I have replaced the 1000uF power decoupling Caps with 2x470uF in parallel today and they do have a difference.
Hard to tell which is better, the sound is more energetic with parallel Caps (good for pop rock), a bit laid back with single Cap....
how about other combinations, like 3x330uF or even 4 to 5x220uF....
will try soon.
cheers.
Hard to tell which is better, the sound is more energetic with parallel Caps (good for pop rock), a bit laid back with single Cap....
how about other combinations, like 3x330uF or even 4 to 5x220uF....
will try soon.
cheers.
That's interesting mdlover. I'm sure some of the speed and delicacy of the GC's is down to the small amount of capacitance used and perhaps using even smaller caps paralleled gives more of the same!
The GC world awaits the results of your further experiments with bated breath and smoking soldering irons
The GC world awaits the results of your further experiments with bated breath and smoking soldering irons
Nuuk said:
I think (correct me if I'm wrong) that Peter tested with BGs.
They are different animals.
Anyway, I always bypass the 1000uf caps with 0.1uf and that gives lower PSU impedance at high frequencies.
In these case, I may not notice any difference in using two 470uf caps.
Or the difference would be subtle.
(gotta jump in sometime.....)
I have been trying to do some Spice on the GC power supply and have noticed that at high current levels (= 2 Amps) the electrolytic is recieving very large ( > 10 Amps) charging pulses. For a Panasonic FC type cap this is way over its limit of RMS ripple current - 2.5 amps.
IMHO, it seems the use of two smaller caps would make this less of a problem.
I have been trying to do some Spice on the GC power supply and have noticed that at high current levels (= 2 Amps) the electrolytic is recieving very large ( > 10 Amps) charging pulses. For a Panasonic FC type cap this is way over its limit of RMS ripple current - 2.5 amps.
IMHO, it seems the use of two smaller caps would make this less of a problem.
Hey~! I guess that means the ESR is lowered when you parellel caps right?? any one tried low ESR caps?? How does it sound...I'm waiting for the chip samples to come...then I will be ready to wack a**(self-censoring)...what kind of rectifiers will you guys recommend...other than standard bridge rectifiers...should be easily available as well...RS Components or Farnell will work for me...will 25V DUAL separate secondaries work well for the LM3875 in this instance?? Just need some ideas...and it's pretty hefty at 4.45A EACH...meaning I can get +-35V at at least 4 Amps?? I got the potted toiodal transformer from RS last time and it has been lying there for a long time...just tested it today and it seems to work well...so any comments and suggestions?? I will probably use the wiring diagram from here
http://www.decdun.fsnet.co.uk/gaincloneFAQ.html
I was wondering if I need to put a .22 Ohm resistor on the amp's output (pin 3) to the speaker...and do I have to add a decopling cap (0.1uF or 1uF) from pin 1 to pin 4?? If so what value would you guys recommend?? Thanks in advance.
http://www.decdun.fsnet.co.uk/gaincloneFAQ.html
I was wondering if I need to put a .22 Ohm resistor on the amp's output (pin 3) to the speaker...and do I have to add a decopling cap (0.1uF or 1uF) from pin 1 to pin 4?? If so what value would you guys recommend?? Thanks in advance.
still setting up the Lab Carlos!!..LOL....I did find a new toroid for my GC from a local company called ILP in Toronto....its a dual 18 volt 3.33Amp (416-667-9914) for you TO guys....I dont know how it will compare to a plitron but when I did buy it the price was right.
I dont go to my fabrication shop often as it is 2 hours away so when I get the time to build a chassis I will....all you guys have me hooked building this now...I am going to be using a Dallas 6 channel 1806 digital pot IC for input gain to put a twist on things as I dont just want to copy all you guys.....the more I unpack the more goodies I find for this project so this should be interesting
Cheers!!The DIRT®
I dont go to my fabrication shop often as it is 2 hours away so when I get the time to build a chassis I will....all you guys have me hooked building this now...I am going to be using a Dallas 6 channel 1806 digital pot IC for input gain to put a twist on things as I dont just want to copy all you guys.....the more I unpack the more goodies I find for this project so this should be interesting
Cheers!!The DIRT®
mikelm said:
Indeed, the original post said "2.5A RMS ripple". The 10 Amp pulses will remain below the RMS spec, but it should also be less than the PEAK value. Unless you are happy with a very short cap life, make sure the ripple and peak current specs are OK.
Also, note that if you increase the capacitance, the pulse current will also increase. That is one of the reasons that if you use very large capacitances in power supplies like 50.000 or 100.000 uF, you need a large xformer just to keep up with the caps. It then seems that a smaller xformer ruins the sound, but in fact it is the excessive capacitance, and to neutralize that you need to buy a more expensive xformer....
Jan Didden
JOE DIRT® said:
I don't know whow much you guys pay for your Plitrons or other transformers, but as I can't find decent ones in the market here, I always order them to a factory here in Portugal, as my specifications.
Two examples: my 2x24V/8A toroid, for my LM3875-based GC cost me 45 Euros (including P&P).
I ordered another one for my father (for a LM3886-based GC), and this beasty 2x22v 12A toroid (528VA!
) cost him 55 Euros (including P&P).And they are very well built.
They even send the fixing disc and a screw.
And I can order anything I whant, they make it and send it in one week.
JOE, I think 3.33A is a little weak, but if it was really cheap...
One of those per channel is OK.
Hi Carlos,
I susbscribe to the 'you can have too much VA' school of thought having read a good article by Hugh Dean (AKSA). However, I'm not sure what 'too much' may be for a GC as it seems to break many of the rules of amplifier building.
My GC's are currently running on 80VA per channel and sound great. They also sound great with a single supply of 120VA! And I know of somebody building GCs with just 50VA per channel!
Just a thought!
I susbscribe to the 'you can have too much VA' school of thought having read a good article by Hugh Dean (AKSA). However, I'm not sure what 'too much' may be for a GC as it seems to break many of the rules of amplifier building.
My GC's are currently running on 80VA per channel and sound great. They also sound great with a single supply of 120VA! And I know of somebody building GCs with just 50VA per channel!
Just a thought!
Nuuk said:Hi Carlos,
I susbscribe to the 'you can have too much VA' school of thought having read a good article by Hugh Dean (AKSA). However, I'm not sure what 'too much' may be for a GC as it seems to break many of the rules of amplifier building.
My GC's are currently running on 80VA per channel and sound great. They also sound great with a single supply of 120VA! And I know of somebody building GCs with just 50VA per channel!
Just a thought!
Well, one thing is to use one transformer you already have, or found in your neighbour's trash can.
Other thing is to go and buy one transformer if you need one.
I asked that factory for a quote on two tranformers before I ordered mine:
1 - 2x24V/6A
2 - 2x24V/8A
Do you know what was the difference in price between the 6A and the 8A toroids?
3 Euros.
I ordered the 8A one.
I'm not saying you need all this current.
For me it was a question of peace of mind and price-performance ratio.
As you see, It wouldn't be much cheaper ordering a smaller transformer, it really had to be much smaller.
I always felt that the most important thing in an audio device is a good PSU, and more specifically a good transformer.
Most brands always cut on the transformers to reduce production prices, and then put some more capacitance.
Completely wrong.
As I'm doing the things myself, I like to give good food to my amps.
These chips work great with 1000uf capacitance, but please don't use too small transformers.
Connect that to 4ohm speakers and take the volume up and you'll have a huge voltage drop.
Not for me.
I'm talking power amps.
In preamps I use any small transformer that has the voltage I need.
Quote from Hugh Dean on the Printed Electronics FAQ page
"We haven't ourselves trialled the Plitron; in Australia we have our own manufacturers, and a lot of imported toroidals as well. Actually, the larger toroids are not quite as good as the smaller, 160VA (or thereabouts). The power supply considerations are essentially conflicting; you want a transformer with good regulation, so the voltage sag on heavy signals will be quickly restored. This means a larger transformer, like a 300VA. However, many of the current demands are rather transient, very quick; so the inductance of the primary and secondary is important, since it prevents current flowing rapidly. A smaller transformer might have worse regulation, but this is essentially a constant current parameter; the transient voltage regulation is arguably something better. We are using 160VA transformers with amorphous cores, and they perform outrageously well. The bass and image depth is really so much more remarkable than ONE 300VA quality toroid. I am inclined to think the best sound doesn't really matter too much in terms of transformer; what is important is the fact that the supplies are separate. The filter capacitors do make a difference, but the onboard, PCB capacitors make a difference too, and you'd probably be better playing with them; (they are much cheaper than altering the main filter capacitors)."
So maybe the answer lies somewhere in between our solutions, ie use two smaller transformers instead of one but go for 160VA, not 80! Now if only I was wealthy!
"We haven't ourselves trialled the Plitron; in Australia we have our own manufacturers, and a lot of imported toroidals as well. Actually, the larger toroids are not quite as good as the smaller, 160VA (or thereabouts). The power supply considerations are essentially conflicting; you want a transformer with good regulation, so the voltage sag on heavy signals will be quickly restored. This means a larger transformer, like a 300VA. However, many of the current demands are rather transient, very quick; so the inductance of the primary and secondary is important, since it prevents current flowing rapidly. A smaller transformer might have worse regulation, but this is essentially a constant current parameter; the transient voltage regulation is arguably something better. We are using 160VA transformers with amorphous cores, and they perform outrageously well. The bass and image depth is really so much more remarkable than ONE 300VA quality toroid. I am inclined to think the best sound doesn't really matter too much in terms of transformer; what is important is the fact that the supplies are separate. The filter capacitors do make a difference, but the onboard, PCB capacitors make a difference too, and you'd probably be better playing with them; (they are much cheaper than altering the main filter capacitors)."
So maybe the answer lies somewhere in between our solutions, ie use two smaller transformers instead of one but go for 160VA, not 80! Now if only I was wealthy!
Nuuk,
Their conclusions were basically that two smaller transformers are better than one bigger transformer.
This is nothing new.
My toroid is 384VA.
I would be better with two 180~200VA toroids, but that would be more expensive.
One toroid for each channel improves soundstage.
Two 160VA toroids for a stereo GC seams to me right on the mark.
Their conclusions were basically that two smaller transformers are better than one bigger transformer.
This is nothing new.
My toroid is 384VA.
I would be better with two 180~200VA toroids, but that would be more expensive.
One toroid for each channel improves soundstage.
Two 160VA toroids for a stereo GC seams to me right on the mark.
Hi Carlos. Yes that's what I would call the optimum transformer specification for the GCs. Now if only all international debates could be concluded so gracefully
I just priced up the cost of 2 x 160VA against one 300VA from Maplins and the extra cost is 10UKP. Is that too much to pay for a bigger soundstage?
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