Simple Design tool for Audio Amplifiers

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caryking

Member
Joined 2021
Folks, I need help... I am a MAC user and am looking for a simple tool to help design a single ended circuit. I was recommended the Broski Tube CAD software solutions; however, they all appear to work on Windows systems.

Any suggestions or a simple online solution?
 
C

caryking

Member
Joined 2021
Jan, I understand that the software can’t design in…. My goal is to create the simplest EL34 Single Ended circuit I can. Test it through simulation, then start a build. If it sounds the way I like, great! If not, keep messing with it…

My goal is to ultimately end up with something that has that old/vintage syrupy midrange that I prefer. Where todays tube amps are far more revealing, in the inner-detail, Im willing to give that up for significant midrange bloom. The reason, I’m choosing the EL34, is that they were closest (as I can remember) to the my older beloved 8417 Quicksilvers.

so, yes, I’m going to start with a simple, simple, circuit design, and go from there…
 
jjasniew

jjasniew

Member
Joined 2002
caryking said:
so, yes, I’m going to start with a simple, simple, circuit design, and go from there…
Click to expand...
Looks pretty simple to me. I like the beefy plate 'BH7. The draftsman should check his thumbs!

QA8417.png
 
C

caryking

Member
Joined 2021
Jan, I guess question is… what’s the proper terminology to use when looking at/for software that people use to design an amp?

jjasniew said:
Looks pretty simple to me. I like the beefy plate 'BH7. The draftsman should check his thumbs!

View attachment 1199697
Click to expand...

yea, I’ve looked at that design, many times over…. I plan on designing a single ended EL34 amp.

thanks though…
 
Diabolical Artificer

Diabolical Artificer

Member
Joined 2014
Valve amp circuit design is really pretty simple. First you start with the output section where the DC & some AC parameters can be lifted straight off the OP valves datasheet, EG it'll give you what the primary Z of the OPT you need, what HT/B+, the cathode bias conditions etc, this is especially true for common power valves like the EL34 & 6L6. For a SE design it's then just a matter of building another stage that will provide the needed AC signal to drive the OP stage with low distortion. As mentioned most of this can be done with a calculator and piece of paper.

Have a look at The Valve Wizards site - https://www.valvewizard.co.uk/ which although slanted towards guitar amp design has excellent articles on valve amp design. If you want to use software tools, as a Linux user, I think you'll find it easier to get an old Windows XP machine which will run the majority of free audio analysis software like Psud2 etc, & use that as your workshop PC.There are other bits of free software for drawing load lines, calculating RC filters parameters and what have you, but there's no software AFAIK that does the whole thing, apart from the MK1 brain software that is.

It's then a matter of knocking up a prototype on the bench & measuring the various DC & AC parameters. Still, we all have our ways of working.
 
jan.didden

jan.didden

AX tech editor
Joined 2002
linearaudio.net
Paid Member
caryking said:
Jan, I guess question is… what’s the proper terminology to use when looking at/for software that people use to design an amp?
Click to expand...
As I mentioned before, there isn't one. After you have a design drawn up you have the choice of verifying it in a simulator or build it and measure.
The design software sits between your ears. But it has no user manual ;-) .

The whole design process is hard to describe. People typically 'just thought about something, maybe use a concertina splitter, or should I use an input xformer' type of thoughts. Based on dissecting many designs, reading books about amplifier designs, chatting up other designers, etc.
Very hard to bootstrap that process. Just like you cannot produce a world champion in, say, skating by explaining the rules.

Edit: there is some design software for simple building blocks, but that's really calculations rather than design. For instance, if you want to design a second order active low pass filter, you find the canonical circuit on the ADI website, and you can fill in some design values and that app calculates the resistor and capacitor values. But the design is already there.

Jan
 
rongon

rongon

Member
Joined 2009
  1. Linux - These simple Windows programs (PSUD2, etc.) should run fine in WINE.
  2. There are some excellent books on tube amp design. Some include tested designs you can build. For instance, there's a pretty nice push-pull EL84 design called "Bevois Valley" in Morgan Jones's book "Valve Amplifiers" 3rd Edition. The 4th edition has a push-pull 6S4 amplifier, but that's complicated by discussion about baffle step correction for a full range speaker. The 3rd edition design example is a better one to start from, imo.
  3. There is a version of LTspice (free) for Mac, or you can run the Windows version in WINE on Linux. It takes a while to learn LTspice (or any SPICE program) but it's worth the effort. There are threads right here on diyAudio dedicated to learning LTspice and there's even the web's best collection of tube models for LTspice here.
  4. There are many, many simple single-ended amplifiers published all over the internet. If you can run SPICE, you can take those designs and 'test' them in simulation, see what they're doing. Or just build one from scratch as a learning experience.
If you're committed to designing an amplifier and you've never designed one before, I'd start with a single-triode common cathode line stage (aka "line level preamp"), That's just a single triode (something like a 6N6P or a 12B4A is good), a 250Vdc power supply for the plate, a 6.3Vac transformer for the heater.
You'll need to know how to take the transformer's AC secondary voltage and rectify it to DC, then smooth it and adjust it to get a clean 250Vdc.
You'll need to know how to use the chosen triode's published load lines to choose the value of plate load resistor and cathode load resistor to set the operating conditions for the triode.
You'll choose an output DC blocking capacitor of the correct value to pass enough bass frequencies into the intended load.
You'll choose the input and output 'pull-down' resistors (grid leak and output load resistors).
If a volume control is desired, you'll need to choose the correct resistance value for least signal loss.

The configuration is called a common cathode amplifier stage because the cathode is coupled close to 0V (common) through the low resistance of the cathode load resistor, while the plate is at higher voltage and the grid accepts the signal. That's basically the first (input) stage of a simple single-ended power amp.

For a power amp, you'll need to design an output stage, which is a power output tube in common cathode configuration with an audio output transformer as its plate load instead of the plate load resistor. The transformer will need to have the correct primary impedance for the output tube you choose. You'll also want to select the correct power handling capacity (in watts), primary inductance, etc. for mating the output tube through the output transformer (OPT) to the speaker load you'll be using.

The simplest two-stage single-ended amplifier is basically two blocks coupled together.
  • Input (line) stage
  • Output (power) stage

Learn to design the basic building blocks in isolation, then couple them and study how they interact when put together.

This is a simple amplifier. There's no negative feedback (deliberately) applied, it's not push-pull so there's no phase splitting, there's no negative bias supply.

If all that seems like too much then I'd recommend building a well-proven kit like Tubelab's TSE or SSE (single ended) designs, or one of the Elekit offerings.

You won't build the perfect amplifier on the first try. The idea is to have fun with it.
 
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