X/Hugh/Vunce/others,
Another observation if I may.
If the voltage rails are not close to +/-26V to +/- 28V as originally designed, one will have to readjust R112 so that the LTP bias is set at about 2.6mA. In the original design, R112 is at 6.8K ohms.
My supply is ~ +/-24.5V, as such I will have to readjust and judging by Hugh's 4 ohm version of this amplifier which uses +/- 20V rails, R112 is then about 5K ohms.
So for +/- 24VDC I figure an in between figure of 6K ohms would work best.
I was also going to initially use a 100R Bourns 3296 pot for R113 so I can zero the dc offset as much as possible.
Thanks,
Anand.
Another observation if I may.
If the voltage rails are not close to +/-26V to +/- 28V as originally designed, one will have to readjust R112 so that the LTP bias is set at about 2.6mA. In the original design, R112 is at 6.8K ohms.
My supply is ~ +/-24.5V, as such I will have to readjust and judging by Hugh's 4 ohm version of this amplifier which uses +/- 20V rails, R112 is then about 5K ohms.
So for +/- 24VDC I figure an in between figure of 6K ohms would work best.
I was also going to initially use a 100R Bourns 3296 pot for R113 so I can zero the dc offset as much as possible.
Thanks,
Anand.
Hi Anand,
If I remember correctly, the temporary trimpot installed at R113 had very little effect on adjustment. Start with schematic values and give it a go, otherwise a bit of manual tweaking is in order.
If I remember correctly, the temporary trimpot installed at R113 had very little effect on adjustment. Start with schematic values and give it a go, otherwise a bit of manual tweaking is in order.
Hi Anand,
When I built my AN 4Rs, I ended up with +/-21v on the DC rails. I chose R112 (R5 on Hugh's 4R schematic) as 5K and used a 200 ohms Bourns trimpot to zero DC offset.
Then I removed the trimpot from its holder (X111) and used a 'nearest value' fixed res for R113. This was 100 ohms - resulting in a DC offset of <10mV.
Andy
When I built my AN 4Rs, I ended up with +/-21v on the DC rails. I chose R112 (R5 on Hugh's 4R schematic) as 5K and used a 200 ohms Bourns trimpot to zero DC offset.
Then I removed the trimpot from its holder (X111) and used a 'nearest value' fixed res for R113. This was 100 ohms - resulting in a DC offset of <10mV.
Andy
Hi Guys,
Always triple check your mosfet wires manually. Follow the schematic and PCB pads / pins to the mosfet GDS pins by eye. My only recommendation is to use three different colors. My usual standard is blue is gate, red is drain and white is source.
The boards in general have a ground loop breaker (an NTC to protective earth). This serves not as a ground lift but a path for current should there be a catastrophic short somewhere that would expose the board to mains voltages. The NTC would then heat up and go to 0.5ohms thereby shunting the short to chassis/earth ground. When cold the NTC is 8-10ohms and this provides a ground loop breaker by partially absorbing ground loop currents.
Always triple check your mosfet wires manually. Follow the schematic and PCB pads / pins to the mosfet GDS pins by eye. My only recommendation is to use three different colors. My usual standard is blue is gate, red is drain and white is source.
The boards in general have a ground loop breaker (an NTC to protective earth). This serves not as a ground lift but a path for current should there be a catastrophic short somewhere that would expose the board to mains voltages. The NTC would then heat up and go to 0.5ohms thereby shunting the short to chassis/earth ground. When cold the NTC is 8-10ohms and this provides a ground loop breaker by partially absorbing ground loop currents.
I’ve ordered 20 NTCs from China:
20Pcs 8Ohms 6Amp 20Mm Disk 8D-20 Power Thermistors Inrush Curren Limiter Ntc sx | eBay
Hopefully they will be OK.
20Pcs 8Ohms 6Amp 20Mm Disk 8D-20 Power Thermistors Inrush Curren Limiter Ntc sx | eBay
Hopefully they will be OK.
That's what I ordered too. I think eBay (does this = fake???) is the only way to buy them. 🙁
I used them on my 4x SLBs - but not on the AN boards. Plus I used them between the 'Active' mains supply and each power traffo (another 4). 🙂
I also added them as inrush limiters on 2 other amps (monoblocs).
Andy
Thank you all for your inputs. Since I have a bench supply, test heatsink, I can experiment to my hearts content!
Best,
Anand.
Best,
Anand.
Hi Anand,
I would use a 2k trimmer for setting the LTP current. So, if you need a total 6K, use a 5.6k and a 2k trimmer. You might always use a 5.1k if you can find one, of course.
All the best with the build!
Hugh
I would use a 2k trimmer for setting the LTP current. So, if you need a total 6K, use a 5.6k and a 2k trimmer. You might always use a 5.1k if you can find one, of course.
All the best with the build!
Hugh
Holà! 🙂
Just a quick question... On the amplifier PCB, R133 and R135 are 100R and you have another 100R resistor on the snubber PCB (R101). Should we jumper the one on the amplifier PCB since the schematic calls for 100R, not 200R (2x 100R in series)? Since V131 collector to V142 Gate and V122 Cathode to V141 Gate?
Thanks
Do
Just a quick question... On the amplifier PCB, R133 and R135 are 100R and you have another 100R resistor on the snubber PCB (R101). Should we jumper the one on the amplifier PCB since the schematic calls for 100R, not 200R (2x 100R in series)? Since V131 collector to V142 Gate and V122 Cathode to V141 Gate?
Thanks
Do
Thanks X!
First module almost complete!
I'll be ordering a new transformer from Toroidy, with quad secondaries. Since I'm assembling the 4 ohms version, I'm aiming for 20-22Vdc output of the SLB. Is 18Vac, assuming a 4v drop from the SLB? I was planning to order 600VA transformer, so that leaves 300VA per PSU. If it's better to get 800VA, please let me know. I know transformer heat will rise with lower VA transformer.
Thanks
Do
First module almost complete!
I'll be ordering a new transformer from Toroidy, with quad secondaries. Since I'm assembling the 4 ohms version, I'm aiming for 20-22Vdc output of the SLB. Is 18Vac, assuming a 4v drop from the SLB? I was planning to order 600VA transformer, so that leaves 300VA per PSU. If it's better to get 800VA, please let me know. I know transformer heat will rise with lower VA transformer.
Thanks
Do
600VA should be fine for stereo. SLB is about 4v drop with CRC and cap Mx. 22v + 4v + 3v sag = 29v / 1.41 = 20.5v secondaries. But that depends on the sag a Toroidy has. If only 1.5v then 25.5v/1.41= 18vac.
So I think 18v secondaries can work. I recall getting 22v with 18v trafos.
So I think 18v secondaries can work. I recall getting 22v with 18v trafos.
Do,
Thanks for clarifying that. That being said, it seems that X’s opinion of having an extra gatestopler resistor has changed? To minimize the potential of oscillation?
See here:
https://www.diyaudio.com/forums/sol...irvana-39w-8ohm-class-amp-49.html#post6018979
Best,
Anand.
Thanks for clarifying that. That being said, it seems that X’s opinion of having an extra gatestopler resistor has changed? To minimize the potential of oscillation?
See here:
https://www.diyaudio.com/forums/sol...irvana-39w-8ohm-class-amp-49.html#post6018979
Best,
Anand.
Last edited:
I use 18v secondaries in my AN 4R (Aussie-made Tortech traffos) ... I used 1x 300VA per channel.
My DC rails came out around 21.3v.
Andy
I don’t think it hurts to have 200ohm vs 100ohm gate stopper. 100 is probably enough. Your choice of you want to keep both. The sound is probably the same.
Hi X,
Planing to build 2 monoblocks of the 8 ohm version.
Since I will have plenty of surface area available, I plan to use 2 large passive heatsinks
on each side of the monoblock. Can I mount the n mosfet on one sink on one side and the
p mosfet on the other? If so will they be of equal temperature?
Also since I have a lot of space available in my monoblocks I plan to use CLC
power suply. Plan to use Hammond 129ZJ choke 10mH, 0.16 ohm, 5A as used by
Andrea Ciuffoli in his 30W class A amp.
Amplifier End by Andrea Ciuffoli
Will this CLC power supply sound inferior to the unobtanium SLB power supply?
Planing to build 2 monoblocks of the 8 ohm version.
Since I will have plenty of surface area available, I plan to use 2 large passive heatsinks
on each side of the monoblock. Can I mount the n mosfet on one sink on one side and the
p mosfet on the other? If so will they be of equal temperature?
Also since I have a lot of space available in my monoblocks I plan to use CLC
power suply. Plan to use Hammond 129ZJ choke 10mH, 0.16 ohm, 5A as used by
Andrea Ciuffoli in his 30W class A amp.
Amplifier End by Andrea Ciuffoli
Will this CLC power supply sound inferior to the unobtanium SLB power supply?
Depending on the CLC dimensions it will not be quite as silent as the SLB but the remaining noise will be a pure sine and you will be very pleased with the results. The chief issue with passive filtering is the cost of the inductor but there are very few voltage drops, particularly if the inductor DCR is less than 0.2R.
Using any of Andrea's circuits will bring happiness!
Hugh
Using any of Andrea's circuits will bring happiness!
Hugh
For Class A power supplies, it’s very tough to beat an SLB for low noise/low ripple and high current. It does have a 3v dropout though so plan your trafos accordingly.
Passive heatsink is fine if you have it. I am using a 4U x 300mm Modushop Dissipante chassis myself.
Passive heatsink is fine if you have it. I am using a 4U x 300mm Modushop Dissipante chassis myself.