| HawkeyeStoob |
I have listened for about 60 hours now and my initial listening impressions to the amp have given me somewhat confusing results.
From the first note the midrange has been outstanding. Open, full, and very detailed. The high end started out very thin. Cymbals and similar instruments were muted and did not carry the tones well at all. At about 20 hours that really started to come around. The notes seemed to open up and sustain much better giving the music a natural and lifelike quality. I am confident that this will continue to keep improving with a little more time. 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.
This leads me to my questions. I have read several posts regarding the use of a zobel network and its advantages or disadvantages. A couple of the posts seem to indicate it has a positive effect on bass output of the gainclone amps.
I am curious to hear what others have found to be the results of this addition.
I would also like to hear from anyone who has installed it and then removed it as to what if any effect it made on the sound of the amp.
I am using a LM3875 kit from Brian with an Avel 250VA 18V+18V transformer driving 4 ohm speakers.
Thanks for your thoughts,
Craig |
|
|
| peranders |
If you want to know, just test to use this filter. It's very easy to attach.
I'm also (really!) convinced that in certain combinations this filter along with the inductor, is pretty unnecessary.... but I'm sure that there are combinations where it's needed. |
|
|
| Mr Evil |
| Aside from stability issues, a Zobel network shouldn't affect the sound at all. If the corner frequency is too low then it can roll off the high end a bit, resulting a slight softening of the sound, but it really should have no effect on the bass at all. If it does, then it may point towards some slight instability or other anomalous behaviour. If you can check the output with an oscilloscope it may reveal the problem. |
|
|
| Nuuk |
I put a Zobel on one of my GC's and the bass control was improved. I suspect it will depend on the loudspeaker concerned as much as anything.
Like Peranders says, it couldn't be much easier to try one with only two cheap components per channel and it fitting 'outside' of the main amp circuit! ;) |
|
|
| GRollins |
Somebody--I think it was Bob Carver--made a big demonstration out of this. Took the same amp, and put in different Zobel networks. With every change, the sound changed. Depending on whether you use inductors or capacitors..and their relative values...you will change the sound of the circuit. This is known as voicing the amp. It's part of the "art" of amp design, as opposed to the science part.
Still, it's relatively cheap fun, so have at it.
Just remember that different is not always better.
Grey |
|
|
| Peter Daniel |
| As the Zobel network is in a signal path, both the components type and the values will effect the sonics. Sometimes it may be a change for better, sometimes for worse. |
|
|
| vladimir |
| quote: | Originally posted by Peter Daniel
As the Zobel network is in a signal path, both the components type and the values will effect the sonics. Sometimes it may be a change for better, sometimes for worse. |
Peter,
I am just wondering, when do you speak about signal path - in my opinion all components in gainclone are in the signal path : input parts define differential voltage on +/- input of the LM, so this is something like "controll signal path", and then after we have current flowing from transformer passing thru diodes (or from PSU caps) and thru LM to the speaker). I do not see any component in this circuit which is not a part of the signal path. Or, am I missing something ? |
|
|
| Peter Daniel |
You just confirmed my point, I don't recall mentioning any part that was not in a signal path ;)
I might add that chassis is not in a signal path, yet it still affects the sonics. |
|
|
| hermanv |
The purpose of a Zobel network is threefold.
1. The series inductor(s) that makes the low pass filter for the woofer is suposed to work into a constant load such as 8 Ohms. At high frequencies the series inductance of the voice coil causes the voice coil impedance to rise making the low pass filter less effective. By putting a resistor in series with a capacitor across the voice coil the load impedance of the voice coil on the series inductor can be made nearly constant. This results in low pass filter that works as intended/calculated.
2. The Zobel network can help to maintain a more constant load on the amplifier. Less important than #1 but usually a good idea.
3. The Zobel network will help dampen any unplanned ringing in the crossover networks.
All that being said, the effects are small but real and are more likely to affect behavior of tube amps than transistor especially low power tube amps that don't much like reactive loads.
Few cheap speakers have them, many expensive ones do. |
|
|
| aHobbit |
| quote: | Originally posted by hermanv
The purpose of a Zobel network is threefold.
1. The series inductor(s) that makes the low pass filter for the woofer is suposed to work into a constant load such as 8 Ohms. At high frequencies the series inductance of the voice coil causes the voice coil impedance to rise making the low pass filter less effective. By putting a resistor in series with a capacitor across the voice coil the load impedance of the voice coil on the series inductor can be made nearly constant. This results in low pass filter that works as intended/calculated.
2. The Zobel network can help to maintain a more constant load on the amplifier. Less important than #1 but usually a good idea.
3. The Zobel network will help dampen any unplanned ringing in the crossover networks.
All that being said, the effects are small but real and are more likely to affect behavior of tube amps than transistor especially low power tube amps that don't much like reactive loads.
Few cheap speakers have them, many expensive ones do. |
:D
The zobel is basically for any eventuality (like that of ringing). The problem may not be there at all, and you may not know when or how it is coming. At least, when it comes, something will take charge of it.
The effect of zobel may vary from user to user, due to the fact that we have varying setup/ environment/ circuit layouts etc. |
|
|
| x. onasis |
(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 |
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 |
| 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 |
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 |
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 |
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 |
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 |
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 |
|
|
|
