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Jsixis
diyAudio Member

Join Date: Feb 2011
Location: Columbus Ohio
Quote:
 Originally Posted by nigel pearson Celsius and Fahrenheit . 16 C = 61 F 28 C = 82 F To a good approximation . 451F = burning point of paper ( it is said ) . 16 to 28 C is a typical British summer .
I'm not good at Celsius, here in the states it is ignored except for scientists.
So I guess I am hoping on a 10 degree C day

 26th March 2013, 09:58 AM #22 nigel pearson   diyAudio Member   Join Date: Mar 2007 Location: Oxfordshire In the UK we mix up metric and imperial for very practical reasons . I am not a mechanical engineer but have work around it for years . We buy aluminum is lets say 2 x 1 x 1/4 inch L section 4 meters long . Nearly all the guys I work with are comfortable using inches ( 50 to 70 years old ) , we conceptualize them better . However to mix up standards is common . For example I will say could I have a 6 mm shaft with 1/1000 " running clearance . A Rizla cigarette paper is 1/2000 " . 2 x 1 x 1/4 is US/Canada sourced and is cheaper . 4 metres is a standard length for shipping . 1/4 = 6.35 1 = 25.4 . When given a cosmetic finish we have 6 x 25 mm . I came up with a very simple formula for my boss who hates maths . ( 22/28) x ( d x d ) is the diameter to area formula ( he needed to know 4 mm square ) . That comes from Pi = 22/7 rather than 3.1415927 . The attraction of inches is the use of fractions . A turntable centre spindle is 9/32 inch ( 7.144 mm ) . The real spindle is usually about 7.1 mm to allow for shrinkage after pressing . I would be very interested in the bridged version of TDA 2050 . Another idea I have yet to try is a class A for TDA2030/40/50 . If an op amp is forced to conduct to usually the negative rail we consider it to be working in class A ( typically below 5 mA ) . If we set up a constant current source we could try pushing the TDA 2050 into class A , after all TDA 2050 is just a high current op amp . A TIP2955 , 2 x 1N4007 ( I always use the 1000 V version ) . 1R 3 W emitter = about 1.3 A , 220 R 3 W for the bias . I suppose a constant current sink would be OK as that resembles a typical 1970's NPN class A stage ( TIP 3055 ) . If the TDA 2050 chip can stand the strain is another question . Some will question a slow transistor . In class A it is less important and sometimes works best . The power supply would have to be beefed up . If the CCS could be signal activated is another question . If so the standing current could be reduced . Replace the 220 R with a cheap MOSFET Perhaps ? The FET wll be faster than the TDA2050 or TIP 2955 . If so the current should be always available ahead of what the amp can do . This is not class AB so not so critical .
diyAudio Member

Join Date: Jul 2012
Location: Montreal
Quote:
 Originally Posted by nigel pearson In the UK we mix up metric and imperial for very practical reasons . I am not a mechanical engineer but have work around it for years . We buy aluminum is lets say 2 x 1 x 1/4 inch L section 4 meters long . Nearly all the guys I work with are comfortable using inches ( 50 to 70 years old ) , we conceptualize them better . However to mix up standards is common . For example I will say could I have a 6 mm shaft with 1/1000 " running clearance . A Rizla cigarette paper is 1/2000 " . 2 x 1 x 1/4 is US/Canada sourced and is cheaper . 4 metres is a standard length for shipping . 1/4 = 6.35 1 = 25.4 . When given a cosmetic finish we have 6 x 25 mm . I came up with a very simple formula for my boss who hates maths . ( 22/28) x ( d x d ) is the diameter to area formula ( he needed to know 4 mm square ) . That comes from Pi = 22/7 rather than 3.1415927 . The attraction of inches is the use of fractions . A turntable centre spindle is 9/32 inch ( 7.144 mm ) . The real spindle is usually about 7.1 mm to allow for shrinkage after pressing.
Things designed in metric are easy, it is when you convert imperial to metric is when it becomes difficult, the dimensions all become "odd ball".

 26th March 2013, 01:48 PM #24 nigel pearson   diyAudio Member   Join Date: Mar 2007 Location: Oxfordshire As said engineers are forced to use both . Whether urban myth or not I am not sure ; it is said a space probe was lost on Mars because someone was thinking inches when others metres . It rammed the planet at speed . Also an aircraft was wrongly fueled when converting to metric for buying jet fuel . Just to make it more complex our gallons are different to US . We have Stones for weight ( 14 = 1Lbs ) . I am OK with Stones or Kilo's . I am baffled when someone says they are 200 lbs . I always remember the old BTU of , to raise one pound of water through one degree Fahrenheit = 1BTU . Also SHC( water ) of 4.183 j/g degree K . Our old money was 12 Pennies one Shilling . 20 shillings one Pound ( with Groats , Guineas and double Florins thrown in for good measure ) . It kept you sharp thinking about it . I miss it and found divisions of 12 very easy . We had 1/8 pounds called Two and Sixpence pieces , the double versions called Crowns . At college we were always told keep it in fractions if we can . Pocket calculators were rare then . I still keep things in fractions when possible . Younger people will have no concept of this . We were marked down for using answers unlikely to be seen in real life examples when doing calculations . 22/7 was Pi . Inch system often is expressed in fractions . British engineers think nothing of using which ever system works best . Typical conversation would be . 6 mm looks OK for that . OK I will start with 1/4 inch stock , grind , polish , harden it . It is obvious that the metric system is marginally preferable . I hate technical drawings in inches , I nearly always convert them . Many will not realize that the ancient BA ( British Association ) thread was based on metric . It is not the same as modern metric threads . Older engineers take a dim view of young ones who can not think in inches . It can even lead to being charged more !!! I would guess Indian engineers equally use to having both systems in use ? Some people buy toys to mind-train . Engineers don't need them .
 26th March 2013, 02:28 PM #25 radiosmuck   diyAudio Member     Join Date: Jul 2012 Location: Montreal I'm orignally from the UK. In South Africa during the early 70's, a British electronics company I worked for decided to go metric. They then picked an "M" day, that is a day when all the imperial drawings and specs would be replaced with metric equivalents, it was planned like a military operation. Like most military operations it was not thought through that well, the machineshop still had imperial leadscrews and dials, no cnc back then. All the machinist had to convert their new drawings back to imperial, no calculators back then either. I seem to remember we went back to imperial after a few weeks.
 26th March 2013, 03:00 PM #26 nigel pearson   diyAudio Member   Join Date: Mar 2007 Location: Oxfordshire Sorry we got off of TDA2050's , great to reminisce . This last bit below . Garrard motor shafts were 4.91 mm . Neither metric nor imperial . Garrard size . We guessed they started with 5 mm stock , hardened ground and lapped . Look after your Garrard bearings , if not it is big trouble . If in trouble take a high grade 5 mm pin . Dill the original self alining bronze bearings to take x 10 x 8 x 5 mm sintered bronzes replacements . Make it a snug push fit ( never a tight fit ) . The worst bit will be extracting the shaft from the rotor . Ream the rotor 4.91 to 5 mm . Fit new shaft with loctite or similar . The shaft should be to > 64 Rockwell hardness and 1 micro finish if possible ( 6 will do ) . Last edited by nigel pearson; 26th March 2013 at 03:20 PM.
Jsixis
diyAudio Member

Join Date: Feb 2011
Location: Columbus Ohio
Pics os set up

Here are some pictures I took tonight.
This is my 1st build. I've had the parts for years except for the assembled 2.1 board. I had the system sitting on my workbench playing with no earth ground and small heat sinks you see on lm317 chips. It worked fine till I turned the sub up to stoopid with 4 ohm load

This will be my workbench amp for the time being.
I want the rca's on the front so I can switch sources easily and a 1/4" guitar input for when I work on guitars.
Yes it is machine grey, only spray paint I had in the shop. I plan on making another front face, just scratched the 1st one up during the learning curve.

I do have some questions, the chassis is plastic;
My star ground on one of the transformer screws.
I need to run a wire from the earth ground of the plug to that point and from the negative lead of the large capacitors. Can I use the -in on the board where the negative secondary is attached?

On the speaker output do I need to run a wire from the negative posts to the star ground? The heat sink is negative, another wire?
Just want to make sure I get the ground proper.

Since the speaker output is a long run should I put a small cap across the outputs at the binding posts? Are twisting those wires required?

The transformer is a radio shack 12.6-0-12.6 2 amps. I know it is small but I had it on hand and it fits in this box. So I put a 2 amp fuse on the mains wiring and 1 amp fuses on each leg of the secondaries?

Yep, I know I forgot the power switch lol
Attached Images
 front.jpg (59.9 KB, 156 views) back.jpg (103.0 KB, 153 views) bottom.jpg (129.2 KB, 147 views) inside1.jpg (190.6 KB, 147 views) inside2.jpg (189.4 KB, 134 views) mains.jpg (166.0 KB, 50 views) power.jpg (158.2 KB, 23 views) input.jpg (181.5 KB, 38 views)

 8th April 2013, 09:41 AM #29 nigel pearson   diyAudio Member   Join Date: Mar 2007 Location: Oxfordshire Bridging would be interesting . Try if you can the same sound levels . The arguments can be bridging gets rid of helpful traits ( ie , bad ) . Or bridging stops returning speaker current through the ground ( ie , good ) . On a tube amplifier one can do tricks with that ( SE driver PP output in long tail pair ) . If I get time I will try a TDA 2040 in classA . The current source a LM317 ( or 337 , perhaps better ? ) . In theory a 1 R resistor should give 1.25 amps . The chip is good for 3 amps . All I need is a big heat sink . My eyes say to me the heat will be a problem ( if it works at all ) . One advantage over traditional class A amps is the TDA2030/40/50 will revert to class AB above 1.25 A . I suspect even 1/2 amp will be doing something ? The LM317 is fast enough to do this . Also class A does not require speed . What should happen is the crossover distortion which is probably higher than discreet amps will be far lower . It will not be dramatic in measured terms . The mechanisms that produced it will be eliminated . Shown is the single voltage rail version . There are 60 V 317's . Look at application notes for additional capacitors .
 8th April 2013, 12:51 PM #30 Mihkus   diyAudio Member     Join Date: Jul 2012 If the chip itself is class AB then how the heck can you have class A Well you have first stage of AB after what you have A. Damn electronis you scary! Ohh yeah, now i got it sorry Last edited by Mihkus; 8th April 2013 at 12:53 PM.

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