46 - Mic Amp & Compressor

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Nick M0NTV builds, tests and fault-finds a mic amp with audio compression based around an SSM2167 board.
NB. This video updates the previous one about this design ( • 28 - Mic Preamp with A... ) with some important corrections.
My second (corrected) schematic is here:
drive.google.com/file/d/1_gcl...
NB. Someone correctly pointed out that the X axis of my graph that I show in this new video was not linear as the Y axis was. It doesn't change the data but it distorted the shape of the curve. So there is a corrected compression chart that you can download here: drive.google.com/file/d/1qzHL...
Thanks very much for watching.
73
Nick
M0NTV

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Опубликовано:

17 ноя 2023

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Комментарии : 42

@acestudioscouk-Ace-G0ACE 8 месяцев назад

If British Rail had made a breakout board, it would have been this one, with "the wrong sort of resistors on the line"! In the wrong position at least. Great work from you and Dave. Note to self, check bought in break out boards. Thanks for another educating and fun video. 73 G0ACE

@M0NTVHomebrewing 8 месяцев назад

Cheers Ace! Hope you're doing OK. 73, Nick

@MarceloRochapoa 3 месяца назад

When analyzing the operation of the board I noticed that something was wrong, I went to check the values of the resistors on pins 7 and 8 of the integrated, and there was the error. I went online to look for information about this problem, if anyone had already detected it, and I found this video confirming the assembly problem. Thanks! 73 PU3MSR!

@M0NTVHomebrewing 3 месяца назад

Thanks Marcelo. It was another ham who alerted me to the issue. That’s the wonder of the internet. Glad you can resolve your issues now. 73, Nick

@colinashley 6 месяцев назад

Thanks Nick, a very useful video, I'll replace the resistors on mine now too.

@M0NTVHomebrewing 5 месяцев назад

Thanks Colin. It's certainly worth looking at. 73, Nick

@alanmacdonald65 8 месяцев назад

Great when things are put together wrong at the factory - so glad that this has been picked up and hopefully word will spread. Looking at the other comments many people have already consigned their boards to the junk box! Nice work as always Nick!

@M0NTVHomebrewing 8 месяцев назад

Thanks mate!

@TheTemporalAnomaly 8 месяцев назад

Commented on your other video instead of here, sorry for the repeat. Great video! I bought two of those units and when tested they just performed like limiter amplifiers. I was short on patience and just thought they were Chineasium fakes and didn`t investigate further. I will pull them out of the piling system and have another go. Just a point about noise, (in any pre amp circuit using electrets), I filter the phantom power to the mic - +v supply through 1k res, 1000uf to gnd, then 4.7k to the mic. This helps a lot getting rid of noise on the supply getting into the mic line. Many thanks, Chris & the lads of 1977khz

@M0NTVHomebrewing 8 месяцев назад

Thanks Chris! That's good advice about the filtering. 73, Nick

@davidbrowne1588 8 месяцев назад

Hi Nick I wired one in to the mic of a ft-817, sounds fine on my Marconi 2955 test set,, seeing your video now, I had to have a look, and yes I had to change over the R1 and R2, Thanks for the great information, Dave 2E0DMB

@M0NTVHomebrewing 8 месяцев назад

Cheers Dave! 73, Nick

@technishn 8 месяцев назад

Interesting video. Note the specification for minimum load on the output is 5k ohm (output Z is 145 ohms) according to datasheet. So if driving a diode double balanced modulator directly, then a unity gain opamp or emitter follower is probably recommended.

@M0NTVHomebrewing 8 месяцев назад

Thanks. Yes I measured about 100-120Ω output Z at 1kHz. You could do some matching (it's about 2:1 SWR) but to be honest as it is going through the W7EL audio diplexer the mixer port will still see 50Ω irrespective of the output impedance of the mic amp. It is certainly something to consider though. Thanks again. 73, Nick

@TheTemporalAnomaly 8 месяцев назад

Good point, I use an emitter follower to drive ring modulators. Otherwise mine ended up sounding really tinny due to the mismatch.

@torbjrnseim5018 4 месяца назад

Good presentation of the SSM2167. Great IC from AD. However, I have seen some 10khz burst on the output (approx. 500ms) after audio silence on the input. I looks like the IC is very sensitive for noise / rippel on the Vcc input pin.

@M0NTVHomebrewing 4 месяца назад

Thanks. I've not encountered any issues with the chip myself but your mileage may vary as they say. Thanks again. 73, Nick

@gordslater 8 месяцев назад

I've never noticed the resistors in the wrong place on all of the boards I've used because I've always fitted pots and used the super-secret advanced technique of "twiddling it until it sounds right". But sure enough, the unused 3 modules I have in my microphone circuits bin have the resistors in the wrong place.

@M0NTVHomebrewing 8 месяцев назад

I know! All mine were wrong too. If Dave hadn't reached out to me I'd still be none the wiser! 73, Nick

@M0UAW_IO83 8 месяцев назад

Those convenient holes in the board are perfectly spaced and sized for vertical multiturn preset pots, think I've had the discussion on the G-QRP mailing list some time ago.

@M0NTVHomebrewing 8 месяцев назад

Hi there! Don't think I've ever come across those. Sound useful though. 73, Nick

@andye2005 8 месяцев назад

Check the Analog devices data sheet It does not have a 470R in series with the supply but it does have a 10uF across the supply to ground That might just about provide enough current for the peaks. I f you want to add a bit of current protection just drop the 470R down tom 100R and add the 10uF Andy

@M0NTVHomebrewing 8 месяцев назад

Hi Andy, that sounds like a perfectly sensible option. Thanks very much. 73, Nick

@curtstacy779 8 месяцев назад

Nick, have you tried any ferrite beads on your test equipment? Oscilloscope, power supplies, or function generator. It fixed a lot of noise by doing this. the power supply, use them on the AC input and the DC output the switching power supplies are very noisy even when not connected to the project. then if you want even better use a battery to power the project while testing. I picked up two boxes of the clamp-on type from Amazon. by the way I didn't stop with test equipment I put it on computer radios everything in my room. Hope this helps you as it did me!

@M0NTVHomebrewing 8 месяцев назад

Thanks Curt, I've got a few of them on various leads in the shack but I could probably use some more! Thanks for the reminder. 73, Nick

@curtstacy779 8 месяцев назад

Just a note I have about three of them on the power cord for my power supply and Ossiloscope. when I got to three it didn't show any more improvement with more. that's why I had to order two boxes and they come in many sizes in the kit.@@M0NTVHomebrewing

@Daklon17 8 месяцев назад

I just have ordered a couple of these boards some days ago, will see if they also come with the wrong resistors. In any case, have you think about any way of modifying the resistor from the arduino? this will allow you to set the compression level from software depending on if you are trying some rare dx or just local ragchew. I've been thinking about it but haven't ended with any solution that i like yet.

@M0NTVHomebrewing 8 месяцев назад

Hi! No I've never considered doing this. I fear you would need a fairly complex switching bank of relays that would put in different values of resistance in each slot. For myself I'm happy to set it at a fixed level and then leave it alone but if you have an idea for a project then go for it! 73, Nick

@SeAfasia 8 месяцев назад

Μy personal opinion is better to desolder the 103 trimmer and add it front panel as Pot...tks for your design Dinos 73

@M0NTVHomebrewing 8 месяцев назад

That's certainly an option if you want to be able to change the output often. 73, Nick

@mahlonkarpaiya252 8 месяцев назад

Good day. I have a few of those little red board. I wanted to make a compressor for a dynamic mic. Is this possible or are these board limited to cb radios etc. Thanks a lot

@M0NTVHomebrewing 8 месяцев назад

Hi there, the boards are simply audio amplifiers with a compression feature. They can be used for any small audio signal. If you wanted to use it with a dynamic mic you'd have to adapt the design though. I only use condenser mics which require a DC bias hence the 4.7K resistor strapped across the VCC+ to the IN+. It is also why I had to include the 1uF electrolytic cap between the tuning tone output and the switch: I didn't want the DC bias getting back into the Arduino. Hope this helps. 73, Nick

@ignitionhighpowersound2753 8 месяцев назад

Thanks a lot

@DAVIDGREGORYKERR 8 месяцев назад

what about pa0fri's design for a speech compressor

@M0NTVHomebrewing 8 месяцев назад

I don't think I've come across that one David. 73, Nick

@oldblokeh 8 месяцев назад

Nick, that 470 ohm resistor looks like it has a green body. Probably a stupid question, but are you sure it's not actually an inductor?

@M0NTVHomebrewing 8 месяцев назад

Yes, I'm certain. Not everything green is an inductor. It is a 0.25W 1% Tolerance Metal Film Resistor (from Switch Electronics). It was the resistance that was the problem. 73, Nick

@oldblokeh 8 месяцев назад

@@M0NTVHomebrewing Ah. It was, as I suspected, a stupid question. Sorry.

@M0NTVHomebrewing 8 месяцев назад

No worries at all. My favourite gaff used to be soldering in my transistors the wrong way around! 73, Nick

@MirlitronOne 8 месяцев назад

Nick, please notice that your chart at 19:05 is misleading because you have fallen foul of an Excel quirk. Notice that your "X" axis (contrary to your "Y" axis) is not linearly spaced! This is because you have asked for a "line" graph. This merely places the "X" values specified at equal spacing, whereas they were not recorded that way! To do a proper comparison, you need to select "XY Scatter" plot which will give linear scales in both X and Y. 73 de Phil M1GWZ

@M0NTVHomebrewing 8 месяцев назад

Cheers Phil! Thanks for the advice. 73, Nick

@M0NTVHomebrewing 8 месяцев назад

I've redone the chart Phil and put a link to it in the video description. Thanks for spotting this and letting me know. 73, Nick