I apologize if this has been discussed before; I’ve searched without luck. My basic question is it possible to use the standard Diyaudio F5T boards in a balanced configuration?
I admit I know little to none about circuit design; I’m only able to follow instructions. I’ve successfully built a pair of mono F5Tv3 with four output boards per channel. I’ve read through EUVL’s thread on his balanced version of the F5; however, the only thing I was able to take away was the output impedance will be reduced by half thus the need to reduce rail voltage by half for more usable class A operation (and probably other reasons unbeknownst to me).
Regardless of whether there are actual benefits for differentially balanced amplification, I would like to give it a try, you know, for the fun of it.
Other than the need to lower the rail voltage and increasing bias. What changes are necessary to convert a typical F5Tv3 single ended build to balanced, if even possible? And how would the wiring of the Diyaudio.com boards look?
Shout-out to 6L6 for the awesome guides and the rest of the community for all their support and information. Thank you!
~JL
I admit I know little to none about circuit design; I’m only able to follow instructions. I’ve successfully built a pair of mono F5Tv3 with four output boards per channel. I’ve read through EUVL’s thread on his balanced version of the F5; however, the only thing I was able to take away was the output impedance will be reduced by half thus the need to reduce rail voltage by half for more usable class A operation (and probably other reasons unbeknownst to me).
Regardless of whether there are actual benefits for differentially balanced amplification, I would like to give it a try, you know, for the fun of it.
Other than the need to lower the rail voltage and increasing bias. What changes are necessary to convert a typical F5Tv3 single ended build to balanced, if even possible? And how would the wiring of the Diyaudio.com boards look? Shout-out to 6L6 for the awesome guides and the rest of the community for all their support and information. Thank you!
~JL
The F5T manual has a base schematic for balanced operation that requires the feedback references to connect to each other rather than ground.
I don't know if the store boards have this possibility incorporated. I actually don't know of any board that does so. You may need to go to veroboard or design a board from scratch.
However you may still get differential operation by using two boards per channel, and wire each input to one polarity of the XLR connector. Pin1 in that case would connect to the board's signal ground inputs, which is usually not a very good idea.
Another way to execute this would be to air wire the required components, the trimmer middle pin and the two source resistors and connect them to each other.
I too am considering changing my F5Tv3 to balanced.
You will need another FE board and there is a hole marked "Link" on the FE board to connect to the other FE board as per Nelson's reccs.
Doesnt seem too difficult to me to implement.
I dont know why you would need to lower the voltage.Seems to me that the output should be the same in the X balanced configuration since total dissipation will remain the same.
Nash
You will need another FE board and there is a hole marked "Link" on the FE board to connect to the other FE board as per Nelson's reccs.
Doesnt seem too difficult to me to implement.
I dont know why you would need to lower the voltage.Seems to me that the output should be the same in the X balanced configuration since total dissipation will remain the same.
Nash
You certainly don't need to reduce voltage, but class A power will be reduced using the same bias. It's a personal choice, and there is no right or wrong answer that will suit everyone. It will depend on the sensitivity and impedance of your speakers, and your ears as to what is best.
Last edited:
I'm rephrasing this to avoid confusion.
Total Class A current will still be 2x idle bias current into load (for each side of balanced circuit) but total class A power into 8 ohms will be less than class AB power into 8 Ohms which will be around 4 x higher than the original F5T.
That's probably clear as mud. Hahaha
I'm giving an example
First off let's assume zero losses to keep it simple.
eg. regular F5T with 32V rails biased at 2A
Current draw from power supply at idle = 2A.
Max Class A current 2 x 2A = 4A
Class A power into 8 ohms = (4^2 x 8)/2 = 64W
Converting stereo F5T (above) into a mono F5T X using same operating conditions.
F5T-X 32V rails biased at 2A per half circuit (same as before into one stereo channel)
Current draw from power supply at idle will be 2 x 2A = 4A
Max Class A current is 4A (each side of circuit produces max 4 A class A (same as before))
Class A power into 8 Ohms = (4^2 x 8)/2 = 64W
Max Class AB power into 8 Ohms = (64^2/8)/2 = 256W
You will obviously need 2 chassis for this, just replicate the same same chassis as first F5T stereo.
Power ratings won't be as high as this as we assumed zero losses to keep it simple.
Edit: Max class A current may go higher if you are using diode in parrallel with source resistors due to Id/Vgs curve of mosfets (thermistor will counteract some of this effect though). Lets keep it simple though.
Last edited:
As posted earlier, the output power is related to the square of voltage so assuming no losses, you get four times the output power from twice the voltage swing. In reality it's a lot more complicated as the source resistor begin to drop more voltage, the power supply has a current limit, and so on.
No. 32 + 32 = 64V across speaker load
P=VxV/R
= 64 x 64 / 8 = 512W peak
= 512/2 = 256W avg
However the true power is probably closer to (56 x 56 / 8)/2 = approx 200W due to losses (just a rough guess)
Thanks.
Not sure about the pin 1 connection. In a balanced amp with XLR input and RCA input, pin2 is connected to RCA center pin and pin1 of the XLR is connected to the RCA shell. When using the RCA use a shorting pin between pin 1 and 3 of the XLR.
But should pin1 of the XLR be connected to the chassis or to the amplifier ground which is in turn connected to the chassis thru a CL60 resistor?
How is pin 1 connected in the Pass commercial offerings?
Nash
Pin 1 is always system ground,
XLR barrel is connected to chassis ground.
Both may be the same electrically but from the circuit point of view they are usually different due to physical resistances etc.
For a circuit like the F5, or other single-ended circuits being adapted to balanced/differential operation, the system ground is used as input ground reference. This is different from true differential operation, where a receiver circuit is used to reject common-mode interference. In that case pin 1 may be connected to chassis ground..
This usually means the input FETs will need to see pin1 as their reference.
Both sides, pin 2/3 or hot and cold inputs therefore need to be shorted to pin 1.
XLR barrel is connected to chassis ground.
Both may be the same electrically but from the circuit point of view they are usually different due to physical resistances etc.
For a circuit like the F5, or other single-ended circuits being adapted to balanced/differential operation, the system ground is used as input ground reference. This is different from true differential operation, where a receiver circuit is used to reject common-mode interference. In that case pin 1 may be connected to chassis ground..
This usually means the input FETs will need to see pin1 as their reference.
Both sides, pin 2/3 or hot and cold inputs therefore need to be shorted to pin 1.
Last edited:
No. Pin1 goes direct to Chassis at the socket.
Using the word "ground" is confusing. Better and less ambiguous to omit "ground" from that sentience. XLR barrel if metal and is a Chassis fixing type would go direct to Chassis.
If a PCB type, then there is no convenient direct to Chassis connection. One would have to use the barrel tag and connect that to Chassis, if the manufacturer left one for that purpose.
Insulated barrel XLR cannot be connected to Chassis, neither directly, nor indirectly.
Again, NO! It is NOT optional.
Pin1 goes direct to Chassis at the socket.
No. The two inputs of a differential amplifier read the difference between the two signals. If these differential inputs are balanced impedance, then there is NO requirement to reference them to Pin1, and no requirement to reference them to amplifier ground.
No.
If the inputs are balanced impedance and the Receiver is balanced impedance, then neither gets connected to amplifier ground.
If one side is unbalanced and the other isde is balanced then the "spare" signal pole needs to be referenced to somewhere other than the Chassis. Certainly not to Pin1.
Last edited:
Pin1 goes direct to Chassis.
If the XLR shell is metal, then that too goes to Chassis. Either directly via the bolted connection, or via the shell/barrel tag to Chassis.
Pin2 could go to the unbalanced but insulated RCA Hot.
Pin3 could go to the unbalanced but insulated RCA Cold/Barrel.
The amplifier reads the voltage DIFFERENCE between Pin2 and Pin3
OR
the amplifier reads the voltage DIFFERENCE between Hot and Cold.
Look at a properly wired unbalanced amplifier input.
It uses TWO wires to connect the RCA to the PCB. The amplifier READS the voltage difference between Hot and Cold and then processes that signal.
Pin1 goes direct to Chassis.
Main Audio Ground (MAG) can go direct to Chassis, or can use a Disconnecting Network. The Disconnecting Network can include a switch. this switch effectively bypasses the power Diode Bridge and makes a direct MAG to Chassis connection.
Pass products should connect the balanced impedance Pin1 to Chassis, without exception.
Andrew, in many of his retail amps, Nelson bridges pin 1 and 3 on the XLR when someone is using the SE input of the amp. In this scenario, where there is not some sort of relay system for choosing input, is it still correct to connect pin 1 directly to chassis? I usually daisy chain the SE input off of the XLR input. I have never had noise issues taking XLR and SE input to the board input.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.