Jan,
R145 shouldn't be in parallel with R130 - that will affect the gain.
The new resistor should sit between R301-R302-R120 etc. star point and R201-R202-R203-R204 star point. Then if you leave it open (R140=inf) you leave the ouptut stage completely out from the feedback loop ("overal feedback free"), or if you have wire link (R140=0) output stage is 100% inside the feedback.
Bratislav
R145 shouldn't be in parallel with R130 - that will affect the gain.
The new resistor should sit between R301-R302-R120 etc. star point and R201-R202-R203-R204 star point. Then if you leave it open (R140=inf) you leave the ouptut stage completely out from the feedback loop ("overal feedback free"), or if you have wire link (R140=0) output stage is 100% inside the feedback.
Bratislav
ACD said:I'm at work right now, but I will hopefully get time to make some mods to the schematic and layout later today.
Are there other suggestions, while I'm at it ????
Jan,
I am definitely no expert on PSB design but anyhow here are my observations/comments:
The board is really small which may be advantage for some builders with limited amp enclosure space but the penalty is if somebody wants to use bigger size components. Also there is not enough space to mount the heatsinks for Q109/110
The tracks should be wider and a component pads bigger – makes it easier to solder and desolder for newbies. Especially the ground track should be much wider for low impedance.
Separate ground paths for signal (R102, C101, C103, C104) and power return currents ( ZD101/102, D109/110) would be beneficial. Star grounding for signal.
Feedback path from output should be separate track from protection circuit connections to output.
Regards,
Argo
argo said:
Both problems could be addressed by using a double-sided board, using the top layer as a ground plane. D/S boards are more robust as the holes are plated-through so it's not so easy to lift a pad when removing a component.
I know the reason for single-sided was so we can make our own boards with a lightbox and some ferric chloride, but it really doesn't cost that much to have D/S boards done by Olimex or similar, and even less if we do a group buy.
Just a few minor comments....
It is really no more problem making a double sided board yourself than making a single sided.....
For standard leaded components, it is as simple as using the component leads as feed throughs, - has been done for ages!
As for plated holes... these can be a real PITA to desolder!!!
Specially for newbies without proper equipment!
It is really no more problem making a double sided board yourself than making a single sided.....
For standard leaded components, it is as simple as using the component leads as feed throughs, - has been done for ages!
As for plated holes... these can be a real PITA to desolder!!!
Specially for newbies without proper equipment!
Thanks for the inputs
Starground, pads etc.:
Please have in mind that we are making a clone of an old amp, not making a design. The few Krell PCB's I have seen didn't have star ground etc. However if the majority wants it, I have no problems in making it so
The pad-size used is quite common, however I can easily make the pads for resistors etc. bigger
PCB-size? Why make it larger than necessary? The tracks are wide where the "high" current flows...... And I see plenty of space around Q109 and Q110 for heatsinks.......
Keep posting your suggestions.......
Starground, pads etc.:
Please have in mind that we are making a clone of an old amp, not making a design. The few Krell PCB's I have seen didn't have star ground etc. However if the majority wants it, I have no problems in making it so
The pad-size used is quite common, however I can easily make the pads for resistors etc. bigger
PCB-size? Why make it larger than necessary? The tracks are wide where the "high" current flows......
And I see plenty of space around Q109 and Q110 for heatsinks.......Keep posting your suggestions.......
Board Design
Hope the holes are large enough. I like using 1/2 watt AB carbon comp resistors in my SS projects. The leads are larger than the modern metal film.
I want to build one of these myself. I will build in in a lower power version. I only need 10 watts or so. I was thinking single pair output transistors, and about 900 ma current. My speaks are 16 ohm, and 100 dB. Have a nice 38 volt, 300 watt Plitron sitting unused in my box, should be perfect.
Once is boards are available, put me down for four.
George
Hope the holes are large enough. I like using 1/2 watt AB carbon comp resistors in my SS projects. The leads are larger than the modern metal film.
I want to build one of these myself. I will build in in a lower power version. I only need 10 watts or so. I was thinking single pair output transistors, and about 900 ma current. My speaks are 16 ohm, and 100 dB. Have a nice 38 volt, 300 watt Plitron sitting unused in my box, should be perfect.
Once is boards are available, put me down for four.
George
I havn't done an online cost check yet, but will do it tomorrow....
Please note that I personally only use www.elprint.com, however when all mods are incorporated to the PCB, I will publish both PDF and Gerber files for free....
Please note that I personally only use www.elprint.com, however when all mods are incorporated to the PCB, I will publish both PDF and Gerber files for free....
Krell clone
I'd be interested in making one of these after I finish a Pass Aleph X.
My feeling is that if you can make it better with some changes such as using a star ground, double sided boards or bigger traces/pads, that would be ok so long as the overall circuit design is close to original, heck I wouldn't mind using newer and better parts so a newer and better layout does not bother me.
I'd be interested in making one of these after I finish a Pass Aleph X.
My feeling is that if you can make it better with some changes such as using a star ground, double sided boards or bigger traces/pads, that would be ok so long as the overall circuit design is close to original, heck I wouldn't mind using newer and better parts so a newer and better layout does not bother me.
ACD said:Thanks to rabstg and mpmarino for the kind Words
Regarding the drill holes for resistores, they ar at this moment set to 31.5 or 0,8 mm....
Bigger or good as it is ????
I do not know, the hole in Kristijan's boards will not accept the leads from the 1/2 watt AB. I had to use 1/4 watt.
From memory it seems his holes are 31.5 also. I think that people using modern metal film resistors will have no problems.
But if possible, drill the next size up, maybe 0.9 mm, the resistors will start in the 0.8 hole but do not want to go far.
Some day I will need to move into the 20th century and start using normal resistors.
George
Parts for Krell Clone
Looking at Newark, all the transistors should be available. There seems to a be a 10 day lead time for the 2SC3955, 2SC2240, and the 2SA970.
The MJL21194 and MJL21193 are a little expensive, 4.65 each. Have others looked into availability of the parts to build this unit?
And excuse me if 4.65 for an output transistor is expensive, I am very cheap.
If the boards like like they are a done deal I will see about getting my parts together.
George
ACD said:Sorry for the delay
Here is an updated layout of the KSA-50
Looking at Newark, all the transistors should be available. There seems to a be a 10 day lead time for the 2SC3955, 2SC2240, and the 2SA970.
The MJL21194 and MJL21193 are a little expensive, 4.65 each. Have others looked into availability of the parts to build this unit?
And excuse me if 4.65 for an output transistor is expensive, I am very cheap.
If the boards like like they are a done deal I will see about getting my parts together.
George