Dinu,
Your email is blocked, send it to me at
aldupon AT sympatico . ca
Replace the At by @ and remove the spaces
I strech it to the right size and will send-it back to you.
Nice explanations about feedback, I didn't use it only the small 33pF cap
i am prowd to say that at the last happening in Montreal. my A75 and CCS-X-Bosoz
got me some nice compliements, and served on about 8 speaker pairs, from
Fostex, and some others 2 3 ways. Giving a "good" sound.
Follow the link :
http://www.freewebs.com/ulzog/journediy.htm
Picts 2,3,4 are from my Bosoz
7 is the Bosoz/Ono PS
8 The A75
Best regards.
Alain.
Your email is blocked, send it to me at
aldupon AT sympatico . ca
Replace the At by @ and remove the spaces
I strech it to the right size and will send-it back to you.
Nice explanations about feedback, I didn't use it only the small 33pF cap
i am prowd to say that at the last happening in Montreal. my A75 and CCS-X-Bosoz
got me some nice compliements, and served on about 8 speaker pairs, from
Fostex, and some others 2 3 ways. Giving a "good" sound.
Follow the link :
http://www.freewebs.com/ulzog/journediy.htm
Picts 2,3,4 are from my Bosoz
7 is the Bosoz/Ono PS
8 The A75
Best regards.
Alain.
I haven't thought about laying out an A75. It shouldn't be too hard to do one channel per board in the free version of Eagle. Like a lot of things there is a steep learning curve at first. I doubt I'd go with gold plating, but if you must...
If you post your first attempt at a layout I am sure the knowledgeable will guide you to a better one. I might be interested in a few, not that I don't already have too many boards. I've got the group buy thing down to a science (let my teenager pack orders) if there is enough interest.
I've been very happy with the service of Advanced Circuits (www.4pcb.com) for the group buys I've done. I Highly recommend them. Let's talk before you order boards.
As for the regulator, are you going to use a separate 60V transformer to avoid the doubler? Watch the power dissipation in R13 - You might want to increase it to >20K. Something I learned when I bumped the rails up on mine.
Jens Rasmussen improved on the version of the A75 regulator I was laying out, which turned into a group buy. The pass devices are darlington connected for greater current gain, there is an option to use a zener, LM329 or LM4040 voltage reference and short circuit protection. I have several boards available, as well as parts kits for15V nominal operation.
On my website under PSU2.2 is a spreadsheet that will calculate component values for you (usable for the straight A75 reg, too) as well as a bit of a tutorial on scaling the voltage.
Enjoy your project.
If you post your first attempt at a layout I am sure the knowledgeable will guide you to a better one. I might be interested in a few, not that I don't already have too many boards. I've got the group buy thing down to a science (let my teenager pack orders) if there is enough interest.
I've been very happy with the service of Advanced Circuits (www.4pcb.com) for the group buys I've done. I Highly recommend them. Let's talk before you order boards.
As for the regulator, are you going to use a separate 60V transformer to avoid the doubler? Watch the power dissipation in R13 - You might want to increase it to >20K. Something I learned when I bumped the rails up on mine.
Jens Rasmussen improved on the version of the A75 regulator I was laying out, which turned into a group buy. The pass devices are darlington connected for greater current gain, there is an option to use a zener, LM329 or LM4040 voltage reference and short circuit protection. I have several boards available, as well as parts kits for15V nominal operation.
On my website under PSU2.2 is a spreadsheet that will calculate component values for you (usable for the straight A75 reg, too) as well as a bit of a tutorial on scaling the voltage.
Enjoy your project.
My intention was to use the oroginal psu board for the regulated supply minus the voltage doubler. I think a dedicated 60v transformer would get me the voltage I need. If you still have some PSU 2.2 boards left that might be even better. Do you think its a better choice for what will probably need to be a 77v supply?
I wanted 2 separate boards for the front end that can include the coupling caps to the power supply and those extra diodes. The output would have its own boards. Do you think it would be a good idea to mount the output power supply caps right on the output boards?
I wanted 2 separate boards for the front end that can include the coupling caps to the power supply and those extra diodes. The output would have its own boards. Do you think it would be a good idea to mount the output power supply caps right on the output boards?
A dedicated 60V transformer would work fine. i used a dedicated transformer in mine since doubling 42VAC would have made caps expensive and the dissipation in the MJEs unacceptable.
The PSU2.2 would theoretically have lower noise and better regulation, but I don't have the equipment to prove it. I have about 20 extra boards on the way. A 15v version did sound a lot better than 7815s in my crossover.
Output caps on the output boards would work fine. Was it Peter Daniel who used a whole bunch?
When laying out your front end boards It would be a good idea to allow more room for heat sinking the FETs (compared to the original layout) and use IRF610 and IRF9610 for the input devices. They sound fine in mine and the IRFDs would fry at your proposed rails.
Also, you'll want to size R11 and R12 to give about 5 mA through the zeners and watch their power dissipation, too. They'll need to be 1W. You could cut down the current a bit, at the expense of a little noise. The LM4040-10 could get by with a lot less than 1 mA, at a buck apiece it's not too expensive. Of course using it would mean recalculating the ccs resistors R's 7-10.
The PSU2.2 would theoretically have lower noise and better regulation, but I don't have the equipment to prove it. I have about 20 extra boards on the way. A 15v version did sound a lot better than 7815s in my crossover.
Output caps on the output boards would work fine. Was it Peter Daniel who used a whole bunch?
When laying out your front end boards It would be a good idea to allow more room for heat sinking the FETs (compared to the original layout) and use IRF610 and IRF9610 for the input devices. They sound fine in mine and the IRFDs would fry at your proposed rails.
Also, you'll want to size R11 and R12 to give about 5 mA through the zeners and watch their power dissipation, too. They'll need to be 1W. You could cut down the current a bit, at the expense of a little noise. The LM4040-10 could get by with a lot less than 1 mA, at a buck apiece it's not too expensive. Of course using it would mean recalculating the ccs resistors R's 7-10.
I downloaded Eagle this weekend and was able to get quite a bit of the schematic done on a train trip from Boston to New York this weekend. I intend to mount all the 220's which will include Q1,2,4 and 5 outboard of the board on a heatsink or the chassis' bottom plate which is 1/8" aluminum. I remember the biggest broblem with the A75 was the very delicate bias adjustment and therefore will try to find a nice multi turn trim pot. Any suggestions are welcome. For the most part, the pad spacing for all the resistors are going to have to accomodate 1/2 watt Rikens which have an almost 10mm body. Some of the resistors like R11,12,25, and 26 are going to be 1 watt Rikens with a 14.3mm body to allow for the additional dissipation due to the higher voltage rails.
Bob, save me one of those boards, I'd like very much to try it.
Alain, thanks very much for compressing my pic but it is still too big. It's getting kicked back.
Bob, save me one of those boards, I'd like very much to try it.
Alain, thanks very much for compressing my pic but it is still too big. It's getting kicked back.
The Bourns 3296Y is either included in Eagle or in one of the downloadable libraries (bourns.lbr). It's a bit hard to find using search. search on r-trimm32*. The 3299W has the pins in a line, if you prefer that arrangement.
Trim_1234-S64YW appears to be a generic pad for either type, but check pins and dimensions.
How about setting up a photbucket account? upload your images there, then copy the tag that they generate and past it in your post. Works like a champ and is free. Still not a bad idea to keep file sizes reasonable though.
[IMG]https://i38.photobucket.com/albums/e123/PreeceInc/PSU/16.jpg
Trim_1234-S64YW appears to be a generic pad for either type, but check pins and dimensions.
How about setting up a photbucket account? upload your images there, then copy the tag that they generate and past it in your post. Works like a champ and is free. Still not a bad idea to keep file sizes reasonable though.
[IMG]https://i38.photobucket.com/albums/e123/PreeceInc/PSU/16.jpg
Hi all,
For the next week until the first, Im in Romania, also working on a new board layout for the A75. The new layout will include film caps in critical locations and a board layout that utilizes all TO220 packages that are populated at the board edge so they can all be mounted on a heat sink.
Til then,
For the next week until the first, Im in Romania, also working on a new board layout for the A75. The new layout will include film caps in critical locations and a board layout that utilizes all TO220 packages that are populated at the board edge so they can all be mounted on a heat sink.
Til then,
Hi all,
I'm back at it. Over the break I started thinking about some power and current values for my design. I figured that using a 45V transformer on the output PS would yield about 63V rails. Each channel will use 16 pairs of Irf240's and complementary 9240's. Bias at about .170A. When I started looking at various speaker loads I came to an unsettling realization. Consider the following.
Supply Vac (transformer) 45.00
Supply Vdc 63.64
Output max Vrms 42.17
Output max Vpk 59.64
VALUES AT 8,4,2 OHM LOADS
Max power output Wrms 222.31 444.61 889.22
Max power output Wpk 506.25 1012.50 2025.00
Max Current Irms 5.63 11.25 22.50
Max Current Ipk 7.95 15.91 31.82
CLASS A BIAS
# of output pairs 16.00
Bias current / pair 0.17
Total bias current draw 5.44
Power dissipation 346.20
Total Power used Wrms 568.50 790.81 1235.42
Total Power used Wpk 852.45 1358.70 2371.20
Total Current draw Irms 11.07 16.69 27.94
Total Current draw Ipk 13.39 21.35 37.26
These values are per channel. I intend to use a 1.5kW transformer per channel.
QUESTUION
1 How do I determine the proper amount of capacitance for the power supply so I can successfully drive the 2 OHM load (If I ever see one).
2 I want to use an array of 3 main breakers in parallel that will allow me to set the max current draw based on the value of the speakers being used. Do I set the breaker values based on Peak current or RMS? Is this atall a good idea?
I'm back at it. Over the break I started thinking about some power and current values for my design. I figured that using a 45V transformer on the output PS would yield about 63V rails. Each channel will use 16 pairs of Irf240's and complementary 9240's. Bias at about .170A. When I started looking at various speaker loads I came to an unsettling realization. Consider the following.
Supply Vac (transformer) 45.00
Supply Vdc 63.64
Output max Vrms 42.17
Output max Vpk 59.64
VALUES AT 8,4,2 OHM LOADS
Max power output Wrms 222.31 444.61 889.22
Max power output Wpk 506.25 1012.50 2025.00
Max Current Irms 5.63 11.25 22.50
Max Current Ipk 7.95 15.91 31.82
CLASS A BIAS
# of output pairs 16.00
Bias current / pair 0.17
Total bias current draw 5.44
Power dissipation 346.20
Total Power used Wrms 568.50 790.81 1235.42
Total Power used Wpk 852.45 1358.70 2371.20
Total Current draw Irms 11.07 16.69 27.94
Total Current draw Ipk 13.39 21.35 37.26
These values are per channel. I intend to use a 1.5kW transformer per channel.
QUESTUION
1 How do I determine the proper amount of capacitance for the power supply so I can successfully drive the 2 OHM load (If I ever see one).
2 I want to use an array of 3 main breakers in parallel that will allow me to set the max current draw based on the value of the speakers being used. Do I set the breaker values based on Peak current or RMS? Is this atall a good idea?
The easy answer is "how much capacitance can you afford?" 
The downside of lots of capacitance is that the charging times are short resulting in high peak currents - watch your rectifier current and dissipation. They will need significant heat sinking. The high power discrete devices that NP suggested would make spreading the heat load easier. If you find that recommendation again, please shoot me a link, I lost it when my hard drive crashed.
The other thing that you may not have factored in is that you will see tremendous ripple at 22A out (and your rectifiers will see roughly double this current).
Use PSU Designer from Duncan Amps to simulate your PSU and watch the interrelationship between capacitance, load current and rectifier current. Be sure to enter your proposed transformer's regulation in the transformer properties, the default is a high voltage transformer with relatively poor regulation/high internal resistance. Also watch the filter charging current. You'd be surprised at how high it can be, both average and peak.
Circuit breakers and fuses have varied response times ranging from super fast acting to slow blow - see their data sheets. This means that you could tailor the protection to trip on instantaneous peaks or allow them to pass but blow on sustained output beyond a certain point.
For practical home use however, the fuses can be quite small. My subwoofer amp is a bridged Hafler DH500 (specs say 800W RMS capable bridged), driven with 6 db of boost at 20 Hz. I have blown one 3A output fuse in over 20 years. It was due to a shorted speaker cable, not high power listening.
Not that having a fuse will do much to protect the amp if there is an internal fault. Those afflicted with audiophilia nervosa will object to fuses. I don't have any in my A75s, but I did fairly extensive testing before I connected them to a speaker. Your modulated arc welder version probably could benefit.
Be sure to plan room for a soft start circuit. With that big transformer and lots of capacitance you'll need it.
Also, consider the safe operating area limits of your output devices. With high voltage rails it may not be safe to draw 2 amps from each device. Be sure to derate for the elevated temperature. IIRC, the X1000 uses twice as many output devices as you propose. If you are planning to use IRFP devices, they are a bit less robust. Figure 3 IRFP for every 2 IRF.
Matey, does ye really wanna design for 900WRMS into 2 ohms? Arr!
With the proposed transformer you'd be dissipating at least 800Win the output stage and power supply and drawing close to 20 Amps from the wall per channel. Your transformer would be right at its limit. 3 KVA would be better (or a 1.5KVA per rail). 
Think 250 pound amp...
The downside of lots of capacitance is that the charging times are short resulting in high peak currents - watch your rectifier current and dissipation. They will need significant heat sinking. The high power discrete devices that NP suggested would make spreading the heat load easier. If you find that recommendation again, please shoot me a link, I lost it when my hard drive crashed.
The other thing that you may not have factored in is that you will see tremendous ripple at 22A out (and your rectifiers will see roughly double this current).
Use PSU Designer from Duncan Amps to simulate your PSU and watch the interrelationship between capacitance, load current and rectifier current. Be sure to enter your proposed transformer's regulation in the transformer properties, the default is a high voltage transformer with relatively poor regulation/high internal resistance. Also watch the filter charging current. You'd be surprised at how high it can be, both average and peak.
Circuit breakers and fuses have varied response times ranging from super fast acting to slow blow - see their data sheets. This means that you could tailor the protection to trip on instantaneous peaks or allow them to pass but blow on sustained output beyond a certain point.
For practical home use however, the fuses can be quite small. My subwoofer amp is a bridged Hafler DH500 (specs say 800W RMS capable bridged), driven with 6 db of boost at 20 Hz. I have blown one 3A output fuse in over 20 years. It was due to a shorted speaker cable, not high power listening.
Not that having a fuse will do much to protect the amp if there is an internal fault. Those afflicted with audiophilia nervosa will object to fuses. I don't have any in my A75s, but I did fairly extensive testing before I connected them to a speaker. Your modulated arc welder version probably could benefit.
Be sure to plan room for a soft start circuit. With that big transformer and lots of capacitance you'll need it.
Also, consider the safe operating area limits of your output devices. With high voltage rails it may not be safe to draw 2 amps from each device. Be sure to derate for the elevated temperature. IIRC, the X1000 uses twice as many output devices as you propose. If you are planning to use IRFP devices, they are a bit less robust. Figure 3 IRFP for every 2 IRF.
Matey, does ye really wanna design for 900WRMS into 2 ohms? Arr!
With the proposed transformer you'd be dissipating at least 800Win the output stage and power supply and drawing close to 20 Amps from the wall per channel. Your transformer would be right at its limit. 3 KVA would be better (or a 1.5KVA per rail). Think 250 pound amp...Anything worth doing is worth overdoing. I meant 1.5KVA per channel and realistically, I'll never have 2R speakers. I have no plans to bridge to drive a sub or anything like that and am very unlikely to listen to any music that loud. This is a matter of having a ridiculous amount of overhead.
You got me worried about my rectifiers. I bought 2 IXYS FRED units from partsconnexion rated at 22A and 600V each. From what you're saying, I'm really pushing them...right? There are 68A units available for not much more money. I can use the 22A units on the front end PSU.
I'm under the impression that that thermistor used on the original design IS a soft start. I'm betting I'm wrong. What do you suggest?
You got me worried about my rectifiers. I bought 2 IXYS FRED units from partsconnexion rated at 22A and 600V each. From what you're saying, I'm really pushing them...right? There are 68A units available for not much more money. I can use the 22A units on the front end PSU.
I'm under the impression that that thermistor used on the original design IS a soft start. I'm betting I'm wrong. What do you suggest?
How much you are pushing the rectifiers depends on how much capacitance you use and how much power you push. PSUD will show you the turn on surge if you do without a soft start. Check the data sheets to see what their surge current limit is.
Using the "standard" derating factor of two and rectifier sees double the RMS current rule of thumb, 22A rectifiers should do for 5.5A rms out. My guess is you're about to place an order for the high current ones.
The thermistor is for inrush limiting. However, at your proposed power, I don't know of a thermistor rated to carry the current. Higher current thermistors also tend to have lower cold resistance, so the effect is lessened.
I'd plan on enough heat sink to keep 500W cool, which means a lot of metal anyway. You can use the AXE-1.2 spreadsheet (link in the AX wiki) to help you calculate the thermal resistance needed. Watch the output device junction temperatures.
The input capacitance of 16 devices means the amp will be a bit slower than the original. You may want to increase the VAS bias and/or add a driver stage to provide enough current to drive the extra gate capacitance (especially if you discover thermal considerations make you want more output devices.)
BTW, 5.4A bias is .3375A per device (~21W), not .17 (total bias/number of pairs). With standard mounting (mica/grease) you'll need a K <.05 C/W to get the junction temperatures below 100C. Half the bias reduces your heat sink requirements tremendously and still allows plenty of class A power at 8 ohms.
Using the "standard" derating factor of two and rectifier sees double the RMS current rule of thumb, 22A rectifiers should do for 5.5A rms out. My guess is you're about to place an order for the high current ones.
The thermistor is for inrush limiting. However, at your proposed power, I don't know of a thermistor rated to carry the current. Higher current thermistors also tend to have lower cold resistance, so the effect is lessened.
I'd plan on enough heat sink to keep 500W cool, which means a lot of metal anyway. You can use the AXE-1.2 spreadsheet (link in the AX wiki) to help you calculate the thermal resistance needed. Watch the output device junction temperatures.
The input capacitance of 16 devices means the amp will be a bit slower than the original. You may want to increase the VAS bias and/or add a driver stage to provide enough current to drive the extra gate capacitance (especially if you discover thermal considerations make you want more output devices.)
BTW, 5.4A bias is .3375A per device (~21W), not .17 (total bias/number of pairs). With standard mounting (mica/grease) you'll need a K <.05 C/W to get the junction temperatures below 100C. Half the bias reduces your heat sink requirements tremendously and still allows plenty of class A power at 8 ohms.
Not quite - You have 16 pairs. The bias goes through the 16 N channel devices and the same current continues through the P channel devices to the negative rail. Total bias is Number of PAIRS x per device bias. 16 x.17. Your 5.4 A is the output current you can deliver in class A, though.
Perhaps a new thread? Higher power A75 or A75 modifications?
Perhaps a new thread? Higher power A75 or A75 modifications?
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