Hi Still4given,
The pic & explanation showing your PSU confirms 2 bolts holding your caps. Did you say that the Central Star Ground is now isolated from the chassis?
Re max power;
Vrms squared divided by load in ohms gives peak power. To convert this to average power (commonly misnamed RMS power) divide peak power by 2 i.e. P=V*V/2/R.
For full classA into your load you need a peak current = Vpk / Rload.
The quiescent current needs to be half the peak current plus a small reserve of about 5% to 10% i.e. Iq=0.55*Vpk/Rload
The pic & explanation showing your PSU confirms 2 bolts holding your caps. Did you say that the Central Star Ground is now isolated from the chassis?
Re max power;
Vrms squared divided by load in ohms gives peak power. To convert this to average power (commonly misnamed RMS power) divide peak power by 2 i.e. P=V*V/2/R.
For full classA into your load you need a peak current = Vpk / Rload.
The quiescent current needs to be half the peak current plus a small reserve of about 5% to 10% i.e. Iq=0.55*Vpk/Rload
NUTTTR said:
Yup that's it! For Class A power output i used the spreadsheet calculator, i actually have a meter for measuring the kW drain on the mainsSo i know exactly what is going in...
For testing power output you really need a scope!
You can take a "guess" by using rail voltage, etc.... Or you can use the spreadsheet for approx values..
Aaron
May I ask what spreadsheet you are refering to? I don't have a working scope yet. I suppose it's not really important to know what the output power is but I guess it's a male characteristic to want to know how your output stacks up against the other guys.
Actually, the bolt without the leads attached goes down through the bottom of the chassis. The bolt with the ground leads attached only goes through the ground plate. If I had it to do it over, I would probably not have mounted the caps above the transformer. I was trying to kill two birds with one stone. I was too lazy to relocate everything to mount the caps on the floor of the chassis so I isolated the mounting bolt and added the other bolt for the star ground. It seems to work fine and kept the case narrow enough to keep the driver transistors close to the inlets for cooling. That was in my mind as I was deciding what size to make the case.
Blessings, Terry
still4given said:
May I ask what spreadsheet you are refering to? I don't have a working scope yet. I suppose it's not really important to know what the output power is but I guess it's a male characteristic to want to know how your output stacks up against the other guys.
Blessings, Terry
The one k-amps i believe it was posted up earlier in the piece - the class a calculator.....
Someone should have it handy... i don't!
Re: Parts Kit
The part #'s for the semis were posted, and the resistors are pretty standard, but the caps still elude me.
If we can get a list of the PCB mounted caps required I will then be able to order and kit.
May I ask everyone interested in a kit to please send me an email with the following?
Name:
email address:
Number required:
Shipping address:
stgrab@yahoo.com
The close deadline for kits will be the 10th... I just threw up that number.
Cost will be determined by number of kit orders, and as promised, this is a NO PROFIT group buy. Well I am profiting on others parts research...
AND A BIG SIDE NOTE!!!
I got several pairs of heat sinks today. I have extra's and will sell them on a first come first serve basis. I will post a picture in the next few days.
googler said:
The part #'s for the semis were posted, and the resistors are pretty standard, but the caps still elude me.
If we can get a list of the PCB mounted caps required I will then be able to order and kit.
May I ask everyone interested in a kit to please send me an email with the following?
Name:
email address:
Number required:
Shipping address:
stgrab@yahoo.com
The close deadline for kits will be the 10th... I just threw up that number.
Cost will be determined by number of kit orders, and as promised, this is a NO PROFIT group buy. Well I am profiting on others parts research...
AND A BIG SIDE NOTE!!!
I got several pairs of heat sinks today. I have extra's and will sell them on a first come first serve basis. I will post a picture in the next few days.
Thank you for your reply and help.jacco vermeulen said:
I was planning on using two 25-0-25 toroidal transformers, but from what you are saying, I must use a minimum of 30-0-30 transformers in order to get 40VDC and therefore be able to obtain a much higher ouput then 50W? Given the higher rail voltage, i won't be able to achieve 150W with the heatsinks I planned on getting (0.11C/W forced cooling per channel); are there any benefits for using a higher voltage?
As for the drivers, I will mount them on the main heatsink as it has been mentioned in earlier posts; would there be a reason not to do that if I am dissipating so much heat?
Paul
You could go for 25 volt transformers and bias for 100 watts in 4 Ohms, that saves a lot on dissipation.
Please consider that if you bias for 100 watts in 8 Ohms you also have 100 watts class A in 4 Ohms, as already mentioned by our tutor Upupa Epops much earlier in the thread.
Biased for 50 watts in 8 Ohms will give 17dBW in 4 Ohms before going to class B, 85 dB/W 4 Ohm loudspeakers will remain in class A till 105dB.
Personally i do not see the point in biasing that high in 4 Ohms, unless you have either ESL's or something like 80dB/W efficiency 4 Ohms units.
Please consider that if you bias for 100 watts in 8 Ohms you also have 100 watts class A in 4 Ohms, as already mentioned by our tutor Upupa Epops much earlier in the thread.
Biased for 50 watts in 8 Ohms will give 17dBW in 4 Ohms before going to class B, 85 dB/W 4 Ohm loudspeakers will remain in class A till 105dB.
Personally i do not see the point in biasing that high in 4 Ohms, unless you have either ESL's or something like 80dB/W efficiency 4 Ohms units.
jacco vermeulen said:
Jacco!! There's a VERY good reason for going that high in class A... Mostly it revolves around the "Because i can" theory
Let's just say, i LOVE the way it sounds biased as it is... I've used lower bias and was not as impressed... 100w full class A @ 8 ohms = 50w Class A @ 4 ohm (approx) (then the rest in class B)... That's why i biased so high, i'm running 5 ohm speakers... So it works REALLY well... i'm yet to run out of steam and i'm not even using the full class A continuous! Mind you, i have 1100wrms to my sub
So i'm cranking a bit of noise out!!Thanks
Aaron
Different subject !
Are you guys aware that Mouser sells 1/4 watt CMF55(RN55) Dale resistors at an affordable rate ?
These come in 0.5% accuracy and a TC of 25PPM .
Like the 1/8 watters of the old Dale series these are T2 types, wattage is tested at 75C instead of 25C.
At lower temperatures a 1/4 watter can do 1/2 watt
(what Mouser calls 1/4 watt rated at 1/2 watt)
Are you guys aware that Mouser sells 1/4 watt CMF55(RN55) Dale resistors at an affordable rate ?
These come in 0.5% accuracy and a TC of 25PPM .
Like the 1/8 watters of the old Dale series these are T2 types, wattage is tested at 75C instead of 25C.
At lower temperatures a 1/4 watter can do 1/2 watt
(what Mouser calls 1/4 watt rated at 1/2 watt)
Upupa Epops said:Aaron, if amp is good designed, NOBODY will listen differnce, if amp is biased for 50 W/8 or for 100 W/8 - all is only superstition or brain washing, I'm sorry.
Which is why I implemented my idea in Post #2530. There were not many comments to that post so we shall see if this works when I try it upon my return from this trip.
- I installed a DPDT PCB switch on my driver boards to change between low and high bias. Had to drill holes in the board, take off some pins on the switch and do a bunch of ugly hacking to get this to fit. Great fun with epoxy too. This is not coming apart.
- The second bias trimpot is 25K instead of 5K. I figured since this is switched in parallel to 5K, it would need to be much larger to keep the same overall resistance range. Swithching in 5K parallel to 5K would give you only 2.5K max resistance.
- As a bonus I put in an LED on each board to indicate high bias level, using a .5W series 3K and 690R to + VCC (38V) through the other switch poles.
- I wired this wrong, so the "green" LED actually indicates "high" bias. The original intent was that "green" = environmenal = low bias. oopsie.
- I also drastically increased the size of the driver heat sinks.
http://www.mmmetals.com/pages/extru...back_heatsink_aluminum_extrusion_4_and_up.htm
1. MM38400 4.000 1.290 0.294 2.749 1.6 33.833 <-- x 4&7/8" long
2. MM11945 7.340 1.312 0.312 5.042 1.1 61.861 <-- 8" wide x 4&7/8" long
3. MM10332 8.350 2.000 0.250 5.906 1.0 57.648 <-- x 15&1/2"
4. No matching M&M part but this profile MM11945, with these demisions, 6&12" wide x 6" tall with 1&3/8" fins
Picture to follow...
1. MM38400 4.000 1.290 0.294 2.749 1.6 33.833 <-- x 4&7/8" long
2. MM11945 7.340 1.312 0.312 5.042 1.1 61.861 <-- 8" wide x 4&7/8" long
3. MM10332 8.350 2.000 0.250 5.906 1.0 57.648 <-- x 15&1/2"
4. No matching M&M part but this profile MM11945, with these demisions, 6&12" wide x 6" tall with 1&3/8" fins
Picture to follow...
heat sinks
Can you tell I cut these with a hacksaw?
What's wrong with it? The heatsinks are huge and should work well. Mechanics? I've installed a bracket to prevent movement of the heat sinks and xistors.
Tekko said:Eww i don´t like that mounting of the heatsinksother than that it looks nice.
Can you tell I cut these with a hacksaw?
What's wrong with it? The heatsinks are huge and should work well. Mechanics? I've installed a bracket to prevent movement of the heat sinks and xistors.
Hi Lgreen,
and these are just the driver sinks!
Remember to orient them so that the fins are vertical when finally installed.
I don't understand your logic with the switchable bias pot.
The low bias pot is the one that is in circuit permanently.
The hi bias pot is added in parallel with your switch and reduces the resistance of the lower leg of the Vbe multiplier, thus giving a higher bias voltage and forcing more current through the output stage. A 5k pot here would be OK, I would use a 2k pot for ease of adjustment and if needed a small resistor in series to ensure I did not run out of travel.
and these are just the driver sinks!
Remember to orient them so that the fins are vertical when finally installed.
I don't understand your logic with the switchable bias pot.
The low bias pot is the one that is in circuit permanently.
The hi bias pot is added in parallel with your switch and reduces the resistance of the lower leg of the Vbe multiplier, thus giving a higher bias voltage and forcing more current through the output stage. A 5k pot here would be OK, I would use a 2k pot for ease of adjustment and if needed a small resistor in series to ensure I did not run out of travel.
AndrewT said:
Yep, those are just for the drivers baby! They will be vertical, the assembly is vertical. I understand what you are saying with the pots, its basically what I thought and is exactly as I have it set up. Except I thought I'd need a higher R and had no idea of the values, didn't know a 2K would suffice. Too late to change now; this thing is getting locked and loaded.
The heatsinks are not in alignment with the boards, that is what is bugging me. I like it when both transistors live on the same side of the heatsink and when its paralell with the board. Yes i can see you cut the heatsink with a hacksaw, you want to file those ends to make them look nice again.