Bridging is not an efficient way to get more power.
It is ONLY feasible when supply rails are limited in voltage.
Adding an amplifier and speaker is far better for added SPL and added reliability.
This gives +3dB @ treble and mid frequencies. At bass frequencies it can give +3 to +6dB
That's why you see stacks of bass speakers in big PA rigs. Each doubling of speaker (with it's amplifier) gives +6dB of bass.
It is ONLY feasible when supply rails are limited in voltage.
Adding an amplifier and speaker is far better for added SPL and added reliability.
This gives +3dB @ treble and mid frequencies. At bass frequencies it can give +3 to +6dB
That's why you see stacks of bass speakers in big PA rigs. Each doubling of speaker (with it's amplifier) gives +6dB of bass.
Here's what I have so far. I have a Gerrard Zero 100c with a Audio Technica 12s cartridge feeding into the phono stage of a Solid State Scott 42wpc receiver. I have the tape out of that feeding a Sansui equalizer. The equalizer drives the tape in of the Scott amp and the tape in of the 30wpc Dynaco.
The Dynaco runs two 130 watt Marantz 3 way acoustic suspension speakers in the front of the room. Two Design Acoustic acoustic suspension speakers in the back of the room wired for Halfler quad. And a 50 watt 12" powered sub made by an unknown company.
The Scott amp runs remote speakers in two other rooms plus some Bose cubes I treated with nail polish to water proof them outside.
It's sounds nice but it does not quite achieve "live" volumes in the main listening area.
It looks like I will need to obtain another sca-80, bridge them and run more powerful speakers in the front of the room. I will probably also need to build a more powerful sub.
Is there a way to modify the sca-80 to invert one channel without using an external bridging circuit?
Thanks!
The Dynaco runs two 130 watt Marantz 3 way acoustic suspension speakers in the front of the room. Two Design Acoustic acoustic suspension speakers in the back of the room wired for Halfler quad. And a 50 watt 12" powered sub made by an unknown company.
The Scott amp runs remote speakers in two other rooms plus some Bose cubes I treated with nail polish to water proof them outside.
It's sounds nice but it does not quite achieve "live" volumes in the main listening area.
It looks like I will need to obtain another sca-80, bridge them and run more powerful speakers in the front of the room. I will probably also need to build a more powerful sub.
Is there a way to modify the sca-80 to invert one channel without using an external bridging circuit?
Thanks!
Also! For ***** and giggles can I increase the rail voltage of an amplifier if I can keep it cool? Take the 70v +/- up to 100v or more and cool the amp with computer case fans. Maybe with a switch that changes the operating voltage and switches the fans on and off at the same time? Are there any relevant threads out there on this topic?
Hmm I guess I'm in the wrong place. I thought I would get a helpful answer from a knowledgeable person who has experience in amplifier design.
Something along the lines of the amp will generate x amount btu's additional heat if you increase the voltage by x amount. So you should use a fan that will move at least x cfm.
Or no you can't do that because x transistor stops working correctly at x voltage regardless of operating temp.
But if you replace it with transistor y it will work.
You know. Helpful answers.
Something along the lines of the amp will generate x amount btu's additional heat if you increase the voltage by x amount. So you should use a fan that will move at least x cfm.
Or no you can't do that because x transistor stops working correctly at x voltage regardless of operating temp.
But if you replace it with transistor y it will work.
You know. Helpful answers.
According to this schematic: http://home.comcast.net/~g.e.dunn/SCA80/SCA80sch2.jpg
The power transformer can be set for 100v or 120v operation. If I change it to the 100v setting will I get 85~v rails? If I also implement active cooling will there be any deleterious effects to the amp?
Thanks!
The power transformer can be set for 100v or 120v operation. If I change it to the 100v setting will I get 85~v rails? If I also implement active cooling will there be any deleterious effects to the amp?
Thanks!
I think you answered your own question in your analogy with the engine. Let's say you keep your lame smog components and only replace the cam with one from the bottom of the page, you know the really big one. How will that engine run? Pretty crappy I would imagine. The same goes for an amplifier it's a whole package. In your amp you'd replace the power transformer, more voltage and current, now will it fit in the chassis? New filter capacitors to go with the new xfmr. Now you have more volts and current so you can add more transistors and heatsinks to mount the xsistors . Now you have to redesign the rest of the amplifier to support the output stage. Can you see what everyone's been trying to tell you?
Craig
Craig
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I see what your saying. I guess amplifiers are harder to upgrade then engines.
If I want to make more power I would need to increase the supply voltage and upgrade the components in the output stage to handle the increased voltage.
Doing so would cost more then buying a more powerful amp.
So I should buy another matching amp and bridge them.
Could the amp withstand changing the transformer setting from 120v to 100v on the primary side if I cool it actively?
If I want to make more power I would need to increase the supply voltage and upgrade the components in the output stage to handle the increased voltage.
Doing so would cost more then buying a more powerful amp.
So I should buy another matching amp and bridge them.
Could the amp withstand changing the transformer setting from 120v to 100v on the primary side if I cool it actively?
llwhtt, I'm not sure what your talking about. why would you run a 120v amplifier at 100 volts and what does that have to do wityh the filter caps. i am a retired musician and played the clubcircuit in LA in the 70's. i also repaired musical instrumentsc and amps. van halen played most of the same clubs i did. he and many other guitar players used marshall amps connected to a variac so they could run the amps at 140vac. i just thought you might find that interesting.
The OP said he wanted to run his solid state amplifier on 120VAC with amplifier set up for 100VAC, I don't think it would last too long doing that. The filters capacitors are rated at a certain voltage with amp set up for proper line voltage, running it at 17% higher line voltage is more than likely over the rated voltage of the capacitor, there probably wasn't much headroom to start with. Your TUBE guitar amps are totally different. I've built 100s of guitar amps for a certain manufacturer and know all about EVH and his Variac. Marshalls have a 1000VDC worth of capacitors in their power supply so at 140VAC you still aren't even close to their max. Tubes are tough components and can stand the abuse much longer than solid state.
Craig
Craig
llwhtt, abot the tubes. I repaired amplifiers and eddy and others still came in with blown tubes every once in a while.
where did this guy get an amp designed to run on 100vac, japan!!
i also owned a company Stewart electronics we manufactured pro audio products under the stewart name. all of our products were designed to operate from 108vac to 132 vac. they would still work at 100 vac but they wouldn't meet spec.
where did this guy get an amp designed to run on 100vac, japan!!
i also owned a company Stewart electronics we manufactured pro audio products under the stewart name. all of our products were designed to operate from 108vac to 132 vac. they would still work at 100 vac but they wouldn't meet spec.
your responses to various suggestion tell me you know very little about the topics.
This last post confirms just how dangerous you are !!!
Running a 100Vac transformer tapping (for Japan) on 120Vac is very likely to result in failure.
If this resulted in a house fire, then your insurance company would disown you.
If someone got injured, the authorities may take you to court for negligent action.
You need to learn before you kill yourself.
I already know your thoughts as you read this, so don't bother with a reply directed to me.
Wadest,
Apparently you didn't read the OP's post, the Dynaco power transformer could be set for 100VAC (Japan) or 120VAC (North America). The OP wanted to run it set for 100VAC on a 120VAC line, not good, well, not for long anyway.
Yes tubes go once in a while, especially with the relatively crappy tubes we have today, but the OOPS factor is much longer with tubes than it is with solid state. There is NO short term red plating in solid state. If a mistake is made with solid state sometimes it's all over before you know it. As far as varying line voltages go some equipment is more tolerant than others.
Craig
Apparently you didn't read the OP's post, the Dynaco power transformer could be set for 100VAC (Japan) or 120VAC (North America). The OP wanted to run it set for 100VAC on a 120VAC line, not good, well, not for long anyway.
Yes tubes go once in a while, especially with the relatively crappy tubes we have today, but the OOPS factor is much longer with tubes than it is with solid state. There is NO short term red plating in solid state. If a mistake is made with solid state sometimes it's all over before you know it. As far as varying line voltages go some equipment is more tolerant than others.
Craig
I said it, nobody listened.
An old dynaco may have 2n3055 select output transistors, RCA 40xxx ones, that can only put out 1/3 of the rail voltage. Newer output transistors like MJ21194 can put out 1/2 the rail voltage, until the heat sink heats up.
You can address the heat sink issue with external fans, or do like I'm doing and attach finned gadgets to the big bare flat places on the dynaco "heat sink"
If your rails are 100 v already, that says your 40 watt/ channel output transistors are old tech. 60 w or more from one pair is pretty doable for "music power", ie symphonies that go loud and soft, mostly soft, not techno rock PA power which has a high duty cycle.
You may need to decrease the feedback resistor to increase the gain, or fiddle around with various resistors in the early stages to increase the gain, but my predecessor dynaco ST120 is as LOUD as my Peavey CS800s on the same speakers on symphonic material: just the ST120 can't do bass guitar PA all day because of the heat sink limitation. I was doing keyboard PA in a church on the ST120 and melted the solder off the output capacitor terminal causing a short: that was before I put the fans on the output transistor sinks.
Then again, if your amp is putting out 15 w/ch, fix it before any modifications. Until you check the power out, you don't know where you are. New filter caps, good, but proof is in the performance, the watts check.
Note putting faster transistors in, you probably need to put 51 pf base to emitter ceramic capacitor on the driver transistors to inhibit oscillation. See the "TIP" mod on the ST120 on Greg Dunn's website, where dynaco came up with this patch for putting 1980 transistors (Ft 2 mhz TIP3055) in a 1966 product designed for 400 khz transistors (2n3055 select RCA 40xxx).
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