Hi Stanley,
That's great to hear you got it working. I guess I'm of the hook for now.
The current values you listed look good, and the DC offset is perfect. If the heatsink is that hot it's probably to small. What size heatsinks are using? What's the voltage across R8? If it's about 25mv, drop it to 15mv. It wont degrade performance from my testing but the amp will run cooler.
Al
That's great to hear you got it working. I guess I'm of the hook for now.
The current values you listed look good, and the DC offset is perfect. If the heatsink is that hot it's probably to small. What size heatsinks are using? What's the voltage across R8? If it's about 25mv, drop it to 15mv. It wont degrade performance from my testing but the amp will run cooler.
Al
the heatsink is running ~29Cdegrees above ambient.
I think this is a bit high. The worst case Tc will be ~37Cdegrees above ambient.
What is your worst case room temperature?
What is the voltage across each of the output emitter resistors?
Heatsink temperature
Al & Andrew,
The heatsink is a bit small (6.5W x 4.2H x 2.0D inch) & I can extend it with aluminum plate.
I attached two photos, the first one is the having the heatsink in the bench position (the fins facing down) & the temp was 55C. The second one is the install position with a bit breathing space under the HS & the temperature was 50C. I lowered the bias current to 16mV across R8, the temp drop to 43C.
The OTs are not matched. I will build up the second channel with matched OTs before I replace the OTs on this channel.
Highest ambient temperature in Sydney can get to 40C and the room is not air-conditioned. I will not listen to music on these hot days.
Cheers, Stanley
Al & Andrew,
The heatsink is a bit small (6.5W x 4.2H x 2.0D inch) & I can extend it with aluminum plate.
I attached two photos, the first one is the having the heatsink in the bench position (the fins facing down) & the temp was 55C. The second one is the install position with a bit breathing space under the HS & the temperature was 50C. I lowered the bias current to 16mV across R8, the temp drop to 43C.
The OTs are not matched. I will build up the second channel with matched OTs before I replace the OTs on this channel.
Highest ambient temperature in Sydney can get to 40C and the room is not air-conditioned. I will not listen to music on these hot days.
Cheers, Stanley
Attachments
hi all, ordered the parts from mouser in the most recent bom pdf file. had a few resistors being out but i found decent substitutes. more tricky where the wima caps, i picked something i think will be a good alternate but not sure if it will fit.
actually most tricky was the backorder of the terminals, i found a 45 degree tilted one that seemed to work so i ordered that.
I ordered the heatsinks, but should i also get a larger heatsink? the ones i ordered doesn't look like anything on this picture.
finally, anyone got a good source for the transformer for this build. looked around but didnt find anything (was kind of tired last night though).
actually most tricky was the backorder of the terminals, i found a 45 degree tilted one that seemed to work so i ordered that.
I ordered the heatsinks, but should i also get a larger heatsink? the ones i ordered doesn't look like anything on this picture.
finally, anyone got a good source for the transformer for this build. looked around but didnt find anything (was kind of tired last night though).
is your proposed heatsink bigger or smaller than the recent pic we saw?
The transformer for the DTV should be about 35Vac about 300VA for two channels @ 8ohms or about 600VA for two channels @ 4ohms.
You can use a centre tapped secondary 35-0-35Vac or a dual secondary 0-35,0-35Vac, both work equally well for a monoblock. Two channels may work better with the dual secondary feeding dual bridge rectifiers.
Hi Parb,
Can you list the BOM components that are out of stock at Mouser. Just the PCB part number is fine. You can try partsexpress for the transformer. You'll need two of them, one per channel if your using the on-board PS. Here's the link.
Parts-Express.com:*Avel Y236654 250VA 35V+35V Toroidal Transformer | TRS transformers transformer toroidal transformer toroidal toroid mounting kits kit gauge copper avel 4 gauge
Regards,
Al
Can you list the BOM components that are out of stock at Mouser. Just the PCB part number is fine. You can try partsexpress for the transformer. You'll need two of them, one per channel if your using the on-board PS. Here's the link.
Parts-Express.com:*Avel Y236654 250VA 35V+35V Toroidal Transformer | TRS transformers transformer toroidal transformer toroidal toroid mounting kits kit gauge copper avel 4 gauge
Regards,
Al
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Hi Parb,
The HS 532-577002B00 specified in the BOM are for the driver transistors. I posted the picture of the main heatsink, it was salvaged from an old Victor AV amplifier. This MHS (6.5 inch W x 4.2 inch H x 2.0 inch D) is only slightly bigger than the PCB and it is a bit small for two pairs of OTs . Just get a bigger HS & the height must be taller than 4 inch (100mm).
The following Wima cap: 505-M10.1/400/5 fits the lead spacing for C7 & C8.
Cheers, Stanley
hi,
i should have been clearer.
the mks2-.1/63/5 is out so i used mks2-.1/63/5T http://mouser.com/Search/ProductDet...Tvirtualkey50520000virtualkey505-MKS2.1/63/5T instead (C1,C2,C9-C14,C26,C27). from reading the mfg docs it seems the 'T' is a different packaging?
next 505-MKS2-4.7/50/10 is out. its listed as optional so i skipped it for now (C25).
the red low current red led is also out so i subbed it with a standard 10mA red led. in the bom it recommends 606-4300F1LC but i used 606-4303F1.
534-1213 which is the terminal was out and this was trickier. i ordered the 534-1212 which i hope will work but i am really not too sure of (it was 2 am and i was getting tired, nothing i saw seemed to be a good replacement for what the bom called for).
aside from this a couple of the resistors where out but that was easy to substitute.
where do you guys order large heatsinks from? i havent really got any and it would be good to know of a great source, both for this and future builds.
thanks for the parts express part number! much useful, i should have looked there too of course..
i should have been clearer.
the mks2-.1/63/5 is out so i used mks2-.1/63/5T http://mouser.com/Search/ProductDet...Tvirtualkey50520000virtualkey505-MKS2.1/63/5T instead (C1,C2,C9-C14,C26,C27). from reading the mfg docs it seems the 'T' is a different packaging?
next 505-MKS2-4.7/50/10 is out. its listed as optional so i skipped it for now (C25).
the red low current red led is also out so i subbed it with a standard 10mA red led. in the bom it recommends 606-4300F1LC but i used 606-4303F1.
534-1213 which is the terminal was out and this was trickier. i ordered the 534-1212 which i hope will work but i am really not too sure of (it was 2 am and i was getting tired, nothing i saw seemed to be a good replacement for what the bom called for).
aside from this a couple of the resistors where out but that was easy to substitute.
where do you guys order large heatsinks from? i havent really got any and it would be good to know of a great source, both for this and future builds.
thanks for the parts express part number! much useful, i should have looked there too of course..
Hi Parb,
534-1212 terminal is one size (.187) smaller than the 534-1213 and it fits the PCB holes, you should order the matching 187 series Faston receptacles : 571-6409171. I think that you can change your Mouser order as long as they have not started the picking.
I would order the main heatsink from local supplier as they are heavy. One suitable heatsink is Wakefield 510-6U or 510-6M, try to google it.
- Stanley
heatsink discussion
Here is one vendor of heatsinks that many have had good trades with:
HEATSINK ALUMINUM EXTRUSION LARGE 7.29" WIDE - eBay (item 180460976138 end time Jan-31-10 18:37:43 PST)
aka "Barred Boss"
There are others.
Let's discuss how long a section of HS would be needed for this amp.
Rod Elliot's very thorough heat sink discussion:
http://sound.westhost.com/heatsinks.htm#1
A heatsink thermal rating spreadsheet:
http://sound.westhost.com/download.htm#hsink
Here is one vendor of heatsinks that many have had good trades with:
HEATSINK ALUMINUM EXTRUSION LARGE 7.29" WIDE - eBay (item 180460976138 end time Jan-31-10 18:37:43 PST)
aka "Barred Boss"
There are others.
Let's discuss how long a section of HS would be needed for this amp.
Rod Elliot's very thorough heat sink discussion:
http://sound.westhost.com/heatsinks.htm#1
A heatsink thermal rating spreadsheet:
http://sound.westhost.com/download.htm#hsink
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Hello fellow diyers, I have a few questions that might be interesting for this thread :
- Can I change q1 and q2 for Bf862 without any modifications ?
- Is it possible (&wise) to feed that first stage with a shunt power supply?
- Is it also possible to change the SymAsym into one with balanced inputs ?
Thanks
- Can I change q1 and q2 for Bf862 without any modifications ?
- Is it possible (&wise) to feed that first stage with a shunt power supply?
- Is it also possible to change the SymAsym into one with balanced inputs ?
Thanks
Hi Al,
I have completed the 2nd channel and it works fine on the bench. I will mount the two channels inside a recycled AV Amp case.
Without the C25, is this amp inverting or non-inverting?
I have two transformers & two external Power Supply boards (dual-mono). Terminal T2 on the SymAsym board acts as the star ground for that channel.
The two heatsinks are electrically connected to the chassis ground. The input RCA sockets & speaker binding posts are electrically isolated from the chassis.
Should I just connect only one SymAsym board ground (Step 12 of Assembly instructions) to the chassis ground.
Best regards, Stanley
Hi Stanley,
With or without the input cap the amp is non-inverting.
As far as the grounding you may have to do so some experimenting. In my case I grounded the PCB ground to the heat sink, like in step 12, but couldn't isolate the heat sink from chassis ground so I had to lift earth ground to prevent AC hum. You can also disconnect the PCB ground from the heat sink as an option. You may have try different things depending on your setup. Whatever you do the amp should be dead quiet (no AC hum) with the inputs shorted to ground. In my set up it's dead quiet with the inputs floating.
Regards,
Al
With or without the input cap the amp is non-inverting.
As far as the grounding you may have to do so some experimenting. In my case I grounded the PCB ground to the heat sink, like in step 12, but couldn't isolate the heat sink from chassis ground so I had to lift earth ground to prevent AC hum. You can also disconnect the PCB ground from the heat sink as an option. You may have try different things depending on your setup. Whatever you do the amp should be dead quiet (no AC hum) with the inputs shorted to ground. In my set up it's dead quiet with the inputs floating.
Regards,
Al
Hello Al,
After reading good things about the Bf862,
http://www.diyaudio.com/forums/pass-labs/146310-bf862-preamp.html
I tried to use them myself on a Pearl phono with good result, somewhat clearer than a
2sk170. Which is of course the mother of all lowpowerfet's
The Bf862 has a higher transconductance than the 2sk170, so not always exchangeable without modifications. I would like to try them but I'm to noobish to know if it can be done with the SymAsym.
Regards, Erik.
After reading good things about the Bf862,
http://www.diyaudio.com/forums/pass-labs/146310-bf862-preamp.html
I tried to use them myself on a Pearl phono with good result, somewhat clearer than a
2sk170. Which is of course the mother of all lowpowerfet's
The Bf862 has a higher transconductance than the 2sk170, so not always exchangeable without modifications. I would like to try them but I'm to noobish to know if it can be done with the SymAsym.
Regards, Erik.
Attachments
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not really.
The BL is a 6 to 12mA device the 862 is 10 to 25mA device.
Look at the BL 12mA example of transconductance. You will see they show 30 to 40mS from 5mA to 10mA Id.
Choosing a very high BL, or a low V grade, will give a similar range of Yfs, if you run them at similar high Id.
I think the 862 would substitute for the 170BL in this amp.
You have to decide what Id to run them at and from there decide if the compensation needs to be altered.
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