P1.7 questions

Mark A. Gulbrandsen · 2nd February 2006, 12:44 AM

What wattage do resistors R-44, 55, 59, and 70 need to be. I'd like to place metal films there but am limited to 1/2 watt in size at the local surplus place...... Thanks for any help on this.....

Mark

jh6you · 2nd February 2006, 01:01 AM

Even 1/4W is enough, acc to 33*(0.7/33)^2 and 22*(0.7/22)^2.

Regards
jh

Mark A. Gulbrandsen · 2nd February 2006, 02:59 AM

Are heatsinks needed on the devices?

kmj · 2nd February 2006, 05:00 AM

Mark, could you post a link to the servicemanual or partslist if you got one?

About the heatsinks, the pictures of other 1.7-projects I've seen has used some smaller heatsinks. That's all I know

jh6you · 2nd February 2006, 05:48 AM

As far as I see, the Vds of Q15 is about 30V and the bias is with about 30mA so that power dissipation = 30 x 0.03 = 1W.

I would summarize power dissipation as follows:

Q15 and Q18: 1W each
Q16, Q17, Q19 and Q20: close to 1W each

Regards
jh

Nisbeth · 2nd February 2006, 06:44 AM

One more question: From looking at the schematic, it seems that both the input and output caps could be a lot smaller than the recommended 10uF/30uF. I've tried calculating the input and output impedances but I'm not sure I have it right

. What's the minimum value for these caps?

/U.

Mark A. Gulbrandsen · 2nd February 2006, 11:52 PM

So I assume that 1 watt is ok without sinks on these devices. From photos of others it looks like some use them and some do not.

BTW: Thanks for all the help here!

Mark

MikeW · 3rd February 2006, 01:35 AM

I did screw up on some of the resister sizes, sorry. Better to be to big that not big enough. If you let that pre-amp run for a while you'll see why there are heatsinks on the MOSFETs.

It was only my second pre-amp project. The next one will be better.

Mark A. Gulbrandsen · 3rd February 2006, 04:39 AM

Mike,

Really... I'm not complaining? I'm very grateful that you sent it. There is not a thing wrong with the boards or anything to complain about at all! If you had more boards I'd love to have several to build up for other people. I decided to take this one to full balanced operation. Had yet to run my 2s in balanced mode at all..... In order to do this there was some re-work that had to be done on both boards. And at the same time I made all the resistors MF's and changed a few others to coencede with the factory version. The ones that I installed were basically the same wattage as yours were...... Regarding the sinks... Some have them and some don't... which has me a bit confused....... So whats up here? Would seem to me that these devices can dissipate a watt free air... or can't they..... I left the sinks on the regulators. If they all need to be on a sink I would consider taking the time to machine a bar of alumnium to thermally connect them all together.

BTW: you ought to hear it in balanced mode

Thanks!

Mark

2nd February 2006, 12:44 AM	#1
Mark A. Gulbrandsen diyAudio Member Join Date: Sep 2001 Location: Salt Lake City	P1.7 questions What wattage do resistors R-44, 55, 59, and 70 need to be. I'd like to place metal films there but am limited to 1/2 watt in size at the local surplus place...... Thanks for any help on this..... Mark __________________ KSA-100 WIKI

2nd February 2006, 02:59 AM	#3
Mark A. Gulbrandsen diyAudio Member Join Date: Sep 2001 Location: Salt Lake City	Are heatsinks needed on the devices? __________________ KSA-100 WIKI

2nd February 2006, 11:52 PM	#7
Mark A. Gulbrandsen diyAudio Member Join Date: Sep 2001 Location: Salt Lake City	So I assume that 1 watt is ok without sinks on these devices. From photos of others it looks like some use them and some do not. BTW: Thanks for all the help here! Mark __________________ KSA-100 WIKI

3rd February 2006, 01:35 AM	#8
MikeW diyAudio Member Join Date: Sep 2002 Location: North of Boston	Screw up I did screw up on some of the resister sizes, sorry. Better to be to big that not big enough. If you let that pre-amp run for a while you'll see why there are heatsinks on the MOSFETs. It was only my second pre-amp project. The next one will be better. __________________ MikeW

3rd February 2006, 04:39 AM	#9
Mark A. Gulbrandsen diyAudio Member Join Date: Sep 2001 Location: Salt Lake City	Mike, Really... I'm not complaining? I'm very grateful that you sent it. There is not a thing wrong with the boards or anything to complain about at all! If you had more boards I'd love to have several to build up for other people. I decided to take this one to full balanced operation. Had yet to run my 2s in balanced mode at all..... In order to do this there was some re-work that had to be done on both boards. And at the same time I made all the resistors MF's and changed a few others to coencede with the factory version. The ones that I installed were basically the same wattage as yours were...... Regarding the sinks... Some have them and some don't... which has me a bit confused....... So whats up here? Would seem to me that these devices can dissipate a watt free air... or can't they..... I left the sinks on the regulators. If they all need to be on a sink I would consider taking the time to machine a bar of alumnium to thermally connect them all together. BTW: you ought to hear it in balanced mode Thanks! Mark __________________ KSA-100 WIKI


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2nd February 2006, 01:01 AM	#2
jh6you Account Disabled Join Date: Aug 2002 Location: Near to the Pacific Ocean	Even 1/4W is enough, acc to 33(0.7/33)^2 and 22(0.7/22)^2. Regards jh

2nd February 2006, 05:00 AM	#4
kmj diyAudio Member Join Date: Feb 2004 Location: Falkenberg	Mark, could you post a link to the servicemanual or partslist if you got one? About the heatsinks, the pictures of other 1.7-projects I've seen has used some smaller heatsinks. That's all I know

2nd February 2006, 05:48 AM	#5
jh6you Account Disabled Join Date: Aug 2002 Location: Near to the Pacific Ocean	As far as I see, the Vds of Q15 is about 30V and the bias is with about 30mA so that power dissipation = 30 x 0.03 = 1W. I would summarize power dissipation as follows: Q15 and Q18: 1W each Q16, Q17, Q19 and Q20: close to 1W each Regards jh

2nd February 2006, 06:44 AM	#6
Nisbeth diyAudio Member Join Date: Jan 2001 Location: Denmark	One more question: From looking at the schematic, it seems that both the input and output caps could be a lot smaller than the recommended 10uF/30uF. I've tried calculating the input and output impedances but I'm not sure I have it right . What's the minimum value for these caps? /U.

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