Hello all, long time listener first time caller. So as a hobbyist I finally decided to get one of those diy kits from China thats loosely based on the marantz 7c. I have made some modifications but my problem is with this wiring diagram. I can read them OK but Ive never seen electrolytic capacitors shown thiis way, just hanging there. Specifically the top 3. What is the polarity? If I was to guess, positive to 1 and 6 (12ax7 triodes), but I hate making things explode so I thought Id ask people smarter than me. I'm sure this is a rookie question, but ive searched a lot and dont see anything like it. Is positive to both sides and that shorthand for nagative to ground?
The coupling caps, 0.1uf & 0.39uf are non polar film caps, so there's no need to show polarity.
Edit: For some reason I thought you were asking about the coupling caps. My mistake.
jeff
Edit: For some reason I thought you were asking about the coupling caps. My mistake.
jeff
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The electrolytics on top 2x22uf and 1x10uf have their positive terminals connected as shown and the negatives are grounded to circuit ground. It's just a shortcut without drawing lines all over.
Really not drawn correctly, don't care what country you're in. Hopefully the schematic is correct.
Should look more like the old school way of drawing grounds:
The chinese drawing is corrrect ! The caps has their minus connection to the signal ground ( single horisontal line)
At the far left you have a 10 ohm with a parallelled cap that connects signal ground to chassies ( 3 horisontal lines formed as an arrow)
The modern schematics ditinguishes between chassies ground and signal ground.
At the far left you have a 10 ohm with a parallelled cap that connects signal ground to chassies ( 3 horisontal lines formed as an arrow)
The modern schematics ditinguishes between chassies ground and signal ground.
There are no negative voltages in this tube circuit, so all cap grounds are negative. The only question might be the 2.2uF output cap but again, the output is zero DC. You could build the circuit without a cap and measure the voltage before installing the cap.
Yep the signs used are correct, just different standard. In Europe we're mostly used to something pretty much the same.
It's worth noting that film caps have "polarity" too. They don't require the voltage on them to be polarized in a certain way to work ok, but it's good practice to connect the outer layer to the point with lower impedance - so to the anode of the prior tube in this circuit. It can act as shielding partially. They even used to be marked in the older times.
You can identify the outer layer with a scope. Connect the cap to the scope, set on low voltage and touch the cap with your finger. Then connect it way around and touch again. You'll notice induced hum will show on the scope. In one case the induced voltage will be greater, and the lead that have the probe to it then shows the outer layer. You of course have to connect the ground to the other lead always.
It's worth noting that film caps have "polarity" too. They don't require the voltage on them to be polarized in a certain way to work ok, but it's good practice to connect the outer layer to the point with lower impedance - so to the anode of the prior tube in this circuit. It can act as shielding partially. They even used to be marked in the older times.
You can identify the outer layer with a scope. Connect the cap to the scope, set on low voltage and touch the cap with your finger. Then connect it way around and touch again. You'll notice induced hum will show on the scope. In one case the induced voltage will be greater, and the lead that have the probe to it then shows the outer layer. You of course have to connect the ground to the other lead always.
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The output coupling cap is film, non-polar, according to the schematic, but the left end is connected to +51VDC at the cathode, and the other end to ground via the 1M leak resistor, so if you use an electrolytic, polarize accordingly.
Its a standard way to show ground in schematics since about the 70's or 80's (certainly for RF) - you've clearly been restricting yourself to old valve circuitry 🙂
It reduces clutter when the emphasis is the signal path.
Positive plate is hollow in UK capacitor symbol for an electrolytic - harder to mis-interpret with hand-drawn diagrams than curved v. straight!
Its an interesting exercise to consider when this outer-foil polarity matters. It usually doesn't in low-impedance circuitry, and many coupling caps it may not... Some film cap type may be symmetrical (stacked rather than wound?).
There are and have been many ways to show ground and many "standards" over regions and history.
Everyone has a favorite and some feel there is only one "correct" way to draw.
Google "ground symbol electrical" for some examples.
The only issue I would take with the China schematic is the ground symbol used is not shown connected to what one assumes to be the main return buss.
It leaves the reader to "assume" what is the main return buss in the design. Leads to possible mistakes and confusion.
I prefer the main return buss to be explicitly defined by showing the ground symbol used in the design connected to the main return buss at some point.
Everyone has a favorite and some feel there is only one "correct" way to draw.
Google "ground symbol electrical" for some examples.
The only issue I would take with the China schematic is the ground symbol used is not shown connected to what one assumes to be the main return buss.
It leaves the reader to "assume" what is the main return buss in the design. Leads to possible mistakes and confusion.
I prefer the main return buss to be explicitly defined by showing the ground symbol used in the design connected to the main return buss at some point.
So... being new here I am not sure of protocol. I have some issues with this build unrelated to my initial thread title. Open a new thread or derail this one?
I would keep going here, and if you wish to split the thread at a later date, I'm guessing a moderator can accommodate your wishes.
jeff
Thanks Jeff.
So I have built the preamp portion of this project. It is polite in its operation, not a lot of line noise or hum, definitely has enough gain, but it sounds like a high pass filter. Absent mids and lows. Given this schematic any idea where I should look at for problems?
It is not in the tubes.
So I have built the preamp portion of this project. It is polite in its operation, not a lot of line noise or hum, definitely has enough gain, but it sounds like a high pass filter. Absent mids and lows. Given this schematic any idea where I should look at for problems?
It is not in the tubes.