SF Dual Showman vs. CBS SF 100W Dual Showman

[trdlasvegas]

Any of you guys know anything about this:

Customer asks me to make his SFDS into a 100W.
The Fender Amp Field Guide says the SFDS is 85W, which I have confirmed it is about 85W into 4 ohms. But if you look at the CBS SFDS, they call it 100W RMS right on the schematic. All the transformers are the same as per the numbers on the schematics.

Where are they coming up with the extra 15 watts???

-Tony

[Tim Swartz]

I think the early one say 80watts. My guess is either they bumped up the voltage a bit (which the schematics do not support), or more likely they just started lying.

[Tremo]

The request to turn an 85 Watt amp into a 100 Watt amp is absurd. I hope you told him that. The difference is only 0.7 dB, you'll never notice the difference. Give it back to him and tell him it's done, and only charge him a 6-pak of beer.

[Paul G.]

1. They're both CBS amps.

2. They both make about 65W at onset of clipping, power ratings for guitar amps are like unicorns.

3. There would be no noticable difference between 85W and 100W in volume or headroom, if those were real numbers.

P.

[trdlasvegas]

I understand all that Paul G., I was just seeing if anyone knew what was the difference between the two amps.

In any case the customer picked it up and said he'll fax me the article where he read about changing the 85W into a 100W. I doubt he'll ever send it.

In any case, at the customer's request I wound up changing the normal channel into a Bassman channel, with a "deep" switch instead of the normal "bright" switch. Hopefully he was happy in the end.

-Tony

[Paul G.]

In the Wild, wild 60s, Chevrolet offered the 427CID V8 in the Corvette in three states of tune--350, 400 and 450 Horsepower.

At a certain point, insurance rules changed, and cars with more than 425 HP became almost uninsurable.

Chevrolet then downgraded the power rating of the Fuel Injected version to 425 Horsepower. They made NO ACTUAL CHANGES in the car, they just changed the rating.

In the '70s, Fender suddenly had competition for its flagship amps from Ampeg, Marshall and HiWatt 100 Watt stacks.

What did Fender do? They called their formerly 85 Watters 100 W amps.

Later the big UL amps were called 135 Watts. Perhaps on Jupiter, but not here.

It's all marketing.

P.

[trdlasvegas]

Paul G.
Thanks for your car anology but thats not true with the 135W Fender amps. These are using totally different transformers and output topologies. Maybe they don't exactly measure 135W, but they are NOT the same as the 85/100W Fenders.
-Tony

[Paul G.]

I understand the differences.

They also make about 65-70 Watts at onset of clipping.

I was referring to the number, not the circuit.

P.

[trdlasvegas]

Originally Posted by Paul G.

I understand the differences.

They also make about 65-70 Watts at onset of clipping.

I was referring to the number, not the circuit.

P.

OK Paul, I'll bite. I don't have one of those to check right now but are you saying it will ONLY do 65-70 Watts into 4 ohms at onset of clipping? I think you must mean into 8 ohms not 4 ohms correct?

-Tony

[jjmantele]

I have a powered subwoofer that says it is 250watts output. Problem is it also says it uses 70watts input. Companies play with wattage ratings all the time. "Peak" watts is the most bogus ratings of all.

[trdlasvegas]

Originally Posted by jjmantele

I have a powered subwoofer that says it is 250watts output. Problem is it also says it uses 70watts input. Companies play with wattage ratings all the time. "Peak" watts is the most bogus ratings of all.

jjman,
Those are two different things. 250W is the output of the subwoofer amplifier. Where as 70W is the AC input consumtion from your AC outlet.

In other words the subwoofer will draw 70W or .583 Amps (Ohms Law I=P/V or .583 = 70Watts/120Volts) from the wall.

The wattage that you typically see written near the AC cord on most amps is AC power not the output power of the amp.
-Tony

[Tremo]

Dude, if the subwoof amp pus out 250 Watts, it has to pull at least that much from the wall, and that would be if the amp was 100% efficient, which it isn't. If it pulls only 70 Watts from the wall, then the power output is probably 50 Watts or less.

[jjmantele]

Originally Posted by trdlasvegas

jjman,
Those are two different things. 250W is the output of the subwoofer amplifier. Where as 70W is the AC input consumtion from your AC outlet.

In other words the subwoofer will draw 70W or .583 Amps (Ohms Law I=P/V or .583 = 70Watts/120Volts) from the wall.

The wattage that you typically see written near the AC cord on most amps is AC power not the output power of the amp.
-Tony

Yes, that's my point. It claims to put out more that it consumes. That's not possible (strictly speaking.) On honest amps the alleged consumption would be more than the alleged power output. Seems that guitar amps are "honest" in this way but home and car audio usually fudge.

[trdlasvegas]

Duh, somtimes I should just shut up. I was trying to show that input power and output power were not the same and completly overlooked the obvious.

You guys are absolutly correct. Conservativly, 65% effeciency is about the best you could expect.
These guys explain it better than me: http://www.crownaudio.com/pdf/amps/138366.pdf

I apoligize for my error.

-Tony