Bi-amp your speakers.
Build a bass oriented chipamp for the bass driver.
Keep Peter's version for Mid/Treble.
Changing the transformer to bigger than 225VA for a single channel is unlikely to extend or lift the bass response.
Increasing the smoothing and the NFB cap is very likely to increase the extent of the bass comensurate with the increase in the input cap.
Build a bass oriented chipamp for the bass driver.
Keep Peter's version for Mid/Treble.
Changing the transformer to bigger than 225VA for a single channel is unlikely to extend or lift the bass response.
Increasing the smoothing and the NFB cap is very likely to increase the extent of the bass comensurate with the increase in the input cap.
AndrewT said:
True, I thought about the bi-amp setup previously but to put (active) crossover before the amp is not my preference since somehow I feel it degrades the signal more.... 🙁 ..
[/QUOTE]Changing the transformer to bigger than 225VA for a single channel is unlikely to extend or lift the bass response.
...... [/QUOTE]
Yeah, with my current setup I'm not sure how big the improvement would be.......
Joshua
Peter Daniel said:
I use 2 way setup : Fostex-87E and Eminence Alpha 15, all are arranged in open baffle.
Joshua
So I assume, there is some type of crossover in a speaker. You can easily replace it by passive filter components in each amp, no need to go active. And because those parts can be much smaller now, you could use better quality parts.
Peter Daniel said:
That is correct, I use 12db/octave crossover at the speaker.
I can try that passive crossover, which one do you think better, to incorporate that crossover at NOS DAC or at GC? Or just built them in separate box..?
Joshua
Well for some reason I am still unable to start a new thread of my own. This isn't related to your kits Peter, but since I have already bought and built one of your kits I thought it might be ok, hehe.
I've built a LM3886 GC using BrianGTs boards and I have an extra set of boards and components that I would like to add to my amp to make a PA100 amp.
The reason I would like to do this is I have my eye on a pair of new Acculine A2 MTM configured speakers that have 4 ohm impedance and I thought this could be a good way to drive them without stressing the chips.
I've looked at national's schematic for the PA100, and to be honest I'm not that good at reading a schematic just yet. Would it be as simple as just adding a .1 ohm resistor at the speaker outputs of each board or am I missing something?
Any advice is greatly appreciated.
I've built a LM3886 GC using BrianGTs boards and I have an extra set of boards and components that I would like to add to my amp to make a PA100 amp.
The reason I would like to do this is I have my eye on a pair of new Acculine A2 MTM configured speakers that have 4 ohm impedance and I thought this could be a good way to drive them without stressing the chips.
I've looked at national's schematic for the PA100, and to be honest I'm not that good at reading a schematic just yet. Would it be as simple as just adding a .1 ohm resistor at the speaker outputs of each board or am I missing something?
Any advice is greatly appreciated.
No, Bi-amp your speakers.joshuajoshua said:
Use one amp to drive the Bass half of the passive crossover, use a second amp to drive the Mid/Treble half of the passive crossover.
Coreyk78 said:
I assume you want to use 2 LM3886 in parallel? Just follow 'red option' in this schematic: http://audiosector.com/lm4780 amp.pdf
A clarification question here.
I assume the Gainclone is ok to drive 4 ohm speakers, so long as the rail voltages are down at 22V (as per the graph that was posted towards the start of this thread.)
Anything else I should be aware of when driving 4ohm loads?
Thanks
I assume the Gainclone is ok to drive 4 ohm speakers, so long as the rail voltages are down at 22V (as per the graph that was posted towards the start of this thread.)
Anything else I should be aware of when driving 4ohm loads?
Thanks
double the dissipation of the heatsink cf National specify.
Page 14 table shows Rth s-a=3.8C/W for Ta=25degC
or
Rth s-a=3.2C/W for Ta=40degC.
Double these values to 1.9C/W or 1.6C/W for each channel.
eg. An internal heatsink for a 4ohm+4ohm amplifier needs 0.8C/W to cool the two channels.
Page 14 table shows Rth s-a=3.8C/W for Ta=25degC
or
Rth s-a=3.2C/W for Ta=40degC.
Double these values to 1.9C/W or 1.6C/W for each channel.
eg. An internal heatsink for a 4ohm+4ohm amplifier needs 0.8C/W to cool the two channels.
Ok, that's not so bad - I've got two 0.7 heat sinks being delivered (one per channel), so it looks like I should have adequate cooling properties, even if they do run a little warmer than the chips with an 8 ohm load.
Thanks
Thanks
Rth s-a = 0.7C/W per channel is enormous. They will appear to run cold (=good).
You could probably increase the supply voltage to +-25Vdc with sinks that big. Maybe even stretch to +-28Vdc.
You could probably increase the supply voltage to +-25Vdc with sinks that big. Maybe even stretch to +-28Vdc.
25Vdc would be the most I'd want to go to to start with. Running the figures through the formula's in the heat sink thread, then 25Vdc rails with 0.7 K/W would give a heatsink temperature of 61c assuming TA is 40c.
Ok, highly unlikely we'll ever get 40c days (in fact almost guaranteed in the UK), but there have been hot summer days last year where my room was approaching 30c (it's a bit of a sun trap), so on those days the heat sink would be 51c.
Ok, highly unlikely we'll ever get 40c days (in fact almost guaranteed in the UK), but there have been hot summer days last year where my room was approaching 30c (it's a bit of a sun trap), so on those days the heat sink would be 51c.
no.
Look at the table again.
I know that 0.7 is off scale but you can estimate that somewhere between Ta=80degC and Ta=100degC would be the recommended max for a 0.7C/W sink when running a 4r0 load at maximum power from +-25Vdc supplies. This is after the supply rails have sagged to +-25Vdc.
Now look at the Tc value. It is 114degC.
Lets assume the maximum allowable ambient is 95degC. Subtract actual maximum ambient from this value leaving 65Cdegrees. Now subtract this deltaT =65Cdegrees from the predicted Tc and you get actual Tc=49degC. The heatsink will be about 10Cdegrees cooler than this i.e. about 39degC.
This is the maximum temperature if the heatsink is still rated @ 0.7C/W for this low deltaT=9Cdegrees. But, that is irrelevant.
The sink should never get to that temperature since you are reproducing music where the average output power <=20dB below maximum power.
The big difference is that the Tj value when Ta=~95degC will just reach 150degC on transient peaks. But, we now know the whole amp runs cooler than this by ~65Cdegrees. So Tjmax<=85degC.
We get more output current passing Spike protection by using a big sink than by using the recommended sink. The result is cleaner sound.
Look at the table again.
I know that 0.7 is off scale but you can estimate that somewhere between Ta=80degC and Ta=100degC would be the recommended max for a 0.7C/W sink when running a 4r0 load at maximum power from +-25Vdc supplies. This is after the supply rails have sagged to +-25Vdc.
Now look at the Tc value. It is 114degC.
Lets assume the maximum allowable ambient is 95degC. Subtract actual maximum ambient from this value leaving 65Cdegrees. Now subtract this deltaT =65Cdegrees from the predicted Tc and you get actual Tc=49degC. The heatsink will be about 10Cdegrees cooler than this i.e. about 39degC.
This is the maximum temperature if the heatsink is still rated @ 0.7C/W for this low deltaT=9Cdegrees. But, that is irrelevant.
The sink should never get to that temperature since you are reproducing music where the average output power <=20dB below maximum power.
The big difference is that the Tj value when Ta=~95degC will just reach 150degC on transient peaks. But, we now know the whole amp runs cooler than this by ~65Cdegrees. So Tjmax<=85degC.
We get more output current passing Spike protection by using a big sink than by using the recommended sink. The result is cleaner sound.
That's my problem with heat sink calculations. The National tables predict that a much smaller heat sink is required than the formula calculations explained here
So which do I use - on the one hand the Heat sink thread says not to trust published tables, and on the other hand you are saying that the National table is a reasonably reliable source as the basis to work out a heat sink that is double what National publish.
I'm confused.
So which do I use - on the one hand the Heat sink thread says not to trust published tables, and on the other hand you are saying that the National table is a reasonably reliable source as the basis to work out a heat sink that is double what National publish.
I'm confused.
Its's the first one at the link below (SK47) and it's 100mm wide. The graph shows 0.7 K/W so it'll be up to the job.
http://www.farnell.com/datasheets/75797.pdf
The question was more about heat sink calculations in general and whether to trust the specs that the manufacturers say are good for the chips. Other threads seem to suggest otherwise.
http://www.farnell.com/datasheets/75797.pdf
The question was more about heat sink calculations in general and whether to trust the specs that the manufacturers say are good for the chips. Other threads seem to suggest otherwise.