AcousticMirror

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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farmosh203

Maybe the items with the T reference designator. Stop being rude, thanks.

farmosh203

I was saying that I saw magnetics all over the place on the "Transformerless" Patent, the schematic you posted does not confuse me AcousticMirror.

AcousticMirror

wait. what was the original point of this thread again...

are tube amps supposed to be warm?

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farmosh203

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.

Roc8995

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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Hi, I'm Colin.

AcousticMirror

i dunno. buy one and test it out?

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farmosh203

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.

Roc8995

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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Hi, I'm Colin.

Kanthras

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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Rackmount Tube Amp Project <<< Updates!

farmosh203

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.

Cathbard

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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Roc8995

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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Hi, I'm Colin.

farmosh203

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.

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.

farmosh203

Well I hope I didn't piss you guys off, but I'm going to bed, g'night .

Roc8995

The input voltage controls the current from cathode to plate. There's a significant amount of current.

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Hi, I'm Colin.

Cathbard

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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Gilchrist custom guitar
Yamaha SBG500
Telecaster
Ibanez Iceman
Roland GP-8
Quadraverb
Abbey Harmonic II
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Marshall 1960A

Cathbard Amplification

311ZOSOVHJH

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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