Wonder why they did not use a baxandall diode across the 10R emitter resistor on the inverter? Those eight pairs would take a lot of base drive, and all would come through the inverter dropping a lot of voltage across even a small 10R resistor. That would drop 5V with 1/2A Ib combined with a 3R load at 60V peak.
What is the rail voltage, Minek? The graphic is blurred; could be 66V or 96V.
Otherwise, front end is identical to the Philips design. Yes, I wonder too........
What is the rail voltage, Minek? The graphic is blurred; could be 66V or 96V.
Otherwise, front end is identical to the Philips design. Yes, I wonder too........
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Looks like 86V.. Rated 300W.
Philips had rails 78V, and 3 pairs of outputs only. Rated 200W.
But interesting thing - it's a triple.
Philips amp got very good reviews at the time, some people still using them, after over 40 years.
I guess for the 70s, it wasn't bad at all.
1978 - let's see - I (or rarther my parents) had mono turntable called "Mr. Hit" with piezoelectric cartridge, and little Thomson cassette player, with 0.5W output. 🙂
Philips had rails 78V, and 3 pairs of outputs only. Rated 200W.
But interesting thing - it's a triple.
Philips amp got very good reviews at the time, some people still using them, after over 40 years.
I guess for the 70s, it wasn't bad at all.
1978 - let's see - I (or rarther my parents) had mono turntable called "Mr. Hit" with piezoelectric cartridge, and little Thomson cassette player, with 0.5W output. 🙂
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So for single die Exicon LATFETs, which supposedly have equal gate capacitances according to the spec sheet, what gate resistance value would be suitable? Based on the supply rails of 42 V, is 50W into 8 ohms with single die devices approximately correct?
Also, I was not able to find a convincing comment or post from Exicon that their single die devices have anything other than a single diode for output protection. Gate protection was not mentioned on their website for single die LATFETs. If you know of a post that has that confirmation from Exicon, then I will become a "believer" so in the interim I will add the option of these to the SL6 board i have designed.
Also, I was not able to find a convincing comment or post from Exicon that their single die devices have anything other than a single diode for output protection. Gate protection was not mentioned on their website for single die LATFETs. If you know of a post that has that confirmation from Exicon, then I will become a "believer" so in the interim I will add the option of these to the SL6 board i have designed.
About the gate protection - I know, they don't mention it anywhere on the current web pdfs.
However, based on previous thread here on DIY, someone got direct response from Exicon confirming that these devices do have gate Zener diode protection.
This subject was discussed several times in the past on this forum, to me it looked convincing. You can do a search..
Example of such claims from Ian Hegglun (who usually knows what he's talking about):
Emitter resistor in HexFet OPS
Also - check attached pdf where "gate protection Zeners" are explicitly mentioned.
If you want - it won't hurt to add additional zeners.
Exicon says in the doc, that even though internal Zeners are present,
"Although the integral zener diode offers some
protection to the gate, external zeners should be
fitted for further protection. (typically 6.2V, 1.3W)"
It seems like internal Zeners are 14V, and external ones may be more restrictive..
As for the gate stoppers, in my previous builds with single die Exicons, I used stoppers from 330 Ohms to 560 Ohms.
Rod Elliot's LatFet amp was using 560 Ohm stoppers.
I would suggest to measure the actual gate capacitance before soldering to make sure they are equal.
Some people say that Exicon is using the same die design as Hitachi used to, which had different gate capacitance (I confirm this, as I also used original Hitachis in the past).
However, based on previous thread here on DIY, someone got direct response from Exicon confirming that these devices do have gate Zener diode protection.
This subject was discussed several times in the past on this forum, to me it looked convincing. You can do a search..
Example of such claims from Ian Hegglun (who usually knows what he's talking about):
Emitter resistor in HexFet OPS
Also - check attached pdf where "gate protection Zeners" are explicitly mentioned.
If you want - it won't hurt to add additional zeners.
Exicon says in the doc, that even though internal Zeners are present,
"Although the integral zener diode offers some
protection to the gate, external zeners should be
fitted for further protection. (typically 6.2V, 1.3W)"
It seems like internal Zeners are 14V, and external ones may be more restrictive..
As for the gate stoppers, in my previous builds with single die Exicons, I used stoppers from 330 Ohms to 560 Ohms.
Rod Elliot's LatFet amp was using 560 Ohm stoppers.
I would suggest to measure the actual gate capacitance before soldering to make sure they are equal.
Some people say that Exicon is using the same die design as Hitachi used to, which had different gate capacitance (I confirm this, as I also used original Hitachis in the past).
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I have taken your SL6 design and changed it in a few places to meet the DRC that is set up on my design PC. The most obvious changes are the removal of the fuses to the PSU board which frees up space for the other changes:
1. Removed through pads and only applied where required for through plating.
2. Removed duplicate pads which caused DRC errors.
3. Used 10mm pitch for resistors (1 exception) to make it easier to build - 10mm is fairly common for thru-hole boards. Retained 5mm pitch for non-electro caps.
4. Increased electro cap diameters to handle slightly larger devices. Some like to use high voltage ratings to gain benefits of better dielectric performance at the low voltages. The larger electro are 13mm dia and the smaller ones are 10mm diameter.
5. Corrected lead spacing for driver transistors to match Fairchild data sheets
6. Added extra pads to allow better choice and fitting if 2N series selected instead of Fairchild signal trannies. - can rotate 2N devices and splay the legs without difficulty.
7. Added pads for option to use protection diodes if desired. Unfortunately these are vertical mounts but should be Ok.
8. Marginally widened board to 65mm
9. Lengthened board to 74mm to better support LATFETS mounting holes when mounted on a heatsink. I did not want holes too close to the edge of the fibreglass.
10. Relabeled devices to match updated circuit schematic.
11. Used 5mm PCB crimp terminals for power and spkr out.
12. Generally improved symmetry to assist troubleshooting and layout.
13. Kept 100n bypass caps as close as practically possible to OpAmp.
14. Removed copper pads for unused OpAmp leads.
The gap on the PCB between the driver BJTs and the predrivers is sufficient to fit a piece of Al for the driver heatsink to run across the devices faces.
1. Removed through pads and only applied where required for through plating.
2. Removed duplicate pads which caused DRC errors.
3. Used 10mm pitch for resistors (1 exception) to make it easier to build - 10mm is fairly common for thru-hole boards. Retained 5mm pitch for non-electro caps.
4. Increased electro cap diameters to handle slightly larger devices. Some like to use high voltage ratings to gain benefits of better dielectric performance at the low voltages. The larger electro are 13mm dia and the smaller ones are 10mm diameter.
5. Corrected lead spacing for driver transistors to match Fairchild data sheets
6. Added extra pads to allow better choice and fitting if 2N series selected instead of Fairchild signal trannies. - can rotate 2N devices and splay the legs without difficulty.
7. Added pads for option to use protection diodes if desired. Unfortunately these are vertical mounts but should be Ok.
8. Marginally widened board to 65mm
9. Lengthened board to 74mm to better support LATFETS mounting holes when mounted on a heatsink. I did not want holes too close to the edge of the fibreglass.
10. Relabeled devices to match updated circuit schematic.
11. Used 5mm PCB crimp terminals for power and spkr out.
12. Generally improved symmetry to assist troubleshooting and layout.
13. Kept 100n bypass caps as close as practically possible to OpAmp.
14. Removed copper pads for unused OpAmp leads.
The gap on the PCB between the driver BJTs and the predrivers is sufficient to fit a piece of Al for the driver heatsink to run across the devices faces.
Attachments
Good changes...
One thing I would maybe revise is the dirty ground trace routed under op-amp, and close to inputs... But most likely it will be ok..
You also removed fuses, I guess they will be located outside of the board? I like to have separated fuses for each channel,
so you can turn-off one channel easily, e.g. to adjust idle current.
One thing I would maybe revise is the dirty ground trace routed under op-amp, and close to inputs... But most likely it will be ok..
You also removed fuses, I guess they will be located outside of the board? I like to have separated fuses for each channel,
so you can turn-off one channel easily, e.g. to adjust idle current.
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ASR Emitter also uses this topology, but with fets instead of bjts in VAS. This amplifier should sound unusually smooooth.
i thought about the trace under the opamp a lot. I was torn between reducing the track length and issues with the topside track under the opamp.
Yeah, the fuses are on the PSU board. its a matter of personal taste. I prefer that sort of hardware to be on the PSU or a PSU rail splitter board.
>its a matter of personal taste
This amp doesn't have source resistors, so you can't adjust idle current by measuring voltage on them.
The only way to set it, is to measure overall current from PSU on one of the rails (or both).
If Zener/VAS/LED take approx 25-30mA, idle current on one rail should be 105mA.
It's easy to adjust idle current at the test bench, but later, when it's mounted in the chassis or case, and adjustement is needed, it might be a problem..
With two channels connected to PSU at the same time, it's impossible - at least for me - I use wires soldered to the pcb,
so I can't disconnect them whenever I want.
Looks like you are going to use spade connectors, so I guess you can always disconnect cables...
This amp doesn't have source resistors, so you can't adjust idle current by measuring voltage on them.
The only way to set it, is to measure overall current from PSU on one of the rails (or both).
If Zener/VAS/LED take approx 25-30mA, idle current on one rail should be 105mA.
It's easy to adjust idle current at the test bench, but later, when it's mounted in the chassis or case, and adjustement is needed, it might be a problem..
With two channels connected to PSU at the same time, it's impossible - at least for me - I use wires soldered to the pcb,
so I can't disconnect them whenever I want.
Looks like you are going to use spade connectors, so I guess you can always disconnect cables...
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My PSU has separate lines with fuses to each amp so not a problem. Using a suitable 10W resistor across each fuse holder/no fuse allows the voltage drop, and therefore total current, to be measured.
I had done the maths on the current and guessed that was how you measured 80mA idle current.
I have moved the trace from under the Opamp since the path length is no different in the version of the board that i uploaded. DRC looks good so will get some made soon.
Thanks for your help.
I had done the maths on the current and guessed that was how you measured 80mA idle current.
I have moved the trace from under the Opamp since the path length is no different in the version of the board that i uploaded. DRC looks good so will get some made soon.
Thanks for your help.
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Great! Good luck with the build.
Why single die devices? Dual die are perfect for this voltage..
Why single die devices? Dual die are perfect for this voltage..
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>I had done the maths on the current and guessed that was how you measured 80mA idle current.
It was easy - my lab PSU shows current load in real time on the digital display,
and also has current limiter built in...
So no need to play around with resistors..
It was easy - my lab PSU shows current load in real time on the digital display,
and also has current limiter built in...
So no need to play around with resistors..
I have lots of single die Exicon devices and I may as well use them. Besides, delivery ex UK is likely to take months with airfreight space very limited by low airline activity from that part of the world. When i originally got the single die Exicons a few years ago, back in normal times, they still took 6 weeks to get to me. In contrast, there's reasonable volumes of air traffic to and from China so getting the boards will take just a week.
Isnt r8 a feedfoward resistor? Meant to bias the opamp slightly into class a?
Im very interested in building this amp too. Would b nice if the voltages were dropped to 35v +/- so that an ic reg can be fitted on the board for the opamp
Im very interested in building this amp too. Would b nice if the voltages were dropped to 35v +/- so that an ic reg can be fitted on the board for the opamp
I personally do not see any difference in functioning of this amp with or without R8. It does not affect bias/idle current..
As for lower rails - it will work with 35V, Zener resistors (R20/R22) will be in this case 2k.
Also gain needs to be lowered: R4=180 Ohm
Everything else can stay the same.
Idle current for single-die latfet: about 40mA should do.
> ic reg can be fitted for the op-amp
What's wrong with Zeners?
As for lower rails - it will work with 35V, Zener resistors (R20/R22) will be in this case 2k.
Also gain needs to be lowered: R4=180 Ohm
Everything else can stay the same.
Idle current for single-die latfet: about 40mA should do.
> ic reg can be fitted for the op-amp
What's wrong with Zeners?
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I would wait until the prototype has been built before getting a boards. However if interested, i can upload the SL6 file and Gerbers and drill files which would allow you to get boards at your leisure. Freight costs are a real pain right now and will cost >3x the board cost.