Selecting an Amplifier for my Solid state modulator

[ke7trp]

The project is comming along nicely.  Time to buy a solid state amplifier.


This amp will run 4 ohms mono in bridged mod. It will modulate Two 4-400s.  I am going to build for max power potential and then back it down.

The trouble seems to be in the RMS vs Peak power ratings of such amplifiers.  In the Radio world... We speak in RMS watts for modulator power.  In the Pro sound world, They use both peak and RMS.  Although the figures they give do not jive.

For example.. I have determined that I would like to have at least 500 watts RMS of modulator power. This should be enough to supply the 4-400s with 100% at max output.

Brand P of amplifier states 1200 watts Mono 4 ohms.  In the manual it states 365 RMS.  Ok. Thats close.. Its clear this amp is not going to be enough.

Other brands will state 2000 watts output into 4 ohms..  Must be peak rating?   Then they list 2400 watts RMS.  How can 2400 watts RMS work out to 4000 peak?

Anyone with any experience running solid state modulators have an idea on an output power I should shoot for?

[Steve - WB3HUZ]

I modulated a Viking II with a 100 watt amp (QSC, IIRC). I would imagine a legit 500 watt amp would do the trick for you.

[ke7trp]

a 500 watt peak amp steve?  Thats easy.. I have three in the other room.  Including a Nice small Carver Cube amp thats rated at 550 bridged. It could sit on the edge of the table and take up almost no room.

A pair of 810s in the current modulator is around 500 watts.. am I wrong to think this is 500 watts RMS? or is this peak also..

If this is true, Thats great news for me.. Since no cash outlay.  I need to be set straight on the Audio power ratings.

Thanks

Clark

[Steve - WB3HUZ]

The amp I used was a pro audio/sound reinforcement grade amp, so it was rated at 100 watts average, not peak. I would try the amp you have. If the modulation is PW, go get a bigger amp. If not, buy some beer with the money you saved. It could amount to a lot of beer!

[KD6VXI]

The project is comming along nicely.  Time to buy a solid state amplifier.


This amp will run 4 ohms mono in bridged mod. It will modulate Two 4-400s.  I am going to build for max power potential and then back it down.

The trouble seems to be in the RMS vs Peak power ratings of such amplifiers.  In the Radio world... We speak in RMS watts for modulator power.  In the Pro sound world, They use both peak and RMS.  Although the figures they give do not jive.

For example.. I have determined that I would like to have at least 500 watts RMS of modulator power. This should be enough to supply the 4-400s with 100% at max output.

Brand P of amplifier states 1200 watts Mono 4 ohms.  In the manual it states 365 RMS.  Ok. Thats close.. Its clear this amp is not going to be enough.

Other brands will state 2000 watts output into 4 ohms..  Must be peak rating?   Then they list 2400 watts RMS.  How can 2400 watts RMS work out to 4000 peak?

Anyone with any experience running solid state modulators have an idea on an output power I should shoot for?

You also have P.M.P.O., which stand for peak music power output.

What you need to concern yourself with is a quality amplifier.  A quality amp will state the RMS rating into 2, 4 or 8 ohms.  Anything else is junk!

A P.M.P.O output amplifier rating will be more like 16-64 times the actual RMS value into 8 ohms.

The other thing to look at is the fuse rating.  If it isn't 1.5 times the RMS rating of the amp (in relation to input vs output power), then its full of sh1t.

Been there, done that.  Certified mobile autosound installer... And one of the guys that saw the EQ / Power Amp combos and bitched that it said it could do 450 watts PMPO in the physical size of 1/2 DIN (car stereo standard size) and all of 6 inches long!

Said amplifier also had a 5A fuse in it.  It never blew, even at 450 watts P.M.P.O.!!!!

--Shane

[KD6VXI]

a 500 watt peak amp steve?  Thats easy.. I have three in the other room.  Including a Nice small Carver Cube amp thats rated at 550 bridged. It could sit on the edge of the table and take up almost no room.

A pair of 810s in the current modulator is around 500 watts.. am I wrong to think this is 500 watts RMS? or is this peak also..

If this is true, Thats great news for me.. Since no cash outlay.  I need to be set straight on the Audio power ratings.

Thanks

Clark

Clark,

BE CAREFUL WITH THE BOB CARVER AMPLIFIERS!!!!! Some of them are known to have no isolation / input (ac) trannies!


As to your ? in email, I am off the road.  If they find a trailer, I can pull it, though, and have done so for MANY people moving like they are.  I'd need about 2 weeks notice.

They going to Lufkin area, or ??

--Shane

[ke7trp]

Ok..  I have all kinds of audio gear.  I will try something I have here.. Before buying anything.

The goal is to get the Rig up and running as an amp in the next week. Once I know the 4-400s run with Bias on them as amp, I will know more about what modulator power I will need.

I have a mackie and some carver amps.  The Small cube amp does alot of power for its size. Otherwise, Its down to the local guitar center for a nice Prograde Live sound type amp. I am going to use the Ultra modulation unit and want enough modulator to go 150 pos if I feel the need.

Shane, They dont have a trailer.. But they are selling the house in Norcal and moving to Kilgore area in Texas on 15 acres. If you figure something out, Let me know. I am sure they would be down for it. Its real expensive to hire movers. Maybe a trailer can be rented?
Clark

[Gito]

Hi Clark

Choosing an Amplifier for modulator,first don't forget the looses power in the Modulator Transformer.There's always looses there and depended on the quality of the M.transformer
Choose an Amplifier at least with power capability  as the power input of Your Transmitter ,So You can modulate it easily  for 100 % modulation.
The Mod amplifier runs " cooler" since,maybe it only use  60 % of its capability ,and I'm sure the sound quality must be good.

I think its a bad idea using An amplifier with full power all the time if the power  of it is just enough to modulate it 100%. 

Especially You want to used the ultramodulation .to modulate Your Transmitter? 

Good Luck

Gito

[W2VW]

My Crest 4001 had no problem modulating a single class C 3-500Z at 1KWDC in using a T368 plate transformer as mod iron with 1/2 secondary connected. That amp was rated at 1400 watts RMS bridged. The final was shunt feed.
I even talked to the Huzman with it.

[N4LTA]

I know that some of the 2000 watt rated output  amps run on 120 volts AC with a standard 20 amp plug. The NEC rates the max for a 20 amp circuit at 1920 VA - so even at 100% efficiency - if isn't possible to output 2000 watts..

[ke7trp]

Yeah.. Alot of marketing BS with these amps.. 4000 watts output out of a 15 amp line.. LOL.   Show me how

At 1 KW carrier, I will need 500 watts to modulate to 100%.   Toss in the transmforer losses,  Then double it so I can go to 150 with the ultra modulation unit. I better look for a 1500 to 2000 watt amp.  Now to find an amp with "real" watts.

Clark

[W1AEX]

Something like a Peavey CS-800 would give you plenty of audio power. It's rated at 800W RMS when both channels are bridged together. They are pretty much indestructible, extremely stable, and if necessary, very easy to repair. They show up used on e-pay now and then for anywhere from 150 bucks and up. I have seen a few in the local pawn shop over the past year. Bands understandably seem to like the much lighter digital amps now as the CS series weigh in at around 50 pounds. The CS-400 will do 400W RMS in bridged mode. I have used the Peavey M-2600, a smaller rack unit (130 watts RMS/channel) in the living room sound system for the past 25 years and it refuses to quit. Their DDT system, when toggled on, will engage compression just before clipping occurs. They're nice looking rack mount units as well.

Peavey has archived the CS-800 manual at:

http://www.peavey.com/support/searchmanuals/archived.cfm?page=C
 

[KD6VXI]

Yeah.. Alot of marketing BS with these amps.. 4000 watts output out of a 15 amp line.. LOL.   Show me how

At 1 KW carrier, I will need 500 watts to modulate to 100%.   Toss in the transmforer losses,  Then double it so I can go to 150 with the ultra modulation unit. I better look for a 1500 to 2000 watt amp.  Now to find an amp with "real" watts.

Clark

If you have the power supply to handle it, a car audio amp would be able the best way to go.

Rockford and PPI DON'T mess with power ratings, IASCA standardized them in the mid 90s.  Unless you decide on a "Pyramid" hahahaha amp, you'll get what you want.  BUT, that's a BIG supply to power a couple thousand watts with.

A nice PA type amplifier would work well. You can also look at Crown and other musician type amps.  I mean, your looking for a LOT more power than most people even think of for the casa... 

--Shane

[ke7trp]

Peavy.. 800.. I had a DJ business when I was in highschool. I had a 800 in the back of my truck. THe tailgate popped down in a corner and the 800 Flew out the truck and down the road. I did not realize this until we arrived at the Gig. We went back and found the amp on the side of the road all scraped up.. LOL.  It was night and nobody saw it laying there. The entire top of the amp was skinned down to the metal.  We plugged it in and the damn thing worked.

I will walk through a few pawn shops in the next couple days. Thats a great idea.

No Car stereo amps for me.. I want this rack mounted in the cabinet.  Simple and self contained.
Clark

[KD6VXI]

Peavy.. 800.. I had a DJ business when I was in highschool. I had a 800 in the back of my truck. THe tailgate popped down in a corner and the 800 Flew out the truck and down the road. I did not realize this until we arrived at the Gig. We went back and found the amp on the side of the road all scraped up.. LOL.  It was night and nobody saw it laying there. The entire top of the amp was skinned down to the metal.  We plugged it in and the damn thing worked.

I will walk through a few pawn shops in the next couple days. Thats a great idea.

No Car stereo amps for me.. I want this rack mounted in the cabinet.  Simple and self contained.
Clark

If you want it in the rack, you need a concert or a PA amp.

ALSO, MCM Electronics has a few decent amps and other associated equipment.  Not AudioPHOOL stuff, but decent solid state amps at decent prices.  Again, stay away from the Pyramid stuff.

I ALWAYS liked Crown.  You might be able to pick up a decent amp at a musicians store, too, since the economy is crap.... Lots of musicians are starting to sell off stuff both in the paper and at "Musicians Superstore" here... Good deals to be had by all!  I've seen VERY few crap Crown amps, and these I believe where offshore clones.  The rest of it was ALL underrated, usually by 10 to 30 or more percent!  And crown makes BIG amps, in the multi kilowatt range, for driving HUGE stacks in concert environments!

--Shane

[KC4VWU]

    Hey, maybe I could use my Peavey Ultra 112 as an outboard modulator! It's rated for 65w RMS with a pair of 5881's. Should work with the VII, right? That is a plus also, 'cause when the freq gets quiet, I could jack the Les Paul into the 2nd channel and play a little Judas Priest or Iron Maiden for a musical interlude!
....... Just kidding!!!
Phil -- KC4VWU

[ke7trp]

Oh yeah..  I got a VOX jaguar. My brother is a guitarist.  Maybe we can mix in some garage band sounds with the normal QSO on 75 meters.. LOL


Clark

[WBear2GCR]

Ok, here's how the power ratings on the pro amps work.

the nominal rating is at 8 ohms.
most pro amps will double the power into 4 ohms (slightly less actually) and are rated into 2 ohms.

The voltage maximum that is supplied to a load is invariant. what changes is the current that the load can draw - and if the PS is large enough and there are enough transistors then it will supply it.

So, a 400watt amp will do 800 into 4 ohms and 1600 into 2 ohms.
The limitation on the last number is clearly the duty cycle and the draw from the line - some of these amps can be wired for 240 vac mains.

The other thing to be aware of is the stability of the amp into reactive loads, some are better than others. The mod iron is a very inductively reactive load.

Amps that I think are worthy of consideration include the Crown Macrotech series, many of the QSC line, and Crest. All of these amps are used by pro sound companies - or were before the advent of lighter amps that use switching technologies. Personally I'd avoid consumer grade "pro" stuff - that includes Peavey imho.

In bridged mode there becomes a low Z limitation because the voltage swing is doubled and usually there is not enough PS or output devices to supply a 2 ohm load, so they are usually rated at a 4 ohm limit... of course that is for high duty cycle application, so for modulator use with a low duty cycle you can likely get away with lower Z as long as you don't run any sinewaves at 100% modulation through it...

I just picked up three QSC amps from a local pro sound house, blown of course, but serviceable. They are a 1700 and a pair of USA 1300, same amp but the 1700 used Japanese output transistors, the "USA" version has Motorola devices instead. If you go to the QSC site you can see the schematic for these amps - simple and powerful. Each amp is rated at 375w into 8 ohms, double into 4 and bridgable with a switch on the  back... they weigh about 78lbs, iirc and there is one big power transformer in it along with either 20 or 24 output transistors. If you bother to look at the schematic, look very carefully at where the connection for the speaker is, and what the output transistors are connected to...!!! Not the usual.

http://www.qscaudio.com/support/technical_support/schems1.htm

Some of the QSC stuff went to the equivalent of a Class H modulator, they have rail switching to reach the higher power levels. I'm not a big fan of this in power amps but it does work... the ones I mentioned are standard in that they don't do that trick.

The Crown does another trick, that is worth reading about, they have the output stage in a floating bridge with the power supply... they get a ton of power out of a smaller package than the QSC, and a super high DF as well - if you care about DF.

                   _-_-bear 

[ke7trp]

Thanks bear. I think its going to be a crown for me. I am searching now.  I see the meth heads are selling this type of gear on Graigslist real cheap out in the east valley. 

I will look through the schematics.


Clark

[KD6VXI]

Thanks bear. I think its going to be a crown for me. I am searching now.  I see the meth heads are selling this type of gear on Graigslist real cheap out in the east valley. 

I will look through the schematics.


Clark

Clark,

As I said earlier, a Crown is great.

I've also had good luck with Sampson, it's a newer line, but man, they REALLY crank out some numbers.  No, it's not audiophool quality, but more concert series (like Crown).  Like Crown, they are also Class H.

Cheap, though, as I get them wholesale.

the SX2800, rated to 900 watts PER channel, RMS, into an 4 ohm load.  Will bridge at 2800 watts, 4 ohms, and 1800 at 8 ohms.

They ALSO have a multitude of inputs, since you have the XLR type, this amp has it as well.  It has XLR and TRS balanced input.

This is a 2U rack mount amplifier.  550.00 plus shipping to your door. 

they also have some others.

450X2 / 1200X1 = 300.00
600X2 / 1800X1 = 400
750X2 / 2400X1 = 500.00

And, the grand pubah, the 550 dollar 2800 watter.  All are rated at 4 ohms.  It will do stereo at 4 ohms, and mono bridged at 4 ohms.... Since it will do mono at 4 ohms, chances are it will do stereo at 2, but I don't have specs on it.....  Other than it says it IS 2 ohm stable in STEREO.

I sent you a link to the manual in .pdf format, it's in your email inbox.


--Shane

In reading the manual, they state NOT to do 4 ohms mono bridged... BUT, for ICAS methods, I'd say it was fine.

They ALSO state that if you want to use them at full power for extended periods of time, it's best to hook them to a 220 source.  They  are sent factory 120, but can be rewired at the install time.

[ke7trp]

Cool man.  Any one of those will work I bet.  I have 220 in the rack. Might as well use it.. I had a 60 amp 220v line run in the room just for the Transmitter. It actualy has 246Volts on it.

Making progress. The entire Mod deck is ripped apart now. The 810s are sold.  I have chokes, Caps, Mod power tranny and sockets all here. I will take pictures and make a list and post it here in case anyone wants this stuff.


Clark

[Gito]

Hi

Clark,I think almost any good solid state Amplifier with enough power can modulate your Transmitter,
But not any amplifier is Radio Frequency interference protected.
So read the Manual carefully ,Is it RFI protected?
Since 1000 watt transmitter is a "big" transmitter and has a big RF output that can fed Back /get into your Modulator  Amplifier,rectified and caused the Modulator Amplifier works incorrectly .
And you gets a " bad" modulation.


Gito

[w1vtp]

Stu AB2EZ has used a Samson amplifier in his HB plate modulated amplifier.  I don't remember which one he used but it put out its full rated RMS power  Here's a link:

http://www.samsontech.com/products/productpage.cfm?prodID=1821&brandID=2

Check out the different models one is rated at 300 watts / channel -- there is a provision for bridging it for 600 watts

http://www.samsontech.com/products/productpage.cfm?prodID=1852&brandID=2

I'm not a salesman for them but I've heard his setup and it sounds great

Al

[Opcom]

I assume you are modulating a tube transmitter. If not, skip it..

One issue to face is the impedance presented by the RF amp and the DC current drawn by it.

For this reason it might be best to use audio step-up transformers made for single ended applications because they are intended for carrying unbalanced (sic) current in the high z winding.

The biggest one I know of is the 75 watt one by Hammond, for two parallel 811's. The nice thing is that if more power is needed, several transformers can be used and the windings can be arranged as the user likes, but respecting the insulation properties of the Hi-Z winding.

This use of more than one transformer came to mind since I have used LTV Ling-Altec TP-850 shaker table amps which do 850W to 1 Ohm and it is difficult to drive things (other than a set of parallel speakers) with them. They can only make 34V RMS, but can do 30A. I have resorted to using large power transformers in the past, but it did not get around the DC issue.

Please advise how this works out.

[ke7trp]

I am going to use a Pro sound amp to modulate two 4-400s to 150% and 90% neg.  The project is comming along. I am going to do it. I have shelled out the money and time for the parts. If it does not work, It wont work.. But at this point, I am sure that it will.  I am overbuilding this thing to run power I cant and wont ever run here.. But I want a nice rock solid, good sounding rig, that I can use for years and years.

The RF deck is setup for use as an amplifier.  This way, I can use it on AM and SSB.

I will post pics along the way!

Clark