Manley SLAM! - Manual (Page 22)

IT MAKES NOISES WHEN THE FRONT PANEL IS TAPPED - An easy one. Some tubes become microphonic over
time. That means they start acting like a bad microphone. Vibration has caused the supports for the little parts in the tube to
loosen and now the tube is sensitive to vibration. Easy - Replace the tube. Which one? The one that makes the most noise
when you tap it. Usually this will be one of the smaller (gain stage) tubes (12AT7A) closest to the front. The SLAM! will
have to be on, connected and speakers up but not too loud for the sake of your speakers. With more gain comes more micro-
phonics so be real about your expectations.
IT GOT HISSY - Also easy. This is again a common tube symptom. You could swap tubes to find the bad boy, but an edu-
cated guess is OK too. Generally the first tube in the path is the one with the most gain and dealing with the softest signals.
The usual suspect is the shorter tubes - the 12AT7A voltage amplifiers. You may find that you need to choose the quietest
tube out of several of that type - like we do at the factory.
DISTORTION - This might be a tube. Swapping is a good way to find out. It may be a wiring thing or mismatch as well.
Wiring problems usually accompany the distortion with a major loss of signal. Mismatches are a bit tougher. The SLAM! has
a high input impedance and low output impedance that can drive 600 ohm inputs of vintage “style” gear. Best place to start is
check your settings and meters. It may not be your first guess.
GETTING DISTORTION WHEN WE BOOST A LOT. No doubt. The SLAM! by itself should have enough headroom
but it has a lot of available gain. Also the VU attenuator might be at -6dB which hints that the next piece may be getting a
very hot signal. You’re gonna have to turn something down, whether it is the signal feeding the SLAM!, the INPUT or OUT-
PUT level or the input level of the next device. You might check that the FET RELEASE isn’t set on CLIP too.
DC OR SOMETHING AT THE OUTPUT THAT IS INAUDIBLE - The 1/4” unbalanced outputs have a frequency re-
sponse that goes way down to below 1 Hz. A little very low frequency noise may be seen as speaker movement when moni-
tors are pushed to extreme levels. The XLRs do not exhibit this because the transformers filter below 8 Hz. Also the unbal-
anced outputs do not like long cheap high capacitance cable. Occasionally a very high frequency oscillation (200 kHz to 400
kHz) may occur in these conditions. Once again use the XLR outputs. Problem solved.
THE GAIN SEEMS OUT OF CALIBRATION - Wait a bit and see if it just needs to warm up. There are two trimmers
inside for adjusting the gain of the two channels up or down a few dB. More than that and you either have a bad cable or bad
tube. In MIC/DI modes there is a huge INPUT Level gain range and most pots do have 20% tolerance of position/value.
Once in a while we get a call from a client with a “digital studio” with confusion about levels. They usually start out by using the digital
oscillator from their workstation and finding pegged VU meters the first place they look and they know it can’t be the workstation. Even a
-6 level from their system pegs the meters. Some of you know already what’s going on. That -6 level is referenced to “digital full scale”
and the converter might have 18 or 18.5 or 20 dB of headroom built in. That -6 level on the oscillator is actually a real world analog +12
or +14 and those VU meters don’t really go much further than +9 attenuated. There are a few standards and plenty of exceptions. One
standard is that normal (non-broadcast) VU meters are calibrated for 0VU = +4 dBm = 1.228 volts into 600 ohms (broadcast is sometimes
+8dBm). Another standard is that CDs have a zero VU analog reference that is -14 dB from digital full scale or maximum. This allows
sufficient peak headroom for mixed material but would be a bad standard for individual tracks because they would likely distort frequently.
This is why digital workstations use higher references like +16 and +20. A VU meter hits red (0VU) at +4 dBm, a digital peak meter hits
red at about +18 dBm to +24 dBm.Peak meters and VU meters will almost never agree - they are not supposed to. A peak meter is intend-
ed to show the maximum peak that can be recorded to a given medium. VU meters were designed to show how loud we will likely hear a
sound and ‘help’ set record levels to analog tape- they are slower and supposed to approximate RMS levels. By ‘help’, we mean that they
can be only used as a guide combined with experience. Bright percussion may want to be recorded at - 10 on a VU for analog tape to be
clean but a digital recording using a good peak meter should make the meter read as high as possible without an “over”. Here is the second
confusion: There aren’t many good peak meters. Almost all DATs have strange peak meters that do not agree with another company’s DAT.
One cannot trust them to truly indicate peaks or overs. Outboard digital peak meters (with switchable peak hold) that indicate overs as 3 or
4 consecutive samples at either Full Scale Digital (DFS) are the best. They won’t agree with VU meters or Average meters or BBC Peak
Programme (PPM) meters either. Each is a different animal for different uses. When in doubt, use the recorder’s meters when recording -
they “should” be set up and proper for that medium. Also important - if your external DAC has gain trims, and these trims are “out” it can
cause distortion, confusion, and a variety of mis-matches. This is not the type of thing “phone support” is usually good at finding. We have
seen guys spend thousands on new gear only to find out a little screwdriver trim would have solved their problems...
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