| Tombson |
| Would this work? Does it need some changes? |
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| janneman |
Would WHAT work?
Jan Didden |
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| audioPT |
Looks Great!
But don't know what ;)
Attach some file or pic :smash: |
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| carlosfm |
| quote: | Originally posted by Tombson
Would this work? Does it need some changes? |
You need some changes.
You need to show us the circuit, because without it, it won't work.:D |
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| Upupa Epops |
| It will be work - it is schematic from application manual and manufacturer isn't any idiot ;) . |
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| audioPT |
Oh yeah!
The old BPA-300 :D
By the way, the new National site product tree design it's just great ;) ;)
A Pic of a VERY CHEAP LM3886 Bridge-Parallell:
and
(with my appologies to BrianGT by using the picture from his server) |
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| carlosfm |
| quote: | Originally posted by Upupa Epops
It will be work - it is schematic from application manual and manufacturer isn't any idiot ;) . |
Wait... that file was not there.:magnify:
Moderation?
Tombson is a new member, maby it's moderation.
Welcome, Tombson.:cool:
That schematic is the BPA200, it should work.:D |
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| MWP |
| quote: | Originally posted by audioPT
A Pic of a VERY CHEAP LM3886 Bridge-Parallell.... |
AFAIK, the Rowland amp isnt bridge/parallel... its 6 * LM3886s paralled per channel. |
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| carlosfm |
| quote: | Originally posted by MWP
AFAIK, the Rowland amp isnt bridge/parallel... its 6 * LM3886s paralled per channel. |
No, that can't be.
Do you mean it has around 50~60 watts RMS at 8 ohms?
I don't think so. |
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| audioPT |
Well, I can't find the photos that illustrate Jeff Rowland as the real Bridge-Parallell application, just like the National PDF file...
I think the amp has about 250W channel... isn't that Carlos? |
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| carlosfm |
I think it has something like around 200~250 wrms at 8 ohms, with lots of current.:D
This thing should double the power at 4 ohms and almost double again at 2 ohms. |
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| Lazyworm |
| quote: | Originally posted by MWP
AFAIK, the Rowland amp isnt bridge/parallel... its 6 * LM3886s paralled per channel. |
That Amp from Rowland (Model12) is indeed bridge parallell, as it is a monoblock you are looking at :)
I have been on my way to clone it for a long time but now finally I think Ill have the time to fix the last things on it .
:) |
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| jkraxi |
| Sorry, I know that is an old post but I have a question for u! Does anybody have a schematic of that (from image) Jeff Rowland's product? PLS!!! |
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| jkraxi |
| By the way! What are those orange lines? |
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| thomasfw |
Dear all,
I can see "Micro Relay" and "Trim Pot" in the photo.
What are they use for ?
Thomas |
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| thomasfw |
Thanks !
Do you know where we can get the chip and PCB(kit) in Hong Kong ?(Good Price)
Wah Fai, Mak's etc
Thomas |
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| transducer |
| quote: | Originally posted by jkraxi
By the way! What are those orange lines? |
I believe that they are the power buss bars. Rowland describes them in one of their reviews or product pages.
I was almost laughing at their "innovative technology" claims. Their marketing guys sure are good.
Ron |
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| thomasfw |
If the trim pot is for off-set, how to connect ?
Thanks !
Thomas |
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| jaudio |
| It go bewteen the + signal input and ground. I connect two of the pin of the trimpot together,that is connect to + signal input and the remaining pin is connected to ground. This is for inverted mode amp. |
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| thomasfw |
| quote: | | It go bewteen the + signal input and ground. I connect two of the pin of the trimpot together,that is connect to + signal input and the remaining pin is connected to ground. This is for inverted mode amp. |
Would You please post the schematic !
Many thanks !
Thomas |
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| jaudio |
| The trimmer value should be the same as feedback resistor in this case 470k. If you cant find a 470k trimmer,500k will do. |
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| thomasfw |
Thank You For Your Post !
Do you think the Rowland M12 is use invert connection
for all LM3886 and use DRV134 at the front ?
Thomas |
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| jaudio |
Your welcome
I dont know about the M12 but if it has the lm3886 and a trimmer more than like it's inverted.
I do know that the concentra is inverted and uses the drv134.
I think M12 uses more lm3886 and is monoblock. |
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| jaudio |
| Here a picture of my ver. |
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| thomasfw |
| quote: | | I do know that the concentra is inverted and uses the drv134. |
Do you know they add "Buffer OP" in front of "DRV134" or after it ?
How do you calculate the feedback R (470k/16k) in your ver. ?
As shown in BPA 200 document, thet are (21.5K/1K).
Thanks !
Thomas |
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| jaudio |
Your welcome
I dont know if concentra uses buffer in front of drv134.
I have the gain 13 on the (+) side and 13 on the (-) that adds up the 26.
The example I post was just an example.
If you use bridged parallel, you must use a lower gain than normal because both side adds up. |
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| thomasfw |
Dear jaudio,
I don't understand why the "trim pot"(R3) value is equal to "Feedback"(RF) ?
because :
R3 should equal to :
R3 = (Rin * RF)/ (Rin + RF)
Best Regards !
Thomas |
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| macboy |
| quote: | Originally posted by thomasfw
Dear jaudio,
I don't understand why the "trim pot"(R3) value is equal to "Feedback"(RF) ?
because :
R3 should equal to :
R3 = (Rin * RF)/ (Rin + RF)
Best Regards !
Thomas |
I can answer that.
Your equation is correct. To minimize the DC offset, you should try to make the resistance to each input pin the same (since the bias currents at each pin are in theory, the same), so:
R3 = (Rin * RF)/ (Rin + RF)
However, note that we are talking about DC offset, and therefore, we must use DC impedances for Rin and Rf, not necessarilly just the resistor values. Note that Rin has a capacitor in series with it, and that changes things. That means that at DC, the impedance (of this R-C network) is infinite (or nearly infinite). Then R3 = ( Rf in parallel with infinity ), which is R3 = Rf.
jaudio also recommends using a trimpot for R3. This is because the bias currents for each input pin are not exactly the same for any given chip. The trimpot lets you adjust the resistance to compensate for variations in bias currents for a particular chip. |
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| thomasfw |
Thank You so much for the detail explanation !!!
One more question :
a)Then how to define the value of "RF" ?
I saw someone use 200K and the BPA200 document use 22K ?
b)Many thing need change if I parall six of LM3886 ?
Thank You For The Sharing !
Thomas:smash: ;) |
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| jaudio |
It depends on the amount of gain,that you want. In inverted mode, an input resistor of 10k and a Rf resistor of 220k will give a gain of 22. So with 1volt in you get 22 out. In bridge mode your get(-22)+(+22)=44. With that amount of
gain get lots of noise. Lower gain would be better.
Just match dc offset with trimmer and match ballast resistors.
I hope this helps |
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| thomasfw |
Thank You For Your Fast Response !
Let me asked in detail :
Rf=200K, Rin=10K, Gain=20
Rf=20k, Rin=1K, Gain also=20
What is the different in between them ?
If I want the total Output=200W,8 ohm (after Paralell & Bridge)
and let the Vin= 1v.
What should I do with the Rf , Rin & Trim Pot ?
Many Thanks !
Thomas
:whazzat: :smash: ;) |
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| thomasfw |
| quote: | | In bridge mode your get(-22)+(+22)=44 |
Dear jaudio, macboy and all,
Please tell me what's wrong with my understanding
By theory, the Output of bridge amp= 4X of single amp
and what is the relationship in between what you said :
Let :total gain =40, Vin=1V, then Vout will be 40V and R=8ohm
Output W=(V*V)/R
= 40*40/8
=200W
Thomas |
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| jaudio |
20k and 1k will have less noise.
You would need a gain of about 24(+24 + -24)
If you plan on making your own preamp,I would incease the preamp gain to 2v output and go with (+12 + -12)
I would go for 4K 48k and 50k trimmer.
If you plan on parallel six use a input resistor with more than 1k resistance. |
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| macboy |
| quote: | Rf=200K, Rin=10K, Gain=20
Rf=20k, Rin=1K, Gain also=20
What is the different in between them ? |
Same gain, but different input impedance.
A 1K input impedance can place too much of a load on say, a CD player line-level output. But note that National's BPA amplifier design has buffered the input with an opamp, which has no difficulty driving a 1K input impedance (in fact, it drives four of them).
If you need a higher input impedance, then you will also need a higher feedback resistor to achieve the same gain . Note that higher resistances create more thermal noise (a.k.a. "resistor noise"). So if you increase it too much, then it will begin to add extra noise into the system, which you can hear as background hiss. (Another way to get high gain, without a high feedback resistance and the noise it makes, is to use a T-network feedback, but that's another thread in itself).
| quote: | By theory, the Output of bridge amp= 4X of single amp
and what is the relationship in between what you said :
Let :total gain =40, Vin=1V, then Vout will be 40V and R=8ohm
Output W=(V*V)/R
= 40*40/8
=200W
|
Correct, that a bridged amp will double the voltage at the speaker terminals, which, by P=V*V/R, gives 4 times the power (P). Note also that the current flowing through each of the amps is also doubled, which is in effect, the same as decreasing the load (speaker) impedance by half. An 8 ohm speaker connected to a bridged amp loads each 'side' of the bridged amp with a 4 ohm load. The National app note describes this and what you need to do about it when designing an amp.
However, your calculation of power above may be wrong. Make sure not to use the peak voltage in your calculations. To calculate RMS power, you must use the RMS voltage, which is (for a sinewave), the peak voltage divided by sqrt(2), or Vrms=Vpeak/1.4142 |
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| macboy |
| quote: | Originally posted by jaudio
...
I would go for 4K 48k and 50k trimmer.
...
|
I'd suggest 3.9K and 47K, which are standard (E24) values.
Also, it wouldn't hurt to use, say, a 43K resistor and a 10K trimmer in series. That would make adjustment a little easier by restricting the adjustment range to 43K - 53K. |
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| thomasfw |
| quote: | | I'd suggest 3.9K and 47K, which are standard (E24) values. |
What is the (E24) ?
| quote: | | 43K resistor and a 10K trimmer in series |
I will take your advise !
| quote: | | National's BPA amplifier design has buffered the input with an opamp, which has no difficulty driving a 1K input impedance (in fact, it drives four of them). |
I plan to use "DRV134" and all LM3886 use "Inverted", what will you think ?
My local time is 2:00 a.m., and I need to go to sleep !
Thomas:bawling: :angel: :angel: |
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| jaudio |
Macboy:
You explain things much better than I.:up: :up: |
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| macboy |
| quote: | What is the (E24) ?
|
Did you ever notice how resistors (and capacitors and inductors) only come in certain values? E24 is a standardized set of values for these components. It defines a set of 24 values per decade. This webpage has a good explaination. Typically, cheap 5% carbon resistors are available in E24 values. More expensive 1% resistors are usually avaiable in E96 values. |
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| jaudio |
Yes I've noticed. Now I know why
I should be more carefully. I pull 4k and 48k out of the air as an example.
Thanks Macboy |
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| thomasfw |
Dear all,
Thank you so much for you help !
Please comment the value of "C" and "RL" !!
(Six LM3886 parallel together)
Thomas:smash: |
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| thomasfw |
Dear all,
Thank you so much for you help !
Please comment the value of "C" and "RL" !!
(Six LM3886 parallel together)
Thomas
:smash: |
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| thomasfw |
Dear Macboy and all,
I found a kit from Tai Wan use another way to adjust the
DC offset.
Please see the attachment !
Thomas
P.S. Regarding to my last post, I plan to use "DRV134".
Is it affect the calculation for the "C" & "RL" ?:smash: |
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| jaudio |
"c"=159155/(4k*10hz)=3.97uf for example
RL depends of the source out impedance. Most amp are bewteen 10k and 100k,these values work pretty good
What is the benefit of adding more parts? |
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| jaudio |
C determines low frequecy cutoff
If you want a cutoff of lets say 20hz and say your input resistor is 4k then 159155/(4k*20).
To ensure that low frequecy is not cutoff above 20hz,you would divide 20hz by 4.
So it will be 159155/(4000*(20/4))=7.9578uf or 8uf |
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| jaudio |
| Thomas is this your first project? |
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| thomasfw |
1st in chip amp, but no for audio.
Buy the way I found that the 3.3uf is very expensive (wima)!!!
I plan to use 12 pcs per channel (6 paralell and then bridge).
Is any alt. way ?
Thomas |
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| jaudio |
| quote: | Originally posted by thomasfw
Dear Macboy and all,
I found a kit from Tai Wan use another way to adjust the
DC offset.
Please see the attachment !
Thomas
|
What was the claimed benefit by using this offset circuit?
Try Ero capacitors |
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| thomasfw |
I don't know about this cap.
In Hong Kong most common is "wima, rel-cap, auricap, Elna etc.,"
Can you give me a link, please !
Thomas |
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| jaudio |
Surplus dealers may here them. I have seen a ero dealer in hong kong. I will search when I get home.
Are you going to use a pcb or use point to point? If you are going point to point then wire each chip amp separtely. If might be a good Idea to wiring at least 20 chips and match 12 as close as possible(match dc offset before adjusting trimmers). Another benefit of wiring separte amp is that you can pull the damaged chipamp module out.
Try to keep it simple. |
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| thomasfw |
Dear Jaudio,
| quote: | | 1st in chip amp, but no for audio. |
Should be "1st time in Chip Amp but not for audio"
I have built many Tube Amp.
By the way, can you tell me how heat (temp) the "Bpa" is when it is full power ?
Thomas |
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| jaudio |
It depends on the size of the heatsink. I have four chips on a 15.5" x 3.5" x 1.75" heatsink. The heatsink gets just alittle warm idle. you will need a larger heatsink,if you use 6 chips. You have built tube amps,so you should have no problem going point to point.
Have you used the 6922 at low voltage? I may need help. |
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| Billy0810 |
Jaudio:
I want to build a BPA200 base on your advices too. (2Paralleled and 2 bridged per channel)Is this schematic OK?(Power supply and the mute resistors are not shown) |
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| jaudio |
Sorry it will not work.
You can not make adjustment on the +signal that way
The lower half has the gain of about 1,so the halve dont match
try this |
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| jaudio |
You can go to www.national.com to get application note AN-1192 look at figure 7.0 page15. Schematic is like yours and you can see your mistakes
Good luck |
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| Billy0810 |
Finally,I understand the mistakes of my schematic,and I`ve given up using this schematic and am planing to build the amp using your schematic,but I have some question about it.Is U1 DRV134?
Do I need to put a buffer before the DRV134?Where do I put the decoupling cap(I am not sure if it is called decoupling cap,I mean the cap to block the DC )?before or after the DRV134?
Thank you very much! |
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| jaudio |
No buffer needed.
The caps go bewteen drv134 output and input resistor of each lm3886. Be sure to match all resistor as close as possible |
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| AR2 |
I have been doing similar concept but it is based on non inverting amp. Here is the schematic that I am using. It is Brians GT amp. I am connecting two of this boards LM4780 paralleled per one side of the bridge. I am not using DRV 134 because I am supplying balanced signal.
My question for jaudio is: on this schematic, where I could put trimpot for DC offset adjustment. Would that be R4 - 22.1 K? I am having hard time putting these boards together paralleled. Any time I try to parallel two boards that have on them 0.1 ohm on each side of the LM4780 chip - they oscillate. Than I started adding extra resistors between boards, and I ended up with 0.5 ohm between. I do not understand why is this happening. Each board because of some reason produces about 150mV DC, but in bridged configuration that gets canceled.
I posted this question in this link, but I never got full understanding of the problem.http://www.diyaudio.com/forums/show...t=&pagenumber=1
post #7 |
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| jaudio |
In inverted mode the input resistor sets impedance. In non-inverted mod impedance is set in the chip, normally it is very high.
Put a trimpot on the (-) signal input and you will get noise.
Here is something Thomasfw posted that might help
I didnt try it,so I dont know if it will work. |
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| jaudio |
AR2
Is that a total of 4 lm4780? |
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| AR2 |
Yes, it is 4 LM4780 per channel. Two and two paralleled in bridged connection.
Thank you |
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| jaudio |
AR2
On the application note,each powersupply rail has a .1uf and a 10uf cap in addition to a 1500uf cap. I dont see the .1 and 10uf caps on the schematic you posted. |
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| AR2 |
| I do have it. The schematic posted is original Brian's schematic, and I didn't modify. I have PS board for each LM board, and each one is snubberized (all together 4 PS boards per channel) I bypassed all caps with .1uF and I have 6300uF per rail per board. |
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| jaudio |
Are there any problem with the .5ohm connected.
Believe Jeff Rowland uses .5ohms or .47ohm. |
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| AR2 |
| No there are no problems, but it is kind of wierd. On the board I have .1ohm on each side on the chip, and between two boards .5ohm. I tried various values but it oscilate on anything below .5ohms. I was expecting that all resistors should be same. |
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| jaudio |
Are all the resistors 1% or .1%?. I didnt bother with the .1ohm output resistors. I used .22ohm.
The only time I got 150mv is when I didnt ground the input properly.
You should email Jackinnj. He has more experience with the lm4780 chip? |
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| thomasfw |
Dear All,
Please see the attachment !
Can I reduce the cost by don't put the "Input Cap" for each LM3886 ?
Thanks !
Thomas |
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| Upupa Epops |
| Don't make it with DRV 134 - it's not quite good sounding circuit :cool: . |
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| jaudio |
| The lm3886 needs a gain of aleast 10. If you want to use a gain of four use the OPA chips (549 or 541). The OPA chips cost 3 times as much as lm3886. You can leave out the input caps,but you might have a problem with dc offset. |
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| macboy |
| quote: | | The lm3886 needs a gain of aleast 10. |
Nice catch. It's no wonder that the amp is oscillating. Do people even bother to read datasheets anymore? |
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| rabstg |
| quote: | Originally posted by Upupa Epops
Don't make it with DRV 134 - it's not quite good sounding circuit :cool: . |
Pavel-
So what do you suggest as a replacement? |
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| mateo88 |
Is it even neccessary to use the DRV134 or a similar chip at the input?
i.e., can you just take two of image 5.2.1 in the AN-1192 datasheet and parallel them? |
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| jaudio |
| quote: | Originally posted by mateo88
i.e., can you just take two of image 5.2.1 in the AN-1192 datasheet and parallel them? |
Two bridged amp in parallel would still require output resistors. Image 7.2.4 would be better. |
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| mateo88 |
| Yes, I know it would still require output resistors. I guess my real question is in figure 7.2.4, why is U5 needed? |
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| jaudio |
| U1 is used to isolate the source from the chips low impedance input. The input without the buffer, would be less than or around 500ohms. Input impedance plays a role in frequecy response. |
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| mateo88 |
Ok, that makes sense. So if I was using a source that could easily handle the 500 ohm impedance, I really wouldn't need u1 at all, correct?
Sorry for the dumb questions, but thanks for answering them for me! :) |
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| jaudio |
| quote: | Originally posted by mateo88
Ok, that makes sense. So if I was using a source that could easily handle the 500 ohm impedance, I really wouldn't need u1 at all, correct?:) |
Yes that's right. Source output impedance should be around 50ohms
| quote: | Originally posted by mateo88
Sorry for the dumb questions, but thanks for answering them for me! :) |
Questions are only dumb,If you have them and dont ask.
Your Welcome |
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| jaudio |
| quote: | Originally posted by AR2
. I have PS board for each LM board, and each one is snubberized (all together 4 PS boards per channel) I bypassed all caps with .1uF and I have 6300uF per rail per board. |
Try using one PS per channel. |
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| AR2 |
| Good suggestion. I was thinking about that. Will try and let you know. |
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| thomasfw |
| quote: | | The lm3886 needs a gain of aleast 10. If you want to use a gain of four use the OPA chips (549 or 541). The OPA chips cost 3 times as much as lm3886. You can leave out the input caps,but you might have a problem with dc offset. |
Hi Jaudio, Macboy and all,
Long time no see and how are you ?
I just received the DRV134 from US, I just finished the PCB layout during the Summer Holiday !
I think you miss understand my draft. The "4X" means use 4 pcs
of LM3886.
Thank You all your valuable advices in this project !!
How about the low voltage 6229, what is the questions ?
Thomas |
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| jaudio |
It is nice to heard from you.
How long will it be , before you have a working amp?
Are you planning to make extra copies of the pcb?
The 6922 buffer project will get put on hold for a 6 weeks. I will Email you in about 5 week with my questions. Thanks |
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| thomasfw |
Dear Jaudio,
Attached the PCB Layout, but I have not checked:smash:
I will try my best to answer your tube project.
By the way, I have just made a tube buffer for my friend.
It connect in between DVD player (Made in China, HKD499) and
a AV amp.
You can't belive how great it is !!!!!!
I plan to do this
Pass Lab Pre-Amp + Tube Buffer+ BPA 200 or
CD player + Tube Buffer + Pass Lab Pre Amp +BPA 200
Thomas |
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| thomasfw |
Dear Jaudio,
Attached the PCB Layout, but I have not checked
I will try my best to answer your tube project.
By the way, I have just made a tube buffer for my friend.
It connect in between DVD player (Made in China, HKD499) and
a AV amp.
You can't belive how great it is !!!!!!
I plan to do this
Pass Lab Pre-Amp + Tube Buffer+ BPA 200 or
CD player + Tube Buffer + Pass Lab Pre Amp +BPA 200
Thomas |
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| thomasfw |
| How to insert a photo ? |
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| thomasfw |
How to insert a photo ?
Thomas |
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| jaudio |
| quote: | Originally posted by thomasfw
Dear Jaudio,
By the way, I have just made a tube buffer for my friend.
It connect in between DVD player (Made in China, HKD499) and
a AV amp.
You can't belive how great it is !!!!!!
Thomas |
Ok I cant resist. Can you Email the schematics to me?
Thanks |
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| thomasfw |
Dear Jaudio,
How can I get your e-mail ?
Thomas |
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| jaudio |
| In the upper left hand column of each post there is an authors name: click the name |
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| jkraxi |
please help me. I desperately need a schematic of JR model 12-concentra.
pls.mail me at jkraxi@yahoo.com
thx, JAY |
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| Mrpong |
| quote: | Originally posted by jaudio
No buffer needed.
The caps go bewteen drv134 output and input resistor of each lm3886. Be sure to match all resistor as close as possible |
Hi JAUDIO,
For the circuit you shown in #62, can I replace the 10uf cap with 1uf? I think the purpose of 10uf is to block DC. Correct? |
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| jaudio |
HI
That cap also act as part of a high pass filter. If you use a 1uf cap with the same resistor value then the cutoff frequency will be
159155/(R*frequency)=C(Capacitor value)
for a 20hz cutoff frequency,you should divend by 4.
5Hz would be your target |
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| Mrpong |
| quote: | Originally posted by jaudio
HI
That cap also act as part of a high pass filter. If you use a 1uf cap with the same resistor value then the cutoff frequency will be
159155/(R*frequency)=C(Capacitor value)
for a 20hz cutoff frequency,you should divend by 4.
5Hz would be your target |
Thank a lot JAUDIO, I think I may misunderstand something
With R=3900, C=1uF, this equation would give
the cutoff freq = 159155/(3900x0.000001) Hz???????? |
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| jaudio |
Hello
For a 1uf cap and a resistor value of 3.9k, the cutoff frequency is 40Hz, which is much too high.
Let say you want a cutoff frequency of 15hz
1. 15Hz/4=3.75Hz
2. 159155/(3900*3.75)=11.3uf
R is the resistor on the inverted input
Remember,I used 3.9k on the schematic
for an example,your value may be different. |
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| Mrpong |
| According to this original BPA200 schematic, I think we can use trimpots at the + input PINs of U3 and U4. However how can we use trimpot at U1 and U2? |
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| jaudio |
| quote: | Originally posted by Mrpong
According to this original BPA200 schematic, I think we can use trimpots at the + input PINs of U3 and U4. However how can we use trimpot at U1 and U2? |
Add trimpots the U1 and U2 wont work, the impedance in the chip is too high.
In the schematic, I posted all the chips are in the inverted mode.
If you use the original BPA200 schematic, you won’t be able to adjust the dc offset. There are a few things you can do to minimize the offset
Increase the output resistor value to .3 to.5 ohms
Use chips with similar dc offset (You will have to buy more chips to match them)
servo s
You should use the original Bpa200 schematic or the schematic I posted. I don’t think the schematics can be mixed together |
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