive the amps these days and how small they can be. Back when I first played before my hiatus just 12 years ago, even small combos seemed to weigh a ton!

Edited December 9, 2019 by invertigo

[lemmywinks]

Let us know how you get on with the BAM200, was looking at that recently but the lack of a Speakon socket put me off. Bax have it for £105 which is nuts, tempting to just pick one up for the sake of it!

[jacko]

One thing no-one's mentioned on this thread is the need to use proper speaker leads, NOT instrument leads. 

[Bill Fitzmaurice]

Making that error impossible is reason enough why only Speakons should be used.

[Dan Dare]

Neutrik makes a jack plug with a fat body for speaker lead use, if you have a head that doesn't have a Speakon socket. I bought a 3 metre speaker lead with them fitted recently so I could use my heads in the event that I encounter a cab that doesn't have Speakons. I cut it in half and attached a Speakon to one end of each of the resultant leads.

Edited December 9, 2019 by Dan Dare

[itu]

On 05/12/2019 at 17:01, invertigo said:

Now, I understand that the 250w power is based on a 4ohm output, and using an 8ohm cab is fine but power is reduced somewhere around 40-50%. My question is, specifically, if I were to need a bit more kick...

Reduced maybe a bit, yes, but the volume difference is not so big, around 1 - 3 dB.

Wattage tells quite a little about the loudness. dB's are the numbers you should be after, but manufacturers tend to babble about watts and watts only.

[invertigo]

Ordered all my bits and cables from Thomann, the speaker cable looks to be about as thick as a rope so I don't imagine it'll be getting mixed up anytime soon. Jack plugs significantly larger than my instrument cables too. Failing that, I'll be wrapping the plugs in a coloured tape anyway to see at a glance, all my instrument cables have a white heatshrink-type plastic round the jack plugs.

[chris_b]

On 05/12/2019 at 15:01, invertigo said:

My question is, specifically, if I were to need a bit more kick and, lets say, wanted to run both an 8ohm 2x10 and an 8ohm 1x15 off of this, does that work considering it has one speaker output and not 2 like larger heads? Can you use a splitter to break it into 2, or would it require a cab with in and out speaker connectors?

Also, another question. The above head has a dedicated headphone output. If I were to want home silent practice, would the amp still need to be connected to the speakers if the headphone output was in use, or does this effectively disable the power amp stage?

If your amp has one output socket just make sure your cab has 2. Most cabs have 2 speakons these days. Then you don't need to worry about splitter cables or when they are running in series or parallel. Just buy a pukka branded cable from a proper shop and it will work.

If you start with a 210 I'd audition another 210 as well as a 115. Depending on what you buy, the 10's could be louder and go lower than the 15. I ran a 115 and 210 and then replaced it with a 112 and 210. The second rig had a better, wider tone, was every bit as loud and was smaller and lighter.

Only valve amps need to be connected to a cab, and these days some of them don't. SS and D class don't need a cab and can be used with headphones only.

[itu]

6 hours ago, chris_b said:

Only valve amps need to be connected to a cab, and these days some of them don't. SS and D class don't need a cab and can be used with headphones only.

This is mostly right, but there are some SS amps that need cab. Rare, but possible.

It is always good to connect the cab first, and then plug and turn the power on. Make a habit of this.

[Chienmortbb]

On 09/12/2019 at 18:53, itu said:

Reduced maybe a bit, yes, but the volume difference is not so big, around 1 - 3 dB.

Wattage tells quite a little about the loudness. dB's are the numbers you should be after, but manufacturers tend to babble about watts and watts only.

If you have two 8 ohm cabinet in parallel to give 4 ohms, the power will be doubled approximately. However the mutual coupling between the two cabinets/drivers will add 3-6dB (depending on which paper/book you read). 
 

So a 6-9dB increase, not to be sniffed at and certainly worthwhile when you consider 10dB is perceived as a  doubling of volume. 

Of course if you just get a 4 ohm Single driver cab, it is a 3dB increase and that is only just about noticeable. 

Edited December 11, 2019 by Chienmortbb
Add detail

[itu]

Yes, my bad, like @Chienmortbb stated, up to around 6 dB more, because of that doubled amount of elements.

[Bill Fitzmaurice]

If you run two identical 8 ohm cabs (or whatever impedance) voltage sensitivity goes up by 6dB compared to one. That's what's responsible for the increase in output, not power. Power goes up because the halved impedance load doubles the current draw, but that's really anecdotal. You don't run two cabs to get more power out of the amp, you run them to take advantage of the sensitivity increase.