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5

The 741 is powered from 0 volts and +12 volts. This means that the maximum positive output voltage is restricted to about +10 volts (on a good day). This voltage is then fed to an emitter follower (Q2) and the maximum output voltage on the emitter will be about 0.7 volts lower than the base hence 9.3 volts. This voltage is further reduced by D6 to maybe 8.7 ...


4

Put the relay between Q4 collector and the positive supply. The relay should be rated for 24 volt operation. With the relay between Q4 emitter and Ground, Q4 is an emitter follower, and its emitter voltage will be about 0.7 volt below the base voltage.


3

it's connected via 2-pole unearthed - 45W MagSafe 2 Power Adapter, which is connecting to a 3-pole earthed power strip Power adaptors of this type need to pass conducted emission testing on their DC output wires and, in the absence of an earth pin, will normally connect the DC output to the live DC side of switching flyback transformer via a low value ...


3

The circuit is designed to operate from a positive only rail so lack of a negative rail shouldn’t be an issue. I think your problem is the DC biasing between the VS1003 and TPA2005. The VS1003 outputs are biased around GBUF which is about 1.2V. The TPA2005 wants its inputs biased around VCC/2 = 2.5V. Since these are not matched you must put AC coupling ...


3

simulate this circuit – Schematic created using CircuitLab The resistors set the voltage ratio for the two signals. With equal sized resistors, the signals are mixed equally, The resistors also present an electrical load to the source that is reasonably predictable. Without the resistors, the two sources would be fighting each other at any time they ...


2

Agree with earlier response that I personally never use electrolytics of any kind; I feel (perhaps no longer true) that they evolve over time since they are liquid-based. Also, the polarized nature implies that its behavior is inherently asymmetric for negative versus positive voltage drops across it, which to me implies some small amount of distortion and ...


2

I am new here so was unable to comment on Neil_UK's post above, but wanted to share my experience for others who may be experiencing noise with their USB audio interface. Using my audio interface (Soundcraft 22 MTK) I had been experiencing quite alot of noise and had tried a number of things to fix it like changing power management settings in Windows, ...


2

The schematic is a bit confusing, or this is a multi-purpose connector. It is being called a stereo jack, yet pin call-outs are (1)=GND, (3)= TIP, (2)=RING, as if it was a telephone switch-board jack from many decades ago. In the days of mechanical switchboards this connect/disconnect feature allowed a used jack to light a small lamp. Each jack had its own ...


2

Obviously, it isn't the electrical connection to ground that's causing the problem. Instead, the physical flexing of the PCB is either causing an open or a short somewhere nearby. In older equipment, it would not be surprising to find a hairline crack in the PCB itself or one of the nearby solder joints. Or, it could be that the tip of the screw itself is ...


2

100 ohms is probably a good starting point for the volume controls. R1,R2 is harder to pick. 1K perhaps.


2

You haven't explained the power supply setup. If this is powered by its own 9 V battery there should be no problem but if you are using a shared power supply with the other pedals you may have created a short-circuit. Check if the other pedals positive or negative ground. (That might cause a short on the 9 V supply.)


2

If you already searched for the chip and didn't find with Google, chances are that you will never find this datasheet... If I were in your situation, I would try to use this module just as every other cheap Bluetooth module. If you succeed, good. But, if don't.. well, with no datasheet, you have nothing to be lost here; the only thing to do would be order ...


1

If I was to use a single speaker without a headphone connection, how would I draw the schematic Page 2 of the data sheet above shows you how to do this (see above). Or if you want to use your schematic look for the nodes Lo/Mo- and Ro/Mo+ and connect the node called STEREO/MONO to Vdd via 100 kohm.


1

Your PCB is attached to a metal plate. There are components on the PCB between the PCB and the metal plate. Very likely there is a component that is just a little too tall. As long as the screw isn't completely tight, there's a tiny gap between the component and the plate. If you tighten the screw really tight, the component touches the plate and causes a ...


1

Figure 1. Close-up of wiring. There is no sign of a ground connection between the black wires at the rear. If my analysis is correct then you have done this: simulate this circuit – Schematic created using CircuitLab Figure 2. A schematic of Figure 1. Connect the two grounds together at the potentiometer.


1

There are two ways that the sound may become muted. Firstly, the power supplies to the VS1003 don't include a negative voltage source. That usually means that the 'ground' is not in the midrange of the AC output signals, and only a coupling capacitor (to block DC) will make a suitable connection to an external device (amplifier input or speaker). The ...


1

You ought to understand how the chip works as a preamp. It has variable gain with AGC and attack/decay rates. https://datasheets.maximintegrated.com/en/ds/MAX9814.pdf I suggest you should be using STP cable with a grounded shield. The microphone isolation is more about acoustic pressure isolation and focus than electrical connections. If the mikes have ...


1

They've provided a very poor drawing. 3 and 4 obviously disconnect when the jack is inserted. I suspect that 5 and 6 do as well but that contact is isolated from 2. That way it can be configured to work the same way as the tip contact by permanently connecting 2 to 5. When the jack is inserted 2 will be disconnected from 6. Alternatively you could leave 5 ...


1

The pot in your photos appears to be very similar to a Bourns PTD902 series unit. The "A" indicates it is a logarithmic taper (aka Audio taper), and the "503" indicates it is a 50kOhm pot.


1

Linear Systems and InterFET still make the J305. Mouser has the InterFET version in stock.


1

You'd be better off using an open collector comparator: unlike an opamp it is well behaved for signals exceeding its rails, and doesn't suffer from not being able to swing to the rails. Choose R1 and R2 to create a threshold voltage, say 0.2V. When positive swing of audio input reaches that threshold the comparator flips low and yanks the capacitor C to ...


1

I just want to know why the resistors are considered necessary, and what happens if you don't include them and just wire together left/right channels. If the signals you are considering mixing are low level line-out type signals then it's likely that you can just simply join them together because there will be resistors inside the output amplifiers that ...


1

That's a typical muting circuit to clamp the output to ground when power supplies are not stable.


1

This is general: Be sure no digital circuit get its ground side supply current through the same wire which is a part of analog circuit ground wiring. Digital GND and analog GND can meet only in a single point which is the output capacitor of the power supply, C1 in your case. Also be sure digital circuits cannot pollute your DC voltages in the analog side. ...


1

The integrated switches are the easiest and most common way of switching off other audio paths. You can find 48 examples here.


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