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V25 Equalizer



The Iron Age V25 is a 500 series format V2 1RU equalizer.

It features a proportional Q, bridged-T circuit topology with fully symmetrical active boost and passive cut, true bypass, and an all-discrete signal path.


You get a no compromise professional tool that works in all phases of the recording process, with an exceptional and unmatched midrange and headroom for days. Any track, any mix, any source - it helps you achieve your sonic goals.

Each equalizer channel is a three-band, selectable frequency design using two hand-built discrete op amps for gain. There are 18 center frequencies divided into three bands (Low, Mid, and High) as shown below:


30 Hz







400 Hz







5k Hz






Each band features up to 12 dB of reciprocal boost or cut in stepped increments of 2, 4, 6, 8 and 12 dB using a bridged-T filter design. The same filter bank is switched between the feedback loop of the amplifier in boost and a passive circuit in cut, which ensures that the boost and cut points are completely identical. 

Passive circuits are separated by discrete transistor buffers, which contribute a unique character to the tone of the unit.

The bridged-T circuit implementation also features a proportional Q: as the amount of boost or cut is increased, the bandwidth of the filter is adjusted by a switched resistor to become more narrow. This allows for a wide range of use from broad-brush shaping to careful tone carving, but ensures that the filtering is never harsh and always musical.

The Low and High bands can be switched between peaking and shelving behavior. In shelving mode, the frequency response hits the indicated boost or cut level at the selected frequency and stays elevated or reduced through the extent of the audible range. This allows for musical shaping of the high and low extremes of the audio spectrum.

Additionally, the EQ features a switchable band-pass filter with -3 dB points at 60 and 16k Hz.

The module has a balanced transformer-less input stage using a third discrete operational amplifier.

The V25 uses the original M2 discrete operational amplifier, designed and built by us. 

EQ Frequency Response

Curves plotted with actual data from a production V2.

Response curves on Tracking Mode with high and low bands set to shelf:

LF icon
Low frequency response
MF icon
Mid band frequencies
HF icon
High band frequency response

User Review

Patrick Meany @pmeanyaudio

The Function:

“Musical” is an easily overused term in the world of EQs, but I promise that from time to time, you’ll find yourself hitting the bypass just to make sure you’re doing something, because every change you make sounds so natural, and always pushes a source towards sounding more like it ought to be.  The 30hz on the Low band will add weight and heft to your sources, and when exaggerated, will start to push the output transformer in a way that helps the low end of your sources speak more when the mix is quiet. The Mid band also sounds great at every frequency point and I found myself adding more often than subtracting. When I needed to take some mid range boxiness  from drum shells, the 400hz was perfect. The Hi band goes above and beyond functions of adding top end. Think of it as a way to add air; to open up the source and bring it to life without ever making it harsh or brittle. Try +9db of 17kHz on a ribbon, and find out what you’ve been missing.


The Form:

Of course, previous users of IAA’s 19” V2 EQ will already be aware of this unit’s sonic advantages. But what’s really new and exciting here is the hardware itself. IAA has a reputation for well designed hardware made by folks who take great pride and care in their designs, and the V25 is no exception. This unit features sturdy, custom-designed knobs that are a pleasure to turn, and I’m inclined to turn them quite a bit. 

The main difference here is that unlike the V2, this unit only has steps of +/-[2,4,6,9,12] which are perfect for making decisions while tracking. And while you’ve lost the ‘fine’ +/-3db control range from the V2, you’ve gained the ability to fit a lot more channels of EQ in a much smaller footprint; a very important consideration for someone who does so much mobile recording. Given 3ru, you could have 6 channels of V2, or potentially up to 8-10 channels of V25, depending on how large your 500 series chassis is. 


When I had this unit to test, I didn’t want to stop using it, and definitely did not want to send it back. The IAA V25 is a remarkable sounding EQ that will soon take priority in my EQ rack. 

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