605A Buzz

[dlp4341]

> I have a pair of Altec 605A's circa 1963.The both have a buzz @ 68 Hz .
> At first I suspected the cabinets ; so I reglued , screwed , ... to no
> avail. Then I tried one out of the cabinet : @ about 3 volts on the LF
> section ( no xover ) I found my buzz .
> Also the impedance curves show a sharp notch at the buzz frequency .
> Any ideas as to what is loose ? Or causing the buzz ?
> Thank you for your help
> Don
>
>

[joyspring]

Don,

It's quite interesting that you have the same problem in both drivers... and the `notch' in the impedance curve is also intriguing.

I would suspect one of four sources of the buzz:

1. Voice coil cement has deteriorated and the coil buzzes against the paper former right at 68hz.

That this would happen on BOTH drivers at the same frequency makes this unlikely but if so, this would necessitate a recone.

2. The LF driver lead tinsels are a bit too long and strike the cone, but only at 68hz. This may be rectified with a bit of glue to `stiffen' the tinsel near the cone.

Again, since this occurs in both drivers at the same frequency, this also seems unlikely.

3. The driver frames are distorted (from bolt overtightening, etc.) with the same deflection on both drivers. Unlikely as well.

4. Poor QC on the original (or replacement) LF cone/voice coil assemblies. This is a lot more common than you'd think.

I would suspect this since the same problem occurs on both drivers and the impedance plots are similar as well. The solution is to recone both drivers.

However, I would consult with Great Plains Audio first before commencing work on a solution.

BobR

[klausesser]

Hi!

Only a thought:
What about "improved" x-over? Could affect both drivers.
Or: did you check your amp . . . . ;-)?
What you don?t realize with other speakers may well come audible with the Altecs.

regards, Klaus