There is the schematic:
http://www.crystalradio.cn/data/attachment/forum/201404/25/111001zipahdh84rpmxg4m.jpg
Simple as wooden wedges, "typical" chinese.
http://www.crystalradio.cn/data/attachment/forum/201404/25/111001zipahdh84rpmxg4m.jpg
Simple as wooden wedges, "typical" chinese.
It has a little separate headphone amplifier inside, it may not be the same circuit.
There's a version for Europe called Mini84ia which is sold as headphone amplifier and has only a single tap for speakers. It has better headphone output and may use the same circuit for speakers and headphone.
There's a version for Europe called Mini84ia which is sold as headphone amplifier and has only a single tap for speakers. It has better headphone output and may use the same circuit for speakers and headphone.
That is not very near field.
Due to the highish output impedance, the impedance curve plays a role. Where the phase angle gets largish, the amplifier needs to deliver current and SETs often have issues with that.
Also, given the speakers age, the XO will need reworking. KEF used cheapish XO parts and likely have drifted.
dave
Thanks a lot for the material, Planet 10.
Is the second graph the impedance curve of the Kef Coda 7?
Is it enough if I replace the crossover capacitors and then try again the speakers?
Is the second graph the impedance curve of the Kef Coda 7?
Is it enough if I replace the crossover capacitors and then try again the speakers?
There is one channel with FB and the other no.
Probably one erro
So the idea of oscillation can be real
Walter
Yes
Maybe. You’ll have to swap them and see. The speakers will sound better, but how that affects your amplifier depends on how much the aged XO has affected phase angle.
Note that with a high Rout you will alsohear the impedance bumps.
dave
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How can you tell that there's negative feedback? Is the cathode bypass capacitor that eliminate negative feedback? Is it because of the value of the capacitor?
There is a link for output to cathode of first stage of 83. In one channel
I think there is an error because in the other channel doesn’t exist
Walter
Ok, thanks anyone. You were most helpful.
I'm driving now the Kef Coda 7 with my nad c316bee but if the crossovers are really gone it may cause overheating even to the Nad.
I will sell them for what I paid for, 90 euro.
Any suggestion for a recent budget bookshelf speaker with a measured sensitivity around 90 db and a relatively smooth impedance curve? Something which I could try also with the small tube amplifier.
Apart from the smaller Klipsch which may not suit my musical tastes. And apart from the Fostex full range kits which I have tried and was not happy with the bass.
It seems that real 90db (measured) is the most you can get from a bookshelf speaker. And it seems that they are few and far between.
I'm driving now the Kef Coda 7 with my nad c316bee but if the crossovers are really gone it may cause overheating even to the Nad.
I will sell them for what I paid for, 90 euro.
Any suggestion for a recent budget bookshelf speaker with a measured sensitivity around 90 db and a relatively smooth impedance curve? Something which I could try also with the small tube amplifier.
Apart from the smaller Klipsch which may not suit my musical tastes. And apart from the Fostex full range kits which I have tried and was not happy with the bass.
It seems that real 90db (measured) is the most you can get from a bookshelf speaker. And it seems that they are few and far between.
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Klipsch typically pay no attention to the speaker’s impedance, they are someof th eygliest i hacve seen.
You want to buy something> Not build?
I can advise on a ton a builds, but buy? Maybe troll the swap meet and see if someone has a smallish single driver FR they want to move on because a half dozen pair are pushing WAF.
Almost any Markaudio, some Tandband, Fostex, Faital Pro, Visaton …
dave
You want to buy something> Not build?
I can advise on a ton a builds, but buy? Maybe troll the swap meet and see if someone has a smallish single driver FR they want to move on because a half dozen pair are pushing WAF.
Almost any Markaudio, some Tandband, Fostex, Faital Pro, Visaton …
dave
Thanks. The little amp is working faultlessly at the moment with the Triangle speakers they were with for the last months.
I purchased on a whim a couple of 30 years old Kef only because of their meaured sensitivity of 90 db. The vendor had said they were never used and were in a closet. When they arrived they looked really brand new and there wasn't even a single scratch on the bottom.
When I tested them with the tube amp the power transformer got hotter than usual.
It was suggested here that the crossovers of these Kef are completely gone. I think it is possible. Maybe more so because they were never used.
If the amp does something wrong in the future with the Triangle speakers I'm using now, (those I had been using previously) I will order the led and the resistor and do what you said.
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