Is there a difference between KB/A30 and KB/A50?

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dak
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Is there a difference between KB/A30 and KB/A50?

Post by dak » Fri Aug 12, 2022 6:09 pm

The manual section contains just the KB/A30, but in the preowned market one sees both KB/A30 and KB/A50 and both appear to be specced at 40W/10W biamped with pretty much identical input sections and weight.

Given the tendency of Peavey to maintain the model name while changing the amp around (adding XLR inputs, changing the controls and similar with a KB300, for example), it would appear strange to have something where the model looks the same but has a different name.

Is there a substantial change apart from the lettering for the model name?

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Enzo
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Re: Is there a difference between KB/A30 and KB/A50?

Post by Enzo » Sat Aug 13, 2022 1:38 am

SOMETHING has to be different, they are not into being mysterious, but I don't know what it might be. Both are described as having 10" woofer with tweeter. On my dealer support portal the schematic file is labelled KBA30_KBA50, so they share a circuit/board at least.

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dak
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Re: Is there a difference between KB/A30 and KB/A50?

Post by dak » Sat Aug 13, 2022 5:29 am

I've taken a look at old web pages from Peavey, and it appears like KB/A30 got replaced with KB/A50 without overlap while the rest of the KB/A series was still around. In contrast, the KB/A50 was offered in parallel for a while with the KB2, its successor in spirit. I've not checked every single snapshot so I might have missed something, but if there is overlap, it is small.

Maybe it really was a marketing decision because KB/A30 was underselling the amp's power? The model numbers for KB/A were mostly in some hand-waving relation to the amp power (from the RMS rating with KB/A15 to double with KB/A300, possibly factoring in the larger efficiency of larger speakers). The KB/A30 is about the only in the series where the number is considerably less than even its RMS rating.

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dak
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Re: Is there a difference between KB/A30 and KB/A50?

Post by dak » Sat Aug 13, 2022 7:21 am

Well, a direct image comparison shows different pot knobs: the KB/A30 appears to have the cheapish knobs of the KB/A15 while the KB/A50 has the kind of beaky retro knob with a sculpted tip rather than a mere arrow mark.

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dak
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Re: Is there a difference between KB/A30 and KB/A50?

Post by dak » Sun Aug 28, 2022 1:36 pm

I am right now working on a KB/A50 and don't have a KB/A30 for comparison. However, this one is clearly of the "PCB layouter has no clue about audio" variety (probably one of the earlier "made in China" iterations when knowhow transfer was iffish): ground is all over the place rather than tracking the signal path. I have so far only been able to get a hold of the KB2 circuit diagram which is sort of the successor in spirit, and the KB2 has separate ground buses to the summing stage so I guess that the routing will likely be proper (like it is in my 1983 KB300 already where the ground bus concept is already present).

Now I have an overland high voltage line and a transformer field for a power plant in about a quartermile of distance. I need good routing. Chances are that in more usual environments, this will not be all that noticeable (I've cleaned up a discrete solidstate amp for my use here, quite more of a challenge than when using opamps, and it's spooky silent when used elsewhere).

But with this KB/A50, volume pots for all inputs need to be at certain settings if I want to get rid of 50Hz hum. And that setting is not zero.

I'll probably cut off the volume pot' wipers' PCB traces and route them in parallel to their other traces in the hope of getting rid of the volume-pot-dependent hum.

This is fun. I already replaced the blown tweeter voice coil after clearing out the ferrofluid remnants. I have decided to get new ferrofluid, and I'll likely replace the 4560 opamps with MC33078 ones which are affordable and have nicer current noise (quite a lower input impedance though which will hopefully not mess up too much).

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