New DIY large condenser circuit in AliExpress?
- Thread starter jacson
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rogs
Well-known member
I simply bought some blank adaptor SOIC to DIP8 PCBs from Aliexpress (see HERE for example) and fitted the OPA1641 opamps myself.
Tiny piece of 'blu tack' type adhesive putty to hold the IC in place while hand soldering. Pin 3 of the adaptor left out, to allow the 1G resistor to be soldered directly to the adaptor pin 3 socket.....As I have shown in my photos...
(Makes it easier to keep that very high impedance connection point away from any flux or dirt.... )
You could of course test things out, using a standard TL071 DIP op amp if you're not keen on soldering the adaptor --- OK, it would be a little bit noisier than a OPA1641, but it should work well enough to allow you to check things out...
As you say, buying the pre-assembled 1641 on an adaptor from Ebay can be a bit of a lottery.....
Good Day! OK, so I tried the mic without the "second" board with both electret and true condenser capsules and got nothing. From this I leap to the conclusion it does something.
I made a simple quickie recording using these low cost boards and a 34mm edge terminated true condenser capsule (acquired on eBay), a home-brewed mic with an 22mm MXL capsule and MXL circuit, and an old Behringer B-1 condenser to provide some sort of very rough comparison. You be the judge as to how each mic sounds, and whether the demonstration has merit. I figure it is more than we had before, and I can re-do it if anyone has a better idea on how I might demonstrate how it sounds vis-a-vis other microphones. I still have my training wheels on! .
Happy trails to all. James
View attachment CHEAP BOARDS VS MXL VS B-1 TEST 1.mp3
Could I use a NE5532 instead I have on me? It can only take a maximum supply voltage of 15v though resistors do need to be adjusted. Maybe not since I don't know how many volts in your LDC circuit flow into OPA1641.
it probably has to be a jfet-input opamp, 5532/34 is pipolar
rogs
Well-known member
As gyraf says - it needs to be JFET op- amp. And it needs to be a single amp - like the OPA1641 or even the TL071 - and NOT a dual opamp like the NE5532.
If you click on the schematic image on my OPIC LDC page it will bring up THIS PDF which includes a circuit description. That includes some indicative voltage levels you might expect to find at various points....(typically 24v as a DC supply for the OPA1641)
I've also noticed this circuit board pop up in another shopping platform I often used. I was skeptical about this product initially given the insanely cheap price.
So this is basically an Opamp based condenser circuit with a "polarization board" and various other passive filter components then? (Good candidate for some modifications to improve noise floor & its frequency response?)
Yes and no. There's an opamp there, but also something that looks like a JFET that the capsule signal first "meets".
I could try to reverse engineer the circuits from the photos posted on the first page of this thread, but no promises on the timeframe or accuracy (there's only so much one can glean from photos, especially with that black soldermask).
Any markings on the active components, by the way?
Good Day Mr. @Khron - What would you like to see better? I am a better photographer than musician and can either examine or photograph them to discover what you need. James
Voyager10
Well-known member
It looks like R10 on the second circuit board is a zero-ohm link between the outer 2 terminals of the 4-pin connector. The other components could be several stages of RC filtering?
There doesn't seem to be any voltage step-up circuit on either board, so perhaps the capsule is running off a low voltage, which explains the poor SNR.
Here's my best guess: the second board was originally intended to be a voltage multiplier circuit, but someone wanted to save a couple of quid (without re-working the first board) so knocked this one up to make it look busy.
There doesn't seem to be any voltage step-up circuit on either board, so perhaps the capsule is running off a low voltage, which explains the poor SNR.
Here's my best guess: the second board was originally intended to be a voltage multiplier circuit, but someone wanted to save a couple of quid (without re-working the first board) so knocked this one up to make it look busy.
Possibly, but I sorta, kinda, almost doubt it. My experience with Chinese knock offs (pirated radio circuits) indicates they shamelessly "Munce" the original circuit, removing as many components as possible while maintaining an acceptable level of performance, until they have scaled down the circuit to its bare minimum. They unabashedly peddle the result as a copy or clone, often using the original product's logo and model number. In the case below, we see a Chinese version of a British software defined radio called the SDRPlay RSP1. The board includes a confusingly similar copy of the SDRPlay logo and the seller represented it is an RSP1. It employs the two MIRICS tuner chips found on a real RSP1, but lacks about 40% of the rest of the original circuit. They have no qualms about selling a minimized circuit as the real deal.
Therefore, considering the number of simplified circuits that save time and money to make, I sorta, kinda, almost doubt they would include an entire bogus board containing several components, just to fool the consumer and make it appear more complicated than it really is.
Sometimes we find rather odd graphics and phrases reminiscent of cold war propaganda. This board says, “It is strictly forbidden to listen to enemy station broadcasts.”
Parenthetically, I cannot explain the meaning or significance of the odd-looking image of the lady on her back in the lower right hand corner. Resellers on eBay refuse to explain it. Several college level Chinese language professors have also refused to comment. Sorta makes me wonder ... Kinda creepy, I think.
Just my take - your mileage may vary. James
Um ... er ... ahem ... Oops -BUSTED! (Getting old ... memory fading ... falling asleep ZZzzzzzz.....) James
rogs
Well-known member
I took another look at my OPIC circuit - which was deliberately designed to be simple - and decided you could probably 'Muntz' it a little more by removing C5,C6,C7 and C8 ... Now, whether that would be a good idea or not?....
