http://infinity-classics.de/technik/manuals/RS_IIIA_technical_sheet.pdf
There is a link to the PDF, not sure why the attached file isn't working, maybe too large.
Infinity RS-IIIb speakers.
One channel ran hotter on previous amp.
Built F4 amp clone, sounded great with 6SN7 tubes in preamp. Increased gain with 6SL7 tubes and listed to rock at high volume.
Left channel fades out, temperature of left F4 amp channel is 25 degree F hotter than the right channel.
Recreated problem a couple of times, but now it happens within two minutes instead of the 20 minutes noticed the first time, I shut down the amp before it gets out of control.
Was troubleshooting preamp and amp when a board member suggested I measure resistance across speaker terminals.
First I measure DC on left channel and get 4.5v which drained.
Resistance on left channel tests as "open loop"
Resistance on right channel starts in 1.5 M ohm range and climbs to 4.5 M ohms over half an hour.
Where to begin?
Here is schematic:
There is a link to the PDF, not sure why the attached file isn't working, maybe too large.
Infinity RS-IIIb speakers.
One channel ran hotter on previous amp.
Built F4 amp clone, sounded great with 6SN7 tubes in preamp. Increased gain with 6SL7 tubes and listed to rock at high volume.
Left channel fades out, temperature of left F4 amp channel is 25 degree F hotter than the right channel.
Recreated problem a couple of times, but now it happens within two minutes instead of the 20 minutes noticed the first time, I shut down the amp before it gets out of control.
Was troubleshooting preamp and amp when a board member suggested I measure resistance across speaker terminals.
First I measure DC on left channel and get 4.5v which drained.
Resistance on left channel tests as "open loop"
Resistance on right channel starts in 1.5 M ohm range and climbs to 4.5 M ohms over half an hour.
Where to begin?
Here is schematic:
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I'm confused. You mention measuring resistance across the speaker terminals, and then say you had 4.5V DC. That doesn't sound like a sensible reading to me.
Are there any other symptoms showing up? Blown bass driver on one side, anything like that?
I'm afraid I can't view the schematic.
Chris
Are there any other symptoms showing up? Blown bass driver on one side, anything like that?
I'm afraid I can't view the schematic.
Chris
To do this easiest and quickest, you are going to need an impedance tester. You can use Room EQ Wizard to do this for cheap, otherwise I like using Dayton DATS.
You will also need some low value resistors (around 4-10 Ohms) to help you test the crossovers themselves.
This will help you test each component thoroughly.
Disconnect drivers from the crossover. Measure the impedance of each. Should be consistent per driver type.
Next, attach your resistors to the output of the crossovers and measure the impedance for each section. L and R should match nearly perfectly. Any mismatch there indicates something went bad. When you have isolated a bad part, or section come back here. 🙂
You can start this all with a multi-meter, but it really is a gross test. 🙂
Best,
E
You will also need some low value resistors (around 4-10 Ohms) to help you test the crossovers themselves.
This will help you test each component thoroughly.
Disconnect drivers from the crossover. Measure the impedance of each. Should be consistent per driver type.
Next, attach your resistors to the output of the crossovers and measure the impedance for each section. L and R should match nearly perfectly. Any mismatch there indicates something went bad. When you have isolated a bad part, or section come back here. 🙂
You can start this all with a multi-meter, but it really is a gross test. 🙂
Best,
E
Also, I'm not seeing the schematic.
The voltage on the crossover is interesting. This should not occur with a "normal" crossover.
Test your amp to see if you have significant DC at idle. This would explain much! 🙂
Best,
E
Best,
E
The voltage on the crossover is interesting. This should not occur with a "normal" crossover.
Test your amp to see if you have significant DC at idle. This would explain much! 🙂
Best,
E
Best,
E
http://infinity-classics.de/technik/manuals/RS_IIIA_technical_sheet.pdf
Virtually no DC offset on the amp at idle. I can get a number to show up every now and then but no more than when a butterfly flaps it wings.
At the time of the first failure I was able to measure a volt + after shutting down preamp.
This might be a case where I take it to a pro, but a bad time to not have speakers I can stand to listen to.
The woofers were definitely moving some air.
reading up on the dayton product...
Virtually no DC offset on the amp at idle. I can get a number to show up every now and then but no more than when a butterfly flaps it wings.
At the time of the first failure I was able to measure a volt + after shutting down preamp.
This might be a case where I take it to a pro, but a bad time to not have speakers I can stand to listen to.
The woofers were definitely moving some air.
reading up on the dayton product...
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Agreed.
It was suggested I measure for DC resistance at the terminals if I recall correctly.
I hooked up the meter which was already set for testing DC voltage and that's when I had the brief reading.
I didn't think that was what I was looking for, so did a quick internet search and tried measuring resistance in ohms.
Deciding on if I should drop $110 on a meter which only has one review on Amazon and it isn't glowing. Not that a single review counts for much...
The speaker people I know aren't morning types but figure I can start sitting in Austin traffic now and for the rest of the week as I try to track them down.
Thanks for the assistance. I realize the lack of a schematic didn't help. When I have more to work with I'll post with (hopefully) meaningful numbers.
Caps failed and so you are measuring a dc short across an inductor.
My hunch is that the impedance is dropping too low at certain frequencies and the cap and inductor compensates so to present the amp with an even load. As the cap is blown that part of the circuit isn't working properly and causing to much current to flow at low frequencies.
. Is that the speaker which is on the hot side of the amp?
My hunch is that the impedance is dropping too low at certain frequencies and the cap and inductor compensates so to present the amp with an even load. As the cap is blown that part of the circuit isn't working properly and causing to much current to flow at low frequencies.
. Is that the speaker which is on the hot side of the amp?
In fact thinking about it, that inductor between the positive and negative terminals is busy getting more and more conductive the lower the frequency content so is effectively shorting your amp when ever any music is being played. I would replace the series bass caps in both speakers as the other will probably fail. Looks like it's, no wait. That's 600mF not 600nF. That's huge. No idea where you find one of those. (or a bank of smaller ones)
Big picture makes difficult to read.
Yes - same side as hot side of amp. But if we are talking about the F4 specifically it doesn't get hot (the described jump starting at 120 F on heatsink that shoots upwards at the same time the speaker fades) until I am driving it with a lot of current - volume at near painful levels but easier on the ears to simulate with a strong bass line.
Is it likely the F4 delivering more current at what I am only guessing to be 25w class A than an Adcom GFA-5300 at clipping ~ 100w class AB?
In the preamp I had been using the 1uf coupling capacitors provided by Broskie. I recently added a pair of .47uf and am using the selector switch. I'm pretty sure I did this originally using the .47uf coupling caps only but possibly the 1uf + 47uf. In the recreation I did it with only the .47uf caps.
Maybe that's a misprint or type on the spec sheet regarding 600 Xf. I haven't torn this away from the glue, but I think it is the big blue one... The glue has hardened with age, or maybe that's the way it always was. Anyhow, I'm worried I will tear the cap apart just trying to read the value. I would probably replace all at the same time, on both speakers. Those wires from the inductors are all over the place, as if it doesn't matter if they touch.
Maybe a good time to put binding posts on instead of ye ole wire clip in style.
Attachments
OK. This is what I think is happening.
Capacitors in series block dc and become more conductive when frequency rises. This property is called reactance.
Inductors work in the opposite way. At dc they act like a piece of wire. As the frequency rises you get what is called back emf and due to magnetic fields in the coil they start to resist more.
Resistance is your ohms for dc. Reactance is known as impendance and this relates to ac. This often changes depending on the type component with frequency, either increasing or decreasing with frequency. Speakers go up and down. They're quite complex devices. It also usually affects the phase of the signal as well.
If your capacitor in this circuit has failed and is essentially shorted becoming a bit of wire then it's not blocking dc or lower frequencies where the capacitive reactance is greatest.
The next thing in the circuit is an inductor going to ground. When lower frequencies are present then the inductor lets more of this through and hence allows greater current to flow. Eventually a short at dc. Possibly more than the amp can cope with.
The circuit relies on the reactance of the capacitor being greater than, for instance, 4 ohms at the frequency when the reactance of the inductor falls below 4 ohms.
If you are running your f4 not too loud (eg not too high volts on out output) then there may be enough reactance from the inductor to limit the current to within the capability of the amp. As you ask the amp to go louder then with the increase in output voltage, a great current demand d is being placed on the amp.
Your other amp maybe able to get to the same sounding volume levelbut because it can deliver 100w into to 8 or 4 ohm, whatever, it may be able to handle the extra current needed when your speaker drops to 2 ohm or less.
My advice is disconnect that cap(you can leave it in place) that you think is suspect and do a continuity test on it. Your multimeter probably does this when set to the 200ohm range and beeps continously if measure less than a few ohms. A good cap should only blip momentarily when performing this test.
Have a look in the other speaker. You may find that the writing is visible in order to get the value.
It will almost certainly be a bi polar electrolytic. Don't try to put a polarised cap. It'll pop.
Hope this helps.
Capacitors in series block dc and become more conductive when frequency rises. This property is called reactance.
Inductors work in the opposite way. At dc they act like a piece of wire. As the frequency rises you get what is called back emf and due to magnetic fields in the coil they start to resist more.
Resistance is your ohms for dc. Reactance is known as impendance and this relates to ac. This often changes depending on the type component with frequency, either increasing or decreasing with frequency. Speakers go up and down. They're quite complex devices. It also usually affects the phase of the signal as well.
If your capacitor in this circuit has failed and is essentially shorted becoming a bit of wire then it's not blocking dc or lower frequencies where the capacitive reactance is greatest.
The next thing in the circuit is an inductor going to ground. When lower frequencies are present then the inductor lets more of this through and hence allows greater current to flow. Eventually a short at dc. Possibly more than the amp can cope with.
The circuit relies on the reactance of the capacitor being greater than, for instance, 4 ohms at the frequency when the reactance of the inductor falls below 4 ohms.
If you are running your f4 not too loud (eg not too high volts on out output) then there may be enough reactance from the inductor to limit the current to within the capability of the amp. As you ask the amp to go louder then with the increase in output voltage, a great current demand d is being placed on the amp.
Your other amp maybe able to get to the same sounding volume levelbut because it can deliver 100w into to 8 or 4 ohm, whatever, it may be able to handle the extra current needed when your speaker drops to 2 ohm or less.
My advice is disconnect that cap(you can leave it in place) that you think is suspect and do a continuity test on it. Your multimeter probably does this when set to the 200ohm range and beeps continously if measure less than a few ohms. A good cap should only blip momentarily when performing this test.
Have a look in the other speaker. You may find that the writing is visible in order to get the value.
It will almost certainly be a bi polar electrolytic. Don't try to put a polarised cap. It'll pop.
Hope this helps.
Thanks! This has been very helpful.
With the help of a dental mirror and flashlight...
Richey
600 Uf 100v (U is in caps, but V is in caps as well so that might not be a detail they care about)
RICHEY ELECTRONICS LTD. ALUMINUM CAPACITOR PROFESSIONAL
I've emailed the sales rep, but will look around for other bipolar / non-ploar caps with same value. (NPE on diagram)
This is job I would pay someone to do, but anyone with a good reputation in Austin has a backlog starting at a month (based on what I have found, I'm not knocking anyone who I haven't run across). I may try it myself.
With the help of a dental mirror and flashlight...
Richey
600 Uf 100v (U is in caps, but V is in caps as well so that might not be a detail they care about)
RICHEY ELECTRONICS LTD. ALUMINUM CAPACITOR PROFESSIONAL
I've emailed the sales rep, but will look around for other bipolar / non-ploar caps with same value. (NPE on diagram)
This is job I would pay someone to do, but anyone with a good reputation in Austin has a backlog starting at a month (based on what I have found, I'm not knocking anyone who I haven't run across). I may try it myself.
Aha!
Remember I said wiht a "Normal" crossover this shouldn't happen? One thing I was thinking was protection circuits, which this has.
Check or just replace the zeners. If mine, I'd probably remove them completely.
They are also pretty cheap, so if in any doubt at all about youre measurement skills, replace them! 🙂
Best,
E
Remember I said wiht a "Normal" crossover this shouldn't happen? One thing I was thinking was protection circuits, which this has.
Check or just replace the zeners. If mine, I'd probably remove them completely.
They are also pretty cheap, so if in any doubt at all about youre measurement skills, replace them! 🙂
Best,
E
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