3. Neve 8078 Consoles, poor frequency response

I had left the electrical drawing office by the time the 8078 console came through and had moved on, first to Sales Engineering, and then to Special Orders. So I missed out on checking over the 8078's circuit diagram. But now, 20+ years later, I'm looking closely at 8078's and uncovering a whole can of worms! Tut! Tut! Guys, what were you thinking of?

The 8078 (and most consoles of that era) were fitted with modules that used either BA440 or 640 output amplifiers and TO129 output transformers which MUST be terminated 600 ohms to function correctly. This was usually achieved by fitting a 1200 ohm resistor to the patchbay and another 1200 ohm resistor on the output XLR or elsewhere in the path.

This provided a loading of 600 ohms normally, and if the XLR connection was severed (by inserting an effects unit into the path) there was still a 1200 ohm load to tailor the response as close to normal as to be not bothersome. Folk who have changed the patchbay and forgotten to replace those resistors will find a huge hump in the response, typically about +6 to 10dB at around 40KHz.

The 8078 has the opposite problem. . . it has a poor frequency response, on some paths being as much as 3dB down at 20KHz. Several reasons exist for this malady and I shall reveal the most obvious one. . . for further response improvements you'll need to call us!

Anyway, the 8078 has a 620 ohm resistor soldered to the module back connector and a 1200 ohm resistor on the patchbay. That's 430 ohms loading the transformer and it doesn't like it, thanks very much! Wilt goes the response at 20KHz and it's not brilliant at 20Hz either!

So the obvious fix is to change the loading such that the module sees no less than 600 ohms. This will make a big improvement to the console's response and for real "dc to light" figures call us and we'll perform the other mods.
If you are thinking of having your 8078 serviced or upgraded, call us for a quote first. That's two design flaws I've revealed in these tip pages . . . and they aren't the only ones!

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