Related Manuals for Oakley Filtrex II
Summary of Contents for Oakley Filtrex II
- Page 1 Oakley Sound Systems Filtrex II PCB issue 2 Analogue Filter Rack Builder's Guide V2.4 Tony Allgood Oakley Sound Systems Carlisle United Kingdom...
- Page 2 Introduction This is the Builder's Guide for the issue 2 Filtrex II rack module from Oakley Sound. It contains the schematic description, parts list and testing procedures. For those of you with an issue 1 Filtrex-II board you should ensure that you have the proper Builder's Guide for your board and not this one.
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Page 3: Parts List
Parts List For general information regarding where to get parts and suggested part numbers please see our useful Parts Guide at the project webpage or http://www.oakleysound.com/parts.pdf. The components are grouped into values, the order of the component names is of no particular consequence. - Page 4 R40, R37, R69 R75, R14, R7, R108, R112 22K, 1% R28, R27, R22, R23 R107 R85, R29, R26, R35, R71, R36, R124, R33, R82, R79 R59, R60 100K R125, R101, R120, R73, R68, R88, R114, R119, R98, R92, R93, R76, R72, R84, R89, R95, R94, R118, R66, R67, R64, R45, R83, R103 100K, 1% R48, R50...
- Page 5 Discrete Semiconductors BC549 or BC550 Q1-15 1N4002 or 1N4004 D8, D23, D9*, D13*, D14*, D18*, D19*, D24* 1N4148 or 1N914 D1, D2, D3, D4, D5, D6, D11, D12, D15, D16, D17, D20, D21, D22, BAT-42 D7, D10 LED 3mm green TRIG LED 3mm red/green LFO LED 3mm red...
- Page 6 Switches SPDT on-on CONT, AUTO, WAVE SPDT on-off-on MODE Miscellaneous Leaded ferrite bead Heatsinks TO-220 clip-on 2 off for U11 and U15 2-way 0.1” KK Molex header 4 off INPUT, SIDE, CV, GATE 3-way 0.1” KK Molex header 1 off OUTPUT 2-way 0.1”...
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Page 7: Circuit Description
Circuit Description Like many complex analogue circuits the Filtrex-II issue 2 circuit can be split up in to little bits. The first bit we will look at is the pre-amplifier stage on page one of the schematic. The input signal comes in through a small network of passive parts: L1 acts as a filter for radio frequency interference. - Page 8 C18 provide AC coupling of the outputs to remove the slight DC offset from the top differential amplifier. The resonance in a moog ladder filter is controlled by the level of audio feedback applied to the bottom pair of transistors from the output of the differential amplifier at top rung of the ladder.
- Page 9 see that the output of the CV summing amp is present at pin 1, while a second CV input is made available at pin 2. The master Filtrex-II will be sending the CV signal via pin 1 on the STV header to pin 2 on the slave's STV header. This way the master Filtrex-II board will also control the slave's cut-off frequency.
- Page 10 often considered to be a balanced signal but in truth the receiving end of the balanced connection cares not for the absolute signal levels on the hot and cold connections but only the difference between them. And because all balanced input circuits do not have an infinite input impedance the source impedance is very important to this differencing process.
- Page 11 possible from the FWR through a diode. The capacitor is then discharged through a resistor, sometimes variable but often not, causing the stored voltage to droop at a determined rate. However, they are often plagued by ripple when used to process certain types of input signal. Ripple is the bumps from the FWR creeping through to affect the required output.
- Page 12 The heart of this unit is the circuitry based around U10b (pins 5, 6, 7). This, along with the ‘up’ and ‘down’ pots, make up the lag generator. What is a lag generator? Basically it is a capacitor, C37 in this circuit, that can discharged and charged at a controlled rate. The level to which the capacitor charges to, or discharges to, is determined by the input voltage applied to pin 5 of U10.
- Page 13 A flip-flop is a sort of a one bit memory, or latch. Once triggered by a positive going pulse at pin 12, it stays latched. You can only reset it by removing the power or a reset pulse at its other input, pin 9.
- Page 14 sweeps fast. If the proportion is small, the integrator sweeps slowly. R116 sets the minimum speed. Don’t be tempted to lower this value any more to get really slow sweeps. Input errors within the integrator op-amp will take over and your LFO won’t oscillate any more. With C52 at 100nF the range of the LFO is about 0.05Hz (one cycle in 20 seconds) to 50Hz.
- Page 15 Audio and Ground Connections You are going to need five 1/4” jack sockets, four mono and one stereo, to connect your PCB to the outside world. Each jack is connected to its respective 0.1” headers on the PCB. The stereo jack socket is to be fitted in the Output position. This is because the audio output of the Filtrex-II is impedance balanced and requires three connections to the outside world.
- Page 16 If you have used metal sockets then you don't need to ground your case via the 'CASE' pad since your case will be grounded very tightly via all the sockets. However, this may cause earth loop problems if you then mount your case into a rack with other pieces of equipment in Please note that grounding a case is not the same as earthing a case.
- Page 17 Power Supply and Power Supply Connections The recommended option is to use an insulated plugtop (often called a wallwart) AC adapter. They are used external to the Filtrex housing and plug into the Filtrex using the two pole barrel connector. They are very safe since all the dangerous high voltage stuff is kept inside the wall-wart.
- Page 18 I do not endorse this method of powering any Oakley equipment. It is up to you to use your PCB wisely. I take absolutely no responsibility for your actions with this board. I will offer no further advice than what you...
- Page 19 Trimmers TRIM: Adjust this trimmer so that the filter bursts into oscillation when the ‘resonance’ pot is moved close to its maximum setting. The filter should oscillate from about 100Hz to over the range of your hearing. Or you can adjust it so that it never goes into oscillation at all. This will prevent you from accidentally damaging your ears, your tweeters and upsetting your neighbour’s dogs.
- Page 20 Housing your unit The PCB has been designed to fit into a standard 1U high 19” rack unit. Your local parts distributor will probably have these. Good rack units are quite expensive, and will contribute heavily to the final cost of your completed Filtrex. Expect to pay around 35GBP or so. In the UK the ones I recommend are made by Bryant Broadcasting or Holt Broadcasting Services.
- Page 21 The other thing to beware is the heatsinks. Don’t let either one of them touch the top panel, since this would cause major problems. This shouldn’t happen if you make sure the base of the regulators ICs are fitted within 10mm of the PCB. For those of you fitting an internal toroidal transformer you must make sure there is no way the bolt that secures the transformer can touch both the bottom and top of the metal case.
- Page 22 Stereo processing with two Filtrex-II modules – Application Hints Author's note: I haven't tried this yet with the Filtrex-II, however, the theory is sound so it should work without issue. I would be interested in hearing from people who have made a dual unit.
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Page 23: Final Comments
Oakley modules. If you can't get your project to work, then Oakley Sound Systems are able to offer a 'get you working' service. If you wish to take up this service please e-mail me, Tony Allgood, at my contact e-mail address found on the website.