so basically like modern cheap amps with a 4 ohm / 8 ohm switch on the back. It drops the rail voltage to keep the power output within what the output devices can actually handle. Nice that it will auto-switch in an effort to save itself though.
phase linear - dual 500 series 2, diagnostics plus updates and some thermals
- Thread starter sae-7125
- Start date
sae-7125
Super Member
fan shows airflow towards the transistors, as one would expect for ideal cooling.
definitely not a cheap cpu fan equivalent.
there is some mention on another forum about somebody who makes a different LED board.
2 different modes.
bias measurement locations.
i will be posting inrush measurements next, looks like around 160a pk-pk which equals 56.5a rms for the first full waveform and then reduces down to a rather disfigured idle waveform.
definitely not a cheap cpu fan equivalent.
there is some mention on another forum about somebody who makes a different LED board.
2 different modes.
bias measurement locations.
i will be posting inrush measurements next, looks like around 160a pk-pk which equals 56.5a rms for the first full waveform and then reduces down to a rather disfigured idle waveform.
sae-7125
Super Member
a few oscilloscope snapshots and waveforms.
a rather messy layout, needed a larger variac since beyond 110v mains tends to pop a 5a fuse (500va variac in background).
idle numbers hi-z mode, dc bias around 350mv each channel, 8r speakers connected.
power caps were discharged down to below 1v prior to every inrush measurement. fairly uniform inrush wave.
focusing on first 16ms (60hz) wave to see max stress on startup. poor little 5a variac fuse, never stood a change against that magnitude of inrush.
one rail voltage when amp is fed 120v mains. something to note when comparing to 125v rated filter caps.
idle numbers for lo-z mode, dc bias around 300mv, i should do an inrush scope photo for this mode (forgot to do so) to compare with hi-z.
one rail voltage in lo-z mode.
and this is the odd waveform when measuring in real-time (amp idle, hi-z). bob is doing a lot of weird things under the hood unless this is textbook class-b.
a rather messy layout, needed a larger variac since beyond 110v mains tends to pop a 5a fuse (500va variac in background).
idle numbers hi-z mode, dc bias around 350mv each channel, 8r speakers connected.
power caps were discharged down to below 1v prior to every inrush measurement. fairly uniform inrush wave.
focusing on first 16ms (60hz) wave to see max stress on startup. poor little 5a variac fuse, never stood a change against that magnitude of inrush.
one rail voltage when amp is fed 120v mains. something to note when comparing to 125v rated filter caps.
idle numbers for lo-z mode, dc bias around 300mv, i should do an inrush scope photo for this mode (forgot to do so) to compare with hi-z.
one rail voltage in lo-z mode.
and this is the odd waveform when measuring in real-time (amp idle, hi-z). bob is doing a lot of weird things under the hood unless this is textbook class-b.
I'm wondering if running the caps to their absolute limits was just a Phase Linear thing. The 700 has 100v caps, mine was running at 107 volts. The new ones are rated 160v. It sounded much better just from changing those main filters than I ever would have expected.
sae-7125
Super Member
there are a few other brands that run power caps at max voltage which leaves little to no safety buffer. most vintage gear txf's were designed for 110v or 115v or 117v so when feeding the ratio device (the mains txf) 120v things are already at or beyond a safe zone. running some sansui gear at 100v mains drops the idle temp favorably, which extends lifespan. i constructed a thread about sansui au-717 and au-719 measurements, it is informative.
i will measure the phase linear rails when the system is supplied with 125v mains since not all power grids are balanced equally. it should help give a better idea as to an upper limit.
updating the big filter caps tends to yield noticeable improvements, bump up their value from 13000 to 18000 or 22000 and things get even better. i was contemplating a pair of 51000uf 160v caps but things get expensive quickly. due to the naturally high inrush current of the dual 500 adding bigger caps will need a mod involving a soft start relay or some healthy sized ntc thermistors. mcintosh used thermistors in some of their designs. fun stuff...
Consider adding a soft start like this one (NA)
sae-7125
Super Member
looks like a useful and cost effective soft start module. a few options exist on amazon when doing a search for "soft start module". idea shopping more than anything.
i should have more measurements and testing data later tonight. if all goes well the amp will be ready for prime time demo'ing. the ceiling tiles typically hate high dynamics exercising of amplifier+speakers, light fixtures not too fond of it either.
i should have more measurements and testing data later tonight. if all goes well the amp will be ready for prime time demo'ing. the ceiling tiles typically hate high dynamics exercising of amplifier+speakers, light fixtures not too fond of it either.
sae-7125
Super Member
lo-z mode has less abusive inrush although txf buzz seems more prominent vs hi-z.
155a pk-pk = 54.79a rms, not a significant decrease vs hi-z except the the system settles down quicker. fewer stressed components at idle temp.
stretched waveform, quicker ramp down even though 80v rails still pack a punch.
idle waveform still looks as odd as hi-z posted earlier.
155a pk-pk = 54.79a rms, not a significant decrease vs hi-z except the the system settles down quicker. fewer stressed components at idle temp.
stretched waveform, quicker ramp down even though 80v rails still pack a punch.
idle waveform still looks as odd as hi-z posted earlier.
sae-7125
Super Member
i seem to have bumped into a rather odd and potentially damaging design issue with the display board.
i replaced the electrically conductive metal nut with a non-conductive zip tie until a more suitable nylon washer is found. shorting the exposed traces to chassis ground seems like a bad idea.
same location, view from another angle.
another potential electrical short to chassis ground. opposite side of the pcb. new 5k pot making a cameo appearance, normally lives in seclusion next to a toasty warm txf.
i replaced the electrically conductive metal nut with a non-conductive zip tie until a more suitable nylon washer is found. shorting the exposed traces to chassis ground seems like a bad idea.
same location, view from another angle.
another potential electrical short to chassis ground. opposite side of the pcb. new 5k pot making a cameo appearance, normally lives in seclusion next to a toasty warm txf.
musicSteve
New Member
Soft start that I use- AIYIMA 2000W Power Supply Soft Starting Board High Power For 1969 Amplifier Speaker DIY 100A Relay Thunder Protection 110V 220V
sae-7125
Super Member
measuring the effects of a mild over-voltage situation (ac mains 125v) while in hi-z mode.
brief evaluation of a slight mains voltage jump, many domestic utility companies specify a max/min residential service voltage.
an interesting, yet brief, conversation on the topic:
still below 125v power cap rating but... when factoring in age of capacitors and an increased voltage drop on many high wattage components (like the 3k 5w twins) this situation can be highly problematic. in this measurement 125v mains = 123v rail (+/- - 246v) = 108v across the 5w resistors (123v - 15v zeners). looking at 3.88w power disipation almost 4 of the 5w component tolerance. and this particular unit had 3w resistors from the factory, i wonder how many other units are in a similar situation??
brief evaluation of a slight mains voltage jump, many domestic utility companies specify a max/min residential service voltage.
an interesting, yet brief, conversation on the topic:
Utility Voltage
I did a residential service upgrade yesterday, and the customer had 129 volts per leg, 258 total. Is this within the variance allowed to utilities? I thought they were allowed 10%, but I wasn't sure. Does anyone know? There are at least 3 other houses on the same xfmr, and the neighborhood has...
forums.mikeholt.com
still below 125v power cap rating but... when factoring in age of capacitors and an increased voltage drop on many high wattage components (like the 3k 5w twins) this situation can be highly problematic. in this measurement 125v mains = 123v rail (+/- - 246v) = 108v across the 5w resistors (123v - 15v zeners). looking at 3.88w power disipation almost 4 of the 5w component tolerance. and this particular unit had 3w resistors from the factory, i wonder how many other units are in a similar situation??
sae-7125
Super Member
dc bias settings and stability measurements.
using 2 dmm's to monitor both channels during adjustment and low signal performance reaction.
hi-z mode idle, stable set point between channels.
idle numbers for the ~365mv bias settings, obviously no dim bulb (wattage choke chain) involved.
the bias numbers drop to around 275mv in lo-z mode +/- 5mv between the channels. overall sonic performance seems decent, not too bad with detail and sound stage width. low volume is relatively good especially vs dc bias set to minimum (noticeably crunchy for obvious reasons). a few more things to do and then off to the demo chamber and into the wild.
using 2 dmm's to monitor both channels during adjustment and low signal performance reaction.
hi-z mode idle, stable set point between channels.
idle numbers for the ~365mv bias settings, obviously no dim bulb (wattage choke chain) involved.
the bias numbers drop to around 275mv in lo-z mode +/- 5mv between the channels. overall sonic performance seems decent, not too bad with detail and sound stage width. low volume is relatively good especially vs dc bias set to minimum (noticeably crunchy for obvious reasons). a few more things to do and then off to the demo chamber and into the wild.
sae-7125
Super Member
cooling fan testing and air flow evaluation.
fan consumption, ac mains direct connection to fan.
fan spins without issue, no age/gunk related noises regardless of horizontal or vertical position.
in terms of air flow on/over/around/through the heated surfaces... i wonder if these end transistors have a higher failure rate? the thick metal screen can block some air flow (one area of inefficiency) but to have a wall that is sabotaging optimal air flow seems problematic. i suppose removing all the metal screens would be an ideal mod but it runs the risk of exposed high voltage dc to any kind of oops event.
the high density of output transistors on a common/shared heat sink guarantees an quick space heater under high output conditions. which in turn subjects all outputs to reflected heat by the neighboring components. since the stock outputs are rated for 200c that might be part of the magic design sauce implemented. i wonder if using half as many outputs although rated for higher wattage would balance the thermal intensity better? a nit pick analysis but it would be interesting to see what little is needed to make something good even better.
fan consumption, ac mains direct connection to fan.
fan spins without issue, no age/gunk related noises regardless of horizontal or vertical position.
in terms of air flow on/over/around/through the heated surfaces... i wonder if these end transistors have a higher failure rate? the thick metal screen can block some air flow (one area of inefficiency) but to have a wall that is sabotaging optimal air flow seems problematic. i suppose removing all the metal screens would be an ideal mod but it runs the risk of exposed high voltage dc to any kind of oops event.
the high density of output transistors on a common/shared heat sink guarantees an quick space heater under high output conditions. which in turn subjects all outputs to reflected heat by the neighboring components. since the stock outputs are rated for 200c that might be part of the magic design sauce implemented. i wonder if using half as many outputs although rated for higher wattage would balance the thermal intensity better? a nit pick analysis but it would be interesting to see what little is needed to make something good even better.
how about installing some of these?
www.westfloridacomponents.com
that would take care of the electrical concern.
TO-3 Transistor Insulating Cover TO3 Aavid Thermalloy® 8903VBG | West Florida Components
Manufacturer: Aavid Thermalloy Part Number: 8903VBG Package: TO-3 Material: Thermoplastic Polyester Color: Black Temperature: 130 RoHS Compliant: Yes
that would take care of the electrical concern.
sae-7125
Super Member
the insulating covers are an interesting thought. one concern would be the 130c continuous use temp, although this amp could spend most of its uptime around 85c/185f which would be no problem. its the 1 or 2 hour thrash on a friday night (+/- beer/pizza) that could easily hit a sustained 150-180c which would give the cooling fan a run for its money, that would be my concern.
a few anodized narrow strip (low thermal resistance) heat sinks might be a possibility. something that is narrow enough to allow air flow around the transistors but also mop/sponge the thermal carnage via a thin finned sink on the top of the rows of outputs. a heat spreader similar to what is used on ddr5 ram sticks or m.2 ssd's. speculative engineering at this point, although a negative energy system (floyd sweet) would take things in a completely different quantum vector.
www.heatsinkcalculator.com
www.allaboutcircuits.com
unfortunately the overall metal chassis seems to be minimally ventilated and no significant thermal exit for the monster txf under the hood. that might explain why some touring companies typically relocated the txf to an external position.
chassis venting might be better than nothing but...
it would be best to run the amp in lo-z mode, especially when turning it on, improved life span of some important components. best to update/overhaul a new acquisition without an initial power up. after a few decades of living in storage this ogre is not like an onion regardless of its layers.
a few anodized narrow strip (low thermal resistance) heat sinks might be a possibility. something that is narrow enough to allow air flow around the transistors but also mop/sponge the thermal carnage via a thin finned sink on the top of the rows of outputs. a heat spreader similar to what is used on ddr5 ram sticks or m.2 ssd's. speculative engineering at this point, although a negative energy system (floyd sweet) would take things in a completely different quantum vector.
Top 3 mistakes made when selecting a heat sink | Heat Sink Calculator-Blog: Focused on Heat Sink Analysis, Design and Optimization
Without some basic understanding of the factors affecting heat sink performance the selected heat sink may be inadequate to meet the thermal requirements of the device being cooled.
www.heatsinkcalculator.com
How to Keep a Power Transistor Cool Using a Heat Sink - Technical Articles
Handling heat in electronics. Which components create heat, which components suffer from heat. Basics of heatsinking.
www.allaboutcircuits.com
unfortunately the overall metal chassis seems to be minimally ventilated and no significant thermal exit for the monster txf under the hood. that might explain why some touring companies typically relocated the txf to an external position.
chassis venting might be better than nothing but...
it would be best to run the amp in lo-z mode, especially when turning it on, improved life span of some important components. best to update/overhaul a new acquisition without an initial power up. after a few decades of living in storage this ogre is not like an onion regardless of its layers.
