R/E/P > Bruno Putzeys (Designer) - Dave Hecht (Master Tech)
The Finer Points of Studer A807 Alignment
Geoff Doane:
I wasn't sure if this question should go in this forum or Bruno and Dave's, since nothing is actually broken, so here goes.
I was asked to line up a studio's A807-4 MK II for ATR tape. I had previously aligned the same machine for some used GP9 that they had, and everything went well. Using the recommended overbias (-2 dB @ 30 IPS), there is insufficient trim to get the 10 kHz level to match the 1 kHz level. It's about 1 dB high with the adjustment at minimum, and keeps on going up until it's about 2 dB high at 20 kHz.
Most of my analog tape experience is with A810s and A820s, and on those I could tweak the record EQ (as distinct from the record treble) to get the response really flat. The A807 manual has a table of the factory RAM values for EQ (in hex values) in section 2.6.4, but no mention that I can find, of how to change them. For those who have forgotten, pressing the TRANS key and the TREB button on the 810/820 put the machine in EQ adjustment mode. There is no TRANS key on the 807, and the SHIFT key doesn't work that way.
GTD
franman:
a little more bias?? (it's been a few years.. sorry if I'm off base here)
Geoff Doane:
--- Quote from: franman on March 16, 2011, 10:05:32 PM ---a little more bias?? (it's been a few years.. sorry if I'm off base here)
--- End quote ---
That was my first thought. I increased the overbias to 2.5 dB, readjusted the 1 K level, and 10 K was still too high, although 20 K had dropped a bit (IIRC). The figured the first case was the lesser of two evils (evenly rising response), so went back to 2 dB and thought I'd poll the experts.
GTD
Dave Hecht:
Geoff,
A couple of thoughts. Just out of curiosity, can you try 3db of overbias and post the results? I don't have an 807 manual at the moment (downloading from the Studer site) but I noticed 2 807 manuals - user and service. Any chance the info you need is in the other manual? I also recently ran into a similar issue on an A800 where the record hf adjustment had a very limited range - traced to bad caps on the head preamp card. Any chance the nachine in question is in need of some new caps?
Dave Hecht
Dave Hecht:
Just finished the service manual download. In section 2 - Startup, Operation, the microswitch id #16 switches the machine into alignment mode for setting audio parameters. Try that and let me know.
Dave Hecht
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