Portable kit for working from home

If you’re looking for portable or non-rack gear to work from home during this crisis, a few suggestions below

I have a Circuit Mono Station arriving soon – that’s guaranteed to spark a few ideas and it’s a great antidote to sitting in front of a screen & clicking a mouse

The Waldorf Blofeld is a synth with lots of depth – definitely worth the time to get to know it. A product of synth pioneer Wolfgang Palm

Keyboards, Synth Modules & Groove Boxes

Novation Circuit Mono Station – excellent groovebox / sequencer with a built-in mono synth
Novation K Station keyboard synth – portable synth with 2.5-octave keyboard
Waldorf Blofeld Synth module (black) – multitimbral, polyphonic, wavetable synth module from German wizards Waldorf


Alesis Micro Limiter (recapped & modified) – portable drum smasher / variable ratio limiter
Really Nice Compressor – the definitive Nice compressor
Really Nice Limiting Amplifier – Nice with a bit more colour to it
Alesis Nano Compressor – more smashing from Alesis, far more capable than you might think


Boss CE-1 Chorus – the definitive chorus
Boss Voice Transformer – for vocal effects & vocoding
Boss RCE-10 Chorus – later Boss Chorus, still excellent
Boss RPH-10 Phaser – cult phaser – expensive but great
Waldorf 2-Pole Analog Filter – stand-alone filter from Waldorf
Alesis Nanoverb – portable, easy and the gated reverb is fantastic
Alesis Microverb 2 – more Alesis portable reverbiness

On the bench: UREI LA4 Compressors

I’ve just finished refurbishing a tidy pair of LA4 compressors. They are late-model silver-face LA4s with the chrome UREI badge so the same kind of age as the 1176 Rev G & H and 1178 stereo compressor

I fitted a new set of incandescent meter bulbs so they give that classic UREI orangey glow when powered up

They’ve been recapped with bigger reservoir caps in the power supply and higher-value bipolar caps in the audio path. They’ve been aligned in standalone and stereo-linked modes and will come with a stereo link cable and a set of new XLR pigtails




On the bench: Altec 1519A & 1612A Preamp Limiters

Two Altec limiters have been on the bench recently for testing & refurbishment. I’ve recapped & modified both units and am hugely impressed with them – they’ve really exceeded my expectations

They seem to be typical of 70s industrial / installation gear with terminal strip i/o, balancing transformers and plugin preamps to match sources. I think a lot were installed in schools, churches & etc and were setup then left alone. They have two inputs – nominally one mic and one line input which are mixed together – and a switchable output limiter

Altec 1591A on the bench for a recap

Altec 1591A audio board before recapping

Shop update January 2020: Keyboards

I have a few new items in stock or arriving soon:

Moog Sub Phatty


Novation Circuit with custom UDG case

Waldorf Blofeld

Doepfer MS-404

Yamaha TX816

Waldorf Streichfett Synth

On the bench: Orban 414A Compressor

This Orban 414A is in exceptional condition and refurbishing it has been something of a labour of love. We’ve rebuilt & recapped the power supply and switched it to 220 Volt via an internal jumper. The electrolytics in the audio path have been replaced with Panasonic bipolar caps and the original incandescent bulbs replaced with white LEDs, dimmed down so they’re not too bright. The back panel had the option for XLR connectors so we’ve fitted Neutrik XLRs wired in parallel with the original barrier strip. This means no pigtails are needed to hook the compressor up…

The whole process took far longer than planned but it’s a great-sounding compressor, beautifully made in the 1980s, and I think it deserves to be brought back to peak performance

Orban 414A in the shop

Orban 414A back panel XLR mounting holes

Orban 414A meters

Orban 414A power supply

Orban 414A meters

Orban 414A label

Shop Update January 2020: dbx stereo compressor pairs

We’ve been working through our stock of dbx compressors, refurbishing them and assembling stereo pairs. These have been tested, cases repainted, metering aligned and knobs & switches replaced as necessary, and they’ve been checked to verify a decent stereo match even when not using a stereo link cable. We have the following stereo pairs packed & ready to ship:

dbx 160A

dbx 160X

dbx 160XT

dbx 163X

Vocoder Obsession

Vocoder Obsession isn’t recognised by the medical profession as an illness but, if you have it, you’ll know the symptom: an irrational desire to buy hardware to make robot noises

Luckily for you, Dr Vocoder is here, ready to prescribe & dispense treatment…


Voocoder Chronology

Year Name
1977 EMS 3000
1978 Korg VC10
Sennheiser VSM201
Electro-Harmonix EH-0300 Vocoder
1979 Roland SVC350
Roland VP330
Bode 7702
Moog Vocoder
Synton Syntovox 221
1981 Synton Syntovox 222
Dynacord SRV66
Echolette SEV66
1986 Korg DVP-1
1987 Roland VP70
1988 Krok 2401
1990 Electronica EM26
1992 Korg Wavestation A/D
1996 Boss VT-1 Voice Transformer
1997 FAT PCP330 Procoder
MAM VF-11 Vocoder
1998 Quasimidi SIRIUS
1999 Electrix Warp Factory Vocoder
2000 Korg MS2000/2000B
Korg MS2000R/BR
Prosoniq Orange
2001-ish Doepfer A129 system
2002 Logic EVOC20
2003 Korg microKORG
NI Vokator
2005 Analog Lab X32
2006 Korg Radias
2010 Electro-Harmonix V256 Vocoder
Undated Sky Soundlab Voice Spectra
© 2020 BN1studio.

Basic list from a Sound on Sound feature via a web forum post. Updated & expanded February 2020

Forum snippets
Vintage synth Explorer “Best Vocoder”

Sound samples
Not all these are vocoder effects but you get the idea…

Chorus Pedals & Rack Effects

Chorus pedals & rack effects are great devices for widening sounds & giving movement in the stereo field. Each one is different and they all have their strengths & weaknesses so, to cover all the bases, I used to buy every one I liked the sound of. Top of the tree – as ever – was the Boss CE-1, closely followed by the Dimension D

Chorus may be out of fashion with some people in 2019 but, for the chorus lovers out here, see my Top Ten and my list of items in stock

Chorus & Phaser pedals & rackmounts in stock:

Aphex Dominator – Hardware Setup

Aphex Dominator II Model 720

The Aphex Dominator is a powerful tool but, at times, it’s not obvious what it’s doing or why. To appreciate it properly you need to patch it into an established signal chain, align it to the peak level you’re working to then set levels to get the required degree of limiting

This guide was written to help setup a Dominator in a podcast / broadcast chain but much of the detail is applicable in other setups

  1. RTFM
  2. Establish the peak level you want in your signal chain
  3. Put the Dominator in the chain & set levels approximately
  4. Set the EQ and density at midpoint >0<
  5. Set the release slightly above midway
  6. Turn the coarse limit control all the way clockwise
  7. Set the fine limit control to the midpoint >0<
  8. Set the range switch at zero (red led lit)
  9. Check for unity gain with the input gain at >0<
  10. Adjust input & output gains on the audio interface to set operating level
  11. Wind the coarse limit setting back so it just lights on program peaks
  12. Turn it one click clockwise so it doesn’t limit
  13. Use the fine limit control to get a nice threshold for limiting
  14. Increase the input level till you see gain reduction (GR) on the meter and hear lots of limiting
  15. Shorten the release time till it sounds good on your program material (see notes below)
  16. Experiment with the density & EQ controls with a bit of GR going on
  17. Back off the input level to reduce GR to a sensible level or till it sounds good to you
  18. Verify that the limited max output level ties in with the level required. If it’s out, rejig DAW input & output gains accordingly
  19. Check for unity gain with no GR, adjust input & output gains accordingly


  • Release time is really critical
  • Release & density make a big difference to the sound
  • The density control balances the contribution of the LF and HF signals to the limiting. With the control in the >0< position the bands are balanced
  • When misused the spectral balance can change quite dramatically
  • LF & HF band controls allow equalisation of the signal
  • There are switches for the turnover frequency of each section
  • Every control interacts and it takes a while to get the best out of it
  • You can make it super transparent or make it pump quite a bit
  • If in doubt back off the input level till GR is sensible
  • Turning the release clockwise makes release time shorter – the opposite of every other limiter ever made
  • Did I mention that release time is really critical?



dbx 900 Series Racks & Modules

dbx 900 Series Rack & Modules

In the early 1980s dbx introduced the 900 Series, a modular processing system using a 3U chassis with built-in power supply. Sound familiar? Yes, it’s one of the progenitors of the 500 rack system

One of the few manufacturers that supported the dbx system was Aphex – now a player in the 500 Series market with both racks & modules

The 900 Series had (at least) two racks

  • FS900, 1U, two-module, self-powered rack
  • F900A , 3U, eight-module, self-powered rack

Compatible modules included

  • 902 De-Esser
  • 903 Compressor
  • 904 Noise Gate
  • 905 Parametric Equaliser
  • 906 Flanger
  • 907 Stereo Gated Compressor Slave
  • 911 Type I Noise Reduction
  • 941A Type II Noise Reduction
  • 942A Type II Noise Reduction
  • 929 Hiss Reducer
  • 993 Mixer module
  • Aphex Compellor 9301
  • Aphex Dominator II 9721
  • Aphex Expressor 9651
  • Aphex Aural Exciter
  • Aphex Equaliser
  • BBE 702


I have a number of 900 Series items in my workshop queue and will update this page when I have more information & photos

Preservation Sound has more info on the 900 Series plus a download link for the original marketing material. More info here

A few forum links & threads for research:

The DBX 900 Series





Valley People Dyna-Mite

A piece of gear that caught my attention early on at Eden Studios was a Valley People Dyna-Mite. Housed in an ugly beige plastic case it stacked two channels of Dynamite in a very small package. Despite looking like a toy, it proved to be a huge-sounding device capable of eye-widening compression. A year later, at Sarm East, I discovered the epically-wonderful Allison Research Gain Brain, a masterpiece of savage compression & distortion

Later on I discovered the shared heritage of these two items, and the story of their creator, Paul Buff. His story has been written about online already and there’s a longer piece here, and more here, so no need to duplicate it

I’ve been working my way through the Valley back catalogue, buying & restoring these remarkable compressors. In the list below, everything with an underlined link is either in stock, or sold previously, and has a description with detailed photos. If you want an unvarnished opinion on the merits of the various models, email me

Significant pieces of Valley gear, in approximate chronological order, include:


Allison Research

Photo Credits: © Universal Audio & © The Telos Alliance

Shop update November 2019: Equalisers

Late 2019 round-up of equalisers, filters & etc. I’ll have an update on some of the more off-the-wall items – like the Realistic inductor stereo equaliser – soon


Filters, Dolby, Vitalizers, etc

On the bench: dbx 160X Compressors

dbx 160X stereo pair with sequential serial numbers

dbx 160X stereo pair with sequential serial numbers

I am working through a delivery of ten dbx 160Xs from the USA. They have been refurbished with new UK power plugs (Euro plugs available on request), pots & switches cleaned and metering aligned. All are in good shape with just a few knob caps required to make them spot-on. As usual with vintage kit they have age-related marks and are not cosmetically perfect

I have made up three stereo pairs – one pair with sequential serial numbers, one with close serial numbers and a third pair which are selected to match age & condition. Links below

On the bench: Valley International 440 Compressor

I have another great Valley compressor in for a 220 voltage swop & power supply recap. Just arrived from the USA, it’s in really tidy condition. These compressors sound amazing – if you’ve never owned one, I can recommend any Valley unit as the ultimate antidote to boring compressors

When it’s ready you’ll find it here. Email if you need more info

Valley 440 on the workbench

Valley 440 on the workbench

On the bench: Orban 622B

Orban 622B

I’ve just taken delivery of a really tidy Orban 622B equaliser. These are great, useable 4-band equalisers with per-band bypass switches like a Klein & Hummel. The example has all-original knobs & switches and looks like it’s been tucked away in a box for the last thirty years

I’ll be refurbishing this with new caps, upgraded power supply and replacement of the troublesome Tantalum caps with electrolytics. When it’s ready it’ll be listed here. Update soon!

Hail the Effectron!

I’m a bit of a Deltalab fan. The first one I used was an Acousticomputer – it was rubbish, but very entertaining rubbish. The later Effectrons really hit the spot and, even now, are great tools for warping & twisting sounds

I am collecting Deltalab & Effectron info together on this page so check back for updates!

Some items have a PDF link to a user manual or catalogue or a schematic

Product links & Info


Super Time Line

Other Deltalab kit


Random weblinks

Preservation Sound


TapeOp forum



Music Electronics Forum


DeltaLab Effectron, I, II, III ADM (Blue) Digital Delays From The 80’s (what I know so far)

Youtube Demos


Youtube demo (weird noises mainly)


Period adverts


Effectron – PDF

Effectron II – PDF

Effectron Ad 1 –

Effectron Ad 2 –

Effectron I - II - III features

Effectron I – II – III features

Effectron Ad 2

The Dolby Trick – Hardware Setup

I had an enquiry recently about how to setup a 361 to perform “The Dolby Trick”. This is the basic setup:

Audio routing

  • DAW (effects send, bus, etc) —> audio interface —> Dolby “line in”
  • Dolby “to rec” output —> audio interface —> DAW channel line in

Send the signal to the Dolby & record the output. You’ll need to compensate for the audio interface latency

Dolby 361 back panel



 Hardware setup

  • Set NR in and Rec on (white & red buttons pushed in)
Dolby 361 with Modified Cat 22 Dolby Trick Card

Dolby 361 front panel


If you’re using a standard Cat.22 Dolby A card the output of the 361 will be the encoded signal – ie the original signal plus the processing. This means balancing the effect will take a bit of juggling with levels to get the effect you want

For a deeper effect & easier use a modified Cat.22 is a useful tool

How it works

As you reduce the level going into the Dolby the effect will increase. Dolby A encoding uses a multiband expander so more level = less effect, the inverse of a compressor, and the inverse of the decode process. For the Dolby Trick there is no decode process, just encoding

The NR in / out switch should give an obvious effect if you monitor the return signal. If you hear no effect, reduce the level into the Dolby


Dolby A passes the audio signal through a four-band compander. A sidechain determines the level of encoding for each band. In the encode process the sidechain-generated signal is summed with the audio, to create the encoded signal, and recorded to tape. On playback the sidechain recreates the encoded signal and subtracts it, decoding the signal

As a compander, Dolby A raises low-level signals during recording and lowers them again on playback. This has the effect of reducing tape noise by the same amount. There’s a lot of subtlety in the details – in the way the bands are chosen, the amount of expansion & compression and how these are optimised for maximum perceived effect and minimum artefacts


The 361 (and earlier 360) are hardware interfaces with no audio electronics but with input & output transformers. They have the power supply and switching to route audio to and from the Cat.22

The Cat.22 has audio electronics, input & output stages, sidechain and four bands of processing on one card. It’s all Class A, transistor-based circuitry

The separation of audio path and support hardware was a highly significant move. It meant Cat.22 noise reduction cards could be used in other hardware interfaces such as the M16 & M8 multitrack units and film playback systems. It also allowed the next generations of noise reduction, Dolby SR, to use existing interfaces

Ray Dolby was a clever guy, a true audio pioneer

On the bench: Yellowhammer

Yellowhammer is a distortion box designed for studio use. It’s at second prototype stage and is being road-tested by a number of producers & engineers

It’s a passive device which uses transformers, diodes, inductors & capacitors to generate distortion & filter the results. All the controls interact, making it a little unpredictable, but it’s easy to navigate once you start using it

The next prototype will be a rackmount version though I think there may be demand for a freestanding unit like this one

For more information or to arrange a demo, email yellowhammer@bn1studio.co.uk 

To hear the Yellowhammer in action, upload your sound samples via WeTransfer to upload@bn1studio.co.uk and we’ll run them through the Yellowhammer

Yellowhammer prototype 2 Sketchup drawing
Top panel layout & drilling template
Input XLRs & transformers being test-fitted
The green-fading-to-yellow paintjob didn’t pass inspection
First set of knobs, before lettering
New knobs & lettering in place – now ready for testing

On the bench: Symetrix 501

This pair of Symetric 501 compressors has just arrived from the USA. They will be tested, switched to 220 VAC and recapped before being listed in the shop

These are great-sounding VCA compressors with a big reputation. They have a switchable sidechain, switchable auto attack/release, stereo link switch and a separate limiter

The 501 came in a couple of versions: early models used the TA-101 VCA – designed by Paul Buff of Valley People fame – whilst later models used a dbx 2181 VCA. I have one of each in stock

On the bench: TC Electronic 1220 Stereo Equaliser / Preamplifier

I’ve just finished recapping & testing this TC equaliser / preamp. It’s a useful, musical-sounding eq with a decent amount (20 dB) of gain in hand. Each channel has two bands of EQ, ±20 dB gain control & bypass switch

This 1220 is in nice condition and still has all the original knobs & switches. It’s in the shop now

TC Electronic 1220

This has the usual TC Electronic upside-down PCB

TC Electronic 1220

Simple EQ section with no electrolytic capacitors

TC Electronic 1220

Power supply and input / output on one board, recapped with Panasonic caps, bipolar for the audio section. PSU bypass caps are on the other side of the board

On the bench: McMartin LR1004C Limiter / Compressor

This McMartin LR1004C Limiter / Compressor came from a radio station in the USA and dates back to the 1970s. The limiter is based on a diode bridge, like the Neve 2254, and the compressor is switchable. Both sections sound awesome when crushing drum tracks – sound samples to follow

I’ve recapped the unit & will replace the power transformer so it can be used on 220 Volts. The attack & release pots are inaccessible so I’ll move them to the front panel & source some suitable knobs

Note the lovely horizontal meter – proper meters like these are an endangered species now and have become diabolically expensive

The LR1004C will be in the shop when ready

Under the hood

McMartin LR1004C Limiter / Compressor

Guts shot

McMartin LR1004C Limiter / Compressor

70s orange plastic compressor in/out rocker switch

McMartin LR1004C Limiter / Compressor

Matching power switch

McMartin LR1004C Limiter / Compressor

Neve-style horizontal meter shows GR or output level

McMartin LR1004C Limiter / Compressor

Compressor board and line output board

McMartin LR1004C Limiter / Compressor

Lots of space for attack & release pots to be added

Audio test files

Drum room test audio file processed through Alesis Micro Limiter and a modified Alesis Micro Limiter

This test is anything but definitive: levels have not been matched and it’s extremely hard to match settings on these units

Original file

File through modified Alesis Microlimiter

File through unmodified Alesis Microlimiter

Misc SR-JV80 links & info

A growing collection of miscellaneous info about Roland SR-JV80 synths such as the JV-1080


Roland synth modules for sale



SR-JV80 expansion boards for sale



List of expansion boards



Compatibility Guide for expansion boards



Roland main SR-JV80 page



Don Solaris



Gearslutz Favourite SR-JV80 expansion boards poll



Nathan Sheldon patches



Soundprogramming.net page


Dolby Noise Reduction

Professional Dolby Noise Reduction

Dolby A noise reduction (NR) was used on millions of 16- and 24-track 2″ multitracks and 2-track masters. It’s a 4-band compander which boosts levels on recording, and compensates on playback, thereby reducing noise

Dolby SR, the successor to Dolby A, offered around 10 dB more noise reduction. Tapes encoded with SR require an SR card for decoding

Domestic Dolby Noise Reduction

Dolby B was a domestic NR commonly used on cassette recorders. In many ways a simplified version of Dolby A, B was s single-band NR system, boosting high frequencies on record and reducing them on playback. As with Dolby A, B required accurate level & frequency response matching for best results. It had the happy by-product of making B-encoded tapes sound brighter on non Dolby-equipped playback systems

Dolby C and Dolby S were later domestic systems

Professional Dolby hardware

Dolby hardware separates the host and NR card. The host typically provides audio input / outputs (via transformers on the 361), power supplies and remote switching whilst the NR card performs audio functions only

Dolby produced hundreds of card types for audio, film, broadcast & etc. In single- and dual-channel models these fell into two main categories, first- & second-generation models.The noise reduction specification (A, SR, etc) remained constant across hardware generations but cards & hosts are not interchangeable between generations as Dolby changed connector standards

First-generation hardware (supports Cat 22 (A) and Cat 280 (SR) cards)

  • 360 – single-channel interface in 1U
  • 361 – single-channel, updated version of the 360
  • 362 – dual-channel in 1U, electronically balanced, front-panel trims
  • 365 – dual channel in 2U, electronically balanced, front-panel trims

Second-generation hardware (supports Cat 350 (SR), Cat 450 (A) and Cat 300 (SR / A) cards

  • 363 – dual-channel in 1U, supports SR & A

For multitrack systems Dolby produced the ubiquitous M16 (16-channel) rack and the later 8-channel expansion. The M16 used standard Cat 22 cards with separate Cat 44H i/o interface cards. The M16 was superceded by the 24-channel XP24 SR rack


More info from Sound on Sound


Reverbs & Effects for sale are here

Page under construction

Before there were digital reverbs there were reverb plates, springs, mechanical reverbs  and – of course – reverb chambers

A reverb chamber is a simple idea – take an empty room, fit a speaker and a pair of microphones and create natural reverb. It’s simple in theory, and hard to do in practice, but there were (and are) some great chambers in larger studios

The plate reverbs was invented by EMT in 1957 and used a suspended steel plate with a transducer and a pickup (later, two pickups for “stereo”). The transducer energised the plate and reverberation was created by the sound waves travelling around the plate. Plate reverbs are still in use, and in production, 61 years later

In the late 1970s EMT began research into digital processes to quantify & generate reverberation. This led to the 1976 EMT 250, still one of the most feted reverbs in the world

The other pioneering reverb company at that time was Lexicon in Waltham, Mass. Lexicon and EMT had one thing in common – Dr Barry Blesser, a founder of Lexicon and designer of the 250 for EMT.

EMT had a background in broadcast and high-end audio products whereas Lexicon was a typical high-tech company which grew in the shadow of MIT


Reverb Top Ten

  1. Lexicon 480L
  2. Lexicon 224XL
  3. EMT 240
  4. Lexicon 224
  5. EMT 250
  6. AMS RMX16
  7. Lexicon PCM70
  8. EMT 244
  9. Quantec QRS/L

Modifications, Upgrades & Recapping


We do a number of modifications including a high-pass filter mod for the Cloud CX335. Email workshop@bn1studio.co.uk for details


We can source output transformers for dbx compressors. We can supply dbx 160X or dbx 160XT compressors with the transformer fitted or retrofit a transformer to your dbx. Email workshop@bn1studio.co.uk for details


We can recap most pieces of gear. Equipment we’ve recapped to date includes:


In Preparation

We have quite a list of gear in prep. When it’s complete it will be for sale in the shop. Till then you can fin it on our In Prep page


Equalisers for sale are listed here

In theory, equalisation is one of the simplest audio tasks. That doesn’t stop there being thousands of EQs to choose from, using hundreds of different approaches to a couple of of basic topologies

The earliest equalisers were used to flatten the frequency response of fixed telephone lines. They were typically LC (Inductor / Capacitor) equalisers followed by a valve gain make-up stage. They were designed for permanent equalisation and would have a fixed HF boost matched to the line

The advent of equalisation in sound recording and cinema audio playback led to variable equalisers like the legendary Pultec EQP-1A. The development of transistors led to equalisers with more frequency bands and greater flexibility

Cost is a big factor. Cheap EQs can work well but are likely to be limited in flexibility and precision. They are also unlikely to be easy & enjoyable to work with

At the other end of the scale, high-end equalisers like the GML 8200 and Massive Passive offer great flexibility, accuracy & repeatability – at a price

The middle ground is where the price / performance ratio works best. Great affordable, usable EQs include

Equaliser Top Ten

  1. GML 8200
  2. Pultec EQP-1A
  3. Massive Passive
  4. Neve 8108 console EQ
  5. Klein & Hummel UE400

Honourable mentions

Shop Update January 2018

Here’s to a successful New Year!

Incoming 2018:

* Empirical Labs Distressor EL8X (pair)
* Empirical Labs Fatso EL7X (stereo)
* MXR Dual Limiter (stereo)
* dbx 160XT (pair) with sequential serial numbers, mint
* dbx 160A (pair) with sequential serial numbers, excellent
* dbx 160X (pair) with output transformers, excellent
* dbx 163X (pair) modified, recapped, rebuilt power supply
* NTP 179-500 Limiters (pair) in NTP 1U rack
* Aphex Dominator cards (pair) for dbx rack, NOS (New Old Stock)
* Valley People Dynamite (stereo) original version in 1U rack, recapped, rebuilt PSU
* SPL Transient Designer (2-channel)
* SPL Transient Designer (4-channel) with XLRs

* UREI 546 Stereo Parametric Equaliser
* UREI 530 Stereo Graphic Equaliser, rebuilt, new slider pots
* UREI 535 Stereo Graphic Equaliser, rebuilt, new slider pots
* White 4100A Stereo 10-Band Equaliser, inductor EQ
* White 4000 Stereo 10-Band Equaliser, inductor EQ