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Thread: biasing a 388 for 0db tape

  1. #71
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    Yeah I hear what you're saying. I definitely need to get a test tape then if I want to move forward from here. As soon as I have the money i'll order one.

    I did the simpler rec/reprod test and it's pretty incredible the difference between tapes. The lpr35 comes back strongly at 10k and the 388 seems to be reproducing what was recorded quite well. So it would seem the calibration hasn't been messed with. I have some older +1 tapes which I love the sound off and they reproduce 10k at less than -10db! The +1 tape always seemed very soft and pillowy when distorted and now I know why. Kind of funny that in some instances it would appear I prefer the sound of an incorrect and inferior tape. I just don't like the brown oxide it leaves on the path which means I have to clean it a lot. I'm also always wondering if I'm wearing the heads out faster than a new modern tape would be. My 35-90 at +3 seems to be a good middle ground between the two in terms of reprod too.

    Anyway, I've learned a lot which looking back on it was the purpose of this thread more than anything. I feel like I can use the 388 and different tape types now depending on what I want achieve and know where I am and what I'm doing where as before I was working a lot more intuitively.

    Thanks for the help everyone. Really do appreciate you all taking the time to school me on the basics here. I think my next 388 related project will be to recap the power supply. I've never done that before and think it would be a good learning experience also

  2. #72
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    The reason the +0 tape has much lower response at 10K is probably because the bias level is too high. That's one of the effects when there is too much bias...decreased HF response. I wish you could see what happens with the HF response when turning the bias level trimmer in real time. That's how it works when setting up a three head machine, because you can record on the record head and reproduce and monitor that while recording, you can inject your 10K tone and monitor the playback of the recorded 10K tone while recording, you can watch the level meter as you turn the bias level trimmer...as you increase the level the HF response rises, rises, rises, and then reaches a peak and then as you continue increasing the bias level you can watch the HF level (the reproduced 10K tone) start to fall.
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  3. #73
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    The supply caps would be a perfect move, if you ask me.

    " incorrect and inferior tape".

    One of your secret weapons. I dunno, is there any tape switching on this deck ? With the mixer right there, you can experiment with your own EQ curves when mis-matching things.

    If you plan on "some" red/brown tape, you can put a wiper on the supply side, somewhere

  4. #74
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    Whilst you are saving and waiting Mr B, (and this in NO WAY excludes the test tape!) might be good to make you own 'sample' tapes at a few frequencies and levels. Then SHOULD urge to tweak be irresistible you have a reference of sorts to fall back on.

    When you DO get the TT it will be instructive perhaps to compare data? Oh! BTW: BEFORE you let a test tape within 300mm of the deck you MUST degauss the heads and tape path! (TOLD you 'tape' was expensive and gadget ridden!)

    Dave.

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    Or, press the DEMAGNETIZER button : )

    Really, though, you can take a snip of tape and pass it close to the tape path to see it goes magnetic anywhere along the line
    Attached Thumbnails Attached Thumbnails dokorder_crop-jpg  

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    @garww : no tape switching on a 388.
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  7. #77
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    Quote Originally Posted by sweetbeats View Post
    The reason the +0 tape has much lower response at 10K is probably because the bias level is too high. That's one of the effects when there is too much bias...decreased HF response. I wish you could see what happens with the HF response when turning the bias level trimmer in real time. That's how it works when setting up a three head machine, because you can record on the record head and reproduce and monitor that while recording, you can inject your 10K tone and monitor the playback of the recorded 10K tone while recording, you can watch the level meter as you turn the bias level trimmer...as you increase the level the HF response rises, rises, rises, and then reaches a peak and then as you continue increasing the bias level you can watch the HF level (the reproduced 10K tone) start to fall.

    Yeah I figured this was the case. I have a tascam 122mkII that came biased for Denon Hd8. I see there are 4 screws on the front, two for bias, and another two for levels. It then has another button which gives an osc at 10k and 400hz. As this is a three head deck maybe I should play around on this one as a learning experiment? I know this machine is well calibrated though and I'm hesitant to mess it up. I'll check the manual and see if I need a TT to adjust levels. I'm sure the level reproduction would be okay as I had it serviced and biased when I purchased it maybe a year ago.

    The supply caps would be a perfect move, if you ask me.

    " incorrect and inferior tape".

    One of your secret weapons. I dunno, is there any tape switching on this deck ? With the mixer right there, you can experiment with your own EQ curves when mis-matching things.

    If you plan on "some" red/brown tape, you can put a wiper on the supply side, somewhere
    Please tell me more about these wipers. The tape I'm using is red oxide...641. Was it common for this tape to shed a slightly larger amount of oxide than more modern back coated tapes? And is this tape rougher on the heads? My 388 has great heads and as they are impossible to find now I'll like them to last as long as possible. Is there anywhere I could read up on the standard maintenance practices when using tape in the 60s? I've found one reference online to a deck having felt tongs that the tape would run through before hitting the heads. This is literally the only info about this stuff I've been able to find.

    Whilst you are saving and waiting Mr B, (and this in NO WAY excludes the test tape!) might be good to make you own 'sample' tapes at a few frequencies and levels. Then SHOULD urge to tweak be irresistible you have a reference of sorts to fall back on.
    Yeah I had this thought but you know... playing with fire. I'd love to hear the bias adjusted to get more 10k on the +0 tape. Then again I like it biased where it is also because I can use +0 tape to get that old 'eq' filter over everything. Then use the +6 for a more contemporary sound. I also wonder if the +0 tape would lose its magic when opening up its 'eq filter' so to speak.


    Really, though, you can take a snip of tape and pass it close to the tape path to see it goes magnetic anywhere along the line
    Hey this is a great trick! Thanks. I'm saving for a handy-mag atm so will try this out!

  8. #78
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    ".641"

    I'm not gonna pull this one out to confirm, but the stubb by the supply guide is a felt roller that doesn't roll, I seem to think the was something under the old Tandberg head block, also


    EDIT oh, stubby is on a tension arm. seems I took another PIC where its above the guide
    Last edited by garww; 1 Week Ago at 05:02.

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