PURE Evoke 1S DAB radio question

[Chris Hogg]

We have had one of the above for a couple of years, one of these:

But, despite the small size of the loudspeaker, there is too much bass or not enough treble for our liking, and there is no treble or tone control (which does surprise me). Is there a preset pot on the circuit board that I can twiddle to adjust the treble, and if so, where exactly is it? I've looked on the net for a circuit or layout diagram with no success. Plenty of user manuals but nothing more technical.

[Andy Burns]

Tried blocking the bass port with high density foam?

[Chris Hogg]

Interesting and potentially easy to do. Is the bass port that vertical slot on the back, and what constitutes high density foam? Can you suggest an example, as I'll only need a little bit and there are lots of bits of foam kicking around the house, anything from foam cushion inners to cavity wall insulation overspill.

Thanks.

[Andy Burns]

Yes

My speakers came with stiffish foam pads, the same grey, slightly rough material as 'egg crate' packing foam (but not convoluted like that)

to be inserted into ports if placed 'too' close to walls, you could experiment with anything from cotton wool, a washing-up sponge, to upholstery foam that you have knocking around

[Brian-Gaff]

No there is not one. I believe it uses a chip amp. It really depends on how they use the volume control. One might if its an old fashioned analogue control, be able to construct a filter of some kind to make it sound more toppy here, but I'd guess it might be either a digital volume or a built in attenuatior controlled by the knob. It does have a good output for a stereo of course so one can then do what one likes with it. I've always found the Evoke and Sonus series to sound quite balanced. A little boxy perhaps, but then, its a little box! The ported speaker at least shows some attempt has been made to make it sound a cut above the others.

Inside if I recall the tuner is on the front panel, and the amp and voltage regulator on the back panel, so it should be relatively easy to get to the interconnections.

Its quite an old design though and as far as I know eats current even in standby, and is not dab+ ready. Brian

[Brian-Gaff]

It does not increase the trebble just makes the bass more boxy. Brian

[Adrian Caspersz]

A bass blocking non-polarised electrolytic cap (or two standard types back-to-back) in series with the speaker lead.

Google "bass blocker capacitor values"

[alan_m]

I have one of the smaller Roberts DAB radios with a single speaker that is the same. Minimal treble with no adjustment (ECO model with inbuilt battery charging).

[Dave Plowman (News)]

A nice mellow tone then. ;-)

Does the tonal balance change with the volume? Too many of these things use a form of loudness control which alters the response with level.

[RJH]

A sock :-)

Anything will do, just block it and see. Also, moving it away from the wall or corners.

[Chris Hogg]

Thanks to all. I've tried stuffing various mufflers etc. into the bass port at the back, without really being able to hear much difference, although that might be due to the age of the ears, but other portable radios we have, have better treble output IMO, e.g an ancient analogue B&O Beolit 700,

I'll explore AC's suggestion of a bass blocking capacitor next. Should be easy enough to fit once I've calculated what value I want.

[Roger Mills]

Have you explored all the menu options? Are you sure that one or other of the knobs doesn't control treble and bass in some menu position?

[Andy Burns]

No mention of the words "bass" or "treble" in the manual, google suggests other people wishing you could alter tone.

[Chris Hogg]

No mention of bass or treble control in the manual (PDF file down-loaded and searched for those terms).

[Bill Wright]

Are you aware that many DAB broadcasts have treble roll off?

Bill

[polygonum]

If that means there is little audible treble, even with tone turned right up, and so it all sounds rather boomy, then I agree.

[Dave Plowman (News)]

Can you be more specific, Bill? In terms of what the speaker on a portable radio is likely to reproduce?

[Chris Hogg]

Er...no! I would ask the same question as Polygonum and Dave Plowman. Is it likely to be the cause of insufficient treble from my radio?

If so, it doesn't say much for the quality of DAB, or perhaps that should be 'just another reason for not having DAB'.

[Dave Plowman (News)]

No. I can switch between FM, DAB and FreeView here all on the same station, listening on broadcast quality equipment. Any difference in tonal balance is subtle, to say the least.

Of course any station may use different processing between the various TX systems if they want to.

[Chris Hogg]

Good point. Just tried mine, and as you say, little discernible difference between DAB and FM. So it's the radio, not the signal.