Can I convert Acoustic B200 ext jack from series to parallel?

GatorDogDoc · #1 12-10-2010, 12:11 AM

I have an Acoustic B200 combo amp. It has a 1x15 speaker with an additional (switchable) tweeter horn, pre-amp effects loop jacks (wired PARALLEL), and an external speaker jack (wired SERIES).

I wanted to plug in another cab (Acoustic B410), but want to run it PARALLEL to avoid the significant wattage drop (calculated a drop from 200 to ~67 watts!) from a series jack (why did they do that?!)

Does anyone know how difficult (or even possible) it is to CONVERT THE SERIES JACK TO A PARALLEL JACK?

I'm not an electical engineer, but handy with wiring (did my home room addition) and a soldering iron (guitar pickups) but have never soldered a board... heck, not even sure this needs a change to the board! Actually, hoping I could just patch in/change over some wires.

I haven't dismantled the amp head yet and would rather not if there is no chance to do what I want. I'm including some specs and part of the wiring diagram.

Any opinions or insight would be greatly appreciated!

B200 head: 200 watts at 4 ohms
internal 15" speaker: 4 ohms (250 watt rating)
B410 cab: 8 ohms (400 watt rating)

Partial wiring diagram:

SurferJoe46 · #2 12-10-2010, 12:15 AM

I don't see any reason why not - I'll look at that again, but it appears do-able to me off the top.

PS: I kinda recognize that drawing too - no problem!

GatorDogDoc · #3 12-10-2010, 12:21 AM

Quote:

Originally Posted by SurferJoe46

I don't see any reason why not - I'll look at that again, but it appears do-able to me off the top.

PS: I kinda recognize that drawing too - no problem!

Saw 1 of your previous posts regarding a salvaged B600H and some rewiring of a cab.... I was thinking this should be a lot easier since I'm not trying to do anything funny with the tweeter switch (like that post).

I've just never messed with the inside of an amp and have NO IDEA what to expect in there!

I was picturing some sort of "jumper" wires. I have an idea of what may be necessary, but not absolutely certain what to move to where, what to disconnect, what gauge/type of wire to use, etc.

I'm going to grab some shut-eye now, but I'll eagerly await your (and anyone elses) response.

fenderhutz · #4 12-10-2010, 12:22 AM

If you change it then you can't run another cab I believe. Internal speaker is 4ohm. Adding another cab would make the ohm load either 2.67 ohms with an 8ohm cab or 2 ohms with a 4 ohm cab.

The answer is no unless you replace the stock speaker with an 8 ohm one. That's why it's wired in series, internal speaker is already 4 ohm.

T-Bird · #5 12-10-2010, 12:29 AM

Hi.

Since the block diagram (or a schematic for that matter) doesn't show the physical construction of the jack or its connection, it's hard to tell whether it's easy, or demanding job.

If the jack is not PCB mounted, it's as easy as wiring the jack parallel to the speaker terminals, ie. T to + terminal and S to - terminal. Why the block diagram shows a short is beyond me, but as anyone who understands the connection, understands it's just a mistake on the drawers part.

There's usually a reason for series connection though so be careful and do label the output accordingly if there's even the slightest chance of misuse.

Regards
Sam

GatorDogDoc · #6 12-10-2010, 12:32 AM

Quote:

Originally Posted by T-Bird

Hi.

Since the block diagram (or a schematic for that matter) doesn't show the physical construction of the jack or its connection, it's hard to tell whether it's easy, or demanding job.

If the jack is not PCB mounted, it's as easy as wiring the jack parallel to the speaker terminals, ie. T to + terminal and S to - terminal. Why the block diagram shows a short is beyond me, but as anyone who understands the connection, understands it's just a mistake on the drawers part.

There's usually a reason for series connection though so be careful and do label the output accordingly if there's even the slightest chance of misuse.

Regards
Sam

Tbird,
Is this what you mean (basically)?

wshines1892 · #7 12-10-2010, 12:34 AM

They did it so you'd have a reason to buy the B200h!

GatorDogDoc · #8 12-10-2010, 12:35 AM

Quote:

Originally Posted by fenderhutz

If you change it then you can't run another cab I believe. Internal speaker is 4ohm. Adding another cab would make the ohm load either 2.67 ohms with an 8ohm cab or 2 ohms with a 4 ohm cab.

The answer is no unless you replace the stock speaker with an 8 ohm one. That's why it's wired in series, internal speaker is already 4 ohm.

Is there a way to check the speaker for its true ohm rating? Is it stamped on it?

I ask because in the Acoustic B115 cab, they list the (supposedly) same speaker as 8 ohms impedance, which would solve my problem.

SurferJoe46 · #9 12-10-2010, 12:42 AM

Seriously there's some good advice there - since you either have to get an 8Ω speaker in there or disable it when you run an extension cab.

Physically, converting to parallel is a snap - it's the Ohms that go goofy if you do trying to use the OE driver in the cab.

JimmyM · #10 12-10-2010, 12:45 AM

it's two different speakers in the combo and the standalone cab. the one in your combo is 4 ohms. so you can't do your mod unless you get an 8 ohm speaker. they do that to put the full power of the head into the speaker but it greatly cuts down on expandability. it's really not worth it, imho. you're better off selling it and getting something else than plopping a lot of money into making it what you want.

SurferJoe46 · #11 12-10-2010, 12:45 AM

You can use an Ohm meter to get a rough idea of the capacity - but it's not 100% accurate without using some lab equipment to get the right values.

If you see 6-10 Ω on the meter, you are pretty close.

GatorDogDoc · #12 12-10-2010, 12:48 AM

Hmmmm..... seems the plot gets even thicker.

The manual lists the B200 as 2 ohm min amp!
If that's true, then the ohm droppage wouldn't be an issue... right?

Here's what it shows:

PRODUCT SPECIFICATIONS
MODEL:
B200: 200 Watts @ 2 Ohms
B200H: 200 Watts @ 2 Ohms
B600H: 200 Watts @ 2 Ohms

This conflicts with what is listed on the website page!

Can anyone out there confirm this?

SurferJoe46 · #13 12-10-2010, 01:13 AM

I've only ever seen the 4Ω rating on that 200 amp series. This would be a new understanding to me too.

One thing that won't help is trying to call the people (maybe that's what they call themselves) at Acoustic. There is supposed to be no phone number and they deny that I ever called them - but I did once and got put on eternal hold.

I think that number was just a shipping warehouse anyway. You can try to send them an e-mail, and I did get a reply once - but it was to tell me that I never called them.

Go figger. As it is, I have not found any place to ask questions or get an answer to this or any other mystery.

They don't even know that you need a special stomp with two buttons and some special design to make the NOTCH and the STANDBY work remotely. They don't even list a pedal, let alone an idea for the right one anyway.

I had to learn that myself in case anyone needs to know.

Let me scan and send what I have in the same book:::

BRB

Got it!

It sure wouldn't look good in court I think.

Wait a minute - I got something else here :::

So it says one thing on the top of the page, and something else in each separate section.

GK guy 94 · #14 12-10-2010, 01:22 AM

ive read alot about that manuel being a typo. b200 = 200 @ 4 ohms im pretty sure.

T-Bird · #15 12-10-2010, 01:30 AM

Hi.

Quote:

Originally Posted by GatorDogDoc

Tbird,
Is this what you mean (basically)?

Yes, but You also have to disconnect the switch(es) connections so the output won't be shorted when there's no extension speaker connected.

BTW, I wouldn't trust the amp to be able to handle 2 Ohm load safely, so the suggestion about swapping the original speaker to a suitable 8Ohm one would be highly recommended. Or the suggestion about swapping the entire combo to something expandable.

Edit:After seeing SurferJoe46's scanned manual, one thing seems pretty certain. You have to look inside to determine whether the speaker out is in parallell or in series. And I still wouldn't trust the 2Ohm statement.
Isn't it great when RTFM only adds to the confusion?

Regards
Sam

GatorDogDoc · #16 12-10-2010, 11:13 AM

Quote:

Originally Posted by SurferJoe46

One thing that won't help is trying to call the people (maybe that's what they call themselves) at Acoustic. There is supposed to be no phone number and they deny that I ever called them - but I did once and got put on eternal hold.

I think that number was just a shipping warehouse anyway. You can try to send them an e-mail, and I did get a reply once - but it was to tell me that I never called them.

Go figger. As it is, I have not found any place to ask questions or get an answer to this or any other mystery.

That was my experience, as well. I emailed them about the series vs. parallel jack discrepancy (manual says parallel, diagram says series). It took 2 months to get a one-word reply.... "Series"---not sure if I trust them, though.

You are right about the phone number... How are they able to hide their phone numbers so well on the internet? There's not a phone number I can track down ANYWHERE!

Maybe the info in the manual is old?...that is, that is how they USED to make them? It would make sense that it is a 2 ohm minimum load amp IF the external jack is parallel and requires a 4 ohm minimum speaker (all as stated in the manual)... that, combined with the 4 ohm onboard speaker would give you the 2 ohms minimum (I think I'm right on this). But that may be outdated info....

2 questions:
1) Seems it would it be pretty easy to determine if the jack is wired parallel or series from what we've discussed... if I open up the head and take a pic of it tonight or tomorrow and post it, would you guys toss in your 2 cents?

2) Is there any way to test the minimal ohm rating of the amp itself using a multi-meter?

SurferJoe46 · #17 12-10-2010, 11:28 AM

Testing for minimum ability is rife with formulas and lab gear I think.

Somehow I have it in mind that you really need to perform THE NASA/US
GOVERNMENT SMOKE TEST and record when/where the smoke gets the
thickest and then you take 60% of that highest value you got as the
MAXIMUM ALLOWABLE LOAD.

I think it's called: 'Destructive Testing', not to be confused with 'Wishful
Thinking' or 'Creative Evaluation' by the electrical ~~engineers~~
er, guesstimators

swspiers · #18 12-10-2010, 11:40 AM

Quote:

Originally Posted by JimmyM

it's two different speakers in the combo and the standalone cab. the one in your combo is 4 ohms. so you can't do your mod unless you get an 8 ohm speaker. they do that to put the full power of the head into the speaker but it greatly cuts down on expandability. it's really not worth it, imho. you're better off selling it and getting something else than plopping a lot of money into making it what you want.

Absolutely correct! That's the situation I'm in. It's a great combo, especially for the price, but there comes a point where it just won't work. Like if you need volume...

I highly recommend it for a beginning or a practice rig. Not so much with a real band. And not really worth trying to work-around, IMHO

(I see a Crown XLS and an Acme Low B2 in my future)

GatorDogDoc · #19 12-10-2010, 11:43 AM

Quote:

Originally Posted by SurferJoe46

Somehow I have it in mind that you really need to perform THE NASA/US
GOVERNMENT SMOKE TEST and record when/where the smoke gets the
thickest and then you take 60% of that highest value you got as the
MAXIMUM ALLOWABLE LOAD.

+1

I'll see what I can do about getting a pic posted.
Now it is about the challenge... and if I can help some poor schmuck down the road with the same question, good for him!

JustOpenYourMind · #20 12-10-2010, 11:48 AM

Don't do this, you'll potentially fry your amplifier...

I'm pretty sure the manual saying 200W@2ohms is a typo or very dishonest marketing on accoustic's part.

If it was true the B200 with the internal speaker would be a 100W combo marketed as a 200W head.

Running an amplifier down to two ohms requires very good heat dissipation and quality components which I highly doubt are present in a budget combo.

Also, If the amps was truly 2 ohm capable why would they design the output jack in series? I'm pretty sure they did it that way so they could design an amp with the cheapest part possible that would sound the loudest with the internal speaker, otherwise they would have needed to design a 400W amp which would have been more expensive.

Bottom line:

I'm pretty sure the B200 was designed that way to save on parts and cost, not to prevent it's user to use it's ''full hidden potential'' that is just a simple mod away.

Also to make things better go read up on the effect of doubling the wattage on an amplifier, (I'm pretty sure there is a sticky on this).

There isn't a significant difference in output between a 100W amp and a 200W amp. Doubling your speaker area will however make your amp louder, even if its wattage is halved.

If you do the mod, you'll likely ruin your combo for very little results.