Taming the tinny sound of a Jag 700P

[mitaux8030]

I'd like to thank Elroy for his idea of the electrical tape X across the speaker cone - it does work quite well. Having said that, I'm wondering if further improvements could be had?
Some mentioned that the source of the issue is the choice of speaker and the design of the cabinet. Swapping out the speaker seems to be a good place to start... does anyone have some donor candidates for swapping? The Jag's OEM speaker is one & thirty-one... hmm sometimes its just easier to use metric measurements... 50mm diamater and 5mm deep.
There was also mention of a deep 1kHz notch in the audio characteristics... has anyone figured out if thats an acoustic thing, or due to the circuit design around Patti and/or DSP?

 

[CSHIFTLT]

adding a felt pad (I think moto called it a dust cover on the old minitors pagers) on the inside has done the best we have found.

 

[Radioman96p71]

My Jag sounds just fine? I guess i hadnt noticed it being really tinny. The worst radio ive heard to date has to be the AEGIS MRK, those things sound like crickets in a tin can! I might tear my Jag apart (again) and see what it has for a driver, or try some of the fixes mentioned above to see if maybe im goin deaf lol

 

[mitaux8030]

That's interesting... I'd put the MPA and LPE nearly on equal footing, with the Aegis M-RK next and the standard MRK behind, with the Jag my least favoured of the lot. Must be a personal preference thing. I tend to prefer audio with a bit of emphasis at 3-4kHz and 400Hz, seems to make the speaker that little bit more intelligible without being tiresome to listen to over a long period of time. It sounds like the Jag has way too much treble response to my ears.

 

[Radioman96p71]

I guess I need to start asking more people how im doing when I run sound for bands haha. Pulled mine apart, nothing special in there as far as sound is concerned. What is this trick to putting tape over the driver? Is it the speaker itself or do you wrap the backside to make it more like a sealed bandpass speaker cabinet?

 

[rbo]

"Audio problems"... (Quote...)

Frankly, ALL Jaguars have "audio problems" in the sense that their audio quality is NEVER particulary good. Some are flat out awful sounding.

You CAN improve the audio quality somewhat by carefully removing the speaker from the front housing, applying an X of electrical tape to the front of the speaker, and then reinstalling it. This tames that nasty shrill tone to a respectable extent. Makes it sound almost usable.

One thing that exists in some Jaguar firmware revisions is an FCC menu option with an EQ selection. By default, if this option is in the radio, it's turned on. It puts a DEEP notch into the radio's audio output at 1 KHz. This notch is so severe that 1 KHz alert tones are almost totally inaudible. I don't have a high opinion of "crutch engineering" like this.

Heaven forbid that they could have switched to a newer version of the speaker...one that didn't suck quite so bad.

But the newest radios (most 7100s) do have better audio. It's still not great, but it's better.

The best sounding audio out of any portable radios ever made would be a three-way tie between the original Saber I, the GE M-PD scan or select model, and the Astro Saber. All are excellent. In my opinion.

Elroy

 

[ElroyJetson]

It's kind of indicative of the relative commitments to quality and performance that Motorola and the (GE family name legacy series of companies) puts into their radio when you just look at the speakers alone in them.

Motorola has been in the habit of using custom-engineered, application-specific speakers in their portable radios since at least the Saber days. All the speakers they''ve put into their top tier radios since the days of the Saber are special purpose speakers designed and built only for Motorola, with all performance parameters optimized for use in that specific portable radio type. But the GE family companies have always used any off-the-shelf speaker they could find, and the audio quality has always been hit and miss. Aside from the M-PD, which is exceptionally good sounding, and M-PAs
are good, too. But their housings are solid cast aluminum alloy, and don't flex much, which helps keep the radio sounding good. Cabinet flex has to be accounted for when designing a speaker for
high performance. If the cabinet doesn' t flex, it's more forgiving of speaker qualities.

Elroy

 

[mitaux8030]

Absolutely, the cabinet and acoustics of that enclosure have a huge impact on resultant sound quality. But it does all begin with the audio qualities being tailored by electronics, and then the intrinsic qualities of the speaker.

It might be interesting to compare the UDC audio out into a good pair of headphones of various models. If they all sound reasonable, then there could be some hope in tailoring the Jags frequency response into something a bit more acceptable; studying the Jags schematics around the audio PA stage reveals several opportunities to do this. Even the UDC audio output has some scope for tailoring the response there too.
And my search for a candidate replacement speaker continues... perhaps might scavenge the speaker out of a Standard HX400 which was a great sounding radio in its day....Will keep you posted of my results.

 

[CSHIFTLT]

after our complaining, the company non response, once we started using in real world, instead of testing, (required to use shoulder mics), it became a moot point, in the fire service a radio wihtout a shoulder mic, isn't used much anyway, and a good quality shoulder mic seems to fix the whole speaker problem anyway, but at least the 5400 sounds much better, but by the time we upgrade there will be another model out anyway.

 

[smackdaddy]

Just an FYI... for those who may or may not prefer the 1k notch / crutch. For Jag (RU ONLY), p5100, p7100, In RPM you can toggle this feature. Under Portable Radio Options, it is called "Analog Voice Equalizer".

In ProGrammer this option is under Jaguar 700p, P5100, P7100 Options... Analog Voice Equalizer.

Cheers,
Scott

 

[ElroyJetson]

Try a speaker out of an XTS5000.

Also, the NEWEST speakers used in Jags are considerably better than the more common older ones.
I don't have the part number but it would be the one for the P7200 portable radio. Order that one and you should get the right one. I'd still do the electrical tape mod to it.

Elroy

 

[smackdaddy]

Well, I was bored this afternoon. And frankly all of your posts inspired me

So, I found one of the new style speakers (KT-011403), and popped it into my P7100 housing. It sounded better, but still a little tinny at high volume levels above 20. I did the Elroy mod on the new speaker (put the "X" of electrical tape on) and it sounded actually REALLY good. But even at volume level 31 I found it way too quiet for my liking now.

So, a bit of studying in the service manual, and found a resistor at the input to the audio amp (R532). This resistor is 56k. For experimentation purposes I just put a bridge across the top of the component, and this GREATLY increased my audio level. Wow, super loud! Not so tinny, thanks to the new speaker with the Elroy mod. So I'm thinking about trying something around 15k-20k in the place of R532. Will likely provide a great balance of super loud volume, reduced tinnyness..

Anyhow, just thought I would contribute my experimentation.

Cheers,
SD.

 

[mitaux8030]

Been doing a bit of the same schematic study myself... looking at the caps around the op amps to improve frequency response for a more pleasing result.
In testing the UDC audio output, it became apparent that there was much less variation in the audio between M-RK, LPE & Jag700P.

Something else became obvious in my investigations. While I prefer the sound of the LPE for a good clean signal, the M-RK was much more understandable with a weaker signal or ambient noise... even though my M-RK is about 4dB less sensitive than the LPE on the bench. The Jag also appeared to have a bit of a Dr Jekyl/Mr Hyde personality... bearable (with Elroy's mod) on analogue, but quite respectable on digital. Perhaps it was designed for IMBE, without regard to 'legacy' analogue audio qualities.

Interestingly the LPE audio plain sucked when used with a UDC shoulder speaker-mic... there was a background whine introduced, sounded like switching DC-DC converter noise. It was the only test where the Jag managed to claw its way off the bottom of the list for preferred audio quality.

With much of my time spent in the vehicle servicing customers, I'm going to aim for audio characteristics like the M-RK - good for weak signal / ambient noise recognition, but also making sure the audio doesn't 'grate' on the nerves for long term listening.

 

[mitaux8030]

Looking at C524 out of Patti (0.082uF) and C538 input to the NJM2073 audio PA (0.1uF) - one or both could stand to be increased in value to improve bass response. Other likely candidates are perhaps C539, C540 around the audio PA, and C510 & C550, part of the feedback network for audio preamp in U504.

 

[mitaux8030]

Been taking a bit more of a scientific approach to this investigation today.

Its really interesting to note that in the LPE, Jag and P7100, the design of the audio amp circuits from Patti through to the speaker terminals is practically identical. That includes the tap prior to the audio PA amp for the UDC too.

So you'd think that the audio out of the UDC would be pretty similar, right? Wrong. I have sampled the audio from the UDC and compared them. The LPE has a bandpass of about 200 to 3600 Hz, while the Jag & P7100 gives you 300 to 3600 Hz. And the LPE definitely has more output below 700 Hz, but rolls off faster than the Jag / P7100 after that point. The difference isn't massive, certainly not as marked as listening to a LPE and Jag with their own speakers side by side.

But I do think that a little tinkering with some of the circuitry can pull things back into line a bit. I think by increasing C524 & C538 to 1uF, and C547 that is unpopulated could be fitted with 0.01uF to add a bit of roll off, and take the edge off the treble content. The only problem with this is that finding 0402 size SMD 1uF capacitors isn't going to be easy. So perhaps the only practical option is to fit C547, and reduce R532 a bit to compensate for the loss introduced.

What about the speaker? Well, I tried an interesting experiment here too. Removing the Jags 'tinny' speaker, as well as another 2 inch traditional paper cone speaker, and a 1.5 inch speaker from a Shinwa and another from a GP300. It became quickly apparent that held in the hand, each speaker had very little bass response... but place it face down on the bench top and the bass response was very much improved. So the mounting of the speaker will have a very big influence on the end result. Face down, on the bench top, the two best sounding speakers were the Shinwa, and - suprise - the Jags.

So its the acoustics of the Jag that really sucks, but I think some gains could be clawed back with some minor circuitry changes.
So far, I've tried increasing C550 (makes the audio a bit louder, and does improve bass response just a little), decreasing C510 (no real effect), and increasing C524 to 0.1uF - not much effect.

Will try some other component changes and see what happens.

 

[radioman2001]

I remember that the original MX portables had some audio issues, I don't knowm specifically what they were. The later MX radios came with a silicon cover over the speaker. It does make a difference, maybe try putting a MX silicone cover over the JAG speaker. It might improve the reflected audio, and increase the loudness, and frequency response by absorbing some of the tinniness.

 

[Radioman96p71]

I can throw a little speaker cabinet building experience in here.

The reason the response of the speakers is better face down on the bench is because it forms a sort of sealed-bandpass box between the driver and the bench top. Effectively, you use the air pressure generated by the speaker to keep the speaker from over-driving and distorting. Vary the size of the air chamber and you can adjust the frequency response of the speaker.

Now covering the front of the speaker will do us no good in a radio, as the sound waves wont make it out of the back of the radio, but if we were to seal the backside of the speaker, good enuf to make it air tight, you could accomplish the same thing. Typically, professional speakers will have a air-displacement chart that will tell you the volume of the chamber needed to achieve a bandpass at x frequency, but I doubt we can find one for these. That means trial and error for the most part, but you could safely assume that putting the largest 'cabinet' behind the speaker inside the case will net some real results, as anything is better than what it has now. The larger the volume, the lower the resonant frequency and the better the low-end response. I might try something similar by making a mold with clay to see just how much room i can get between the driver and the circuit boards, then make a cover for the back of the speaker out of fiberglass, epoxy or maybe auto-body plastic filler. Sealed to the back of the radio with silicone or RTV would be good enuf for this application.

 

[mitaux8030]

Some improvements

Warming up the SMD pencil iron yesterday, a few component changes have helped the sound become a little better:

C524 from 0.082uF to 0.1uF
R532 from 56k to 33k
C538 from 0.1uF to 2uF (2 x 1uF soldered double-decker style); if you can find a 0402 sized 10uF cap, that would be even better!
C547 & C548 which are deleted from all but the earliest models of Jaguar: add 2 x 4.7nF caps. If these are already there, leave them in. If only one is present, add one 4.7nF cap.

C547 & 548 add a bit of roll-off to the sound, reducing the highs a bit more than the lows... but this reduces the overall level of input to the audio PA, hence the replacement of R532 to 33k... that brings the overall resulting amplification back to original, perhaps just a little more.

I left the PVC tape cross on the speaker cone too.

Oh, if you have an RU model Jag, take C550 from 220pF to 390pF - it's effect will only be very minor, but since it was a circuit revision made in the P7100 (which is pretty much identical to the Jag) then it won't hurt to do this while you're tinkering with the Jags internals.

These mods only get me about half way to the end result I was wanting. Further improvement could definitely be had by replacing C524 from 0.082 to 2uF (or more!) but this then sends too much level out to the UDC, overloading connected devices... which means that the UDC coupling C537 would need to be reduced. The audio still has far too much 'high' emphasis, not quite enough 'low' emphasis, and the roll-off needs to be a bit sharper, towards the treble end.

I've yet to try altering C539 & C540 around the audio PA to see what effect they have. I'm not really sure what the circuit action here will be; never seen a dual op amp connected this way to give a 'push-pull' like output. But I'll continue to experiment and report my end findings.

I suspect that in the end, the acoustics of the speaker mounting is going to be critical, and electronic adaptation to the poor acoustics will only go so far.

 

[mitaux8030]

I've had a good play over the last few days, and have come up with the following conclusions.

Increasing coupling caps to higher values with the idea of getting more bass response is not very effective. It seems there's little bass content to begin with.
While the Jaguar speaker is reasonably decent as far as response is concerned, compared to other speakers I have tried, the speaker is only one part of the equation... the mounting in which it goes is equally as vital to the resultant sound. And in this department, the Jag sucks.
It seems there are four avenues left, then:

Adding circuitry to shape the response to compensate for the poor speaker / mounting arrangement. Not a lot of real estate to go doing this with, so lets pass on that one.
A lot of the audio shaping (eg de-emphasis) is done in the DSP in the digital domain even before the signal reaches Patti. So, presumably some tinkering with the DSP file could have a favourable effect on audio response too. But this is beyond my knowledge or capabilities. Moving along...
Another avenue would be to attempt modification of the speaker mounting to alter its acoustics. I tried this, using cardboard & urathene spacers to help isolate the speaker from the case, using foam to seal the space around the speaker, and a few other such tweaks. To be honest, none works as well as Elroys idea of the electrical tape to help dampen the speaker response at higher audio frequencies.
The last (and probably least desirable) avenue is existing circuit modification to reduce the level of treble content.

In a nutshell, I think the best overall result so far has been to:
1) place a 1/4 inch wide electrical tape X across the speaker face.
2) change R532 to 33k
3) add in 2 x 10nF caps in positions C547 & C548
Minimal change was observed with the other capacitor changes for C524 & C538.

I'll experiment with a few other speakers, but honestly, I'm not expecting much improvement from where I am at the moment. Bit disappointed with the results, but at least the received analogue audio is somewhat usable now. The poor audio qualities are far less noticable with digital voice, which is interesting. Perhaps that might point to the largest gains coming from alterations to the DSP software?

 

[ElroyJetson]

1/4 inch wide electrical tape? I use 3/4" wide electrical tape. I've even experimented with die-cut
circles of PVC tape that were almost an exact match for the diameter of the speaker cone, and it didn't have any notable difference vs. just using a cross of 3/4" tape. But 1/4" tape is too small. It won't give you the kind of damping you really want in the higher frequencies.

Digital sounds better because of one thing: It has little if any stray noise in the high frequency ranges. It's far more bass/midrange balanced, with just enough treble content to enhance intelligibility.


Elroy