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Old 5th February 2008, 11:45 PM   #571
fab is offline fab  Canada
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Default Re: Re: Lme49830

Quote:
Originally posted by jackinnj

The LME49830 data sheet only became available a few weeks ago. I am still waiting for samples. You won't need a driver stage even with the IRF parts.
Quote:
Originally posted by felixx

Indeed.
http://www.national.com/pf/LM/LME49830.html
Thoughts?
On Hafler sch. was 2 pairs of mosfet's.For that topology I think the 49830 do the job easy.But I want to use 4 pairs of 2SK1058/2SJ162.
Considering these do you think there is a MUST for another driver stage?
Thanks Jackinnj and felixx !

Based on the block diagram provided it looks that the driver stage is already part of the chip. 50 ma drive current seems OK for my 3 pairs and even for my 5 pairs mosfet amps!
Slew rate is good also. But I am curious on the topology used (input, VAS, ...) in the chip? Is it diamond buffer for the driver stage?

It means a really simple pcb artwork for the front end of the mosfets then...
Do you plan to use the suggested National pcb artwork?

Thanks
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Old 5th February 2008, 11:57 PM   #572
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Quote:
Originally posted by eyoung
Tom,

Just about all your questions have been answered in previous posts in this thread, my best advice is to go back and read them.
I have printed out some of them for reference. really good reading.

Almost everything good thats a real improvement has been done on the pc19 boards.
Good reading,
Elwood
Elwood,
Thanks for having a look. In fact I have read the previous posts (and there are many). But my specific questions have not been addressed.

re: the Input Z - there was additional components around the input and I did not know if these were also required.

re: rectification - mention was made of tackling this but no specifics were given about the part and wiring (it seemed to be part of a larger mod)

re: inrush limiter - again no specific part was mentioned - I am unfamiliar with these

re: larger PS caps - I did not see any suggested values

Thanks,
-Tom
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Old 6th February 2008, 12:18 AM   #573
fab is offline fab  Canada
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Quote:
Originally posted by WithTarragon


Elwood,
Thanks for having a look. In fact I have read the previous posts (and there are many). But my specific questions have not been addressed.

re: the Input Z - there was additional components around the input and I did not know if these were also required.

re: rectification - mention was made of tackling this but no specifics were given about the part and wiring (it seemed to be part of a larger mod)

re: inrush limiter - again no specific part was mentioned - I am unfamiliar with these

re: larger PS caps - I did not see any suggested values

Thanks,
-Tom
a) Input can be increased easily from 22k to 47k. Just change the corresponding feedback resistor from 22k to 47k too. Since the gain of the amp is determined by the ratio of the 2.2k and the 100 ohms there is no problem.

b) larger PS caps: I use 2 x 30000uf in one DH-200 and also 4 x 14000uf in another DH-200 with no problem. For the latter I use 2 rectification bridges (one for each channel).

c) "BTW, I will be also be adding bypass caps on the input coupling caps and also a bypass cap on the 470uF electrolytic (C5)":
good idea.
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Old 6th February 2008, 12:35 AM   #574
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Tom,

You can up the filter capacitance to around a pair of 26K uF devices but they verge on the chance that switch and bridge rectifier might be damaged. If using such large capacitance you might want to look into soft start circuits.

Yes, you can put a thermistor in series with the incoming AC. Some just hang this device on the left channel thermal switch. Some question the use of a thermistor with an AB class amp as it might limit the dynamics when a lot of current is required. But, the DH-500 amp went to the use of such a device to protect its switch and bridge.

The 22k resistor cannot be changed. It must match the other 22k resistor in the feedback circuit, else a lot of DC offset will occur. There is more to determining input impedance than just on resistor.

Rectification? Rectification of what?
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Old 6th February 2008, 12:37 AM   #575
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Quote:
Originally posted by Dick West
Tom,
...
The 22k resistor cannot be changed. It must match the other 22k resistor in the feedback circuit, else a lot of DC offset will occur. There is more to determining input impedance than just on resistor.

Rectification? Rectification of what?
Dick,

yes it can be changed see my previous post.
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Old 6th February 2008, 12:42 AM   #576
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Fab,

I meant it can't be changed with replacement of just ONE resistor. But, as you also point out, the gain of the amp is also changed.

Cheers....
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Old 6th February 2008, 12:49 AM   #577
eyoung is offline eyoung  United States
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Fab,

What value cap are you bypassing the electrolytics on the driver board with, I have seen the 100uf caps bypassed with .1uf
and I have seen suggestions to make the 100uf caps 220uf since the modern caps take up less space. Whats your take on that???


Elwood
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Old 6th February 2008, 12:50 AM   #578
fab is offline fab  Canada
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Quote:
Originally posted by Dick West
Fab,

I meant it can't be changed with replacement of just ONE resistor. But, as you also point out, the gain of the amp is also changed.

Cheers....
Dick,
For clarification, the gain of the amp is determined MAINLY by the ratio of the 2.2k and the 100 ohms and not the 22k (or 47k) resistor. However, a small amp gain change is due to the divider of input circuit:
22k / (22k + 2.2k) = 91% compared to 47k / (47k + 2.2k) = 95%

Also, the 2.2k is in parallel with the feedback resistor which gives an additional 5% increase if 47k is used instead of 22k.

But, it will cause no harm to the amp.

Thanks
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Old 6th February 2008, 01:00 AM   #579
fab is offline fab  Canada
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Quote:
Originally posted by eyoung
Fab,

What value cap are you bypassing the electrolytics on the driver board with, I have seen the 100uf caps bypassed with .1uf
and I have seen suggestions to make the 100uf caps 220uf since the modern caps take up less space. Whats your take on that???


Elwood

Elwood,

I have no test result to justify that but 0.1 uf bypass is ok in my book for bypass as per almost every other design.

Increasing from 100uf to 200uf may help but it is really the quality of the cap that is making the difference. Since I use a regulated supply for my DH-200 amps, I have not testd the difference between 100uf and 220uf.

Thanks
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Old 6th February 2008, 07:44 AM   #580
felixx is offline felixx  Romania
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Quote:
But I am curious on the topology used (input, VAS, ...) in the chip? Is it diamond buffer for the driver stage?
I don't know...yet..(searching..). about the topology but if I have any news I will post.
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