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 Chip Amps Amplifiers based on integrated circuits

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 13th February 2003, 07:10 AM #691 JDeV   diyAudio Member   Join Date: Oct 2002 Location: Hemel Hempstead Thanx for the effort Dave I measured the output yesterday by connecting a fat 8ohm resistor and applying a 200Hz sine wave. It started to clip at 10.6v Trms. Now if I calculate correct: Pout=V²/R =10.6² -------- 8 =14 Watt What do I miss?
 13th February 2003, 07:38 AM #692 2002tii   diyAudio Member   Join Date: Apr 2002 Location: Norway Peter D. has mentioned that his 18V supply sounds better than his 24V. Can the reason be that the chip is "linear" up to around +/-28V dc, so when you (like I do) use 24V trafo`s the output power in 4 and 6ohms decrease. By the graph it looks like my GC (running +/-36V dc) puts out around 60W in 8ohm, 12W in 6ohm and <10W in 4ohhm... It looks like the chip behaves more like an ordinary amp. as long as the voltage is below +/-28V dc. Just a tought.... __________________ Regards Dan M.
Steve Eddy
diyAudio Member

Join Date: Sep 2002
Location: Sacramento, CA
Quote:
 Originally posted by JDeV Thanx for the effort Dave I measured the output yesterday by connecting a fat 8ohm resistor and applying a 200Hz sine wave. It started to clip at 10.6v Trms. Now if I calculate correct: Pout=V²/R =10.6² -------- 8 =14 Watt What do I miss?

The 22 volts you mentioned previously that you measured on the rails, was that the unloaded voltage? And are you using just 1,000 uF of filter capacitance?

Be aware that under load your transformer's voltage will be less than the unloaded voltage. What's the regulation figure for the transformer you're using? Also, if you're using just 1,000 uF of filter capacitance that those caps are going to be drawn down quite a bit between refresh cycles so your average power supply voltage will be less as well. Both instances mean that your amp will start to clip sooner compared to what you would expect basing your expectations on the unloaded rail voltages.

se

JDeV
diyAudio Member

Join Date: Oct 2002
Quote:
 Originally posted by Steve Eddy Your math's fine. The 22 volts you mentioned previously that you measured on the rails, was that the unloaded voltage? And are you using just 1,000 uF of filter capacitance? se

Indeed, 22V on rails while unloaded and only 1,000uF. I plan to fit a pair of 10,000uF and also some other PSU improvements once current setup burnt in, to be able to do reasonable comparison between "before" and "after."

planet10
frugal-phile(tm)
diyAudio Moderator

Join Date: Oct 2001
Location: Victoria, BC, NA, Sol III
Quote:
 Originally posted by 2002tii Peter D. has mentioned that his 18V supply sounds better than his 24V. .... Can the reason be that the chip is "linear" up to around +/-28V dc, so when you (like I do) use 24V trafo`s the output power in 4 and 6ohms decrease.
This is what my recommendation of 18-0-18 trafos is based on.

dave

planet10/whose chips are still in their anti-static bags
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Peter Daniel
diyAudio Member

Join Date: Jul 2002
Quote:
 Originally posted by 2002tii Peter D. has mentioned that his 18V supply sounds better than his 24V.
I did not say it sounds better with lower voltage. I said it produces more bass. Depending on the rest of the system, it may change the tonal balance and be actually something unwanted. The person who is using my first gainclone, said that he prefers the sound of the higher voltage supply, which is using Plitron 400VA , 22-0-22 V transformer. This transformer is so powerfull that I actually see 24 V all the time because of regulation factor, which doesn't apply here.
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coffin
diyAudio Member

Join Date: Oct 2002
Location: Taiwan
Hi,
There's a paralell version schma.
Check this
http://www.fortunecity.com/underworl.../lm3875x4d.jpg
cheers

Coffin
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 16th February 2003, 08:05 PM #698 Mats J   diyAudio Member   Join Date: Aug 2002 Location: Seattle If you take four(4) inverted GC's, parallel pairs (so you then have two amps), remove the pots and feed each parallel pair with a phase from a Jensen Transformer model JT-10KB-D. Would that work as kind of a BPA-200/High power GC?
Steve Eddy
diyAudio Member

Join Date: Sep 2002
Location: Sacramento, CA
Quote:
 Originally posted by Mats J If you take four(4) inverted GC's, parallel pairs (so you then have two amps), remove the pots and feed each parallel pair with a phase from a Jensen Transformer model JT-10KB-D. Would that work as kind of a BPA-200/High power GC?
Basically, yes. But why use a 4:1 stepdown transformer? Just use an 11P-1. You'll need to use a pair of 5k resistors in series across the output taking your ground reference from the node between the two resistors.

se

 18th February 2003, 08:40 PM #700 2Bak   diyAudio Member   Join Date: Apr 2002 Peter Daniel, what kind of power plugs do you use here? http://www.diyaudio.com/forums/showt...281#post104281 Would it not be good idea to use XLR's for power?

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