Tascam 388 calibrated to Quantegy 407 question
- Thread starter MagnumPI
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ethyrvalve
Norman Nanoweber
I think they should be quite close.
Here's Q407's specs:
Coercivity: 330 Oe
Oxide coating 10.1µm
Retentivity: 1300 Gs
LPR35
Coercivity: 320 Oe
Oxide coating: 11µm
Retentivity: 1660 Gs
I'd think the bias would be pretty much a wash with 407's slightly higher coercivity and lpr35's slightly thicker coating. The main difference is the retentivity spec. If you record a series of tones at -10db (dbx switched off for this) take note of the discrepancy between playback. I'd guess that the LPR35 might play back at a slightly higher level. You could probably leave it completely as-is and get quite good results (especially if you take note of the input level vs playback discrepancy and compensate for it). Or you could tweak the record level (which isn't as tortuous as setting the bias on these machines).
Here's Q407's specs:
Coercivity: 330 Oe
Oxide coating 10.1µm
Retentivity: 1300 Gs
LPR35
Coercivity: 320 Oe
Oxide coating: 11µm
Retentivity: 1660 Gs
I'd think the bias would be pretty much a wash with 407's slightly higher coercivity and lpr35's slightly thicker coating. The main difference is the retentivity spec. If you record a series of tones at -10db (dbx switched off for this) take note of the discrepancy between playback. I'd guess that the LPR35 might play back at a slightly higher level. You could probably leave it completely as-is and get quite good results (especially if you take note of the input level vs playback discrepancy and compensate for it). Or you could tweak the record level (which isn't as tortuous as setting the bias on these machines).
Last edited:
sweetbeats
Reel deep thoughts...
RMGI is proper width. Ampex/Quantegy slitters were not as tight tolerance, so to avoid tape ever being WIDER than the standard, they slit it slightly under...
sweetbeats
Reel deep thoughts...
You're welcome. Everybody else in the world slit tape very close to the standard for the given tape width, but Ampex/Quantegy tape was known for "country laning" in the guides because sometimes a batch was on spec and other times under spec. We're talking about a few thousands of an inch here, but that small amount can be enough to cause a little headache if your tape path has a wear pattern established by under-spec Quampex and you put some on-spec RMGI/BASF/EMTEC/AGFA/3M/Scotch/whatever tape on the machine and the heads don't have edge slots cut in them.
sweetbeats
Reel deep thoughts...
What millivolts output are the 388 bias amps currently set for?
ethyrvalve
Norman Nanoweber
Before tweaking the bias voltage (you need to own a wide bandwidth AC Voltmeter for this), I'd recommend just doing a test. The bias should be very close to ideal.
Try recording a sine sweep from 30Hz to 16kHz (the free mac/pc program Audacity will let you create this sweep tone) at -10dB on your meters with DBX switched off (the EQ set to the middle natch). The manual specifies +/-3dB for this range. Make sure the tape path is clean. Record the sweep and then play back and note the frequency response.
If you want to be sure it's working well, I'd also recommend verifying the azimuth of your machine (which is far more important IMO than a tiny bias tweak). A rough way of doing this would be to record a 10kHz tone on channels 1 & 8 at -10dB. Play back the tones with the input monitor down but the channels 1 and 8 inputs' set to 'RMX'. Pan the tracks hard left and right and use the fader to bring them both to about -6dB on the master VU. Next, pan the channels to the centre and check that they 'add'. Ideally, you'd see a 0VU but on such a narrow track machine any noticeable reinforcement is probably OK (the service manual suggests shooting for <90º phase error, which is a little too lax a standard for my taste). You can read more about this approach on AnalogRules.
I've had no problems with country-laning on my 388 switching between tape brands. Like Cory said, it's wear related. If it affects your machine, it's not hard to diagnose. The tape will noticeably ride up and down the head and sound weird.
You could also just try the machine with the new tape. And if it sounds good, it is good! I love the 388 but it isn't a Studer A820.
Try recording a sine sweep from 30Hz to 16kHz (the free mac/pc program Audacity will let you create this sweep tone) at -10dB on your meters with DBX switched off (the EQ set to the middle natch). The manual specifies +/-3dB for this range. Make sure the tape path is clean. Record the sweep and then play back and note the frequency response.
If you want to be sure it's working well, I'd also recommend verifying the azimuth of your machine (which is far more important IMO than a tiny bias tweak). A rough way of doing this would be to record a 10kHz tone on channels 1 & 8 at -10dB. Play back the tones with the input monitor down but the channels 1 and 8 inputs' set to 'RMX'. Pan the tracks hard left and right and use the fader to bring them both to about -6dB on the master VU. Next, pan the channels to the centre and check that they 'add'. Ideally, you'd see a 0VU but on such a narrow track machine any noticeable reinforcement is probably OK (the service manual suggests shooting for <90º phase error, which is a little too lax a standard for my taste). You can read more about this approach on AnalogRules.
I've had no problems with country-laning on my 388 switching between tape brands. Like Cory said, it's wear related. If it affects your machine, it's not hard to diagnose. The tape will noticeably ride up and down the head and sound weird.
You could also just try the machine with the new tape. And if it sounds good, it is good! I love the 388 but it isn't a Studer A820.