Few more questions, what is the function of VR1 and VR2 ,which one is Bias and which one is DC offset?
What the points C and D on the driver board?
If I had the choice of building Pink mouse boards or above, which one should I choose?
Thanks
What the points C and D on the driver board?
If I had the choice of building Pink mouse boards or above, which one should I choose?
Thanks
Sorry, haven’t used that board. I do have a typo in my answer, its 2sc4793 not 4791.
Post 9542 above specifies all these bjts and subs.
The bias pot should have 1k ohms from the base of the Bias transistor (Q15) to the common two legs of the pot. The other pot should be dc offset.
Post 9542 above specifies all these bjts and subs.
The bias pot should have 1k ohms from the base of the Bias transistor (Q15) to the common two legs of the pot. The other pot should be dc offset.
Attachments
Both 4148 diodes need to be grounded to ground (ground plane) for the circuit to work properly. The other end of each diode goes to a 47k resistor then to the + and - power supply rails.
You should be able to visually check to see if the diode is grounded or use a meter to check continuity.
Thank you for your help
Like you said above, In the picture below, diode under the tick mark - one end is connected to ground and other end is connected to 47.5K resistor.
However the dioder under the cross mark, one end is connected to the 47.5K resistor and other end is connected to nothing. It needs to be connected to ground plane. The two blue dots on the picture need to be connected
@Dave murrey sussed it out after having a fault on his board.
Like you said above, In the picture below, diode under the tick mark - one end is connected to ground and other end is connected to 47.5K resistor.
However the dioder under the cross mark, one end is connected to the 47.5K resistor and other end is connected to nothing. It needs to be connected to ground plane. The two blue dots on the picture need to be connected
@Dave murrey sussed it out after having a fault on his board.
The 968/2238 transistors are VAS transistors in this design. These type of transistors are usually used as drivers, but obviously they can work as VAS transistors too.
I think the KSA1381/KSC3503 are a better choice for VAS transistors. Also, the "middle" MJE15030 is the bias transistor and a KSC3503 would work better here although almost every DIY version of this amp probably used a 15030.
I think the KSA1381/KSC3503 are a better choice for VAS transistors. Also, the "middle" MJE15030 is the bias transistor and a KSC3503 would work better here although almost every DIY version of this amp probably used a 15030.
This Class A design is very forgiving in a lot of areas with some operating points and component substitutions.
The Zener references for the push-pull diff amp can be just about any voltage value; 10V~27V. Just have to scale the Zener dropping resistor accordingly.
The 3k3 emitter follower resistor can be reduced to allow more "drive" to the VAS. I think 3k3 is a bit low especially if you use the original transistors (MJE15xxx). I use 1k2 with MPS42/92's.
Even MPSA42/92's have been used for the diff amp with excellent results.
The Zener references for the push-pull diff amp can be just about any voltage value; 10V~27V. Just have to scale the Zener dropping resistor accordingly.
The 3k3 emitter follower resistor can be reduced to allow more "drive" to the VAS. I think 3k3 is a bit low especially if you use the original transistors (MJE15xxx). I use 1k2 with MPS42/92's.
Even MPSA42/92's have been used for the diff amp with excellent results.
Which resistors are recommended for use? Most values for Vishay Dale are out of stock with a lead time exceeding a year, and the ones that are available are excessively priced, with one resistor costing £5.98!!
https://www.digikey.co.uk/en/products/detail/vishay-dale/CMF6047K500FHEK/3634656
Am I looking at the correct series ?
Thanks
https://www.digikey.co.uk/en/products/detail/vishay-dale/CMF6047K500FHEK/3634656
Am I looking at the correct series ?
Thanks
I cannot edit my previous post, is 0.6w resistor fine for the main board, or it has to be 1w ?
Looking at pictures of the original board, the 25R5 seems like a 2w resistor, am I correct?
Thanks
Looking at pictures of the original board, the 25R5 seems like a 2w resistor, am I correct?
Thanks
Standard 0.25W/1% metal film resistors are more than adequate. Odd values like 47k5 can be 47k and so on. The 25r5 can be a 22r/0.25W. The 25r5 only has 0.65V & 30mA across it so it has hardly any dissipation going on.
Here is one channel of mine. Still have not put it into a chassis, but works great! Dead quiet and exceptional performance.
On my version, I am tracking the output transistors for bias instead of the drivers. No issues.
On my version, I am tracking the output transistors for bias instead of the drivers. No issues.
Perhaps a safer bet would be a non mil specs but better than average resistors from trust worthy suppliers like RS, mouser, digikey etc. So that it wouldn’t burn your house down.
There are fairly good China made resistors but most of them sold on the market are counterfeit, not only counterfeit Dale, but also counterfeit decent China brands too!
Taking the cue that some said that the KSA-50 is sweeter than its more powerful siblings with more output transistors. Wonder did anyone try running it KSA-50 board with lower VCC (+-20?) and only a pair of power transistors for each channel, and changing whatever resistor value to make it work.
How would it sound?
How would it sound?