troystg said:
Well I swapped boards and compared the voltages. They are pretty much the same (recommended voltages in parenthesis), so whatever is happening is happening on both boards:
-C3 -36V (-32.5)
+C8 +36V (+32.5)
+C6 +11.75V (+12)
-C11 -11.75V (-12)
-C1 -36V (-32.5)
+C2 36V (+32.5)
+C14 +16.75 (+24)
I was able to get music out of this board but there are a couple of issues:
The first time I turned on the amp, I heard an awful LOUD SCREEECH. My family upstairs called down, "what was that?" I turned off the amp immediately, checked all connections and tried again. This time... music! So, I tried turning it on and off a couple of times, no more screech. Then I listened to an entire song (~3 minutes) at normal listening levels. When I turned off the amp, SCREECH. This one was quicker than the first one but just as loud!
Also, I noticed the faint smell of burning plastic. All the caps look normal, but then I noticed the insulation of the wires that I am using for the amp input (coming from the RCA) had receded slightly. Sort of like what happens when you heat a wire too long while soldering.
Then I felt the heat sink, HOT!!! I know they are small, but since everyone seemed to indicate that these amps don't get very hot and suggested using a CPU heat sink, I didn't expect it to get REALLY HOT!
So, I've included pictures below. Any clues?
You can see the album with full size images here. Or just click on the thumbnails below to see the full size image:
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
I had this same crazy sound and then burning in a chip amp once. It died instantly though. I would not fire that back up til you figure it out. Luckily this is built better than my little gainclone was.
Mine ended with a resistor on fire and burnt legs on the LM3886.
I thought mine had to do with my power supply at the time. I was using two switched supplies like soong was talking about a few posts back but they were adjustable. When you adjusted them both perfectly to 24V then ground really was 0V but I think I actually had + or - voltage on ground the day it died. So my thought is that either
1. you have one rail higher than the other which means ground is not 0V
2. you do not have your chips well insulated from the heatsink (if this is causing one of those oh shizzle moments I bet thats it). If your heatsink has the ab...........what?
I just looked at your sink. I dont think we need to think this through any further. Get a decent heatsink on there and you wont have SPIKE protection kicking in.
Uriah
edit: And if you dont use thermal paste the size of the heatsink wont help any. You must use it on both sides of your insulating pad. Also if you dont use insulating washers then your bolt will take negative voltage from your chip to the sink and it will go to ground which will leave you with a fried chip. I just dont see any paste. I see your first washer but is it a shoulder washer or a flat one?
Mine ended with a resistor on fire and burnt legs on the LM3886.
I thought mine had to do with my power supply at the time. I was using two switched supplies like soong was talking about a few posts back but they were adjustable. When you adjusted them both perfectly to 24V then ground really was 0V but I think I actually had + or - voltage on ground the day it died. So my thought is that either
1. you have one rail higher than the other which means ground is not 0V
2. you do not have your chips well insulated from the heatsink (if this is causing one of those oh shizzle moments I bet thats it). If your heatsink has the ab...........what?
I just looked at your sink. I dont think we need to think this through any further. Get a decent heatsink on there and you wont have SPIKE protection kicking in.
Uriah
edit: And if you dont use thermal paste the size of the heatsink wont help any. You must use it on both sides of your insulating pad. Also if you dont use insulating washers then your bolt will take negative voltage from your chip to the sink and it will go to ground which will leave you with a fried chip. I just dont see any paste. I see your first washer but is it a shoulder washer or a flat one?
Thanks, Troy. I'm glad that someone might benefit from my experiments and recommendations. I maintain that the quality of the input cap is paramount, and requires the most careful evaluation. Everything else is secondary, but all circuit path components benefit from improving over the adequate parts supplied in the kit.
I would expect that, given the cost and difficulty of obtaining them, exotic transformers would probably be pretty low on the list of significant improvements. I must admit I don't have a lot of experience with different types. I would like to hear the difference sometime, but I'm not gonna spend the money to find out. No doubt that power supply is important, but only to a certain point. Adequate capacity and quality of transformer is probably more important. There is really no point in cutting corners there to save a few bucks.
Dario, I'm happy to see that you removed bypass from input cap. I was thoroughly confused by your recommendation. Even though some people use them, I can't imagine a worse place to put a bypass cap. If your input cap sounds so bad that it needs a bypass, upgrade the cap.
The cost of Blackgate cap at C9 is justified, in my opinion, but I'm not sure that additional ones would be.
Any decent quality resistors, especially in signal path, are probably a worthwhile upgrade over Xicons, as cost is not so great.
I think hook-up wire and inputs/outputs contribute to sonics, and I favor adequate gauge solid OCC copper with teflon insulation. I never liked the sound of silver anywhere in my system except as speaker wire for the low end of biwiring (NOT the highs/mids!). I splurged on Vampire solid copper/gold plated output terminals, but my input jack is a PE cheapie. It's decent, but that might get upgraded to solid copper/gold plate, as well. I would prefer to get brass and other alloys out of the signal path.
One of my amps is still broken, but I've got a strategy now and I think I can get it running. I've built three good ones, so it can't be that difficult to find and fix what's wrong. Bluegti has too little voltage at C14; I have too much. Maybe I could send him a few of my extra volts and we would both have working amps.
I use a nylon bolt for connecting chip to heatsink. Obviously, no shorting problems, no expansion/contraction problems, and it's not so strong or rigid that I risk overtightening the bolt.
From his description, it doesn't sound like the problem is thermal. I think that's a symptom, but not the cause.
Peace,
Tom E
I would expect that, given the cost and difficulty of obtaining them, exotic transformers would probably be pretty low on the list of significant improvements. I must admit I don't have a lot of experience with different types. I would like to hear the difference sometime, but I'm not gonna spend the money to find out. No doubt that power supply is important, but only to a certain point. Adequate capacity and quality of transformer is probably more important. There is really no point in cutting corners there to save a few bucks.
Dario, I'm happy to see that you removed bypass from input cap. I was thoroughly confused by your recommendation. Even though some people use them, I can't imagine a worse place to put a bypass cap. If your input cap sounds so bad that it needs a bypass, upgrade the cap.
The cost of Blackgate cap at C9 is justified, in my opinion, but I'm not sure that additional ones would be.
Any decent quality resistors, especially in signal path, are probably a worthwhile upgrade over Xicons, as cost is not so great.
I think hook-up wire and inputs/outputs contribute to sonics, and I favor adequate gauge solid OCC copper with teflon insulation. I never liked the sound of silver anywhere in my system except as speaker wire for the low end of biwiring (NOT the highs/mids!). I splurged on Vampire solid copper/gold plated output terminals, but my input jack is a PE cheapie. It's decent, but that might get upgraded to solid copper/gold plate, as well. I would prefer to get brass and other alloys out of the signal path.
One of my amps is still broken, but I've got a strategy now and I think I can get it running. I've built three good ones, so it can't be that difficult to find and fix what's wrong. Bluegti has too little voltage at C14; I have too much. Maybe I could send him a few of my extra volts and we would both have working amps.
I use a nylon bolt for connecting chip to heatsink. Obviously, no shorting problems, no expansion/contraction problems, and it's not so strong or rigid that I risk overtightening the bolt.
From his description, it doesn't sound like the problem is thermal. I think that's a symptom, but not the cause.
Peace,
Tom E
" I splurged on Vampire solid copper/gold plated output terminals, but my input jack is a PE cheapie. "
Mr. Gerald uses and likes the Vampire stuff. I changed the binding posts on my B&W 805's to some Vampire terminals and did not see any sound difference <good thing> but a HUGE convenience difference. I hated the original round binding posts and I love the hex head Vampires.
http://www.vampirewire.com/pc-46-16-bphex.aspx
Let me tell you, I called over there to order some spade terminals for a friends cables I was making and that man was a "trip". Nice guy, very knowledgeable.. But I called to order some terminals and the whole time he is telling me NOT to put the terminals on the ends of the cables because the bare wire sounds better.
Now I was NOT going to argue with him on the sound issue as I'm sure he has done extensive listening and testing, but I was doing this for a friend who was ALL about the ease of hookup. He not only definitely WANTED spades, but he wanted the spades on banana plugs so they could be plugged and unplugged as his wife redecorated....
It took over an hour to finally get 16 spades ordered and shipped. This was before HTTPS and secure internet ordering.
Mr. Gerald uses and likes the Vampire stuff. I changed the binding posts on my B&W 805's to some Vampire terminals and did not see any sound difference <good thing> but a HUGE convenience difference. I hated the original round binding posts and I love the hex head Vampires.
http://www.vampirewire.com/pc-46-16-bphex.aspx
Let me tell you, I called over there to order some spade terminals for a friends cables I was making and that man was a "trip". Nice guy, very knowledgeable.. But I called to order some terminals and the whole time he is telling me NOT to put the terminals on the ends of the cables because the bare wire sounds better.
Now I was NOT going to argue with him on the sound issue as I'm sure he has done extensive listening and testing, but I was doing this for a friend who was ALL about the ease of hookup. He not only definitely WANTED spades, but he wanted the spades on banana plugs so they could be plugged and unplugged as his wife redecorated....
It took over an hour to finally get 16 spades ordered and shipped. This was before HTTPS and secure internet ordering.
bluegti said:
I must be lucky, I've had problems with Gainclone but never with MyRef...
Your Silmics are bigger than mines...
Have you checked that C9 leads doesn't touch or are too near to anything?
Your cap has 7.5mm lead spacing vs the 5.0mm of the position so you had to bend them, right?
madisonears said:
Hi Tom!
It's nice to ear you
The cap isn't bad at all but, sometimes, even the best cap could benefit from a bypass.
For sure in this case no bypass is better
madisonears said:
You're talking about elcos, right?
Also C6 and C11 swap (with Silmics in my case) has an audible effect that justify an expense of 0.66$
Regarding resistors I think that Xicons are already decent, to have more you have to spend more on Takmans, Dale RN55, PRP, etc.
I agree that hook-up wire makes a difference, I've used solid core copper for outputs and a nice OFC shielded cable for inputs.
look at page 14 of the 3886 datasheet.
Find +-36Vdc on the graph (=72V)
Go up to 8r0 loading.
Go horizontally to the far left.
@ Ta=25degC National recommend between 2.4C/W and 3C/W
@ Ta=40degC they say 1.9C/W and 2.5C/W.
For an internal heatsink with resitricted flow of cold air use the Ta=40degC.
Now find a heatsink that has double the dissipation of the National recommendation. i.e. use ~1.1C/W for each channel.
That is not 5times your existing sink, it's about 25times the dissipation.
If you mount the heatsink externally you can reduce it to ~1.3 to 1.4C/W
Find +-36Vdc on the graph (=72V)
Go up to 8r0 loading.
Go horizontally to the far left.
@ Ta=25degC National recommend between 2.4C/W and 3C/W
@ Ta=40degC they say 1.9C/W and 2.5C/W.
For an internal heatsink with resitricted flow of cold air use the Ta=40degC.
Now find a heatsink that has double the dissipation of the National recommendation. i.e. use ~1.1C/W for each channel.
That is not 5times your existing sink, it's about 25times the dissipation.
If you mount the heatsink externally you can reduce it to ~1.3 to 1.4C/W
AndrewT said:
As always good advice, however PC heat sinks have been used since the dawn of the Overture amps and are proven to be acceptable under real world usage. They are "roughly" 5 times the size of his sink.
I don't expect him to slap 5 of his current sink on a piece of flat stock to increase the dissipation <although that probably would work>, instead I offered him some good ones that only cost an email.
With the exception of a few threads on this forum "most" of the work can be safely done in "approximation." When a hobby becomes too technical or tedious most hobbiest loose interest.
But as always you are correct, and if your advice is followed it WILL work and be "right".
ClaveFremen said:
Hi Tom!madisonears said:
It's nice to ear you
The cap isn't bad at all but, sometimes, even the best cap could benefit from a bypass.
For sure in this case no bypass is better
Today I've removed bypasses also from SACD Player's output caps (Mundorf Zn): much better!
Tom I think you're right
Try a few jumpers from the output of your CDPs DAC and take that straight to some new output caps then to new RCAs and give it a try
You remove the whole analog output section from your CDP. Chances are it will be wonderful. But you have to have either the output caps of DC blockers somewhere after this mod because the DAC can put out a few volts of DC.
Uriah
You remove the whole analog output section from your CDP. Chances are it will be wonderful. But you have to have either the output caps of DC blockers somewhere after this mod because the DAC can put out a few volts of DC.
Uriah
Got question regarding DC offset for any one who got the answer...
Is it necessary to have 0mv DC offset to go for DC couple in Myref? How about 1.0mv or 0.1mv for example.....????
Secondly if we combine a 'passive' preamp like the Lightspeed, would there be a DC offset problem arise....???
Thanks
Is it necessary to have 0mv DC offset to go for DC couple in Myref? How about 1.0mv or 0.1mv for example.....????
Secondly if we combine a 'passive' preamp like the Lightspeed, would there be a DC offset problem arise....???
Thanks
gabanyayaya said:
If you have output caps in you CD player and/or your pre you already have no DC offset
Same thing for the passive pre, if you have output caps in your CD player you can DC couple MyRef.
As always, pay attention to other equipments you could connect, also them must have NO DC offset.However the answer to 'how much DC offset is safe' it depends on the gain of the amplifier.
For example if you have 1mV DC offset and the ampli has a gain of 20 the output DC offest would be 20 mV that is safe.
Someone knows the MyRef gain?
ClaveFremen said:
If you have output caps in you CD player and/or your pre you already have no DC offset
Same thing for the passive pre, if you have output caps in your CD player you can DC couple MyRef.
However the answer to 'how much DC offset is safe' it depends on the gain of the amplifier.
For example if you have 1mV DC offset and the ampli has a gain of 20 the output DC offest would be 20 mV that is safe.
Someone knows the MyRef gain?
Output cap on CD player........!!!! I think all CDP got an output cap right...??? So there's no DC offset.....the passive pre like the Lightspeed did't have any hence no DC offset since considering the output of the CDP is protected....am I wrong here???
So Dario this mean 20mV from your example is a bad or good ?
with your amp running you can measure the offset from the amps outputs. Where you connect the speakers. Just put the dmm there on ground and signal to speakers and measure. Some people have got as low as 3mV with DC couple which is awesome. I read somewhere that anything under 50mV is pretty good and you shouldnt hear it either. 100mV is probably okay to. DC will cook your speaker so thats why we want very little to none of it. In order to test this you should turn everything on and have a song playing or a tone.
Uriah
Uriah
ClaveFremen said:
Yes, quite all CD players normally have output caps or DC servos but it's always safer to to measure it with a multimeter...
For Gainclones usually an output DC offset of 100mV is considered safe.
thanks for the advice....
udailey said:
Uriah, is it possible running 2 input rca in each channel....one with connection to input cap and the second one without filter cap (short wire to amp)....??? This sort of channeling the DC offset to somewhere else......if possible
I head this from your previous comments regarding DC offset in Myref......
BTW I still haven't got the bridge rectifier yet (621-GBJ804-F)....anybody care to help me with this...???
I am not entirely sure what you mean but I would put each RCA signal through an input cap if you measure any DC from your CDP. A poorly constructed preamp can give some DC if its active and a poorly constructed passive pre can make noise but I dont think its going to generate any DC. If you have no ouput caps on your CDP then your amp should have them. A CDP can give a few volts of it without a cap in the way of DC on each channel. This would destroy your speakers quickly. So measure then make your choice. Dont try to figure it all out first. Measure then decide.
Please email me the parts you would like again and I will order from Mouser for you today.
Uriah
Please email me the parts you would like again and I will order from Mouser for you today.
Uriah