Zobel network.....Better bass? Yes or No - Page 2

x. onasis · 9th December 2004, 03:22 AM

(from the peanut gallery)

My limited experience is that the LM3875 just doesn't love 4ohm loads like 8ohm. The bass is where it fails first. I then built the BGT4780 and it was a different story all together, but I was thinking it was just tons more power and that was the difference. This newer kit however, has the Zobel network.

Are you guys saying that the Zobel is at least worth a try and perhaps this "voicing of the amp" is a possible next step for the 3875 to be happier with a 4 ohm load? Are the values the same ie, 2.7ohm R and .1uF cap.... and if I might ask, what other values are logical to try?

(wish I knew what I was talking about)

HawkeyeStoob · 9th December 2004, 05:50 AM

Thanks for all of the quick answers.

I will give it a try this weekend when I get a little bit more free time, I hope.

Thanks for the info on the BGT4780 kit. I would like to give one of those a try once he gets them back in stock. I would move the 3785 to my computer then.

Craig

XELB · 9th December 2004, 07:29 AM

Quote:

The bass however is a complete mystery to me. What is there is very tight and controlled sounding, but it is lacking any sense of impact or force. This seems to hold true at whatever volume I listen at. My speakers are very capable of delivering good tight bass, but it is not there now.

Witch capacitors are you using ?

In my opinion and becouse you are using 4 oms speakers maybe you need capacitors with more capacity.

I have a 6 oms speakers and they Rock with a amp of 300VA and 40000nF of capacity.

Regards.

HawkeyeStoob · 9th December 2004, 08:37 PM

I am using the caps that come with the BrianGT kit.

They are "1500 uF 50v Panasonic FC Capacitors"

I know that the boards are set up to accept some different types of caps. I would appreciate any specific suggestions that anyone would have on a different size or type of cap.

Craig

300_baud · 9th December 2004, 09:07 PM

You know what guys? The zobel network actually made things worse for me. With my lm3886, the highs became a little softer (that was to be expected), but the worst thing is that the soundstage collapsed. It's like the amp became mono..

Seriously, only use the zobel if you're having problems with the amp.. otherwise best to leave it out, IMHO. (at least, from my experience)

Take care,
300_baud

300_baud · 9th December 2004, 11:12 PM

Yeah tried a zobel again, but this time i used:
1) 0.47 uf Wima Cap
2) 2x Holco 10 ohm 1/4 watt in parallel (5 ohms as a result)

And the soundstage was okay.. i think the reason why the zobel didn't work for me before was because i was using a generic 1 ohm carbon resistor...

With these settings, the treble has a little more perk. I'd have to listen more for bass.

HawkeyeStoob · 15th December 2004, 07:09 PM

I added the zobel and finished the case this weekend.

One word on the zobel WOW!!! The bass is back.

The only other change that I see in the amp with the addition of the zobel is that the chips now run a little bit hotter. About 138 deg f with the zobel added, before about 120 deg f.

Thanks for everyones input and advice once again.

Here is a quick picture of my finished chasis.

Shoog · 15th December 2004, 07:51 PM

I didn't like the effects of a Zobel, but I only tried 1ohm and 0.22uf. Seemed to kill something in the overall presentation and made things sound harsh.
I respect other peoples positive comments on different values, and someday will try them.

I use a 10ohm resistor with 10turns of enamel wire around it, to little ill effect. My speakers are easy to drive so I can't comment on if this works on hard to drive speakers.

Shoog

9th December 2004, 03:22 AM	#11
x. onasis diyAudio Member Join Date: Jan 2003 Location: NYS	(from the peanut gallery) My limited experience is that the LM3875 just doesn't love 4ohm loads like 8ohm. The bass is where it fails first. I then built the BGT4780 and it was a different story all together, but I was thinking it was just tons more power and that was the difference. This newer kit however, has the Zobel network. Are you guys saying that the Zobel is at least worth a try and perhaps this "voicing of the amp" is a possible next step for the 3875 to be happier with a 4 ohm load? Are the values the same ie, 2.7ohm R and .1uF cap.... and if I might ask, what other values are logical to try? (wish I knew what I was talking about) __________________ onasis

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9th December 2004, 05:50 AM	#12
HawkeyeStoob diyAudio Member Join Date: Oct 2004	Thanks for all of the quick answers. I will give it a try this weekend when I get a little bit more free time, I hope. Thanks for the info on the BGT4780 kit. I would like to give one of those a try once he gets them back in stock. I would move the 3785 to my computer then. Craig

9th December 2004, 08:37 PM	#14
HawkeyeStoob diyAudio Member Join Date: Oct 2004	I am using the caps that come with the BrianGT kit. They are "1500 uF 50v Panasonic FC Capacitors" I know that the boards are set up to accept some different types of caps. I would appreciate any specific suggestions that anyone would have on a different size or type of cap. Craig

9th December 2004, 09:07 PM	#15
300_baud diyAudio Member Join Date: May 2004 Location: Toronto, Canada	You know what guys? The zobel network actually made things worse for me. With my lm3886, the highs became a little softer (that was to be expected), but the worst thing is that the soundstage collapsed. It's like the amp became mono.. Seriously, only use the zobel if you're having problems with the amp.. otherwise best to leave it out, IMHO. (at least, from my experience) Take care, 300_baud

9th December 2004, 11:12 PM	#16
300_baud diyAudio Member Join Date: May 2004 Location: Toronto, Canada	Yeah tried a zobel again, but this time i used: 1) 0.47 uf Wima Cap 2) 2x Holco 10 ohm 1/4 watt in parallel (5 ohms as a result) And the soundstage was okay.. i think the reason why the zobel didn't work for me before was because i was using a generic 1 ohm carbon resistor... With these settings, the treble has a little more perk. I'd have to listen more for bass.

15th December 2004, 07:09 PM	#17
HawkeyeStoob diyAudio Member Join Date: Oct 2004	I added the zobel and finished the case this weekend. One word on the zobel WOW!!! The bass is back. The only other change that I see in the amp with the addition of the zobel is that the chips now run a little bit hotter. About 138 deg f with the zobel added, before about 120 deg f. Thanks for everyones input and advice once again. Here is a quick picture of my finished chasis.

15th December 2004, 07:51 PM	#18
Shoog diyAudio Member Join Date: Aug 2002 Location: Eire	I didn't like the effects of a Zobel, but I only tried 1ohm and 0.22uf. Seemed to kill something in the overall presentation and made things sound harsh. I respect other peoples positive comments on different values, and someday will try them. I use a 10ohm resistor with 10turns of enamel wire around it, to little ill effect. My speakers are easy to drive so I can't comment on if this works on hard to drive speakers. Shoog