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Old 26th July 2010, 02:06 PM   #1
bigwill is offline bigwill  United Kingdom
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Smile Microcontrollers in tube amps

I have ordered an Arduino for messing with, and the chip it's based around is available very cheaply. I was thinking about making some kind of overall amp control thing that could include: an HT delay (not necessarily because of the cathode stripping myth), output relay, bias monitoring (using the inbuilt ADCs in the chip), individual tube status LEDs, imagination is the limit!

It sounds like great fun to play with and I can't wait until it arrives to be honest!

Has anyone else played with this kind of thing? Did it turn out to be overkill or did it prove itself as useful?
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Old 26th July 2010, 02:53 PM   #2
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813 SE triode amps

A processor in an amp is very interesting, I think. Seems like they are in just about everything these days, except for food and hand tools.
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Old 26th July 2010, 03:56 PM   #3
Serge66 is offline Serge66  Switzerland
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Hi,

It is exactly what I intend to do!
I found some relays that can be activated via a serial link from the Arduino.
A LCD panel (2x16) is also in my project to display heater and HV values.
Go for it.

Cheers,

Serge
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Old 26th July 2010, 04:25 PM   #4
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Quote:
Originally Posted by bigwill View Post
I have ordered an Arduino for messing with, and the chip it's based around is available very cheaply. I was thinking about making some kind of overall amp control thing that could include: an HT delay (not necessarily because of the cathode stripping myth), output relay, bias monitoring (using the inbuilt ADCs in the chip), individual tube status LEDs, imagination is the limit!

It sounds like great fun to play with and I can't wait until it arrives to be honest!

Has anyone else played with this kind of thing? Did it turn out to be overkill or did it prove itself as useful?
I have used PIC micros in my designs for a good while now.
Output relay control (power up delay).
DC protect supervision controlling output relay.
Bar graph driver.
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Old 26th July 2010, 05:49 PM   #5
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Check out this link: 813 SE triode amps

I think it would be great to have something to adjust fixed bias automatically. I'd be curious if I could do that with an anti-thermistor
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Old 26th July 2010, 07:50 PM   #6
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The ATmega32 only has 8 muxed ADC inputs, so you'll need to add more muxes if you want to dip your hand into every single part of the amp. It has no onboard DAC, so if you want to adjust things, you either need a particularly good lowpass filter to clean up the PWM channels (2 x 8-bit, 2 x 16-bit), or an external DAC (parallel or serial, and the ability to program it).

Tim
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Old 26th July 2010, 10:43 PM   #7
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The arduino mega (based on the atmega1280) is a much more "useful" uC, though the 128/328's found on the smaller unit's have there place to I suppose.


C# is my forte, But I really don't see the use of a uC in a tube amp, the highest logic level you could ever need would be a "re-purposed" 555 timer to generate PWM for cooling fans



I digress, The use of a uC to do nifty reporting of tube bias and voltage might not be so bad, but the thing about tubes that interest me, is there mechanical nature, so a good vintage bias meter, and voltage meter, to me, is more par for the course.

IMHO


YMMV
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Old 27th July 2010, 01:13 AM   #8
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Micro's are the bomb for housekeeping.
I have built a couple of guitar amps that used gates and flip-flops to control channel switching, but now I'm working on a multi channel version with some built in effects and, using logic ic's, the schematic is taking over my desk.
A micro is the only practical solution in my case.
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Old 27th July 2010, 01:53 AM   #9
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Micros + tubes = versatility. Whether this versatility is useful or not is up to the user.

In the live performance for musical instruments arena it is almost a necessity. Commercial "midi tube preamps" have been around for a long time. I have an old ADA MP-1 that I have used for about 10 years, and I got it used on Ebay. It uses a micro to control a pair of 12AX7's. You can tweak the controls until you find the sound of your dreams and save it in memory. Then one stomp of a pedal and this sound is back. Several sounds can be stored and recalled at will in a live performance situation. The MP-1 is an old design and the user interface sucks. SO.....I designed my own. It used a bit more sand and it was 10 years ago, but it used a PIC16 series chip controlling some National Semiconductor EQ and gain control chips in the forward and feedback paths of a tube preamp. There is a new one in the works using much more modern parts, and it goes inside the guitar, and so does the tube preamp. It deserves to be seen, so I built my own guitar with a clear Lexan pick guard to show off the chips, mosfets, and tubes. It won't be done for a while, but it will be seen here when done.

In the home HiFi world a micro can easilly handle bias control, power supply sequencing, and even store setups, data log bias voltage VS tube current to report tube condition to the user. You could even use your amp to match tubes. How far can the micro go in a tube amp? Well you could use a specialized micro like a dsPIC to design a modulated SMPS for serious efficiency improvements. Sound far fetched? Not really, I built one of those too. It won a prize in a Circuit Cellar design contest. Details, including the entire project submission is here:

Microchip 16-bit Embedded Control Design Contest
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Old 27th July 2010, 05:40 AM   #10
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Yep, fully aware of the uC applications (im a programmer/cisco network eng by trade) as-well as a avid developer on the arduino forums.


I like my tube amp tec, crusty
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