Hi Sonic Art,
Your offsets are fine now. See? Just like magic!
Don't bother with the other channel. It will not change the sound and it is operating just fine. Do not mess with things that are operating properly.
Odd markings on those transistors. I have never seen them with what looks like a gain range mark. Ever. As long as you buy from an authorized distributor you should be okay. IF you don't ... well hey!, may as well buy a lottery ticket while you're at it. So, where did you get them from?
-Chris
Your offsets are fine now. See? Just like magic!
Don't bother with the other channel. It will not change the sound and it is operating just fine. Do not mess with things that are operating properly.
Odd markings on those transistors. I have never seen them with what looks like a gain range mark. Ever. As long as you buy from an authorized distributor you should be okay. IF you don't ... well hey!, may as well buy a lottery ticket while you're at it. So, where did you get them from?
-Chris
thanks Chris, they are from a Chinese supplier who has a good rep with parts, I questioned the lack of the F on the part, they showed me the bulk box of devices. might send the pic to fairchild see what they say. they measured really good!
I will check around if anyone has some name brand locally but it's often hard to get these things off the shelf.
I will check around if anyone has some name brand locally but it's often hard to get these things off the shelf.
Thats fair enough, they are performing well though, sound is balanced, plenty of detail on the left side of the stage 
lol.
Here is a pic sent to me by a local supplier, didnt realise they stocked these semis, they say they dont know the brand but their stock comes from a large German distributor. Looks similar to what I bought.
lol.Here is a pic sent to me by a local supplier, didnt realise they stocked these semis, they say they dont know the brand but their stock comes from a large German distributor. Looks similar to what I bought.
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Hi Sonic Art,
All I am going to say is that I refuse to take chances with parts. It simply doesn't pay in the long run. You may get lucky - and that's great.
Top notch parts will be less noisy, and last longer compared to knock-offs, remarks and total fakes. As far as noise is concerned, you often won't notice it, but you can sure measure it sometimes in a complete circuit. We can measure noise of individual parts, but that test is a pain to set up and characterize. Of course the big concern is device failure.
Often an under-rated part can survive for a while, maybe even years. However when it does fail, it can take out a lot of far more expensive things (including speakers in your case). So given the cost differential, it simply makes zero sense to even touch a part you have any doubts or concerns over.
When I was young, I couldn't afford anything. I got all my parts from old Television sets and radios. I measured them to make sure they were good, but at least the things were real. We didn't have any problems with fakes, pulls or remarks, that probably started in the late 1970's with TV parts. I know the Sony SG-613 was the one part I heard of that had a real problem with fakes and remarks. That and TV horizontal output transistors. Later we saw remarked audio outputs, then drivers and on to signal transistors. Even IC circuits!
Today I do not trust anything that doesn't come from an authorized distributor. Earlier remarks and fakes were obvious, today this isn't so. The markings are very good these days. The only eal defense is to buy from verified supply chains, and this is a lot less expensive than risking a fake.
-Chris
All I am going to say is that I refuse to take chances with parts. It simply doesn't pay in the long run. You may get lucky - and that's great.
Top notch parts will be less noisy, and last longer compared to knock-offs, remarks and total fakes. As far as noise is concerned, you often won't notice it, but you can sure measure it sometimes in a complete circuit. We can measure noise of individual parts, but that test is a pain to set up and characterize. Of course the big concern is device failure.
Often an under-rated part can survive for a while, maybe even years. However when it does fail, it can take out a lot of far more expensive things (including speakers in your case). So given the cost differential, it simply makes zero sense to even touch a part you have any doubts or concerns over.
When I was young, I couldn't afford anything. I got all my parts from old Television sets and radios. I measured them to make sure they were good, but at least the things were real. We didn't have any problems with fakes, pulls or remarks, that probably started in the late 1970's with TV parts. I know the Sony SG-613 was the one part I heard of that had a real problem with fakes and remarks. That and TV horizontal output transistors. Later we saw remarked audio outputs, then drivers and on to signal transistors. Even IC circuits!
Today I do not trust anything that doesn't come from an authorized distributor. Earlier remarks and fakes were obvious, today this isn't so. The markings are very good these days. The only eal defense is to buy from verified supply chains, and this is a lot less expensive than risking a fake.
-Chris
100% I get it, I have searched for original devices high and low, even Mouser shows various brands, but no photos for comparison. I will get more and swap those 6 out just to be safe. Am going to measure the old ones today just to compare.
So what does everyone think about the second pic I posted of the single 2N5551? That comes from one of the biggest suppliers here in OZ, and they took the actual photo and emailed it to me when I asked yesterday, pretty decent service. They say all their stock comes from a German distributor, so do I trust these chips? they are not expensive, 30c USD or so each.
So what does everyone think about the second pic I posted of the single 2N5551? That comes from one of the biggest suppliers here in OZ, and they took the actual photo and emailed it to me when I asked yesterday, pretty decent service. They say all their stock comes from a German distributor, so do I trust these chips? they are not expensive, 30c USD or so each.
Hi Sonic Art,
I don't know them, so I can't comment. I would be measuring beta, interelectrode capacitances and breakdown voltage at the minimum. I use an HP 6186C current source for that, 300 VDC compliance voltage (rated). it goes a little higher, and I have very high voltage supplies if I need. Most people can't do that, so it's easier to buy the real thing or a current replacement type number.
For me, even though I can do some basic tests - it simply is not worthwhile. Luckily I did buy enough stock when they were current to be able to avoid some of this. But even then, I'll simply select a current device that will work as well or better.
I don't know them, so I can't comment. I would be measuring beta, interelectrode capacitances and breakdown voltage at the minimum. I use an HP 6186C current source for that, 300 VDC compliance voltage (rated). it goes a little higher, and I have very high voltage supplies if I need. Most people can't do that, so it's easier to buy the real thing or a current replacement type number.
For me, even though I can do some basic tests - it simply is not worthwhile. Luckily I did buy enough stock when they were current to be able to avoid some of this. But even then, I'll simply select a current device that will work as well or better.
I have to order parts today for another job so will get 10pr from the local supplier, check them out and if they measure as good as the "other ones" I will swap the 6 out.
I measured the old devices, the 5550 all measured the same, the 5401 measured a little different, two were close, one was a bit out, maybe 10%. I guess I could pair up the two close ones and likely get the DC under 10mv like that!
I measured the old devices, the 5550 all measured the same, the 5401 measured a little different, two were close, one was a bit out, maybe 10%. I guess I could pair up the two close ones and likely get the DC under 10mv like that!
Hi Sonic Art,
I don't know what to tell you. I don't want you to waste money, and I do not know the companies you are dealing with. They may be perfectly fine.
It really comes down to knowing who you are dealing with with certainty. I have many decades worth of experience with components and fakes - remarks. Many of us do and that gives us an advantage. When you're starting out, it is simply very hard. THese pages are perhaps the best source of information you have. They sure don't teach this is any school!
Without having the part in hand, no one can tell you with certainty unless they have had the same part exactly in their hand, preferably from the same vendor.
-Chris
I don't know what to tell you. I don't want you to waste money, and I do not know the companies you are dealing with. They may be perfectly fine.
It really comes down to knowing who you are dealing with with certainty. I have many decades worth of experience with components and fakes - remarks. Many of us do and that gives us an advantage. When you're starting out, it is simply very hard. THese pages are perhaps the best source of information you have. They sure don't teach this is any school!
Without having the part in hand, no one can tell you with certainty unless they have had the same part exactly in their hand, preferably from the same vendor.
-Chris
I get you, been in audio commercially for a long time but haven't had to deal with old stock ic's much in the post
past.
the supplier here is about the largest local one, they deal with a lot of stuff that has to be complied for Aus use, I trust what they tell me but cannot vouch for their suppliers of course! one would hope that the German distributor is selling them quality parts.
past.
the supplier here is about the largest local one, they deal with a lot of stuff that has to be complied for Aus use, I trust what they tell me but cannot vouch for their suppliers of course! one would hope that the German distributor is selling them quality parts.
I have a question for the DH200 experts, I have read much about linking the spk fuse in/out on the board then running the spk out to the fuse then post.
in the original design is the fuse directly in the signal path? circuits are not my main thing so it's nice to get more detailed explanations from the experts!
in the original design is the fuse directly in the signal path? circuits are not my main thing so it's nice to get more detailed explanations from the experts!
Fuses work by raising the element to melting temperature. When you do that, the resistance changes a fair amount. So during music when you have the levels up, a fuse will modulate the load impedance. That equals distortion. The best you can do is then place that fuse within the feedback loop, but it will still affect the sound.
If it were my amplifier, I would remove the fuses from the signal path completely (short them!). However I also believe it is irresponsible to not have a form of effective way to protect the speakers. To that end, I would install a speaker relay protection / timer PCB.
If it were my amplifier, I would remove the fuses from the signal path completely (short them!). However I also believe it is irresponsible to not have a form of effective way to protect the speakers. To that end, I would install a speaker relay protection / timer PCB.
Contacts are the least detrimental to sound quality (relays). However they are a maintenance item, as they wear, and if they do protect your speakers, expect the contacts to be damaged. So periodic replacement may be required. Always turn the volume right down before turning any amplifier on or off.
Having said that, a few relays have been found that can badly affect sound quality. I believe in every case, the armature also served as the signal carrying connection. Standard audio relays are generally very good.
Any fuse made will badly affect sound quality. No matter what the metal is for the element, it must reach the melting point. So, it's resistance will have changed a great deal. It's just physics.
Having said that, a few relays have been found that can badly affect sound quality. I believe in every case, the armature also served as the signal carrying connection. Standard audio relays are generally very good.
Any fuse made will badly affect sound quality. No matter what the metal is for the element, it must reach the melting point. So, it's resistance will have changed a great deal. It's just physics.
well my original good channel is now giving me grief lol. found some 470uf BG bipolars in my box and thought cool now I don't have to hunt for muse to fit in the feedback circuit.
swapped out the caps and now I have 250mv dc on the channel.... sigh.. have checked every component I can, I been moving the heatsink around on Q8, I couldn't have upset these metal can ic's could I?
what else can cause dc across the output other than the differential pairs?
the 0.5ohm resistor (2.2 in this amp) is fine, diodes measure good, the critical resistors were all changed, amp was running fine. yes I know don't touch things once they are good lol too late now need to figure out the cause.
swapped out the caps and now I have 250mv dc on the channel.... sigh.. have checked every component I can, I been moving the heatsink around on Q8, I couldn't have upset these metal can ic's could I?
what else can cause dc across the output other than the differential pairs?
the 0.5ohm resistor (2.2 in this amp) is fine, diodes measure good, the critical resistors were all changed, amp was running fine. yes I know don't touch things once they are good lol too late now need to figure out the cause.
If you can measure between the bases of like pairs (diff pairs) you can see if they are balanced.
The Vas can upset your DC offsets, and that bipolar cap, or the one across it can if it is leaky or shorted. A shorted cap gives you gain at DC, not what you want. With the cap, your gain is about unity at DC.
The Vas can upset your DC offsets, and that bipolar cap, or the one across it can if it is leaky or shorted. A shorted cap gives you gain at DC, not what you want. With the cap, your gain is about unity at DC.