JayCar has what looks to be a nice 160VA 25-0-25 transformer (MT2114) for $24us. One of those per chanel wold be just fine.
Nope. 😉
They have different sites for different countries. They are based in Australia.
US: http://www.jaycarelectronics.com/
OZ: http://www.jaycar.com.au/
They have different sites for different countries. They are based in Australia.
US: http://www.jaycarelectronics.com/
OZ: http://www.jaycar.com.au/
Jaycar torroid tranny
try this
http://www.jaycarelectronics.com/pr...&pageNumber=&priceMin=&priceMax=&SUBCATID=539
2 for 21.50 ea.
4+ for 19.25 ea.
try this
http://www.jaycarelectronics.com/pr...&pageNumber=&priceMin=&priceMax=&SUBCATID=539
2 for 21.50 ea.
4+ for 19.25 ea.
Have used a little Jaycar 25+25 160VA in an ESP P19 amp last year and it was dead silent and ran cool. Nice little transformers 
😉
😉rabstg said:
One thing to keep in mind as one changes the zeners is that the shunt regulator current is dropping. If you have a +-30v power supply then the standard implementation has 30v - 12 v / 1000 ohms for a total available current of 18ma. When you raise the zener voltage to 18v this drops to 12ma. According to the datasheets, the LM318 draws around 5ma, so the standard design has about 13mA headroom. This will primarily be sunk by the zener until needed by the LM318.
When we change the zener to 18v the total current is 12ma. From that we need to provide 5ma for the LM318 + whatever current you use to bias it into class A. If you bias the LM318 with 7ma as Russ suggested it looks like you are getting close to the edge.
I implemented this change in my amps this afternoon. I used some 2SK170BL jfets to bias the LM318 with about 5.5ma. I used 18v zeners and I paralleled R1, R4, R24, R27 (each 1kohm) with another 1.3kohm resistor. This makes their effective value 565ohms. Since my power supply is +-29v, this gives 29v - 18v / 565 or 19.5ma total available current, slightly more than the stock amp but still in the same ballpark. But when you consider the added current draw now that the LM318 is biased into class A, its still has slightly less current headroom but it should still be OK.
The amps burning in right now so I'll comment about the change in sound quality at a later time.
---Gary
Yes you are correct Gary. 🙂 In fact you posted about this just before I was getting online.
My rails are approching 31.5-32V.
I actually backed off on the curtrent source to about 4ma and still get great results. I also changed the 1K power resistors out for 2 x 1.5K (750R effective) in parallel. This should give the LM318 more than enough juice. 🙂 I found a 100R pot to use for testing bias values with the LM334.
Still, I did not have any trouble even with the bias set at 7ma, but I was not really pushing it either.
I did some A/B tests at home with my brothers and wife, and while there is a noticable improvement I would not call it huge. If anything it just seems even more smooth than it was before while still retaining all the accuracy.
Cheers!
Russ
My rails are approching 31.5-32V.
I actually backed off on the curtrent source to about 4ma and still get great results. I also changed the 1K power resistors out for 2 x 1.5K (750R effective) in parallel. This should give the LM318 more than enough juice. 🙂 I found a 100R pot to use for testing bias values with the LM334.
Still, I did not have any trouble even with the bias set at 7ma, but I was not really pushing it either.
I did some A/B tests at home with my brothers and wife, and while there is a noticable improvement I would not call it huge. If anything it just seems even more smooth than it was before while still retaining all the accuracy.
Cheers!
Russ
Problem with one channel
I fired up my My Ref ver. A today. ONe channel is good one was non-working. AFter a brief few minutes I found my large output resistor has a cold joint. Upon reflowing to put it back in circuit, the dead channel started working, but is now very distorted.....
I wonder if I blew up one of the LM3886 chips? It sounds like they have a bunch of protection to prevent this, but the amp was working on driving no load for a few minutes.....is it possibly to blow these so easily?
While debugging I found the non-working LM3886 chip was getting extremely hot. While the one that worked was fairly cool.
Maybe I have something else wrong, so I'm going back in to debug. Any suggestions would be appreciated.
thanks,
Tommytube
I fired up my My Ref ver. A today. ONe channel is good one was non-working. AFter a brief few minutes I found my large output resistor has a cold joint. Upon reflowing to put it back in circuit, the dead channel started working, but is now very distorted.....
I wonder if I blew up one of the LM3886 chips? It sounds like they have a bunch of protection to prevent this, but the amp was working on driving no load for a few minutes.....is it possibly to blow these so easily?
While debugging I found the non-working LM3886 chip was getting extremely hot. While the one that worked was fairly cool.
Maybe I have something else wrong, so I'm going back in to debug. Any suggestions would be appreciated.
thanks,
Tommytube
Driving no load should not be a problem at all.
My guess is you have a solder bridge somewhere. Or another cold joint.
My guess is you have a solder bridge somewhere. Or another cold joint.
Hi Tommy, if you are talking about R3/R26(sense resistor) it is in the feedback loop, and so I suppose a cold joint there could have deprived the whole circuit of some feedback (affecting stability). I am not sure right now what effect that would have, but I wouldn't be too surpised if that could fry both opamps. I would try swapping them out if everything else looks good.
If I could count the number of times I have done something like that.
At least neither part is very expensive.
Cheers!
Russ
If I could count the number of times I have done something like that.
At least neither part is very expensive.
Cheers!
Russ
Dead channel
Russ,
Yes it is the .47/7W (R3/R26) which had a cold joint. It was only one of them. Again I got no sound at all with the cold joint. Now it's putting out music, but severly distored. The other channel appears to be working fine.
We went over the board this morning touching up joints, etc. but didn't find anything. We even used a rework microscope we have access to.
Since the LM3886 was super heating pretty darn fast, I suspect the output is somehow shorted to ground.....but no impedance measurements on the device confirms this. I don't have any extras of the LM3886, so I ordered a few (should be here by midweek).
I do have an extra LM318 which I may change out just while I wait. Still looking, but no problems found yet.
Thanks for the response.
Tommytube
Russ,
Yes it is the .47/7W (R3/R26) which had a cold joint. It was only one of them. Again I got no sound at all with the cold joint. Now it's putting out music, but severly distored. The other channel appears to be working fine.
We went over the board this morning touching up joints, etc. but didn't find anything. We even used a rework microscope we have access to.
Since the LM3886 was super heating pretty darn fast, I suspect the output is somehow shorted to ground.....but no impedance measurements on the device confirms this. I don't have any extras of the LM3886, so I ordered a few (should be here by midweek).
I do have an extra LM318 which I may change out just while I wait. Still looking, but no problems found yet.
Thanks for the response.
Tommytube
If the 3886 is getting hot, I would check for oscillations... that may also explain the distorsion ("SPiKE" protection coming into play). Do you have a scope(*) at hand?
(*) an high frequency one, at least some 10MHz...
(*) an high frequency one, at least some 10MHz...
bad channel
Yes, I have an older 100MHz Hitachi scope. I'll take a look at it tonight.
I did change out the LM318 at lunch and still had the same problem.
Thanks for the input!!! I'm still thinking damage to the LM3886 despite all the talk on the datasheet about all the neat protection features the chip has.
Tommytube
Yes, I have an older 100MHz Hitachi scope. I'll take a look at it tonight.
I did change out the LM318 at lunch and still had the same problem.
Thanks for the input!!! I'm still thinking damage to the LM3886 despite all the talk on the datasheet about all the neat protection features the chip has.
Tommytube
Re: bad channel
I do not know how it happened, but the first one I built blew a LM3886. The chip was not heating up, but two of the small caps started to bulge a little. It must have shorted internally somehow. The voltage on one side was -34 at the rail, and -26 to the metal tab on the chip.
The other working channel read -34 at the rail and the metal tab. Since the caps looked like they might blow, it got parted out.
Never did anything that might damage it.
George
tommytube said:
I do not know how it happened, but the first one I built blew a LM3886. The chip was not heating up, but two of the small caps started to bulge a little. It must have shorted internally somehow. The voltage on one side was -34 at the rail, and -26 to the metal tab on the chip.
The other working channel read -34 at the rail and the metal tab. Since the caps looked like they might blow, it got parted out.
Never did anything that might damage it.
George
A good question
By mail I was asked if the Jaycar transformer was 240 or 120 V. I find no indication on the website answering this question. I hope I've led no one into a bad trade.
Who knows the answer to this?
By mail I was asked if the Jaycar transformer was 240 or 120 V. I find no indication on the website answering this question. I hope I've led no one into a bad trade.
Who knows the answer to this?
Re: A good question
Just spoke to the techstore sales line.
The tranny is 240v.
I don't know what the output would be with 110v, I guess half and probably pretty useless...
If anyone gets stuck with them, I'll buy a couple from you, but I guess the freight will be a killer - might be better to return them instead.
The US Jaycar website has the identical product list to the AU one, just there is a pricing transformation applied for the different currency.
Michael
bg40403 said:
Just spoke to the techstore sales line.
The tranny is 240v.
I don't know what the output would be with 110v, I guess half and probably pretty useless...
If anyone gets stuck with them, I'll buy a couple from you, but I guess the freight will be a killer - might be better to return them instead.
The US Jaycar website has the identical product list to the AU one, just there is a pricing transformation applied for the different currency.
Michael
That's weird. I asked them by email a few weeks ago and got this reply:
Hello Brian,
These transformers have dual 115V/230V primaries.
Regards,
Claire Bianco
Techstore Sales Team
Free call Aust: 1800 022 888
Direct: (02) 9741 8571
Fax: (02) 9741 8559
Web: http://www1.jaycar.com.au/
Hello Brian,
These transformers have dual 115V/230V primaries.
Regards,
Claire Bianco
Techstore Sales Team
Free call Aust: 1800 022 888
Direct: (02) 9741 8571
Fax: (02) 9741 8559
Web: http://www1.jaycar.com.au/