Shure Mike Model #444 ??? / Freq scheme SSB

[Space Varmint]

OK this is it and you were dead wrong. That chip does need a driver or it isn't loud enough. You see I changed it to a current amplifier and killed two birds with one stone. I got the extra drive and matched the Z.

 

[Nigel Goodwin]

You can use head phones in a direct conversion receiver. In fact it is nearly impossible to use a speaker in a DC receiver.

No, there's no such limitation, a DC receiver can run a speaker just as well as anything else - what difference could there be?.

 

[Space Varmint]

Perhaps you would care to go through the design of one of the stages?, it's reasons for been there, and how (and why) you calculated the values.

Actually, I would love to. I want to hear your reasoning behind what you think should go there.

 

[Nigel Goodwin]

OK this is it and you were dead wrong. That chip does need a driver or it isn't loud enough. You see I changed it to a current amplifier and killed two birds with one stone. I got the extra drive and matched the Z.

OK, we'll go through it a piece at a time.

Q28 and Q29, why a darlington?, and why there at all?.

R100 and R38 constitute an attenuator, and you're only getting half the signal you started with - so you're making a net loss for no reason.

Connect C54 to pin 1 of the output IC, and replace R38 with a 47K - you're now no longer making that loss, and you've saved two transistors, four resistors, and three capacitors (and are getting twice as much gain). By removing those parts you're reducing noise and reducing distortion.

The output of the opamp is a low impedance, and can easily feed the power amp through a 10K pot, and a 47K input resistor is high enough to have no significant effect.

I won't go forther until you address those points, but you still don't have an electrolytic on pin3 of the opamp? (we'll discuss it's odd connections later).

 

[audioguru]

I went through the circuit and found that the value of the very first audio coupling capacitor C104 is so small that it attenuates all audio frequencies about 64 times. It cuts the low frequencies and makes the sound tinny.

There is a dead short from the collector of Q39 to the input of the 741 opamp.

The values of all coupling capacitors are so high that very low frequency rumble frequencies are passed and amplified.

The darlingtons are not needed.

There is a lot of attenuation which requires too many amplifier stages.

 

[Nigel Goodwin]

Actually, I would love to. I want to hear your reasoning behind what you think should go there.

Just like to point out, we posted at the 'same' time, I didn't ignore this post

However, AG has gone through it even more than I was planning, and done it in one go - I was doing it a bit at a time - although he hasn't approached the lack of stage decoupling.

From the style of your disgram, would I be correct in assuming you're 'designing' using a simulator? - if so I presume you're just sticking bits of circuits together and changing values until you get something out?.

 

[Space Varmint]

Just like to point out, we posted at the 'same' time, I didn't ignore this post

However, AG has gone through it even more than I was planning, and done it in one go - I was doing it a bit at a time - although he hasn't approached the lack of stage decoupling.

From the style of your disgram, would I be correct in assuming you're 'designing' using a simulator? - if so I presume you're just sticking bits of circuits together and changing values until you get something out?.

Now this is funny. I got a kick out of this one...lmao. Nah, me a simulator? Forget it.

And guru? It chopes low freqs, not highs as much but the trade off is worth it.

Why a Darlington? Because it is good design. That's why....any more?

 

[kchriste]

The values of all coupling capacitors are so high that very low frequency rumble frequencies are passed and amplified.

And some of them (C54) are backwards and will fail/leak prematurely.

 

[Mikebits]

And that op amp symbol is just plain funky looking.

You seem to worry about dynamic range, but the point is moot as your front end RF amp has no dynamic range, remember IP3?

Have you measured the loss through your preselector? If it is high your MDS/NF/Signal to noise will suffer.

 

[Mikebits]

I just received the latest Mini-Circuits catalog this week. Lots of nice RF goo in there. You should look into replacing your front end amp with something from Mini-Ckts ERA-series. NF as low as 2.8, IP3 up to +32 dBm.

Also consider Changing your first stage mixer to a Mini-Ckts SRA series. This would improve your NF and IP3 greatly. This assumes your preselect has less than 3 dB loss. If your loss is greater then you should do a rework on it.

Your design needs to be optimised from the front end first then to the back. A great audio amp is of little use with a bad front end.

BTW, the ERA parts are less than a few bucks, the mixer should be less than $10.00

 

[Space Varmint]

I just received the latest Mini-Circuits catalog this week. Lots of nice RF goo in there. You should look into replacing your front end amp with something from Mini-Ckts ERA-series. NF as low as 2.8, IP3 up to +32 dBm.

Also consider Changing your first stage mixer to a Mini-Ckts SRA series. This would improve your NF and IP3 greatly. This assumes your preselect has less than 3 dB loss. If your loss is greater then you should do a rework on it.

Your design needs to be optimised from the front end first then to the back. A great audio amp is of little use with a bad front end.

BTW, the ERA parts are less than a few bucks, the mixer should be less than $10.00

You know what Mike? I just haven't gotten around to it yet. I'm gonna change it. Did you say that was a JFET your were using? I would think low impedance would be best. I might try an LNA. I had a few but they got stolen. I want to put something really nice in their but I don't trust a JFET. For one thing I don't have the room in that can to add any more amplifiers and I don't think I can get the same gain without pushing it into a part of the square law curve I don't want.

So I'm not saying it is perfect. In fact the damn preselector completely changed on me when I put RG-58 coax on it with a PL-259. I built it around a piece of RG-174U which is 50 ohms. So I don't get it. That don't make sense really.

But never the less, the radio is working damn good. So I'm putting together a modulator. I built the audio and thought I needed more audio than a 741 and a high impedance buffer to drive it, then I started getting some funky feedback so I tore it out. Then I found that just the 741 would due by reading this really cool site: **broken link removed**

It looks like he choked the crap out of the circuit. I can see feedback just from my hand moving around the mike. I got it from a friend who moved away and the Mic has VOX built into it, but he bypassed it. So I might have something wrong on the 8 pin connector.

But I just want to put it on the air. I got two old amps I built a while back. One is adjustable 0 to 10 watts and the other is an MRF454 80 watter. I just got me a new SWR/Power meter because it looks like my Diamond meter got stolen too...lol. Damn thieves! So I'll get back to the receiver after I get my transmitter operational and get a few QSO's under my belt.

 

[audioguru]

A lousy old 741 opamp is too noisy for a mic preamp (hisssss and rummmble). An audio opamp should be used instead. An OPA134 has very low noise.
The mic preamp should be shielded in its own cat food can.

 

[Space Varmint]

A lousy old 741 opamp is too noisy for a mic preamp (hisssss and rummmble). An audio opamp should be used instead. An OPA134 has very low noise.
The mic preamp should be shielded in its own cat food can.

LOL...yeah I know. I mean the shielding. Well I tried a 386 and it was even more hissy so I think I'm gonna try this guy's method with the 741 (the link). I found out the carrier oscillator is where you want your power. The handbook say 6 times the audio amplitude. So I'm gonna choke the hell out of the audio and wait to see how it sounds when I finish the modulator.

 

[Space Varmint]

I just found the problem. Pin #1 is the ground...lol. I had the other two right for the PTT and mic hot. It has a beautiful audio.

 

[Space Varmint]

Here's the audio for the sure mic.

I'm gonna attempt a VXO that will go 10KHz above crystal frequency so I can slide the balanced modulator output right into a filter made with same crystals. Anyone got any good plans?

 

[Mikebits]

The op amp has a high input impedance so I do not see the purpose of the emitter follower proceeding it.

Your audio coupling caps range from .47uF down to .1uF then up to 4.7uF. I don't understand the logic for that.

 

[Space Varmint]

I put the connector for the mic in this one. The extra parts will be the balanced modulator.

 

[Space Varmint]

The op amp has a high input impedance so I do not see the purpose of the emitter follower proceeding it.

Your audio coupling caps range from .47uF down to .1uF then up to 4.7uF. I don't understand the logic for that.

Filtering. But remember I had the wrong ground originally. I'm just gonna leave it and move on. It looks great. I got allot of stuff to put in this yet. I realized I just ordered some Amidon T-80-02's that I can make a wholloping BFO out of. If I pad it down and keep the variable cap away from the can, I can make it very stable. Then I could just buffer it into the balanced modulator....should work!

 

[Mikebits]

With a .1uF cap your filtering your audio, at 1kHz your cap Z is about 1.5K

 

[Space Varmint]

With a .1uF cap your filtering your audio, at 1kHz your cap Z is about 1.5K

It also acts as an attenuator and if I lean into the mic, it will clip. It's just what I want.