The Alpine 3401, a proper parametric.
Behold, a new page and a new project.
Being a capricious and insatiable aspie, I became weary of the narrow-band limitations offered by the conventional graphic equaliser, when tweaking my pianos to the system's speakers. I toyed with building a stereo parametric EQ as they are persistently pricey, but I realised that the arduous challenge, the 'person hours' involved and the self-defeating expense were all too immense, and all for a piece of shabby and inferior electro-folk-art.
Being a capricious and insatiable aspie, I became weary of the narrow-band limitations offered by the conventional graphic equaliser, when tweaking my pianos to the system's speakers. I toyed with building a stereo parametric EQ as they are persistently pricey, but I realised that the arduous challenge, the 'person hours' involved and the self-defeating expense were all too immense, and all for a piece of shabby and inferior electro-folk-art.
I spied a rare auction possibility on Feebay, a bid in the last seconds with a sniping opportunity, I won, bravo Old Bean. It's an automotive antique Alpine 3401, seven band, proper parametric equaliser at a grand total of just under fifty quid. I was, and remain elated. Coincidentally the Alpine was delivered by Yodel. Disappointingly my local friendly hipster courier was not Yodelling an Alpine melody as 'they' handed over the goods. This curio in a carton was claimed to be destined for the dump, but I was there to undo its impending doom.
It is described as a 'trunk-mount unit, adjusted at the time of installation (no user-adjustable controls)'. Of course it has user-adjustable controls, I can see them! It would be bolted into a highly-advanced boy-racer's car-boot, one tweaks the non-protruding pots with a suitable screwdriver, but imagine the outrageous expense of a studio equivalent - probably many Shekels worth.
Having formerly fiddled with the aforementioned automotive Altai B005HE parametric EQ (which is disingenuous, it's just a graphic equaliser with turny-knobs and switch-selectable bands, but still a useful stereo mini-EQ), I know that as long as you use a well smoothed, 12 volt electro-magnetic transformer supply, car equipment is just dandy for the humble home studio.
As advertised, there were the obligatory dodgy RCA connectors on the rear. This happens as the sockets are flow-soldered by machine directly to the circuit board, the low quality shallow solder joints end up cracking, often stressed by the force needed to insert and remove the plugs. A simple case of sucking-up the aged solder and resoldering with good-old lead-based solder.
I spotted a gruesome repair job on one of the small separate Audio IN / OUT PCBs, an output 'Ground' track had bafflingly been burned-out or butchered, someone had barbarically bodged in a grotesque bit of wire to rejoin the regions. Needless to say, it was hastily reworked.
I spotted a gruesome repair job on one of the small separate Audio IN / OUT PCBs, an output 'Ground' track had bafflingly been burned-out or butchered, someone had barbarically bodged in a grotesque bit of wire to rejoin the regions. Needless to say, it was hastily reworked.
The 3401 requires a 12 volt DC supply, positive and negative, and a 'Remote' positive connection which would normally be supplied by the car radio to 'wake up' the Alpine EQ. I made a lead with an inline 2.1mm DC socket which connects to positive and negative, the positive bridges to the 'Remote' terminal to keep it switched on.
Upon testing, I was pleased with the new EQ and its authentic parametric-ness, very effective indeed. However, there was a load of noisy hash and hiss in the external audio wires. The issue was not caused by the DC supply, the 3401 has good DC regulation with a pair of 2200uF electrolytics and an inductor, and my 12 volt 500mA adapter is smooth.
I read a forum which suggested that the Alpine 3401 creates a noisy ground loop and compensates with noise rejection circuitry, I believe this is nonsense. The lack of a physical ground is the problem. My probing discovered that there is a ground connection on the output 'common' wires, but no ground for the input 'common' wires, the ground is separated by a 47uF capacitor, as are the left and right signal wires. Alpine ironically call this their 'balanced input section - for complete isolation of the signal path from the vehicle's electrical system, assuring noise-free installation'!
This means that when you connect a shielded lead to each of the four inputs, the shield is not shielding as it is capacitively coupled to both of the inverting inputs of two of the C4570C input op-amps, and these aren't grounded either. The inputs have some sort of figuratively floating fictitious ground, presumably reliant on a grounded shield of the input source device (car radio). Maybe this works in a car with the battery's shared negative terminal, but not in my retro hardware setup. Remember, it's good to have the positive signal wires capacitively coupled, as capacitors remove any DC lurking in the lines whilst allowing the alternating signal to pass, but the cable's shield must be directly grounded or it won't shield the signal wire inside. It works with the floating ground, but your leads will act as detectors of spectres, hissing and sizzling like bacon grilling. This is unacceptable, and fortunately easily fixed.
By grounding the two common wires of the front and rear inputs on the small connector PCBs, (on the external side of the ground capacitors), we are not connecting the unwilling op-amp inputs on the main PCB to negative as the associated 47uF capacitors block the connection, but we succeed in grounding the all-important audio input cables without obliterating the op-amps, so those pesky ground capacitors prove to be most helpful.
There are two small input / output PCBs, the front IN / OUT board and the rear IN / OUT board. As the outputs have a negative DC grounding track already on the connector PCBs, we can solder a wire from the output's ground to the non-grounded input ground. Bingo! The woeful noise is entirely banished whilst maintaining full audio quality and signal level. One could install a DPST switch which would be what I propose a 'ground lift' switch does.
We can see the noise by using my homemade line-level super-stereo sound meter. When the gain control is at zero it reads the true input line level, when set at MAX, the internal amplifier accurately doubles the input voltage. This booster circuit was added for reading small levels on obscure occasions like this.
I created DJ's level meter with a VU (Volume Unit) meter (based on the LB1409 IC, nine LED VU driver) from a deeply damaged 1980s cassette deck, which is fed by my internal dual op-amp bonus booster circuit and housed in a very wooden aspie chassis, devised to set the levels correctly around my devices. Consumer line level is -10dB, 0.447V peak or 0.316V RMS (voltage above zero), double these for peak to peak voltage. The first green LED is not a level reading, it's a power on light, overshadowed by the unnecessary radiant red power light. The noise level before the Alpine's grounding modification was an outrageous -12dB. After my modification, the silence is golden, even when the gain control was set to MAX. The parametric equaliser is now most marvellous, and another small triumph in my futile existence.
The Alpine uses a complement of C4570C dual op-amp chips to mix the bands and buffer the inputs and outputs, these op-amps claim to be of superior audio quality compared to others.
The EQ's power consumption is about 190mA. The capacitors are dated 1990, so I have another recent-retro gem, and apart from the tiny 0.125 watt resistors, there are no shrunken surface-mount components in sight.
This sonic sculptor measures 24 x 16 x 4cm and offers three stereo modes:
A two channel / one input mode - (front input / rear output) 7 band EQ.
A four channel / one input mode - (front input / front and rear output) with three front EQ bands and four rear EQ bands.
A four channel / two input mode - (front and rear input / front and rear output) with three front EQ bands and four rear EQ bands.
There are also two EQ bypass switches to compare the effected sound and individual front and rear output level controls.
All input impedances appear to be about 11k ohms, the output impedance is 980 ohms for the front and 1.3k ohms for the rear.
This sonic sculptor measures 24 x 16 x 4cm and offers three stereo modes:
A two channel / one input mode - (front input / rear output) 7 band EQ.
A four channel / one input mode - (front input / front and rear output) with three front EQ bands and four rear EQ bands.
A four channel / two input mode - (front and rear input / front and rear output) with three front EQ bands and four rear EQ bands.
There are also two EQ bypass switches to compare the effected sound and individual front and rear output level controls.
All input impedances appear to be about 11k ohms, the output impedance is 980 ohms for the front and 1.3k ohms for the rear.
When set to a four channel mode, the front and rear channels are completely separated from each other, this is an unexpected treat. Having tested this phenomenon, I put one piano through the front stereo channel which is effected by a three band parametric EQ, with the front stereo output going into my mixer. I can have another piano through the rear stereo channel, effected by a four band parametric EQ and feed this into a second mixer channel. It is the same as having two independent parametric EQs.
Alternatively, one can feed a stereo input into the front channel and then apply two separate parametric EQs, then the two channels appear individually effected at the front and rear outputs. Maybe not that useful for me, but clearly useful in a car. The third option is the full seven band parametric EQ with a single stereo channel - front in, rear out format.
Alternatively, one can feed a stereo input into the front channel and then apply two separate parametric EQs, then the two channels appear individually effected at the front and rear outputs. Maybe not that useful for me, but clearly useful in a car. The third option is the full seven band parametric EQ with a single stereo channel - front in, rear out format.
It takes a bit of getting used to this type of EQ, it is easy to over do it and unleash horrifying howling. A super boosted band will increase the output line level, which will need to be tamed. One must use it shrewdly whilst using the bypass switches to make a comparison with the original source signal.
The Q-factor bandwidth control is a fantastic concept, (Q stands for Quality, or is it Quotient?). By expanding the width of the chosen frequency band creates a more natural sounding result, when a wider section of sonic spectrum needs to be enhanced and boosted. The ability to then tweak the centre frequency allows for an instant way of targeting the audio region in need of attention. Q factor and bandwidth are the same thing but opposite, a Q of 1 is a wide bandwidth, a Q of 10 is narrow like a conventional graphic EQ.
It's safe to say that I'm impressed with this highly effective new addition to my gadgetry, although it's a challenge to cut the unwanted frequencies and boost the desired frequencies, and get it just right. I envisage the epitome of super EQs which will combine a 31 band graphic for cutting frequencies and a parametric EQ for boosting, or maybe I could buy a real piano and a tuning tool.
I'm just not yet sure how I'll rearrange everything, but I've crafted an over-engineered angled stand for the Alpine EQ and hope that it will assist in my ambitions of minimalism.
It's safe to say that I'm impressed with this highly effective new addition to my gadgetry, although it's a challenge to cut the unwanted frequencies and boost the desired frequencies, and get it just right. I envisage the epitome of super EQs which will combine a 31 band graphic for cutting frequencies and a parametric EQ for boosting, or maybe I could buy a real piano and a tuning tool.
I'm just not yet sure how I'll rearrange everything, but I've crafted an over-engineered angled stand for the Alpine EQ and hope that it will assist in my ambitions of minimalism.