I have a quad 405 that I know next to nothing about. It's serial number is just below 14000 so I'm not sure how old that makes it, but I know it's older than me. 😉Jessjh said:
I've had it apart, and the two 10,000uF caps are leaking dielectric goo! Also, one of the wires from each cap has come off, so I assume the solder has melted at some point.
I remember it working at one point tho.Now I'm not really sure of the specs on this amp, so I'm gonna have to do some digging, but I've got some elna cerafine caps that happen to be 10,000uF and 63 volts, so I plan to put these in there.
Now, if I was to put these in there, is there a chance the new caps could get damaged at all? As they are good caps and I don't want them to release thier goo like the old ones!
Maybe I'll but some cheapy 10,000uF audio caps, just for testing.Now I'm gonna have a lok at the links posted in here... It would be lovely to have RCA's on this thing.
If you need any pics of mine, I'll be more than happy to post some. It does seem really nicely made, and very heavy with a large heatsink on the front. They certainly don't make 'em like this anymore!
If the rectifier is good your new capacitors will be happy. Also, I'd suggest to clean well all remains of electrolyte, it is conductive!
Hi MikeHunt79,
I've repaired a few of these over the years. It's a nice little amp.
-Chris
Not to mention corrosive. Wavebourn is probably correct in suggesting the rectifier is okay. Test it to make sure. They are old by now and I have seen many die of old age.
I've repaired a few of these over the years. It's a nice little amp.
-Chris
Luckily the electrolite has only leaked onto the tops of the caps, and no further. I've just been reading through the links in this thread, and I now want to mod it. 🙂 I'm gonna test the rectifier when I can find my meter with a scope on it, just to be on the safe side.
It seems that people are using 20,000uF in their mods, so I'm tempted to get these, as they seem very good value for audio grade capacitors:
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=7623949510
Would these work or would it be better to get another pair of cerafines?
It seems that people are using 20,000uF in their mods, so I'm tempted to get these, as they seem very good value for audio grade capacitors:
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=7623949510
Would these work or would it be better to get another pair of cerafines?
I would not rush to mod it. I'd suggest to listen and compare to the mod prototype before doing that. 😉
Measurements are tricky: they tend to ignore audible and unpleasant distortions, but report well less audible ones that don't bother audiofools...
Measurements are tricky: they tend to ignore audible and unpleasant distortions, but report well less audible ones that don't bother audiofools...
Ok, thanks... I'll just try cap replacement for now and see how well I get on.
TBH, my speakers aren't really going to do this amp justice anyway, so I'm also on the hunt for a nice pair. 🙂
TBH, my speakers aren't really going to do this amp justice anyway, so I'm also on the hunt for a nice pair. 🙂
Hi MikeHunt79,
One thing I know helps the sound quality for sure is to get rid of all ceramic caps. Use mica or polystyrene to replace them. Don't buy those nutty expensive brands. Replace the low value electrolytics with film types (Wima makes 1 and 3u3 caps, 4u7 also). Bypassing the feedback electrolytic with 4u7 (use 3u3 or 1u0 if you can't get those) yields benefits. Replace the other with 85 ° caps at higher voltage ratings. The 85 ° have lower dissipation reading than the 105 ° types I have found. They may be marginally cheaper too.
Since you have it open, you may as well do this too. The lower value electrolytics may be bad anyway. If you measure them, you will see the dissipation value increasing over new ones.
-Chris
One thing I know helps the sound quality for sure is to get rid of all ceramic caps. Use mica or polystyrene to replace them. Don't buy those nutty expensive brands. Replace the low value electrolytics with film types (Wima makes 1 and 3u3 caps, 4u7 also). Bypassing the feedback electrolytic with 4u7 (use 3u3 or 1u0 if you can't get those) yields benefits. Replace the other with 85 ° caps at higher voltage ratings. The 85 ° have lower dissipation reading than the 105 ° types I have found. They may be marginally cheaper too.
Since you have it open, you may as well do this too. The lower value electrolytics may be bad anyway. If you measure them, you will see the dissipation value increasing over new ones.
-Chris
quad 405
Hope you don't mind my coming in on this thread but you all sound like you know what you are talking about so I'd appreciate any help from those who know the circuit.
I have a quad 405 which had blown a power transistor on one channel - a 2sd676. I replaced the transistor (albeit with one from a different manufacturer). When I turned on the amp, there was a small flash from the area around the three small transistors (TR3, 4 and 5) however when I connected a signal the amplifier was working. The only problem is that there is a loud click (or clack) when I turn it on and this channel is noticeably louder than the other one.
As you all seem to understand the circuit, would a blown transistor in this part of the circuit produce these results - or could the slight flash be a false lead. It occurred to me that it could be a mismatch between the two different manufactures of power transistors, but it will be a little expensive to change the other one just on the off chance.
I can take the components out one at a time and test them, but a pointer in the right direction could save me a lot of time and money.
Cheers
Nick
Hope you don't mind my coming in on this thread but you all sound like you know what you are talking about so I'd appreciate any help from those who know the circuit.
I have a quad 405 which had blown a power transistor on one channel - a 2sd676. I replaced the transistor (albeit with one from a different manufacturer). When I turned on the amp, there was a small flash from the area around the three small transistors (TR3, 4 and 5) however when I connected a signal the amplifier was working. The only problem is that there is a loud click (or clack) when I turn it on and this channel is noticeably louder than the other one.
As you all seem to understand the circuit, would a blown transistor in this part of the circuit produce these results - or could the slight flash be a false lead. It occurred to me that it could be a mismatch between the two different manufactures of power transistors, but it will be a little expensive to change the other one just on the off chance.
I can take the components out one at a time and test them, but a pointer in the right direction could save me a lot of time and money.
Cheers
Nick
Re: quad 405
I know that Ana..Chris will agree with me-in DIY world (not in clock ticking repair job environment) best way is to dismantle entire pcb from amp (mark all wires and their places on pcb!!!),then desolder and check one by one (I repeat-one by one) semiconductor ,put it back or replace if needed;
check also suspicious (if any ) resistors, replace all elkos.........
without mucho miles under the b(elly) you can't count on "speedy finding the culprit " approach
nick holme said:
I know that Ana..Chris will agree with me-in DIY world (not in clock ticking repair job environment) best way is to dismantle entire pcb from amp (mark all wires and their places on pcb!!!),then desolder and check one by one (I repeat-one by one) semiconductor ,put it back or replace if needed;
check also suspicious (if any ) resistors, replace all elkos.........
without mucho miles under the b(elly) you can't count on "speedy finding the culprit " approach
Hi Zen Mod,
Of course I agree with you! Your approach is also valid in a commercial repair enviroment if the equipment is good. Anything but doing the job twice!
I often would check every transistor in a channel, and that has saved me a lot of troubleshooting time.
I still like "Choky" as a handle.
Nick, with Japanese semiconductors, there is only one manufacturer per device number. So if there is a different name with the same type number, it's a fake! I also test new parts before installing them.
-Chris
Of course I agree with you! Your approach is also valid in a commercial repair enviroment if the equipment is good. Anything but doing the job twice!
I often would check every transistor in a channel, and that has saved me a lot of troubleshooting time.
I still like "Choky" as a handle.
Nick, with Japanese semiconductors, there is only one manufacturer per device number. So if there is a different name with the same type number, it's a fake! I also test new parts before installing them.
-Chris
I think you are right. Looking at the other amp, TR5 has already been replaced so I'll start there. Incidentally, what are ELKOs?
Nick
Nick
Hi Nick,
I think he means electrolytic capacitors. Worthwhile to replace at this time if you don't have an expensive cap checker.
-Chris
I think he means electrolytic capacitors. Worthwhile to replace at this time if you don't have an expensive cap checker.
-Chris
Hi all,
that's interesting about fake transistors. When I look, the old one was Hitachi 2sd676 and the new one is Tesla 2sd676. The Can looks quite different and the legs were thicker - I had to drill out the holes in the circuit board in order to mount it. Is having transistors from two different manufacturers likely to cause the effect that I quoted (crackle on switch on and this amp louder than the other) as the small transistors are all testing OK. Also I notice that the other amp has Toshiba 2sd424 power transistors. Although a spec sheet that I found on the web quotes these as being alternatives, could this explain the difference in loudness?
Also, Is it only the two electrolytic capacitors C5 and C10 that need changing?
Cheers
Nick
that's interesting about fake transistors. When I look, the old one was Hitachi 2sd676 and the new one is Tesla 2sd676. The Can looks quite different and the legs were thicker - I had to drill out the holes in the circuit board in order to mount it. Is having transistors from two different manufacturers likely to cause the effect that I quoted (crackle on switch on and this amp louder than the other) as the small transistors are all testing OK. Also I notice that the other amp has Toshiba 2sd424 power transistors. Although a spec sheet that I found on the web quotes these as being alternatives, could this explain the difference in loudness?
Also, Is it only the two electrolytic capacitors C5 and C10 that need changing?
Cheers
Nick
Hi Nick,
The Tesla 2SD676 isn't a real part, it is a fake.
Toshiba 2SD424 and 2SB554 are excellent transistors. They where a standard part I used to stock. They are no longer available new. At this point I would be looking at On Semi MJ15022 / 23, MJ15024 / 25 or MJ21193 / 94, MJ21195 / 96. Make sure you buy from authorized On Semi distributors. Never shop on price alone!!
-Chris
The Tesla 2SD676 isn't a real part, it is a fake.
Toshiba 2SD424 and 2SB554 are excellent transistors. They where a standard part I used to stock. They are no longer available new. At this point I would be looking at On Semi MJ15022 / 23, MJ15024 / 25 or MJ21193 / 94, MJ21195 / 96. Make sure you buy from authorized On Semi distributors. Never shop on price alone!!
-Chris
Thanks Chris. I have a source for 2sd424's so I'll replace both power transistors for a pair of these and see what happens.
Nick
Nick
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Hi again.
Well, I have replaced the two power transistors with a pair of Toshiba 2sd424's and the volumes are now about the same on both amps.
All i'm left with now is a very loud "clack" when I switch on. I also notice that there is a faint noise also after I switch off for about 1.5 seconds as if a capacitor was discharging. The noise on switch on is loud enough to cause the speaker cone to move quite some distance - I'd worry about damaging my speaker if I was to leave it like this. Any ideas what this could be?
Cheers
Nick
Well, I have replaced the two power transistors with a pair of Toshiba 2sd424's and the volumes are now about the same on both amps.
All i'm left with now is a very loud "clack" when I switch on. I also notice that there is a faint noise also after I switch off for about 1.5 seconds as if a capacitor was discharging. The noise on switch on is loud enough to cause the speaker cone to move quite some distance - I'd worry about damaging my speaker if I was to leave it like this. Any ideas what this could be?
Cheers
Nick
Hi Nick,
You really have to check the rest of the parts in that amp. Something is clearly not right. It sounds like you have a DC offset that takes time to correct. It could be an open or leaky transistor, open resistor - anything.
Pretend you've never seen the amp before and check everything. Do not assume anything, write down what you actually measure as you go.
-Chris
You really have to check the rest of the parts in that amp. Something is clearly not right. It sounds like you have a DC offset that takes time to correct. It could be an open or leaky transistor, open resistor - anything.
Pretend you've never seen the amp before and check everything. Do not assume anything, write down what you actually measure as you go.
-Chris
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