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Switchable impedance & voltage

gleneg61

gleneg61

Jan 10, 2008
384
85
Kyoto, Japan
#1
Apologies if this has been answered but I did a search & didn't find anything so here goes my 2 cents.
Q1. Can anyone explain why 99% of makers WON'T allow amps to be 100/120/220/240 volt switchable? Genz Benz auto detects & Eden has a switch & a few other makers do allow it but most don't: WHY? :eyebrow:
Q2. The same question about changeable impedance or ohmage, as on the Fender Bassman, Orange & even Epifani speaker cabs allow it, so why don't most makers?? Would this not cut down on the expense of having to produce different circuits etc? Do tubes V solid state make a difference in this? Please educate me!
 
#2
A1: Switch-mode power supplies are easier to make multi-voltage than a conventional "linear" power supply. It can be done, but it requires power transformer with multiple taps and windings on the primary side. Very do-able, but it costs more, and could also make the amp heavier. Some amps actually can be converted to a different voltage, but a tech has to open up the amp and move a jumper wire.

A2: Yes, tube vs. solid-state makes a big difference here. In general, solid-state power amps don't care too much about impedance as long as the load is not under its designed minimum. For SS, higher ohms means less power transferred and less work for the output transistors.

With a tube amp, there is always an output transformer and matching the impedance between the output trans and the speaker load is needed for the maximum power transfer. If the impedances don't match, then the transformer is forced to absorb some of the amp's power, and that makes it heat up. If the transformer gets hot enough, the insulation melts, shorts out the transformer and probably takes out some of the power tube circuitry as well - resulting in an expensive repair.

Yes, amps can be designed to have switchable output impedance, Marshall guitar amps and many others do. Again, this is done with taps or separate windings on the secondary side of the output transformer. Reasons it's not done are expense - a transformer with multiple windings costs more than an output transformer with a single winding.
 
#3
Some country's electrical codes don't allow it. When I first arrived in Canada I got a job servicing consumer electronics. One of the tasks I was assigned was swapping out power transformers with multi voltage primaries for ones with a single 120V primary That was in '73. My Highwatt DR201 was modified to remove the voltage selector and wired directly to the 120V tap. That one also carries the '73 date. I'm not sure if it has changed today or not.
 
#5
gleneg61 said:
Q2. The same question about changeable impedance or ohmage, as on the Fender Bassman, Orange & even Epifani speaker cabs allow it, so why don't most makers?? Would this not cut down on the expense of having to produce different circuits etc? Do tubes V solid state make a difference in this? Please educate me!
Click to expand...


A little confused by this question.............

Are you talking about AMPS or CABS having switchable impedances ?

If you are talking about CABS, I believe you are confusing ad copy with the cab actually being switchable.

Many cab companies offer their cabs in EITHER an 8 ohm or 4 ohm configuration. The ads/spec pages then tend to read that the cabs impedance is "4 or 8 ohm".

This just means it is available as either/or NOT both.

There are some companies that offer an impedance switchable cab, but they are specially loaded with speakers that have dual voice coils, and there are very few offering this at the current time.
 
#6
gleneg61 said:
Apologies if this has been answered but I did a search & didn't find anything so here goes my 2 cents.
Q1. Can anyone explain why 99% of makers WON'T allow amps to be 100/120/220/240 volt switchable? Genz Benz auto detects & Eden has a switch & a few other makers do allow it but most don't: WHY? :eyebrow:
Q2. The same question about changeable impedance or ohmage, as on the Fender Bassman, Orange & even Epifani speaker cabs allow it, so why don't most makers?? Would this not cut down on the expense of having to produce different circuits etc? Do tubes V solid state make a difference in this? Please educate me!
Click to expand...

For Q1, my guess is that it is an option that a VERY few customers care about. I've been playing at a reasonably high level for the last 30 years, and have only played in other countries a few times, and ALWAYS had backline provided. So, even though this option would be very handy for a small group of players (I would guess a very small group of players), it probably isn't worth the cost and weight for many manufacturers to bother with.

For Q2, kind of similar. The only way to really have switchable impedance on cabs is through dual voice coils, which are expensive, and with multiple speaker cabs, can do strange things to the efficiency of the cabs. With the large number of amps that now can run all the way down to 2ohms, the ability to switch impedance on cabs is, again, a relatively useless option for most, and it doesn't work particularly well anyway from what I've read (and based on the Bass Player review of the Epi DIST cabs).

So, combine expense, weight and (IMO) very niche group of players who are even interested, and it is pretty clear that most amp makers (and cab makers) can spend their money better on other features.

IMO!
 
#7
Let me answer the switchable voltage feature...

Having a switchable voltage feature costs more, and the amp must conform to the most stringent safety standards throughout. So, for a product where "cost is everything", saving a "few pennies" is paramount a single voltage power supply is a "good" choice for a customer base that generally does not need it.

On the other hand, on a product that is targeted towards a more professional player, especially one who tours internationally and wants to travel with their own electronics at least, switched or selectable voltage (AND 50/60Hz compatability) may be of major importance. There are a lot of folks touring internationally with our products, I spend a fair amount of time supporting them out on tour, and for these players, being able to carry a Shuttle or Streamliner over their shoulder into a gig is a very big deal. To them, spending a few pennies more is completely insignificant, they are using these products as tools to do their job as well as they can and their performance is a reflection on themselves. I would imagine that the same basic argument would hold true with most manufacturers.

So it depends on what YOUR particular needs are... is cost the most important thing or do specific performance and operational features drive your ship.

Regarding the impedance question, I'm not sure if the OP was talking about amps or speakers.
 
#9
BassmanPaul said:
Switchable impedance cabinets, IMO, is an answer searching for a problem.
Click to expand...
i could totally see it on a 2x10 cab that was made to match up with a specific 4x10 to make an evenly-powered 6x10 stack.

the 2x10 could switch between 8Ω for solo use or 16Ω to sit on top of a matching 8Ω 4x10.

yes, you could just load it with regular 8Ω speakers and wire it to switch between series and parallel, but a 4Ω 2x10 might be in too much danger of getting overpowered by less-informed players.
 

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