I am building a set of monoblock F5 Turbos based on the DIYAudio store PCBs. I am having an issue getting enough bias. My build has approximately 32v rails, two pair of output MOSFETs with cascoded input using 2 10K resistors for the voltage divider. R5/R6 are 1K ohms. I left off the diodes across the bias resistors (which are parallel 1ohm).
With the trim pots fully opened, I'm only getting a little over 100mv across the bias resistors. The amp will produce music, but the bias is obviously way too low. Any assistance would be much appreciated.
Thanks,
Jay
With the trim pots fully opened, I'm only getting a little over 100mv across the bias resistors. The amp will produce music, but the bias is obviously way too low. Any assistance would be much appreciated.
Thanks,
Jay
Thank you muchly, that's really good to know!
The reason I ask is because the pair of heatsinks look pretty good to me, however, going by the specs (only 100mm high) I'm wondering if more suitable for the standard F5
I have been thinking about also using some light air cooling which could make this work.
I know it doesn't help not knowing it's rating but I kinda like them!, another idea also is to use one more heatsink say on the rear of the chassis and mount a couple of transistors on this sink too to spread the load.
Basically I guess my thoughts are.. the 5U diyaudio chassis is a bit large for me! Plus this heatsink has more fins than the sinks on those
there are my thoughts anyway.
Approx. 400mm long by 116mm high by 64mm deep. Two flat areas with tapped fixing holes, which run the full length of the heat sink for mounting devices
The reason I ask is because the pair of heatsinks look pretty good to me, however, going by the specs (only 100mm high) I'm wondering if more suitable for the standard F5
I have been thinking about also using some light air cooling which could make this work.
I know it doesn't help not knowing it's rating but I kinda like them!, another idea also is to use one more heatsink say on the rear of the chassis and mount a couple of transistors on this sink too to spread the load.
Basically I guess my thoughts are.. the 5U diyaudio chassis is a bit large for me! Plus this heatsink has more fins than the sinks on those
there are my thoughts anyway.
Approx. 400mm long by 116mm high by 64mm deep. Two flat areas with tapped fixing holes, which run the full length of the heat sink for mounting devices
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Well, I ended up getting those 2 above and then 8 of these babies.
"taken from power amplifiers. Approx. weight 2.6kg each, 414mm long by 112mm high by 35mm thick, two milled flat areas for mounting devices which run the full length of the heat sink. Lots of slots for screw fixings etc. "
Either way, If I make an upright amp or lay them on the side (400mm deep chassis is a lot larger than the typical amp chassis), I will put two together each side of the amp and Ill probably make (4 sinks per) Monoblock F5 Turbo (V2), or does that sound heatsink overkill?
although have been looking at the Aleph-J and X! maybe ill do both with all 10 sinks
"taken from power amplifiers. Approx. weight 2.6kg each, 414mm long by 112mm high by 35mm thick, two milled flat areas for mounting devices which run the full length of the heat sink. Lots of slots for screw fixings etc. "
Either way, If I make an upright amp or lay them on the side (400mm deep chassis is a lot larger than the typical amp chassis), I will put two together each side of the amp and Ill probably make (4 sinks per) Monoblock F5 Turbo (V2), or does that sound heatsink overkill?
although have been looking at the Aleph-J and X! maybe ill do both with all 10 sinks
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Finished my monoblocks
I've finally finished my F5T monoblocks. This is my first DIY audio electronics product in over 40 years. Around 1980, I build a Pass A40, and then a couple amps of my own design, but with career and family getting in the way (and more disposable income), I haven't had a chance to get back to DIY projects. I built a set of GR Research NX-Oticas and stereo triple OB subs last fall, and decided an amp project would be a good way to get through the pandemic. Well, I'm now hooked.
My monoblocks use the DIYAudio Store boards with two pairs of output transistors and cascoded input, but no diodes on the bias resistors. I'm using Antek 4225 transformers, XRKAudio's 'Soft as a Feather Pillow' soft start boards (mounted underneath the power supply) and 'Smooth Like Buttah' PSU boards (with 18,000uf caps). I also have a separate PCB with a Jensen transformer circuit for balanced input, and a switchable inline MiFlex copper cap with a ~70 hz rolloff. The latter allows better integration with my powered servo subwoofers. I also added 65C thermal shutoffs on each heatshink.
With this power supply configuration, the rails are running about 32 volts, but I've set the bias at around one amp (just over) to allow the amp to run a bit cooler since I don't really need the extra power. My current speakers are 93db/w efficient, and I'm planning to build a set of line source OB speakers this fall which will be around 98db/w.
With this bias, the heatsinks are running at about 36 degrees C, so just a bit warm to the touch. I've only had them running for a few hours, but there is no hum or noise and they are sounding pretty good.
Thanks to Nelson Pass for sharing his design and XRKAudio for the excellent products.
I've finally finished my F5T monoblocks. This is my first DIY audio electronics product in over 40 years. Around 1980, I build a Pass A40, and then a couple amps of my own design, but with career and family getting in the way (and more disposable income), I haven't had a chance to get back to DIY projects. I built a set of GR Research NX-Oticas and stereo triple OB subs last fall, and decided an amp project would be a good way to get through the pandemic. Well, I'm now hooked.
My monoblocks use the DIYAudio Store boards with two pairs of output transistors and cascoded input, but no diodes on the bias resistors. I'm using Antek 4225 transformers, XRKAudio's 'Soft as a Feather Pillow' soft start boards (mounted underneath the power supply) and 'Smooth Like Buttah' PSU boards (with 18,000uf caps). I also have a separate PCB with a Jensen transformer circuit for balanced input, and a switchable inline MiFlex copper cap with a ~70 hz rolloff. The latter allows better integration with my powered servo subwoofers. I also added 65C thermal shutoffs on each heatshink.
With this power supply configuration, the rails are running about 32 volts, but I've set the bias at around one amp (just over) to allow the amp to run a bit cooler since I don't really need the extra power. My current speakers are 93db/w efficient, and I'm planning to build a set of line source OB speakers this fall which will be around 98db/w.
With this bias, the heatsinks are running at about 36 degrees C, so just a bit warm to the touch. I've only had them running for a few hours, but there is no hum or noise and they are sounding pretty good.
Thanks to Nelson Pass for sharing his design and XRKAudio for the excellent products.
