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Old 11-22-2010, 02:39 AM   #61
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R (Z actually) changes with frequency. It's a complex load. However the lowest impedance presented to the lowest frequency will be pretty close to the rated impedance.
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Old 11-22-2010, 02:39 AM   #62
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It is not a simple linear equation. If you don't get that, we can't help you.


It is. What equation are you using? The equation is V = IR, it's that simple.

You're also getting confused because the voltage coming into the amplifier is 120 Vrms whereas the 300V for the tube is DC. You need an AC / DC converter for this. Sure the voltage on the amplifier is 300V, but that's the positive rail, not a fixed voltage, the amplifier varies from 0-300V.

I can only tell you so many times, you can't break the rule V = IR.
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Old 11-22-2010, 02:41 AM   #63
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I'm not sure what the problem is, here.

Are you trying to measure the voltage of your power amp, or something? It seemed you were having trouble understanding just how much tube amps amplified at first, but now I'm not sure where the misunderstanding is.

I think another thing you'll find interesting that you aren't considering Impedance. You're treating the speakers like resistors, but they're not! If you measure resistance of an 8 ohm speaker, you won't get 8 ohms. The fact that it's called an "impedance" implies there's an imaginary component.

EDIT: This post was WAY late. I need to refresh after reading threads.
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Old 11-22-2010, 02:42 AM   #64
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What I am telling you is that you cannot cancel out I because it is not equal on both sides of the equation. Power is being added to the system.


I'm sorry, I honestly don't mean to be rude, but I don't think you understand what you are talking about.

You can ignore the 120Vrms coming from the wall, that's the input voltage to the AC/DC converter. You have a tube where the Anode (sorry if I'm using the wrong terminology, I'm used to FETs, which would be the Drain of an NFET) is connected to 300V. This 300V is your maximum voltage, it doesn't hold the voltage at a constant 300V.
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Old 11-22-2010, 02:44 AM   #65
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Ok... so I agree that there is an imaginary component, but you aren't going to go from 50W to 100W just by changing the frequency of the signal and keeping the voltage constant (well within 20-20kHz).

You can ignore the 120Vrms as the input voltage. This just goes to a power supply, you only look at the output voltage of the power supply and then just do an efficiency calculation of the power supply.

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Old 11-22-2010, 02:47 AM   #66
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As I know nothing of electronics, this thread is blowing my mind...
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Old 11-22-2010, 02:50 AM   #67
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I'm real sorry, I think I read the original question wrong. I've been up too late.
I still don't think you're doing the power equations properly, but we can put that aside. Someone else can set us both straight on that if need be.

I really do think the tubes have a lot to do with the warmth of a tube amp. There are a few tube amps that do not have output transformers and they are plenty warm. However, the OT does add something to the tone as well. The people I talked to with the OT-less design had to do quite a bit of electrical gymnastics to get the sound right, though I don't remember 'warmth' being one of the things they had to re-inject. It seemed more like compression and 'fatness' were the things lost with the OT.
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Old 11-22-2010, 02:52 AM   #68
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Colin knows full well what he's talking about, and everything he's said that I've read is true.

Tubes take the power from the outlet and use it to amplify the signal from your guitar by a HUGE factor. The voltage is amplified, then, as Craig explained earlier, the voltage is stepped down so that the current can be stepped up which drives speakers. Where's the misunderstanding?
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Old 11-22-2010, 02:57 AM   #69
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Tubes take the power form the outlet and use it to amplify the signal from your guitar by a HUGE factor. The voltage is amplified, then, as Craig explained earlier, the voltage is stepped down so that the current can be stepped up which drives speakers. Where's the misunderstanding?


If you have a static load (ok so it's not 100% static but you aren't going to get variation of impedance from 1 ohm to 8 ohms in a 20-20kHz bandwidth), and decrease the voltage, it's impossible for the current to increase. If you have an ACTIVE load, then sure, you can hold voltage constant and your current is going to change because your load is changing.

Ok, the 120Vrms comes from the wall and goes to an AC/DC power supply. This power supply supplies 300V. In this process, you're either going to have less or more current than the input to your power supply (I haven't done an AC/DC power supply design and I don't want to look up for the formula for rectification...).

So let's just say for very simplistic sake, that the wall voltage is 120V DC, which it isn't, but let's just say it is. You would feed this to a boost converter, which would boost your voltage to 300V. So if you're driving an 8 ohm speaker at 30Vrms, your output power is 112.5Watts.

Assuming 100% efficiency in the power supply, your current coming from the wall would be 120*current = 112.5Watts, which would mean your input current is 112.5W/120V = 0.9375Amps.

What was the current at the output? Well 112.5W / 300V = 0.375Amps.

Can we all agree on this?

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Old 11-22-2010, 03:01 AM   #70
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I really do think the tubes have a lot to do with the warmth of a tube amp. There are a few tube amps that do not have output transformers and they are plenty warm. However, the OT does add something to the tone as well. The people I talked to with the OT-less design had to do quite a bit of electrical gymnastics to get the sound right, though I don't remember 'warmth' being one of the things they had to re-inject. It seemed more like compression and 'fatness' were the things lost with the OT.


I hate to argue with you more, but how did they drive the speaker without a transformer? The tube has way too high of an output impedance.
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Old 11-22-2010, 03:04 AM   #71
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They used some sort of induction system - I looked up the patent, and it wasn't a whole lot more specific than that. I'm trying to dig up the conversation now so I can get more specifics. The amp was new at NAMM 2009, I think. It definitely didn't have an OT.
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Old 11-22-2010, 03:04 AM   #72
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omfg. can we agree that you have no idea wtf is going on. there's so much ish going on here that your not accounting for.

1. your guitar pickups pick some shit up and send it to the output jack. It doesn't matter if you have actives or passives. The output will be at a certain range.

2. plug it into a pedal or whatever..pedal boost signal by some amount.

3. plug into the guitar amp. - The first stage after the input is an impedance buffer. You lose a lot of signal strength due to impedance coupling.

4. first volume pot soaks up more of the signal.

5. any additional stages will distort at the input and be stepped down at the output until the

6. phase inverter which splits the signal and sends it to the power tubes.

the signal prior to the pi needs to be impedance matched, that's why effects loops require buffers that supply unity gain when switching from lo-z to hi-z and back.

think about it logically and then you can work it out when you get to the other equations in your text book...what's coming out of your guitar output jack is very quiet. what's coming out of your pedal...still very quite. What's coming out of your loudspeakers...very loud.

the science is going to back up the reality.

dude must be homeschooled

https://docs.google.com/viewer?url=...enumber=1&w=764

otl amps have been around forever.
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Old 11-22-2010, 03:07 AM   #73
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Ah, found it. Here's the guitar amp version. I know there are a few guys that use this for hi-fi stuff as well. Pretty neat stuff. It does, of course, match the impedance, but I think we can agree it takes what we'd traditionally call an OT out of the equation.

http://www.milbert.com/
http://davidberning.com/technology/comparison

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Old 11-22-2010, 03:11 AM   #74
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apparently otl's are dangerously dangerously unsafe since there is no isolation tranny.
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Old 11-22-2010, 03:16 AM   #75
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the signal prior to the pi needs to be impedance matched, that's why effects loops require buffers that supply unity gain when switching from lo-z to hi-z and back.

think about it logically and then you can work it out when you get to the other equations in your text book...what's coming out of your guitar output jack is very quiet. what's coming out of your pedal...still very quite. What's coming out of your loudspeakers...very loud.

the science is going to back up the reality.

dude must be homeschooled


All I'm saying is V=IR, why are you trying to argue with me? I must be homeschooled because V = IR?

Look, I measured about 5V coming out of my pedal peak to peak. 5V goes into the amplifier. Want 30W of power to an 8 ohm load? Amplify 5V by about 80. What is there to argue? V = IR, V=IR, do I need to repeat myself more?

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Old 11-22-2010, 03:18 AM   #76
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That's the first page of the patent, more for demonstration purposes than as a full explanation. Read the rest, or one of the other explanations on the site. It's a matching device, but since it's so different it really doesn't apply to the OT discussion we were having. From what I understand it has almost nothing in common tonewise with a usual OT.
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Old 11-22-2010, 03:24 AM   #77
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I may be dumb but that schematic just confuses me. I'm trying to figure out how that's transformerless when I see magnetics all over that schematic.
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Old 11-22-2010, 03:25 AM   #78
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Originally Posted by farmosh203
I may be dumb but that schematic just confuses me. I'm trying to figure out how that's transformerless when I see magnetics all over that schematic.


https://docs.google.com/viewer?url=...enumber=1&w=764

what piece is the transformer.
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Old 11-22-2010, 03:28 AM   #79
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This thread is epic. Makes me feel much better about myself, thanks guys.
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Originally Posted by farmosh203
I may be dumb but that schematic just confuses me. I'm trying to figure out how that's transformerless when I see magnetics all over that schematic.
We're talking output transformerless, that schematic doesn't have an OT. On the schematic, find the output tubes, trace the wire out of the plate through the coupling cap towards the resistor called "load". That's representing the speaker.
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All I'm saying is V=IR, why are you trying to argue with me? I must be homeschooled because V = IR?

Look, I measured about 5V coming out of my pedal peak to peak. 5V goes into the amplifier. Want 30W of power to an 8 ohm load? Amplify 5V by about 80. What is there to argue? V = IR, V=IR, do I need to repeat myself more?
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Old 11-22-2010, 03:29 AM   #80
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Optimus prime is a transformer. The thing in the patent is a transformer. The idea is that it's so unlike a traditional transformer that you can call it not-a-transformer. They're similar in name only, and in very very basic function.

Look at that schematic against a traditional tube amp schematic, you'll see the difference right away.
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