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Old 22nd November 2011, 01:35 AM   #1
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Default Basic op amp question

Can I tie the source and sink pins of an LME49810 or LME49811 to use them as a standard op amp audio amplifier (only one output)?
If so, does anything else have to be done with external components (capacitors, resistors) to protect anything?

Thanks for the help!

Last edited by Tube Noob; 22nd November 2011 at 01:36 AM. Reason: content
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Old 22nd November 2011, 03:50 PM   #2
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a) Yes you can.
b) No it doesn't...

But then again: What is the point with the LME-family, if you decide to do so?
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Old 22nd November 2011, 04:02 PM   #3
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Thank you for the response.

I'd like to experiment with driving a tubed KT88 output stage. Ideally I would want a voltage swing of around 70VRMS, and the LME family is one of the few I have found that can approach this. I will also be trying the 4780, but I'd like to see how the LMEs do as well.

Please let me know if you have any further suggestions/ideas.
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Old 22nd November 2011, 06:03 PM   #4
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Quote:
Originally Posted by Tube Noob View Post
Thank you for the response.

I'd like to experiment with driving a tubed KT88 output stage. Ideally I would want a voltage swing of around 70VRMS, and the LME family is one of the few I have found that can approach this. I will also be trying the 4780, but I'd like to see how the LMEs do as well.

Please let me know if you have any further suggestions/ideas.
This will probably sound like a solid state amplifier, as in less fun, more clear. But, the approach is kind of backwards, since you didn't need the tubes for it.

So, I would suggest getting some little triodes and using them to drive solid state output devices. When feedback is applied, the triodes at small signal will force the whole thing to sound like a tube amp. See how that's different? If the device is purpose made to sound like a tube amp, then you've got triodes at the input.


Sections of tube amp sound and their possible solid state counterparts:

Tube: Output transformer affects speaker drive
SS: Variable Current Drive (presence) dial can be added when supporting classic speakers.

Tube: Known for soft clip
SS: PI filter and emitter resistor overdo softens clip noise somewhat. . . although the main approach is increasing power output capacity beyond speaker capacity so as to avoid clipping entirely.

Tube: Predrive / preamp does harmonic filtering replacing rough tones with fun tube errata from various little triodes
SS: Mosfet if used at small signal is capable of a very similar sound, especially IRF510. See also the MooseFet project. Most "sandglass" design does use fets.

Tube: Input transformer causes the source device to drive somewhat differently.
SS: Many options in discrete design give a similar tone. Lightspeed Attenuator does a slight amount of similar effect in a much different way. Some buffers, particularly those highlighted at Decibel Dungeon, contribute a similar "open" effect. That topic isn't exactly input impedance of an amplifier but rather it is output impedance of a source.

Its fun to have trick preamps for each source that needs it. Filtering can be fine too, such as removing the pilot tone from radio, a phono amp to level the response from records and a DAC so that your CD doesn't sound exactly like a fax machine.

On that topic, you may discover that you greatly desire a small triode for filtering HD Radio, mp4 and similar droning codecs like aac, avc, and Satellite radio, all of which are the latest technology for getting a headache. Unfortunately, if/when removing the small signal triodes from a tube amp, you have lost its harmonic filtering features. Instead, the excellent quality, clean little op-amp will let you hear what these modern sources really sound like, and they're freakin awful.
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