BSOZ Question- Caps and Rs

lgreen · 9th July 2003, 04:55 PM

Hello everyone, here is another question on my BSOZ preamp that is currently under construction. I have some parts modification questions that I figured you could help me with, so here goes.

1. Can I use a smaller value for the coupling capacitors than 10uF? I am looking at "approved" capacitors and at 10uF they are quite big in relation to how much space I have for them, they are also very expensive. I don't know whether this value is absolutely necessary or not, but at the amount of money involved I figured I would ask. Recommendations on this would be appreciated.

2. Having heard that the 3 watt 750 ohm resistors (R1-R6) get very hot, I am thinking of using thick film 20 watt resistors in a TO-220 package such as these:
http://rocky.digikey.com/scripts/Pro...&M=TAH20P750RJ
The problem is spacing and heat sinking, I don't know if I will have room to heat sink each resistor. However, they are kind of overkill rated at 20 or 35 watts (with heatsink), do you think they would work happily without a heatsink? Also, do they all get hot, or could I just substitute a couple with these devices?

moe29 · 9th July 2003, 05:02 PM

the amp works wonderfully as described in the article. The
750 ohm resistors do run hot - but i've had no problem with my
BOSOZ. I guess i'm trying to say, build the preamp as described
and listen to it... you may not feel that the extra money and time
to add "better" parts is worth it. On the other hand, after you
listen to it stock, you can substitute in the other parts and see if
they make a difference... a nice little upgrade path.

jwb · 9th July 2003, 05:16 PM

The 750Ω resistors do get very hot, but they do not exceed their 3W rating. Heatsinking will be more trouble than is warranted.

For the coupling capacitors I used Hovland Musicap, and I agree they are too expensive and too big. I have switched to standard 10µF film caps, and these are also large but not as expensive. If you use a smaller capacitor you will lose some low frequencies. You could try two 4.7µF in parallel, although I have no idea how that will impact sound.

Mad_K · 10th July 2003, 02:46 PM

1. Not any smaller please (because smaller= higher LF cutoff)

2. Those resistors look great! I use Caddock MP930 myself (TO220)

see my BZLS here: http://www.diyaudio.com/forums/showt...007#post111007

9th July 2003, 04:55 PM	#1
lgreen diyAudio Member Join Date: May 2003 Location: San Diego, USA	BSOZ Question- Caps and Rs Hello everyone, here is another question on my BSOZ preamp that is currently under construction. I have some parts modification questions that I figured you could help me with, so here goes. 1. Can I use a smaller value for the coupling capacitors than 10uF? I am looking at "approved" capacitors and at 10uF they are quite big in relation to how much space I have for them, they are also very expensive. I don't know whether this value is absolutely necessary or not, but at the amount of money involved I figured I would ask. Recommendations on this would be appreciated. 2. Having heard that the 3 watt 750 ohm resistors (R1-R6) get very hot, I am thinking of using thick film 20 watt resistors in a TO-220 package such as these: http://rocky.digikey.com/scripts/Pro...&M=TAH20P750RJ The problem is spacing and heat sinking, I don't know if I will have room to heat sink each resistor. However, they are kind of overkill rated at 20 or 35 watts (with heatsink), do you think they would work happily without a heatsink? Also, do they all get hot, or could I just substitute a couple with these devices?

10th July 2003, 02:46 PM	#4
Mad_K diyAudio Member Join Date: Sep 2002 Location: Norway	1. Not any smaller please (because smaller= higher LF cutoff) 2. Those resistors look great! I use Caddock MP930 myself (TO220) see my BZLS here: http://www.diyaudio.com/forums/showt...007#post111007 __________________ Mads K

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9th July 2003, 05:02 PM	#2
moe29 diyAudio Member Join Date: Dec 2002 Location: Florida	the amp works wonderfully as described in the article. The 750 ohm resistors do run hot - but i've had no problem with my BOSOZ. I guess i'm trying to say, build the preamp as described and listen to it... you may not feel that the extra money and time to add "better" parts is worth it. On the other hand, after you listen to it stock, you can substitute in the other parts and see if they make a difference... a nice little upgrade path.

9th July 2003, 05:16 PM	#3
jwb diyAudio Member Join Date: Mar 2002 Location: San Francisco, USA	The 750Ω resistors do get very hot, but they do not exceed their 3W rating. Heatsinking will be more trouble than is warranted. For the coupling capacitors I used Hovland Musicap, and I agree they are too expensive and too big. I have switched to standard 10µF film caps, and these are also large but not as expensive. If you use a smaller capacitor you will lose some low frequencies. You could try two 4.7µF in parallel, although I have no idea how that will impact sound.

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