Iron Age Audioworks

I've gotten to hear this stuff. Sounds great! Clean details and yet not sterile but very lovely sounding.

I have some M2s here Im burning in to test in some gear as well. Really excited to hear them!

Cool to see your stuff coming out Matt!

Here's the 1222.

Been running around. I’ll try to post a couple of clips soon. 

I have a pair. They are standard 2520 foot print. I'm doing an open amp shootout with them and a bunch of others. 

Yes, we make the M2 (the one blackdawg has) as well as a 2520 style (ADO), a Neumann OA10 style (NDOA), a Jensen 918 (JDOA), and a Quad Eight AM10 (QDOA).

They’re all a little different in amount and color of distortion, as well as their break over point for class A / AB operation and ideal source impedance for noise. I have a little write up about this I’ve been working on but it’s not quite finished yet.

kcatthedog

Differences between real op amps are things like slew rate, phase margin, gain, etc. but these all kind of add up to what we hear, which is distortion.  Distortion is just the difference between what we put in, and what we get out. If you have a perfect op amp distortion would be zero, because it would have infinite slew rate, open loop gain, and so on – a linear, 1:1 transfer function, or map between the input and output. But real op amps can’t do it – and that’s why they all sound different. Distortion products come from a nonlinear, non-1:1 transfer function.

Distortion comes in harmonics, or multiples, of the input signal. What that means is, if you put a sine wave at 1kHz through an amplifier, you will get out a large signal at 1kHz, but also smaller signals of 2k, 3k, and so on. We call even multiples of the input signal (the fundamental frequency) even-ordered, and odd multiples odd-ordered. If the transfer function is asymmetrical in its nonlinearities, you get even-ordered harmonics. If the transfer function is symmetrical, you get odd harmonics. All amplifiers make both. Single-ended circuits (where an output device is producing the entire output waveform, like class A amplifiers) are asymmetrical, so they tend to have more even harmonics. Push-pull circuits (where two output devices are each contributing parts of the output waveform, like class AB amplifier) are symmetrical, so they tend to have more odd harmonics. Op amps can be both!

Most discrete op amps have the output stage set up in a way that the complimentary or quasi-complimentary pair are class A for low output currents and class AB for higher output currents. In class A mode each output transistor is fully replicating the output waveform. In class AB the current demand is too much, so the upper and lower output transistors each make their respective half of the waveform, and sit idle during the other half. What this means is at higher loads the distortion is going to increase significantly due to crossover distortion (caused by the part where the transistors are “handing off” the signal). That sets up a situation where we may love the way an op amp sounds at low levels, but not so much at high levels…or vice versa. Or maybe there’s a sweet spot there. Higher order distortion products tend to be more present or audible than lower order products, but lower order distortion can mask higher order distortion. So, generally speaking, we want to make sure that higher order products are lower in amplitude than lower order products.


Even order distortion is made up of octaves of the fundamental frequency, and is often described as “sweet” or “harmonious,” but can also sound “thick” or “muddy”. Odd-order distortion is commonly described using words like “bright” or “detailed,” but can also be “gritty”. So the specifics of the music you’re working with or listening to may favor one op amp over another.
Or just personal preference.

Here's an example. This is just a simulation in LTSpice, so it's only as good as the transistor models you use, but it should give you an idea of what these differences could sound like.  The simulation is a balanced input at unity gain, with a +4 dB signal going through it with a 10k load. 

I tried to make a graph to kind of envision what this would look like. The vertical axis is the amount of even-ordered distortion, and the horizontal is the amount of odd-ordered distortion. The numbers are in %THD *  1 million (to make nice round numbers).  So the OA10 point is showing a THD of 0.0018%, which is almost all even-ordered (17.7 vs .29). But you can imagine that this would sound very different than a 2520, which has much less overall distortion (0.0003% THD) but the same amount of odd-ordered distortion! 

This should be not too surprising, right? The 2520 is called edgy and bright, while the OA10 has a reputation of being thick.



Of course, it isn't quite as simple as all this because lower order harmonics tend to mask higher order ones, and all of these op amps have strongly even-ordered distortion. Also, I’m doing a simple percent sum of each harmonic, and in reality they sum by squares. So this is just a way to compare, not without flaws.

And every circuit is going to have a different kind of map like this, because the load, source impedance, etc. that you give the op amp will make them behave differently. But these small differences are what we hear.

I just appreciate that the first photo has a MOTU 16a in it. Love that thing. And really digging this summing mixer and that 4ch pre on the site! Might need to get me one

The next product up for release is the CS1. 

The CS1 is a three module channel strip. It began life as the channel strip for a console I wanted to make for myself. It has a triple input module using a shared amplifier for gain duties. The mic input comes in through a Jensen input transformer and has a pad and +48v controls. The DI is an unbalanced high impedance circuit, and the line input uses a discrete balanced transformerless amplifier (socketed DOA 1). These three feed the shared amplifier (socketed DOA 2) with a common gain knob and a transformer balanced output using a Cinemag steel core low inductance transformer. This is terminated with a continuously variable trim. This feeds a post-trim, balanced mic-pre out patch point.

From there, the signal goes into the EQ via an op amp (socketed DOA 3) and into a simple high pass filter circuit, selectable between 50 or 80 Hz. This is isolated from the EQ by a discrete buffer which adds a touch of character to the tone. The EQ itself is a three band peaking Baxandall style inspired by one of my favorite designs. Each band has +/-15 dB available on five switched frequencies and an "off" position so the gain knob doesn't need to be perfectly centered when not in use. It uses two op amps (DOA 4 and 5) and has a balanced insert / EQ out patch point available via a second Cinemag output transformer.

The third module is a balanced insert return (DOA 6) feeding a console style line amplifier (DOA 7) with 12 dB of gain in hand at the "fader" knob. This feeds the direct out, balanced by a third Cinemag transformer.

As you might imagine, there's a lot of tone possibilities here. The gain staging can be adjusted to your needs, and it's really versatile as a tracking box as you can take the signal at any point you like out of the chain. The box comes with the M2 op amp, which is a tight, clean op amp with very high headroom. This pairs really nicely with the Cinemag steel core low inductance transformer for some heft and weight. It just sounds like a console.




Like all of our stuff, this is made in the USA. The cases are made and painted in the USA, and everything is soldered by hand and wired here in Texas.

Also like all of our stuff, customization is welcome. Frequency points, op amps, output transformers, multiple channels in a box...you name it, we'll figure it out. The one Vinnie posted a picture of earlier was a custom two channel box using Quad Eight op amps and transformers throughout.

We're preparing for the first production run now. You can order one in advanced from the website.

Looks really good Matt can’t wait for a couple of guys to tell us how they sound.