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Old 11-22-2010, 03:29 AM   #81
AcousticMirror
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Quote:
Originally Posted by Kanthras
This thread is epic. Makes me feel much better about myself, thanks guys.
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.


hey you don't get off that easy. you were this stupid once too. don't make me use the search boy.
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Old 11-22-2010, 03:29 AM   #82
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Maybe the items with the T reference designator. Stop being rude, thanks.
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Old 11-22-2010, 03:32 AM   #83
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I was saying that I saw magnetics all over the place on the "Transformerless" Patent, the schematic you posted does not confuse me AcousticMirror.
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Old 11-22-2010, 03:33 AM   #84
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wait. what was the original point of this thread again...

are tube amps supposed to be warm?
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Old 11-22-2010, 03:34 AM   #85
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Also what's the point of that "Output Transformerless" design if you have to use transformers for the DC/DC power conversion? Sure the output stage doesn't have a transformer but you still have to use a transformer.
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Old 11-22-2010, 03:34 AM   #86
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Yes, there are transformers. Again, it has to have some sort of matching device, but the deployment is novel enough to be called transformerless. It's like a wireless phone - it's got wires, but for all practical purposes, you can call it that. Let's not drag the PT into this - I really don't think you can lump it in with the OT as far as tone changes go.


My purpose in posting that was to show that there are approaches that do away with traditional transformer design, and the tone changes that might come with them. Can we not agree on that?

There are a lot of reasons not to use an OT. They're the most expensive part of the amp, they're overly sensitive to cabs, they're heavy, and they're not hugely reliable.
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Old 11-22-2010, 03:34 AM   #87
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i dunno. buy one and test it out?
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Old 11-22-2010, 03:38 AM   #88
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My purpose in posting that was to show that there are approaches that do away with traditional transformer design, and the tone changes that might come with them. Can we not agree on that?


It is interesting indeed, I'll agree on that.

My whole point of this thread was that an amplifier is more of an impedance matching device rather than amplifying the signal by a lot.

Assuming you guys are right, what I understand is that the harmonic distortion content of a tube amplifier is what gives the "warm" sound. I was suggesting that the "warm" sound was coming from the output transformer because the amplifier isn't gaining the signal by a huge amount.
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Old 11-22-2010, 03:43 AM   #89
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I think it is multiplying it by a lot. The input power is very low, maybe a tenth of a watt. Output power is 50 to 100W - that seems like quite a bit to me, at least in this application. If your background is in SS devices then that probably doesn't sound like a large gain factor.

The reason the tubes color the sound so much is that they're such low-fi devices, and they're being run very close to (or often, beyond) their maximum specs. The OT isn't as low-fi and isn't being stressed as much, so it contributes less. It does add something, though. If you ever have the chance, listen to an amp before and after an OT change. A 100W OT in a 50W amp adds a bunch of girth and low end, and an undersized OT adds a fair bit of compression and even a bit of distortion.
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Old 11-22-2010, 03:43 AM   #90
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Yeah, you can't really deduce what's happening inside a guitar amp by measuring the input voltage and output voltage and comparing that.
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Old 11-22-2010, 03:48 AM   #91
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I think it is gaining it by a lot. The input power is very low, maybe a tenth of a watt. Output power is 50 to 100, that seems like quite a bit to me, at least in this application. If your background is in SS devices then that probably doesn't sound like a large gain factor.


I think you're getting a little confused here because the input power doesn't matter, it's all about the input voltage. You just need to put an op amp at the front end of the guitar amplifier (high input impedance, low output impedance), so that 5V will be able to drive any circuitry inside the amplifier after the buffer stage.

If you're comparing input power to output power, that's just impedance matching. I'm more familiar with FETs, but I assume tubes are voltage controlled amplifiers.
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Old 11-22-2010, 03:51 AM   #92
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Instead of using a normal oscilloscope and just measuring the output voltage, try hooking up a spectrum analyser to it. Then you might get a better idea of what's going on. A guitar amp that amplifies cleanly will sound like smeg. Try plugging your guitar into a high end hi fi amp - sounds dreadful doesn't it? Even an MG sounds better.
Here's an exercise for you. Compare a valve preamp to a SS preamp. There is no OT in a preamp, they are just capacitively coupled. There is a huge difference in sound still.
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Old 11-22-2010, 03:52 AM   #93
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Quote:
Originally Posted by farmosh203
I'm more familiar with FETs, but I assume tubes are voltage controlled amplifiers.


Ah, that's where our difficulties lie. The power tubes increase the current when the input voltage changes. They run at a constant voltage.
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Old 11-22-2010, 03:55 AM   #94
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Instead of using a normal oscilloscope and just measuring the output voltage, try hooking up a spectrum analyser to it. Then you might get a better idea of what's going on. A guitar amp that amplifies cleanly will sound like smeg. Try plugging your guitar into a high end hi fi amp - sounds dreadful doesn't it? Even an MG sounds better.
Here's an exercise for you. Compare a valve preamp to a SS preamp. There is no OT in a preamp, they are just capacitively coupled. There is a huge difference in sound still.


Don't have a spectrum analyzer handy but it would be interesting to see what's really going on on different kinds of amplifiers.

I understand why you guys are saying the tube has the "warm" sound, because of how the signal acts when it distorts.
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Old 11-22-2010, 03:56 AM   #95
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Ah, that's where our difficulties lie. The power tubes increase the current when the input voltage changes.


But aren't tubes voltage controlled voltage sources? The inside of a tube is an open air gap, right? So you aren't going to get much current (if at all?).

That's the whole reason you need the output transformer, because the tube can't drive enough current through the speaker.
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Old 11-22-2010, 03:58 AM   #96
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Well I hope I didn't piss you guys off, but I'm going to bed, g'night .
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Old 11-22-2010, 03:58 AM   #97
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The input voltage controls the current from cathode to plate. There's a significant amount of current.
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Old 11-22-2010, 04:16 AM   #98
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Originally Posted by farmosh203
But aren't tubes voltage controlled voltage sources? The inside of a tube is an open air gap, right? So you aren't going to get much current (if at all?).

That's the whole reason you need the output transformer, because the tube can't drive enough current through the speaker.

Actually with valves you are more interested in transconductance.

There is another important need for an OT apart from reflecting an 8K (or so) load to the valves - dc isolation. You feed the centre tap of the primary with about 400V. We don't want that sort of dc voltage on the speaker leads now do we? Apart from blowing up the speaker, 400V hurts. Trust me I know. Ouch!! We don't run +/- rails with a valve amp.
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Old 11-22-2010, 05:52 AM   #99
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Originally Posted by farmosh203
Well I hope I didn't piss you guys off, but I'm going to bed, g'night .




Good luck with whatever the stuff is you are working on.


PS: you triple posted within 3 minutes not too long ago. I'm not pissed, I'm just disappoint. oktnxbai
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Old 11-22-2010, 06:21 AM   #100
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Originally Posted by AcousticMirror
hey you don't get off that easy. you were this stupid once too. don't make me use the search boy.
I was not ever this stupid, you silly troll.
Perhaps a touch antagonistic, but hey, I learned to take the chill pill every now and then.

And I really hope you're not speaking of the whole "talkback debacle". I'm not getting into it, but I still think it's a stupid term.
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