tfpro p5 ( Box Full of Optical Compressors )

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    I bought a used tfpro p5 (Box Full of Optical Compressors) at an auction some time ago.

    It was delivered with a wrong power supply – 12V DC instead of AC, after exchanged to one providing 12V AC everything worked good.

    I really like to use the p5, but recently unfortunately the stereo channel started to deliver different levels on left and right,

    although it is feed with the very same level on both inputs.

    I took a look inside and could see nothing conspicuous apart from the wire connecting the link switches, which had lost connection to channel five.

    I assume this doesn’t affect the levels.

    What would be recommendable to put the p5’s function right?

    I would appreciate any advice,



    Ted Fletcher

    Do make sure the cables are OK! I get a lot of apparent problems with stereo compressors that turn out to be faulty cables…. be particularly suspicious if the level difference is 6dB, that usually means a faulty balanced connection somewhere; the P5 has unbalanced inputs and balanced connection outputs, it’s unusual to have problems with these.

    If there is really a fault and you would like me to fix it, I’m happy to have a look at it.

    Just send it to me at the Sound House, for older equipment I charge a fixed £30 plus the cost of returning it to you. :)


    Hello and thanks for your help!

    I checked my cabling and couldn’t find a fault there.

    The p5 input is feed from an balanced source, here i use a unbalanced cable ( where pin 3 is connected to pin 1 on the xlr ) which connects to the balanced out of the sending device.

    The p5 out is connected to the balanced input of the receiving device via standard balanced cable.

    It seems that levels match better when In and Out Gains are set to very different values like very low input and high output or vice versa.

    Around the zero position settings – which I use most – levels tend to match less.

    Would it be worth a try to clean the pots with something like DeoxIT?

    Thanks for offering the opportunity to sent the p5 to you, but I would rather not prefer to because I’m located onshore ( vienna ) and I am afraid of possible troubles due poor treatment during transport over to the royal island.



    Ted Fletcher

    DeoxIT looks OK from the info I have, but I always use WD40….. any other cleaner is dangerous because it can damage the track surface of the pot. I would recommend WD40, just a VERY small spray into the back of the pot and work it a few times. :)



    Unfortunately cleaning the pots did not help much.

    Basically it works, but I would not put the stereo channel into a group or master bus.

    Though it would be o.k. for me to use only one side of the stereo channel as mono, I’m thinking about trying to replace the pots.

    What kind of pot should be used for the stereo in and out?

    Would a 10 K/Ohm logarithmic type fit?

    If i can’t find pots that fit dimensional, would it work if i hook up the pots into a little housing outside the p5?



    Ted Fletcher

    Firstly, looking again at your level difference problem….. is the level difference there with no compression? If it is, then I still strongly suspect a cabling or connection fault, this is by far the most common problem; in fact, straightforward level faults are almost unknown.

    If the levels are OK without compression, but wander a great deal under compression, then it is caused by a slight displacement of the opto cells. On the stereo compressor the two opto cells (under the black cover) are close to and operated by an LED. By altering the distance of the cells from the LED you can adjust the balance. It’s tricky and takes a little time, but it works. The cells are normally about 1.5mm away from the LED, increasing that distance on one of them will alter the balance by reducing compression on that side only.

    On pots, yes both the input and output pots on the P5 are 10Klog. Generally, the matching on log pots is quite poor and it’s common to get 2 or 3dB errors in the tracking.

    Lin pots are very much better….. If you would like me to send you a couple of 10K lin ganged pots I can do that. they should fit the PC board OK. The only difference will be that the law of the control will be different, but still perfectly useable.

    Pls email me direct (

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