Beolit 707 - Disappointed with sound

[Steve_Bell]

After many years of trying to acquire one at a decent price, I've finally got one. I cleaned up the case, etc. and really like the way it looks. I set up the audio section quiescent current and centre point voltage as per the service sheet. It works well but I'm disappointed with the sound.

For such a large speaker, which is in good working order, I was expecting more bass and it seems to begin distorting at volume level 6-7. It sounds similar with battery or mains power. Is this expected performance?

[simpsons]

With such a good advertised 60Hz - 15Khz on axis response from the loudspeaker, the sound should be very good.

Looking at the schematic, available from Browse Beolit, shows frequency response shaping from a tap on the volume control, 0.22 uF and, a 2.2 uF coupling from Tr6 to Tr7. These are both electrolytics which could dry out and would be my first suspects.

Chris

[Synchrodyne]

Originally Posted by Steve_Bell

For such a large speaker, which is in good working order, I was expecting more bass and it seems to begin distorting at volume level 6-7. It sounds similar with battery or mains power. Is this expected performance?

I suspect not, at least based upon a small sample of one which I’ve had from new in 1977.

These days I use mine in my (fairly small) home study, and it is almost permanently tuned to the regional RNZ Concert programme FM transmitter. RNZ Concert is our “equivalent” to BBC R3, and was originally modelled on the BBC Third Programme. RNZ Concert still maintains very high technical standards on FM transmissions with minimal compression. The Beolit 707 sound is nicely balanced for a receiver of its kind, both on music and spoken-word programmes, and does not offend an ear that is accustomed to listening to that kind of sound (“BBC neutral”, if you like) via a pair of 1995-vimtage KEF Model 3 speakers driven by a Quad 66/606. Volume control settings of 6 or 7 are well above what I normally use, but today I pushed mine up to that region for as long as I could handle it, with no evidence of distortion.

Today I also tuned into one of the local commercial stations – heavily compressed (the kind that apparently has “boy racers” driving Optimods instead of proper engineers) and where the announcers shout at you at 200+ wpm, and at the highest levels I could handle, did not hear any additional distortion.

That accounts for the FM side. The AM side of the Beolit 707 is less happy. The audio bandwidth is only 4.5 kHz, but that aside, there is an underlying distortion that I guess might come from the final IF stage or the demodulator. Mine was like that from new. These days I do not use it for AM, but several years ago, I connected my Sony SRF-A100 headphone output to the Beolit auxiliary input. The Sony is limited by its very small speakers, but it has a very good AM side, and via the Beolit, AM was noticeably clearer than from the Beolit, even with the Sony in narrow-band mode. To be fair though, I don’t think that the Beolit 707 on AM is any worse than is typical for transistor portable receivers with diode demodulators.


Cheers,

[Hybrid tellies]

It depends on the IF bandwidth of the AM receivers. Many radios of this age used brutal nasty brickwall filters that cut the audio response off just above 4Khz and they did sound dreadful.
My three top AM performers, Hacker Hunter RP38A, Bush TR130 and my ITT/KB Tiny super all use diode detectors but have a wider IF bandwidth with the audio response gently rolling off at 6.5Khz. These radios do sound good on all the AM stations available and are as pleasant to listen to as many FM stations.

[Andrew2]

I'd be content just to own one simply to gaze on its beauty. What a piece of styling.

[Leon Crampin]

If the set has been stored for some time, the 'speaker cone suspension may have become stiff.

Connect an audio generator to the AF input and sweep the LF region of the audio band to find the 'speaker cone resonance. Run the set face down into a blanket for some time at resonance to free the suspension. The blanket provides some damping and sanity for the operator.

Be careful not to overdrive the 'speaker - which is very easy to do at resonance - I would aim for a cone excursion of +/- 3 mm. Position a pencil point 3 mm from the cone in its neutral position, and increase the drive until audible contact is made. Some 'speakers take quite a while to free off.

Leon.

[stuarth]

I always thought the older, bulkier 1960's plastic cased models sounded better than the slimline (but much more stylish) 1970's models. The older sets also had separate treble and bass controls.

In particular, I liked the late 60's Beolit 700 - I thought it sounded better then its more expensive, wooden cased sibling the Beolit 800.

Maybe the soft plastic cases were more acoustically "dead" and less prone to resonances.

Stuart