Heil HC-5 replacement element for D-104 issue

[n7lrg]

Hey all. I replaced the element in my D-104 mic and getting reports that I have lost all bass response....sounds "tinny". I followed the attached instructions. The element fits tightly in the supplied foam support and the element is all the way forward to the front screen. It got reassembled as shown in the pic with the yellow pads pancaked correctly. The conflict I read is that by covering the rear port will de tune the element causing it to lose low end response. If so, why is it shown with the yellow pad being installed between rear port and back plate?

The kit came with the HC-5 element, a capacitor and a transformer. The paragraph above the pic mentions using the cap and transformer for ICOM brand radios...My rig is a President McKinley and running it as a base station. Power supply is a Samlex 1235M and D-104 base unit is a amplified T-UG8 stand. Battery checks out at 9.2v.

The paragraph below the pic confuses me. It states, "Remove the D-104 preamp. That is NOT a preamp. It is an active impedance matching circuit used to drive CB radio mic circuits, not needed for the solid state rigs of todays' world. It goes on talking about how the transformer helps vintage high impedance transmitters etc. Well I am running a CB and when I was using the old element audio was ok. One thought was maybe to switch the red and white wires I soldered to the HC-5?

Please read the attached instructions and see if I am missing something here. Thanks in advance.

 

[prcguy]

If you have a preamp D-104 sell the Heil kit and be happy because the Heil will never, ever sound as loud and punchy. Otherwise for your radio you would use just the Heil element wired with no transformer and probably no capacitor. Check to see if you have any voltage on the mic element leads when you transmit like around 5 to 8 volts. If not don't use the capacitor.

If you wired all the crap up including the transformer, that's why it sounds thin and lifeless. You have a low impedance radio that needs some audio voltage and current, albeit small from the mic element. Older high impedance radios need more voltage and no current to speak of from the mic element and the the transformer bumps up the low impedance Heil element to high impedance. If you use that on a low impedance radio it will load down the transformer and there will not be enough current in the audio to drive the radio mic circuits. The back plate is important to the sound but has nothing to do with your problem. If not done right you will get a hollow sound like your talking into the bottom of a coffee cup but your setup has other issues you need to fix, like put the D-104 back together.

The amplified D-104 should be able to give really loud and good sounding transmit audio that is crispy and punchy due to its piezo element that favors the mid and high freqs. The Heil element is a great replacement for stock crap low impedance dynamic mic elements in most radios giving a mid range peak that is more intelligible and articulate than the junk mic elements supplied with the radio. However where you can sit back 4ft away from the amplified D-104 and sound loud, you will have to literally eat the mic with a Heil HC-5 element inside. They are not known for high output. If this was a mobile setup then the Heil might be beneficial but on a base radio where you already have an amplified D-104, no.

If for some reason the D-104 was sounding way too crispy and needed more bass, I can tell you how to EQ out some of the highs with a single capacitor and mellow it out and still keep the huge drive level the amplified base can provide.

I have a couple of Heil HC-5s here and love them for certain things but not for a base CB. The HC-5 and HC-4 were discontinued and have gone crazy with prices, I used to get them for $15-$20 used and now they fetch at least $50 used and sometimes much more.

 

[n7lrg]

I did not use the cap or the transformer. Tell me about the capacitor. I have many, thanks.

 

[prcguy]

On the D-104 element and any piezo or ceramic mic element that is really high impedance, you can put a capacitor of a certain value right across the mic element in parallel with it and that will roll off high frequencies by loading down the mic element but only at higher frequencies. You have to find the exact value needed so it has no effect on the bass. There will be a knee in the response where below a certain audio frequency there will be no attenuation and above the knee it will roll off at about 3dB/octave attenuating the highs and making the bass appear to be louder.

There are a couple of ways to determine the value of the capacitor, measure the impedance of the D-104 element and its preamp then calculate the value of capacitor needed to roll off highs in the right spot, or use a capacitor substation box and an audio spectrum analyzer to determine the best value or listen on air while you switch capacitors around. I did that later with a mobile D-104 hand mic and I will have to open up the mic to see the value I used and it was a slight compromise due to the parts I had on hand. Later today I'll dig out the mic and look at the capacitor value. It should be in the ball park for a D-104 base version since they both use a piezo element.

I did not use the cap or the transformer. Tell me about the capacitor. I have many, thanks.

 

[n7lrg]

Cool, that would be great. Weird though that since it is a Heil product it should be of quality and it is made for D-104 mics.

 

[prcguy]

I looked inside the mobile D-104 M6B on my Uniden 980 and I put 1500pf across the mic element to tame the highs. For an amplified D-104 base mic I might start with a 220pf disc ceramic across the element and see how that sounds and if it needs more roll off on the highs move up to 470pf then 1000pf, etc. You can solder the cap right across the element or down in the base where the element connects to the preamp board.

Heil makes some good products and some that are all hype and not that useful. A kit to put an HC-5 in a D-104 head is one of those questionable products. I suppose if you had a non amplified super high impedance D-104 and a modern low impedance radio the D-104 would be useless and an HC-5 would be better, but nothing like an amplified D-104. You can almost drive a speaker right from an amplified D-104, they will drive anything.

Cool, that would be great. Weird though that since it is a Heil product it should be of quality and it is made for D-104 mics.

 

[n7lrg]

Haha understood! I wrote Heil Sound to see what they have to say...
I will try your suggestion and report back. Thanks for your help!

 

[138BG]

Rebuilt my D104/TUP9 with kit sold by W2ENY. Easy install. Electret cartridge is better match to todays radios (like McKinley). No tinny audio, right amount of mid-range and bass. Always get good audio reports on SSB. $25 or so. Very happy.

 

[prcguy]

The electret cartridge they use runs about a dollar new. They do have higher output than a stock dynamic element and they can sound better depending on the radio.

Rebuilt my D104/TUP9 with kit sold by W2ENY. Easy install. Electret cartridge is better match to todays radios (like McKinley). No tinny audio, right amount of mid-range and bass. Always get good audio reports on SSB. $25 or so. Very happy.

 

[138BG]

They do have higher output than a stock dynamic element and they can sound better depending on the radio.

The OP stated he wished to use his D104 with a President McKinley. The stock mic for all current President offerings uses an electret element. My post was an effort to help the OP based on experience with another President radio, not to show off any vast knowledge of microphone technology.

 

[n7lrg]

Update...I purchased/installed the W2ENY element. It was larger then the heil so I carved out enough of the blue foam to support it. I soldered it along with the resistor that mounts in the base. I used shrink tubing to insulate the connections. My reports now are excellent...great audio on both am and ssb (sounds like me too) and not over-driven with internal amp adjusted to about 60%. Thanks to all who gave advice. I appreciate it.