DaveM said:
F4 is 0dB voltage gain power amp. So, single stereo (F4) or two mono blocks (F4/F4) are equally requiring the same voltage gain from the pre for your purpose. There will be, however, the most benefit with the two mono blocks, which will be the increased total output current capacity for the low impedance speakers . . .
I think John will answer your question about the voltage gain of his amp.
Babowana said:
F4 is 0dB voltage gain power amp. So, single stereo (F4) or two mono blocks (F4/F4) are equally requiring the same voltage gain from the pre for your purpose. There will be, however, the most benefit with the two mono blocks, which will be the increased total output current capacity for the low impedance speakers . . .
I think John will answer your question about the voltage gain of his amp.
Perhaps I'm all wet, but I'm under the impression (misguided?) that the choke load doubles the efficiency of the gain stage. I just assumed that this also doubles the voltage swing as well. It seems to play considerably louder than with a source resistor.
With 110db horns, there's no problem with gain. At present, the F4-dual jfetBOZ combo is delivering the same volume level as my ZV7-T, and uses the same volume setting from the X-over--which ain't much compared to the rest of the system's amplifiers.
Horns are set at level 3, while the rest of the system is demanding level 9 from a 10 level dial.
I'm certainly going to use dual F4s on the midbass.
I guess that means it will be up to me to determine if it will be enough. The only way I know is to build one. Hmmm... I will do a little inventory tonight and see what I am missing. I know I will need another pot at minimum.
I have been postponing doing a
because I love the simplicity of the J-BOZ. I have also been waiting to see what Sy's tube pre looks like. With the number of parts in the signal path, it is kind of hard for such a simple circuit not to sound good.
So carpenter, you are using this as a simple gain stage between a receiver pre-out and your F4? You should try taking that receiver out of the look and see if you are losing anything in there.
I have been postponing doing a
because I love the simplicity of the J-BOZ. I have also been waiting to see what Sy's tube pre looks like. With the number of parts in the signal path, it is kind of hard for such a simple circuit not to sound good.So carpenter, you are using this as a simple gain stage between a receiver pre-out and your F4? You should try taking that receiver out of the look and see if you are losing anything in there.
DaveM said:
I have been postponing doing a
So carpenter, you are using this as a simple gain stage between a receiver pre-out and your F4? You should try taking that receiver out of the look and see if you are losing anything in there.
I, too, enjoy the simplicity of the JfetBOZ. It's the perfect learning tool to experiment with--not to mention, Nelson has given us a boat-load of examples. I learn far more with the hands-on approach than I could ever learn from a text alone.
My reason for using the receiver is to capitalize on the Dolby 5.1, and DTS features. I love movies, especially musicals!😀
When I build the Chang horns (8" full range Pioneer, single-driver, with a tiny-tiny tweeter) I'll use the pumpkin with a pair of dual F4s per channel. The JfetBOZ will not be necessary in that project.
For now, though, it's full steam ahead with the current project.
carpenter said:
Yes, Carpenter, you get a magical twice the swing in voltage than you started with... Amazing this choke load stuff. 😀
The gain however is a function of the Load R or Xl of the choke. At low currents it's easier to use huge chokes like 10-20H. Absolutely huge effective AC load R! Like a current source!
😀
flg said:
OMG! Did I read you correctly? I can purchase huge H chokes for peanuts as long as I can put up with higher resistance. I didn't realize that this extra resistance could be an asset. I thought the R had to be as low as possible. Hot damn........😀
carpenter said:
I hope you were thinking about drain R, not source R.
Yes, the choke efficiently stores the energy into the B-field.
By the way, the load impedance = (R^2+XL^2)^0.5,
where the XL values are variable for the different frequencies.
Therefore, I think that the internal R needs to be relatively
greater than XL for the even value of the load impedance as you
do not have negative feedback loop.
Just my small thinking as a hobbyist . . .
Babowana said:
I hope you were thinking about drain R, not source R.
Yes, the choke efficiently stores the energy into the B-field.
By the way, the load impedance = (R^2+XL^2)^0.5,
where the XL values are variable for the different frequencies.
Therefore, I think that the internal R needs to be relatively
greater than XL for the even value of the load impedance as you
do not have negative feedback loop.
Just my small thinking as a hobbyist . . .
Yes, you're correct, I meant "drain" resistor. I, sometimes, get my left and right backwards, too.
Please explain more of your thoughts. They're interesting. Perhaps I should consider a bit of negative feedback?
I was refering to R as a Drain load resistor. Or, a choke replacing it! Of coarse DCR of a choke fits in somewhere too. 😉
The gain is dependant on the Drain R, or the Xl of the choke. It is very difficult to come up with a big enough Xl (mostly inductor value), with the DC current capability, to drive a speaker load. However, in this case, where the Drain load (Xl) can be higher, and current can be lower, we can play L Loading games like tubies do.
You can easily find chokes with 10H or higher L ( maybe 100 ohms DCR) that would make a very high impeadance load. Like one might do in a tube circuit 😱
Carpenter, You can possibly have much higher Xl with your Drain inductor as the load, than the original 2.2K drain R. More Gain! And because there is a choke in there, the voltage swing will be doubled
A little F.B. 😕
A little SuSy 😕
😀
The gain is dependant on the Drain R, or the Xl of the choke. It is very difficult to come up with a big enough Xl (mostly inductor value), with the DC current capability, to drive a speaker load. However, in this case, where the Drain load (Xl) can be higher, and current can be lower, we can play L Loading games like tubies do.
You can easily find chokes with 10H or higher L ( maybe 100 ohms DCR) that would make a very high impeadance load. Like one might do in a tube circuit 😱
Carpenter, You can possibly have much higher Xl with your Drain inductor as the load, than the original 2.2K drain R. More Gain! And because there is a choke in there, the voltage swing will be doubled
A little F.B. 😕
A little SuSy 😕
😀
carpenter said:
I hope not, but you might have weak bass due to the L load.
Then, I think that it would be better using R load instead.
If your feeling is ok with bass sound, the feedback might be
considerable. But, first we need to know the open loop gain.
If you have a scope and signal generator, you could measure
the open loop voltage gains at certain frequency interval.
Babowana said:
I hope not, but you might have weak bass due to the L load.
Then, I think that it would be better using R load instead.
If your feeling is ok with bass sound, the feedback might be
considerable. But, first we need to know the open loop gain.
If you have a scope and signal generator, you could measure
the open loop voltage gains at certain frequency interval.
feedback , but just via source degeneration........
Zen Mod said:
Yeah . . . increasing source degeneration might be effective
regarding the stability of the amp.
But, if we want to seek flat frequency band with the L load,
the feedback loop might provide us with real effect.
I'm estimating so . . .
Babowana said:
Yeah . . . increasing source degeneration might be effective
regarding the stability of the amp.
But, if we want to seek flat frequency band with the L load,
the feedback loop might provide us with real effect.
I'm estimating so . . .
Lots of great ideas. Thanks guys.
I think I've allowed the necessary resistors for source degeneration. I did notice that Nelson doesn't use much resistance on the source pin. At least it's there on the pcb to experiment with.
I'll be looking for larger H chokes. Surplus Sales of Nebraska has a ton of light duty chokes--inexpensive and lots of fun!
Hi,
I've tried my Jfet Boz (original one) and replaced the 2.2 drain resistor with a choke. (ok, a 220 v primary of a 50 w transformer)
I got more voltage at the output, but did not like the sound, even at lower volumes. It was somehow more shrill, and had some metallic egde to the sound that resistor loaded somehow smoothed out. Perhaps the inductor was just more revealing.
Nevertheless, I wouldn't seriously consider Jfet boz as a preamp if you have 0 voltage gain amp (I've used an OTA). It distorts. On the other hand, if you've got a power amp with at least 10 db voltage gain, a Jfet BoZ could sound sweet ;-)
Vix
I've tried my Jfet Boz (original one) and replaced the 2.2 drain resistor with a choke. (ok, a 220 v primary of a 50 w transformer)
I got more voltage at the output, but did not like the sound, even at lower volumes. It was somehow more shrill, and had some metallic egde to the sound that resistor loaded somehow smoothed out. Perhaps the inductor was just more revealing.
Babowana said:
Yeah . . . then we could build a nice Class A int. amp in one box,
couldn't we . . . ?
Nevertheless, I wouldn't seriously consider Jfet boz as a preamp if you have 0 voltage gain amp (I've used an OTA). It distorts. On the other hand, if you've got a power amp with at least 10 db voltage gain, a Jfet BoZ could sound sweet ;-)
Vix
It sounds great with my 1000 watt plitron.😀 Unfortunately, I'm deaf on the very top end, so shrill to you may be "just-right" to me.😉
carpenter said:
Yeah . . .
That’s why different sounds work different ways to different people.
😀
You will find that circuit works amazingly well when coupled with your receiver. Some benifits you might not have been looking for -- it works very well to cut down on ground noise and hum you might get driving your amp with your receiver. At least, it does in my system--I used the same basic circuit to eliminate hum from my pro sound subwoofer amp.
Any defiencies in the sound of your receiver will pass right through this circuit -- I found it to be nicely transparent.
JJ
jupiterjune said:
If you're talking about the circuit I've presented, then I'm in complete agreement with you. It seems to do everything just the way I like.🙂