Vivek said:
Vivek,
If you have a shopping list I might be able to find what you wish like MKTs and silver mica instead of ceramic, Metal Film Resistors, MKP 1.0uF, 10,000uF 63V at about a $1.00 Cnd I think, if you want me to shop about. It would take me 2-3 weeks to do with my schedule. I already have commitments for this weekend. For sure the MF Resistors are easy for me to souce and likely the silver Mica. I am certain I can get you 1uF MKP if you wish with gold plated leads at good price. The 10,000uF I have to check if still available. Give some thought and let me know or if someone else closer can for you that is great as well. Other than the 63V 10,000uFs it would be a small package to mail. If the source resistors you bought are carbon 5W types I suggest you stay with them rather than wirewound types.
I think MF Resistors are $0.10 each at an electronics part store locally. Capacitors will vary from $0.20 - $2.00 with most being under $1.00. The only part I will not be able to source is the BiPolar for the gound leg of the NFB.
Regards,
John L. Males
Willowdale, Ontario
Canada
07 August 2007 22:08
Official Quasi Thread Researcher
John, Hari, thanks for your offer to shop for me.
I actually did not ask for silver mica capacitors. I will go back and check for silver mica and 200V caps. But what do I do about the 47uF non-polar caps? I got the 0.1uF capacitors which are like little boxes. I suppose they are polyester. They are called "box type" capacitors.
Getting the 10,000uF, 63V PSU caps is not a problem here.
If I would not be taking too much risk in using 1/4W resistors, I can get MFRs.
Check out this http://www.toroidal.com/t_toroidal.html link. I can either buy two small ones or one big one (custom made). The standard range had 35-0-35 7.14A and 8.92A. Or if an EI transformer will do, I can get one made. Something like a 35-0-35 12A.
I actually did not ask for silver mica capacitors. I will go back and check for silver mica and 200V caps. But what do I do about the 47uF non-polar caps? I got the 0.1uF capacitors which are like little boxes. I suppose they are polyester. They are called "box type" capacitors.
Getting the 10,000uF, 63V PSU caps is not a problem here.
If I would not be taking too much risk in using 1/4W resistors, I can get MFRs.
Check out this http://www.toroidal.com/t_toroidal.html link. I can either buy two small ones or one big one (custom made). The standard range had 35-0-35 7.14A and 8.92A. Or if an EI transformer will do, I can get one made. Something like a 35-0-35 12A.
Hi Vivek,
35-0-35 @ 8.92A is a 625VA toroid.
This can give upto 400W of power.
The 35Vac is suitable for +-50Vdc.
This suits 100W into 8ohm and 200W into 4ohm.
Two channels @ 4ohm each will deliver 200W + 200W = 400W capacity from the 625VA transformer.
Do not get a custom made EI, just use the standard toroid.
It's about time you got the calculator out.
The 1/4W metal film resistors will be much more stable than the 1/2W carbons.
Check the power dissipation in each of the resistor locations. If any exceed 50% (1/8W) then use a bigger resistor for this location only. You can use two resistors in parallel to get 1/2W capacity from the pair. Each resistor in this case is double the value of the specified resistor. The second resistor can be fitted on the back of the PCB or if the first is stood off the PCB the second can be strung between the long legs. eg 1k5 resistor with 11mA passing dissipates 0.011*0.011*1500=0.182W This exceeds 125mW so use instead 3k0//3k0 and each dissipates 91mW.
Get that calculator out again.
35-0-35 @ 8.92A is a 625VA toroid.
This can give upto 400W of power.
The 35Vac is suitable for +-50Vdc.
This suits 100W into 8ohm and 200W into 4ohm.
Two channels @ 4ohm each will deliver 200W + 200W = 400W capacity from the 625VA transformer.
Do not get a custom made EI, just use the standard toroid.
It's about time you got the calculator out.
The 1/4W metal film resistors will be much more stable than the 1/2W carbons.
Check the power dissipation in each of the resistor locations. If any exceed 50% (1/8W) then use a bigger resistor for this location only. You can use two resistors in parallel to get 1/2W capacity from the pair. Each resistor in this case is double the value of the specified resistor. The second resistor can be fitted on the back of the PCB or if the first is stood off the PCB the second can be strung between the long legs. eg 1k5 resistor with 11mA passing dissipates 0.011*0.011*1500=0.182W This exceeds 125mW so use instead 3k0//3k0 and each dissipates 91mW.
Get that calculator out again.
Vivek said:
Vivek,
The places you would use the silver mica would be C3, C4 and C9. The silver mica should not be a expensive item, but will be a bit more than a ceramic. The next best choice for C3, C4 and C9 would be a MKT. I do not think MKP is worth the expense for C3, C4 and C9 unless you find those values in MKP in surplus at good price. The box type capacitors are good for the bypass 0.1uF. The C1/C2 should be film capacitors such as MKT or MKP. C7 should be a film capacitor, MKT is appropriate.
The NoPolar, i.e. BiPolar capacitor, C8 is actually 100uF, not 47uF on the schematics for some time. If you are using the quasi parts list it is rather old so I would suggest you work from the schematic to find the current values other than those that are dependent on the rail voltage and gain you need to set. You can use a standard electrolytic for C8. or back to back 200Uf in series with eith the polarities facing each other like Hari has accomodated for on his PCB design. Quasi uses a single electrolytic. For the actual voltage that C8 will see, the DC offset, an electrolytic C8 will behave like a BiPolar at such voltages due to the leakage current of the capacitor at such low voltages. C8 can be anything from 25V and up, but in theory should be at least the rail voltage. As pointed out a few times in the thread if the DC offset is more than a few hundred milivolts other things will be wrong with the amp and other parts will be blowing up so it is not a big deal for C8 to be at rated rail voltage.
Just so you are aware, you can user a higher capacitance for C8 if you wish which will improve LF response a bit more.
Some builders like to bypass the C8 like capacitor with a flim capacitor when they use an electrolytic for the C8 like capacitor. The value varies what builders will use, but typical values builders on diyAudio use in such cases are 0.1uF and 1uF. Hari's PCB has accomodation for bypassing his antipolar C8 capacitor with a film capacitor. Such a C8 like bypass capacitor should be at least a MKT, and ideally an MKP.
One comment about resistor wattage ratings for the amplifiers. Quasi has indicated what resistors need a higher rating and also posted a schematic with the key current flows on the schematic so voltage drops and ratings could be calculated. It has not been discussed in this thread, but in other threads builders and designers often comment about using at least a 2W resistor for the NFB resistor. In the quasi amp design this would be R18.
Regards,
John L. Males
Willowdale, Ontario
Canada
08 August 2007 (08:55 -) 10:25
Official Quasi Thread Researcher
So the bipolar capacitor thing is sorted out. I will check for the silver mica capacitors.
So the 1 ohm R27 to R35, R12, 13, 14, 15, 20, 21, 22 should ideally be 1/2W types since they have higher currents passing. Or like Andrew said, i could just try things out with 1/4W MFRs. If it begins to get hot, I could use two in parallel with double (or approximately double) the value.
So the 1 ohm R27 to R35, R12, 13, 14, 15, 20, 21, 22 should ideally be 1/2W types since they have higher currents passing. Or like Andrew said, i could just try things out with 1/4W MFRs. If it begins to get hot, I could use two in parallel with double (or approximately double) the value.
Vivek said:
Vivek,
R27-35 are specified on the schematic for the NMOS200 as 2W. R34 is not 1R0, but 10R0. I think R34 should be at least 5W and not 2W considering you are using 4 ohm drivers with a 200W+ amplifier module. Again if you used 2x20R0 2W in parallel for R34 then you should be just fine.
Regards,
John L. Males
Willowdale, Ontario
Canada
08 August 2007 18:58
Official Quasi Thread Researcher
Vivek said:
Vivek said:
Vivtek,
Hari is designing a 2 pair TO-247 version and has a single pair TO-247 version as well that are the NMOS350 in a NMOS200 like PCB for stacking via an "L" bracket to the heatsink. Hari has not designed a TO-220 version. You will need to use the Quasi TO-220 version PCB if you wish to use TO-220 devices.
Quasi's PCB are in Adobe PDF format which means it should print on any printer of any OS that Acrobat supports at true scale. If either the printer or Acobat are configured to "scale" the document to the page you can end of with differences as you have encountered.
Regards,
John L. Males
Willowdale, Ontario
Canada
11 August 2007 10:23
Official Quasi Thread Researcher
Nmos350 / 500 parts.
.
Hi folks,
Some time ago I mentioned in this thread that I might put kits together for the Nmos series. The kits will comprise of all the parts except for the heatsinks and the PCB. Prices are based on the value of components only.
If anyone is interested, a kit for the Nmos350 / 500 is now available on my web site.
Cheers
Quasi
.
Hi folks,
Some time ago I mentioned in this thread that I might put kits together for the Nmos series. The kits will comprise of all the parts except for the heatsinks and the PCB. Prices are based on the value of components only.
If anyone is interested, a kit for the Nmos350 / 500 is now available on my web site.
Cheers
Quasi
I only find this : http://www.mikado.ro/files/products/radiator1_2.jpg
123 x 10 x 2.5 cm (of course i trim him)
It is good ?
And ... if i put BC550 & BC560 (better noise figure) will be better ?
123 x 10 x 2.5 cm (of course i trim him)
It is good ?
And ... if i put BC550 & BC560 (better noise figure) will be better ?
