I've used point to point for tube circuits and on rare occasions for solid state. I've heard people argue that it sounds better, but I've never actually taken the time to build the same circuit two different ways and listen to both. I make my own PCBs for the stuff I do.
Input wiring can be almost any gauge since there's no current to speak of. Power supply and output wiring for a smallish amp like the Mini-A can be something along the lines of 16 ga., but if you want to use bigger wire feel free to do so. The lengths are going to be pretty short, so there won't be a lot of resistance added.
The question of whether to use one cap or many in turn raises other questions. If you really want to get arcane about it, you can sit down and read the spec sheets to compare ESR and such things. On a more practical note, I think you'll find that the big computer grade cans are quite a bit more expensive than the equivalent capacitance in a PC-mount capacitor. Whether the ESR is better one way or the other will depend on the individual caps in question.
You might see what you can find at the various surplus websites. Caps come, caps go...you never know what you might find.
Grey
Input wiring can be almost any gauge since there's no current to speak of. Power supply and output wiring for a smallish amp like the Mini-A can be something along the lines of 16 ga., but if you want to use bigger wire feel free to do so. The lengths are going to be pretty short, so there won't be a lot of resistance added.
The question of whether to use one cap or many in turn raises other questions. If you really want to get arcane about it, you can sit down and read the spec sheets to compare ESR and such things. On a more practical note, I think you'll find that the big computer grade cans are quite a bit more expensive than the equivalent capacitance in a PC-mount capacitor. Whether the ESR is better one way or the other will depend on the individual caps in question.
You might see what you can find at the various surplus websites. Caps come, caps go...you never know what you might find.
Grey
I am quite interested in the MINI - A as a primary project. I happen to have some Fairchild FQP28N15 mosfets which would appear to be a suitable substitute for the IRF644 variety.
They seem to be quite similiar with the exception of current rating which as I recall being noted by Mr. Pass as important ; lower being more desirable. Input capacitance is quite the same for each type (1300-1250 pf) while the Fairchild device is the winner on Rdss (.067 ohm vs .28).
Cost is a factor ,as well as the Aleph reputation, in my consideration. I have large heatsinks ,a suitable transformer as well as (probably) the small resistors.
I certainly would appreciate your comments on the semi's.
They seem to be quite similiar with the exception of current rating which as I recall being noted by Mr. Pass as important ; lower being more desirable. Input capacitance is quite the same for each type (1300-1250 pf) while the Fairchild device is the winner on Rdss (.067 ohm vs .28).
Cost is a factor ,as well as the Aleph reputation, in my consideration. I have large heatsinks ,a suitable transformer as well as (probably) the small resistors.
I certainly would appreciate your comments on the semi's.
GROLLINS
Sorry -I neglected to mention the the max volt/amp characteristics.
Fairchild 150V 28A
Sorry -I neglected to mention the the max volt/amp characteristics.
Fairchild 150V 28A
Hello and thank you for your answers,
After the possible solution of wiring point to point exist the solution of the teflon pcb wich is renown as the best pcb possible for audio project.
Does somebody have the typon to make such a pcb?
Thanks: David
After the possible solution of wiring point to point exist the solution of the teflon pcb wich is renown as the best pcb possible for audio project.
Does somebody have the typon to make such a pcb?
Thanks: David
It's not that lower current is desirable but that--all things being equal--lower current tends to indicate lower capacitance at the Gate. The Ciss is often rated on the datasheet so you can compare this more directly. In the case of the Mini-A, the capacitance is a little more important than usual because the rail voltage is low. MOSFET capacitances drop as the voltage across them increases (read this as higher rail voltage) and since the Mini-A runs on 15V rails the capacitance is a little higher than it would be if it used 25V rails, for instance. But if it ran on 25V rails it would be an Aleph 3, not a Mini-A, and this thread wouldn't exist. All in all, it's not something to lose a lot of sleep over. As Charlie Papazian says, "Relax. Don't worry. Have a homebrew."
There are scads of Mini-As out there (the project has certainly become more popular than I ever expected) and quite a few satisfied owners if the posts I've seen are any indication. Don't fret too much over one or two pF...just build it and let the music out. You can always modify it later if you want. Or build another. Or build a "real" Aleph. Or...
Grey
There are scads of Mini-As out there (the project has certainly become more popular than I ever expected) and quite a few satisfied owners if the posts I've seen are any indication. Don't fret too much over one or two pF...just build it and let the music out. You can always modify it later if you want. Or build another. Or build a "real" Aleph. Or...
Grey
mpopovics said:
WHOA!!!!That's pure DIY Beauty. The BLUE RIBBON is YOURS.
What devices did you use for outputs??? 15volt rails??
mpopovics said:
Really nice work.. apparently it is no longer is in use.. My mental picture of my upcoming MINI-A (needed an amp under 10 watts) is quite similiar..difference being TO-220 output devices with much smaller pins.
Will have to find alternate means to support the rig.
JTP
need some mini aleph help
Hey guys,
asking for a little help with the mini. I purchased Briangt boards with the intention of building the aleph 30, but only need about 1/2 the wattage and the heatsink requirements are huge.
How can I get a little more power from the mini, (15-16 watts), and what c/w rating for the heatsinks would I need for (2) mosfets. I think I found they need to dissipate 36watts each. An ebayer has 12 inch sinks that are rated at .375 c/w, would that be enough?
I also have two 20-0-20 transformers already, are they too high of a voltage?
thanks in advance.
Hey guys,
asking for a little help with the mini. I purchased Briangt boards with the intention of building the aleph 30, but only need about 1/2 the wattage and the heatsink requirements are huge.
How can I get a little more power from the mini, (15-16 watts), and what c/w rating for the heatsinks would I need for (2) mosfets. I think I found they need to dissipate 36watts each. An ebayer has 12 inch sinks that are rated at .375 c/w, would that be enough?
I also have two 20-0-20 transformers already, are they too high of a voltage?
thanks in advance.
Fuling said:
Does this help??Raising the bias is covered in the early posts (changing R18-R19&R11) .
The 20-0-20 transformer will push you into a full blown Aleph 3 provided you have the VA rating.
I recently purchased a 24VCT 10 amp transformer for $32 dollars shipped . Allectronics has 22000Uf 25v caps for under $2 apiece .
Hi Sandyhooker,
On page 2 Grey talks about raising the rail voltage for power, but I cant find a voltage limit for the 2 devices, or how much this will increase the power. Also I have read on the bias voltage adjustment, but going to the 1.6 amp as Grey did or 2 amps as has been suggested, how much does this increase the power? I am running 8 ohm 95db drivers. (just fyi)
About the c/w rating of the heatsinks, given the need to dissipate 38watts/device, doesn't the rail voltage affect the requirement? So at a given voltage, how is the requirement calculated to c/w?
I am new to the amp building, so please have patience. I have read this thread about 4-5 times though.
thanks for your replies
On page 2 Grey talks about raising the rail voltage for power, but I cant find a voltage limit for the 2 devices, or how much this will increase the power. Also I have read on the bias voltage adjustment, but going to the 1.6 amp as Grey did or 2 amps as has been suggested, how much does this increase the power? I am running 8 ohm 95db drivers. (just fyi)
About the c/w rating of the heatsinks, given the need to dissipate 38watts/device, doesn't the rail voltage affect the requirement? So at a given voltage, how is the requirement calculated to c/w?
I am new to the amp building, so please have patience. I have read this thread about 4-5 times though.
thanks for your replies
I'm not sure what your listening requirements are but 95db speakers should provide a great deal of music at 10 watts. As Grey Rollins pointed out the Mini-A had much to do with current economies.
If your transformers are large current capable [what's the VA rating?] and your sinks are LARGE [12"X WHAT??] go for the Aleph 3. Unless you are seriously worried about your electric bill
.. you can never have too much power.
Some of the ZEN designs would put your transformers to good use and provde a very good 15-20 watts . They also are very well documented which is helpful to the beginner. Go to Passdiy.com . I have a set of ZV4 boards available if you were interested.
20-0-20 would be more than the MINI-A could swallow as drawn.
If your transformers are large current capable [what's the VA rating?] and your sinks are LARGE [12"X WHAT??] go for the Aleph 3. Unless you are seriously worried about your electric bill
.. you can never have too much power.Some of the ZEN designs would put your transformers to good use and provde a very good 15-20 watts . They also are very well documented which is helpful to the beginner. Go to Passdiy.com . I have a set of ZV4 boards available if you were interested.
20-0-20 would be more than the MINI-A could swallow as drawn.
With regard to the sinks it seems they would be adequate and yes the rail voltage figures into the equation but the bias level is the hitter .
Big difference between 1 and 2 amps.
Big difference between 1 and 2 amps.
What output devices are you going to use? Most suitable devices would have to be rated at least 3 or 4 times the voltage across them .
The best thing to do at this point is to stop, sit down, and come up with a plan...before doing anything else.
A 20-0-20 transformer is going to put you into an Aleph 3, which translates as 25W per channel. It uses two pairs of devices per channel. If you intend to stick with the Mini-A circuit at those rail voltages, you're going to be looking at some pretty serious warmth for a single pair of devices if you bias them at Aleph 3 levels. You will want to lower the bias.
I'm not clear how you've decided that 10W or so from a Mini-A is not enough, 25W from an Aleph 3 is too much, but 15W is just right. However, the rail voltage for 15W isn't that much higher than what's required for 10W. You'll need to reduce the rail voltage coming from that 20-0-20Vac transformer, either by regulating the rails or using resistors in a CRC filter. Either way will create a fair amount of heat.
I'm also a little hazy as to why you want to increase the bias, especially since you say your speakers are 8 Ohms. Yes, it will make things sound better, but it also increases the amount of heat you have to dissipate, which kinda starts being a problem. You don't specify what current the transformers can deliver, but if they aren't up to delivering the current, you're going to have problems there.
Amplifier design goes like this:
--Pick a target load. In your case, you're saying 8 Ohms.
--Pick a target power into that load. You're saying 15W.
--You then calculate the rail voltage you'll need to swing that much voltage (remembering to subtract Vgs for the output devices--in this case, rough it off at about 4V ea. or 8V total).
--Using the power you chose and the load, calculate the current you'll need. A push-pull output stage will deliver twice its quiescent bias, so you only need to bias for half the current.
--Multiply the rail by the bias current to see how much heat you'll dissipate.
--Choose the device (with one eye on how much power it can dissipate--this is heavily dependent on the case style) and play with what-if scenarios to decide how many you'll need in order to dissipate the heat safely. Nelson routinely runs things hotter than I do. He will tell you that you can run up to 50W per device if you have sufficient heat sink capability and are willing to run a little risk. Note, however, that he usually runs his outputs closer to 20-25W ea. I regard 35W/device as about the limit and generally run 25-30W ea.
--Choose your heatsink according to the maximum temperature you're willing to accept. Nelson accepts grill marks on his hands. I like to be able to leave my hand on the heatsink indefinitely.
Just sit and think for a while. Then act. Not the other way around.
Grey
A 20-0-20 transformer is going to put you into an Aleph 3, which translates as 25W per channel. It uses two pairs of devices per channel. If you intend to stick with the Mini-A circuit at those rail voltages, you're going to be looking at some pretty serious warmth for a single pair of devices if you bias them at Aleph 3 levels. You will want to lower the bias.
I'm not clear how you've decided that 10W or so from a Mini-A is not enough, 25W from an Aleph 3 is too much, but 15W is just right. However, the rail voltage for 15W isn't that much higher than what's required for 10W. You'll need to reduce the rail voltage coming from that 20-0-20Vac transformer, either by regulating the rails or using resistors in a CRC filter. Either way will create a fair amount of heat.
I'm also a little hazy as to why you want to increase the bias, especially since you say your speakers are 8 Ohms. Yes, it will make things sound better, but it also increases the amount of heat you have to dissipate, which kinda starts being a problem. You don't specify what current the transformers can deliver, but if they aren't up to delivering the current, you're going to have problems there.
Amplifier design goes like this:
--Pick a target load. In your case, you're saying 8 Ohms.
--Pick a target power into that load. You're saying 15W.
--You then calculate the rail voltage you'll need to swing that much voltage (remembering to subtract Vgs for the output devices--in this case, rough it off at about 4V ea. or 8V total).
--Using the power you chose and the load, calculate the current you'll need. A push-pull output stage will deliver twice its quiescent bias, so you only need to bias for half the current.
--Multiply the rail by the bias current to see how much heat you'll dissipate.
--Choose the device (with one eye on how much power it can dissipate--this is heavily dependent on the case style) and play with what-if scenarios to decide how many you'll need in order to dissipate the heat safely. Nelson routinely runs things hotter than I do. He will tell you that you can run up to 50W per device if you have sufficient heat sink capability and are willing to run a little risk. Note, however, that he usually runs his outputs closer to 20-25W ea. I regard 35W/device as about the limit and generally run 25-30W ea.
--Choose your heatsink according to the maximum temperature you're willing to accept. Nelson accepts grill marks on his hands. I like to be able to leave my hand on the heatsink indefinitely.
Just sit and think for a while. Then act. Not the other way around.
Grey
Hi Grey,
I already have Briangt Aleph boards, and as I stated was aiming to make the Aleph 30. Maybe I will go ahead with that, but the heatsink requirements loomed large. Thus I thought if I could get just a little more power from the Mini Aleph, it would be great. I dont have to use the transformers I have, its just that I have them. They are 400va by the way.
I guess jumping into this thread sort of implies that one would have a pretty good grasp of the working design(s),and not be a novice, but I couldn't find much in that realm. I also have used the search feature quite a bit, but haven't really found my answers either.
I have not decided 25 watts is too much, just goes back to cooling. I have done a lot of searching for heatsinks but have not found a decent supplier with good c/w ratings. Looking at Mr. Pass' Aleph 30, the sinks are quite large. Maybe an Aleph 30 with lower rail voltages, but haven't been able to locate any info about what advantage/disadvantage that would bring.
What appealed to me about the Aleph series was the sonic detail descriptions, with the 'tubelike" sound. I have had a few expensive amps, but nothing equalled the BAT VK-60 I once owned. I use HawthorneAudio open baffle speakers, bi-amped. Although I dont usually listen too loud, they also double as Home Theater and was concerned about headroom if using 'only' 10 watts.
I do thank you and anyone else that helps or answers in my quest of sonic bliss.
thanks again,
andy
I already have Briangt Aleph boards, and as I stated was aiming to make the Aleph 30. Maybe I will go ahead with that, but the heatsink requirements loomed large. Thus I thought if I could get just a little more power from the Mini Aleph, it would be great. I dont have to use the transformers I have, its just that I have them. They are 400va by the way.
I guess jumping into this thread sort of implies that one would have a pretty good grasp of the working design(s),and not be a novice, but I couldn't find much in that realm. I also have used the search feature quite a bit, but haven't really found my answers either.
I have not decided 25 watts is too much, just goes back to cooling. I have done a lot of searching for heatsinks but have not found a decent supplier with good c/w ratings. Looking at Mr. Pass' Aleph 30, the sinks are quite large. Maybe an Aleph 30 with lower rail voltages, but haven't been able to locate any info about what advantage/disadvantage that would bring.
What appealed to me about the Aleph series was the sonic detail descriptions, with the 'tubelike" sound. I have had a few expensive amps, but nothing equalled the BAT VK-60 I once owned. I use HawthorneAudio open baffle speakers, bi-amped. Although I dont usually listen too loud, they also double as Home Theater and was concerned about headroom if using 'only' 10 watts.
I do thank you and anyone else that helps or answers in my quest of sonic bliss.
thanks again,
andy