fotios said:
Not an exact clone, but approximately the same capabilities. +/-84V rails, around 400W/4R and 600W/2R. About the same amount of heavy metal and output as in the 1977-issue CS800. What I meant by "old school" is the old version. I think they cheapened up the modern ones - the new ones are only 400W/2R and less at 4 of course.
I still call the one I use in the living room a "CS800 clone", even though the circuit is different. 7 pairs of outputs, full complementary, triple darlington, on the same front end (exactly) as the new monster I'm working on. Uses a 1.5KVA EI core (Magentek, scored for $65!), +/-84V, 2x20.8kuF, and puts out 2x 440/4R and 620/2R.
400W to 600W as load resistance halves is a loss of 1.25dB.
Your clone is even worse:- 440W to 620W is a loss of 1.52dB.
An amp you should be proud of will lose substantially less than 1dB and my target is <=0.6dB
Your clone is even worse:- 440W to 620W is a loss of 1.52dB.
An amp you should be proud of will lose substantially less than 1dB and my target is <=0.6dB
wg_ski said:
You know something? I preffer like you the old good EI xformers, instead toroids. And the reason it is that there is not any constructor in Greece which can make a correct toroid. Instead, there are at least two constructors which can make EI xformers of amazing quality, with LESS radiation of magnetic flux and without any mechanical noise. If you are indeded to pay arround 180 to 200 USD, you can get a real monster of up to 1,2KVA with one internal (between primary and secondary) and one external belly band earthed, E and I laminates not from common Si-Fe alloy offering thus bigger magnetic permeability and less magnetizing current. After their completion, the xformers are dipped in a good bath of epoxy varnish under vacuum for perfect impregnation and when the varnish is dried thorougly, then these xformers are solid like rocks.
I like the old good school of EI xformers! 😎
Fotios
AndrewT said:
But you need a $1000 6kVA transformer for that, not one that you score for $65 at Skycraft. The whole thing didn't cost me $300. And what can you buy for that? A Behringer EP1500? Three guesses which one sounds better.
wg_ski said:
I remember very well that, Dirty Harry supplied with +/-82Vdc and driven from a sinus of 20Hz under a 8Ù dummy load presents in its output a Vpeak = 73V (loss 9Vp) which means an output power of 333Wrms. At 50Hz 75Vp (loss 7Vp) thus P = 351Wrms. At 100Hz 77Vp (loss 5Vp) thus P = 370Wrms. Each channel was supplied from a 650VA EI xformer and from two 18000ìF caps. For 4Ù load, i don't remember the values.
Fotios
fotios said:
Im not rich, i work just like you guys, but being only 27 and holding several certifications ( including Automotive Service tech, Licensed Pressure welder, Millwright and CNC Operator and Machinist ) makes it invaluable to my employers to have me on their team and getting top Pay !
Currently working 2 jobs..
One at Ford as Assistance Service Manager and the other as a QC at a local machining and fixture company.
I put my $$ into investment accounts as my goal is to have enough $$ saved up that i can retire at 35 or 40 and travel the world.
I have set a $1500 budget for everything i need for a small "repair shop" setup. No.. i'm not going into that, but it will be something to play around with
BTW...
I have ordered a soldering station yesterday from a local supplier $145 along with a magnified inspection light.
Tthe station is a Xytronics Auto-Temp 137ESD, because they had one on "Demo" ans played a lil bit with it. Really nice unit, comfortable and easy to use and has an option for Hot Tweezers which they can order in for $80 if i needed 😉
As far as Meter goes i have a cheapie one, but want to get a mid range unit but torn between the Analog/digital war as some ppl say that the digital is slow.
you will be surprised then that a 1kVA @ ~$80 (£50) will achieve better than <0.6dB.wg_ski said:
AndrewT said:
Why not look at it another way? Let's compare two amps with the same rated power in 2 ohms instead of comparing two amps with the same rated power in 8 ohms. The two stereo amps have the following power ratings in 8/4/2 ohms:
A: 170W/290W/500W (3 times the 8 ohm power in 2 ohms, just like you want)
B: 250W/435W/500W
Amplifier A will probably be bigger, more expensive and heavier. What are the advantages of amplifier A? It might be able to do full power sine wave into 2 ohms continuously but why would we want that? How much does it weigh?
Amplifier B gives the same or higher power into all impedances compared to amplifier A. What are the disadvantages? It weighs 20kg and is 2U high. (it is a Crest CA-4)
I could take amplifier B and modify it with a voltage clamp to make it 125W/250W/500W if you want 😉 Wouldn't that be even better than amplifier A? 😀
I'd choose amplifier B because it is cheaper, lighter, smaller and will give me more power when running high impedance loads. If you worry about protection circuits activating on freak peaks it would be cheap and doesn't weigh much extra to use a beefier output stage than strictly needed.
in my experience that type of power profile results in Amplifier A sounding better than amplifier B when driving the middle impedance load.
megajocke said:
The problem with amplifier B is that they typically go just a bit too far in making them cheaper, smaller, and lighter. If you took amplifier B and put in some decent size caps (keeping the same trafo iron), a bit more heatsink and a couple more pairs of outputs, adding about 5 pounds of weight it WOULD sound just as good as amp A.
Neither one will drive 2 ohms sine wave continuously. But you do need enough heat sink/fan/SOA to be able to drive 2 ohms with music, overdriven enough to where it resembles inter-station static on the radio with nothing bad happening. Amp A could do that, but B would have trouble. Again, 5 miserable pounds more and it would do it.
True,
the CA-4 could use more output transistors, the low 2 ohm power is due to the current limiter (which controls the gain of the amplifier, not a VI limiter type) operating before reaching voltage clipping in 2 ohms as the output devices wouldn't have enough SOA to reliably do full power in reactive 2 ohm loads.
The transformer is probably big enough though, but it needs more output devices.
Amplifier B would of course only be used on 2 ohm loads in an emergency. But what about at 4 ohms? I wasn't suggesting 2 ohm use (maybe I was unclear).
the CA-4 could use more output transistors, the low 2 ohm power is due to the current limiter (which controls the gain of the amplifier, not a VI limiter type) operating before reaching voltage clipping in 2 ohms as the output devices wouldn't have enough SOA to reliably do full power in reactive 2 ohm loads.
The transformer is probably big enough though, but it needs more output devices.
Amplifier B would of course only be used on 2 ohm loads in an emergency. But what about at 4 ohms? I wasn't suggesting 2 ohm use (maybe I was unclear).
AndrewT said:
A power drop of only 0.6dB is something to be proud of. If the power supply is adequate, most of your loss will be the increased voltage drop across the output stage.
People like to see an amp double its power as the load impeadance is halved. That is impossible unless you use half of the 4 ohm power as the 8 ohm rating.
AndrewT said:
That will depend a great deal on what the 8 ohm power is.
In my experience, a good amp will be able to deliver at least the transformer rating to the load (at low impeadance) for short peroids - say up to 5 minutes. So, with a 1KVA transformer and a good output stage, you can deliver 1KW to a low impeadance load. Really not much need for a 6KVA transformer unless you need 6KW output at low impeadance.
...I am always reading 6kVA... also reading 2 torroids... so you are going to use a 6kVA transformer (or multitransformer combi) at a standard single phase mains plug?
Even if you just use it at moderate power in oder not to blow your mains breaker, even then you will notice sooner or later that the tafo spec and caps will not be sufficient to determine the output voltage sagging. You will have to take into account the sagging of your mains. ...and when calculating this you have to consider the low power factor current consumption of such simple non PFC designs, which is resulting in remarkable current peaks.
Even if you just use it at moderate power in oder not to blow your mains breaker, even then you will notice sooner or later that the tafo spec and caps will not be sufficient to determine the output voltage sagging. You will have to take into account the sagging of your mains. ...and when calculating this you have to consider the low power factor current consumption of such simple non PFC designs, which is resulting in remarkable current peaks.
Steve Dunlap said:
It is if you want a +/-84V supply to stay anywhere near +/-84V. This is needed if you want the amp to double as you halve the impedance. Real trafos start dropping their DC from the very first ampere of load and the lion's share of the voltage drop occurs at fairly light load. You have to get something way oversized that's barely loaded to keep it stiff enough to double power at half Z.
wg_ski said:
This may be true of some amps. Not mine. Two % regulation on a 1.6KVA transformer will get you a power supply that doesn't sag much until the load goes really low.
AndrewT said:
I thought you were completely clear.megajocke said:
The 2r0 resistive test gives an indication of the current ability of the amplifier.
If it can't drive a 2r0 for a few seconds then it will have problems driving a reactive 4ohm speaker.
I haven't tried it yet but a I suspect that the resistive test load for a 4ohm amplifier would be ~ 1r4 and for 8ohms ~ 2r8.
This test would get nearer to the peak current that real speakers demand.
Hi,
The "..... But what about at 4 ohms? I wasn't suggesting 2 ohm use (maybe I was unclear). " part was directed at wg_ski, I think he read it as that I wanted to drive 2 ohm loads with it.
I'd say a 2 ohm resistive load test doesn't say much about the suitability for driving higher impedance reactive loads:
You could make an amp that has it's VI limiter designed to give only 1A or so at 0V output but increasing fast enough that a 1 ohm resistive load can be driven to voltage clipping at 2kW. It would still be totally unsuitable for driving even an 8 ohm speaker load to more than 10W or so.
The reverse is also true for other kinds of protection circuitry - for example an averaging load impedance detector. It could be made to trigger at 2.5 ohms for example. It would drive any current into a 4 ohm (2.6 + xj ohms) speaker but would shut down with any 2 ohm load.
As far as the power supply is concerned it is less stressful to drive a 4 ohm reactive speaker than a 2 ohm resistive load. These peak currents you are talking about (it's the ones Bob Cordell wrote about, right?) only last for a few milliseconds. They might trigger amplifier protection which isn't expecting them but the power supply won't care.
The "..... But what about at 4 ohms? I wasn't suggesting 2 ohm use (maybe I was unclear). " part was directed at wg_ski, I think he read it as that I wanted to drive 2 ohm loads with it.
I'd say a 2 ohm resistive load test doesn't say much about the suitability for driving higher impedance reactive loads:
You could make an amp that has it's VI limiter designed to give only 1A or so at 0V output but increasing fast enough that a 1 ohm resistive load can be driven to voltage clipping at 2kW. It would still be totally unsuitable for driving even an 8 ohm speaker load to more than 10W or so.
The reverse is also true for other kinds of protection circuitry - for example an averaging load impedance detector. It could be made to trigger at 2.5 ohms for example. It would drive any current into a 4 ohm (2.6 + xj ohms) speaker but would shut down with any 2 ohm load.
As far as the power supply is concerned it is less stressful to drive a 4 ohm reactive speaker than a 2 ohm resistive load. These peak currents you are talking about (it's the ones Bob Cordell wrote about, right?) only last for a few milliseconds. They might trigger amplifier protection which isn't expecting them but the power supply won't care.
I don't recall if Bob C spoke about them.
My sources are from this Forum long before Bob C joined us.
My sources are from this Forum long before Bob C joined us.
Is it the same effect then? Flipping drive signal polarity when cone velocity is at its highest?
Would you consider this double full power low frequency modified square wave a valid signal?
Not that it matters for the power supply unless you have severely underdimensioned your smoothing caps.
Would you consider this double full power low frequency modified square wave a valid signal?
Not that it matters for the power supply unless you have severely underdimensioned your smoothing caps.
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