anatech said:Hi Fotios,
We meet again.
The time constant of the collector and die is probably what makes the difference. I normally use small TO-92 transistors. A small hole is drilled into the heat sink that the transistor just fits into. Some thermal compound helps minimize air pockets.
Interestingly Denon, on some models, installs a pair of diodes between the collector and emitter leads of the driver transistors to sense their temperature. This seems to be effective as well. The thin Zetex parts in their modified TO-92 case may fit in between very nicely.
-Chris
Hi Chris
. Where were you so many days? I lost you. I know very well this scheme that you propose; because as you know it is used in the amplifiers of a well known American company of which i am authorized service technician for 20 years. I quote below the circuit arangement and you understand.An externally hosted image should be here but it was not working when we last tested it.
"fotios
" "fotios"Verry good approach. All diodes are fitted in the heatsink with thermal compound. The only problem it is the "special selected" double diodes MZ2361. Indeed, in the case of fault i was forced to pay 10Euros! for each one in the central service in Greece to replace them because they provided directly from the factory found in Mississippi state
"fotios"Before some years I used a BC549 mounted in a drilled hole on heatshink with thermal compound - as you exactly - but now I use a BD137 or a BD139 mounted exactly at the center of heatsink with success and for easiness in mounting. You can detect this transistor in the photo bellow between the two drivers. Don't confuse with the TO220 in the right of BD137, it is simply a temperature sensor LM35DT.
An externally hosted image should be here but it was not working when we last tested it.
Nordic said:
Hi colleague Nordic
I know the brand WIMA but i don't know the type FKP. I suppose it is polypropylene type (from last character KP). If you throw a carefully glance in the photo, the grey color caps are of MKP type, instead the orange are MKT. The only difference that i know about these two types, it is that MKT are faster and more abrupt in discharge cycle from the MKP type. I know this from a suggestion of a technician of a company from which i was buy caps for snubber use in the past when i builded Dimmer Packs. He said me that the use of MKT cap in the snubber it is in place to cause damage in the Triac due to its fast discharge, and prompted me to chek it with the scope and to use MKP type cap. Indeed, i maked the experiment and ascertained that he was right. Of course this it take effect in mains electric of 50 to 60 Hz applications. Thus, i am bothering maybe the MKT type generate some oscillations in circuits which operate in higher frequencies. On the other hand from experimenting i discovered that, when a little buzz it passes to supply rails in the amplifier PCB the MKT cap it rejected this much more from the MKP. I don't know for the last and i can't to confirm it because maybe it was incident in a concrete implementation of a concrete amplifier.
Fotios
Hi fotios,
For audio use you should choose capacitors in this order. Versus (obtainable) dielectric: 1. polystyrene: 2. non-metalized polypropylene 3. metalized polypropylene
Versus manufacturer: 1. Wima 2. Roederstein (I agree with Nordic)
You are currently using poor quality capacitors.
Your assumptions in post #24 are nonsensical. The subject is investigated thoroughly and you can very unlikely make new (correct) findings.
For audio use you should choose capacitors in this order. Versus (obtainable) dielectric: 1. polystyrene: 2. non-metalized polypropylene 3. metalized polypropylene
Versus manufacturer: 1. Wima 2. Roederstein (I agree with Nordic)
You are currently using poor quality capacitors.
Your assumptions in post #24 are nonsensical. The subject is investigated thoroughly and you can very unlikely make new (correct) findings.
janneman said:
Hi Jan
It is "mine" design. Actually it is a compilation of different - well known - topologies in each stage. It is exactly of the same architecture of "Dirty Harry" - if you remember it - but implemented with higher quality parts. I have made a prototype before 2 years with success and beautifull sound - for a class A-B type- . That you see in the photo, it is a trial revision in which i will replace the small MPSA-55/56 with the better 2SA970/2SC2240 of Toshiba. I have ordered already the transistors ( from Farnell
) and some better type caps. The output devices are the common MJL21193/21194 and the VAS EF pair (according D.Self) and the drivers are MJ15030/15031. The emitter resistors are MPC (non inductive).Unfortunatelly, because the PCB constructors are speculators in Greece i am forced to make in home the few prototypes such this in photo. Necessity knows no laws! When i finished the prototype i will post it for review from you and some other persons (there is no need to report their name, they know who are from alone).Please take a look below for the cap discussion. I need also your advice.
Fotios
Hi NordicNordic said:
Unfortunatelly form WIMA i can't find the capacities that i use. From Roederstein yes. From the two brands offered only metalized MKP caps. In the place of Cdom and generally in the filters it is good the silvered mica type (because it is offered in all of pF range)??
Fotios
Lumba Ogir said:
Hi Lumba Ogir
Thanks for the advices. Indeed the type of electrolytic caps it is poor but i have ordered already Panasonic ECA series for replacing. The rest: 1) All the ceramic caps will be replaced by silvered mica type. 2) The grey colour capacitors are indeed metalized polypropylene for decoupling purpose and in the tail of zobel network. 3) For the orange caps i am not sure if they are MKT or MKP type because there is not mark on them and they are of the same case style exactly. To this i will order again some pieces to be sure. The light blue are MKT type but they used in the VI limitter circuit. There is reason to replace them with MKP type?
As for the brands you report i can find only from Roederstein. Also i need for a preamplifier that i build - for the line input - non metalized polypropylene caps of 2,2mF (such as those used in loudspeaker crossovers) but i can't find them. Have you any suggestion to this?
I am waiting for your reply
Regards
Fotios
Lumba Ogir said:
Finally i found non metalized polypropylene caps of brand "LCR" at 2,2mF/630V in Maplin Electronics for 5,5 Euros each. These capacitors are big in size and usually used in loudspeaker crossovers. It is appropriate for my preamp. line input? LCR it is a good brand? The only alternative that i have in my stock it is 2,2mF/63V MKT type of logical size. What may i do furthermore? Please, i am confused this moment. It is worthy the improvement of audio quality and how much by replacing these capacitors? Because i may to spend again money. And because all of them ordered from UK either from Farnellfotios said:
or from RS components or from Maplin may added the shipping cost which is from 13 to 20 Euros for each dispatch. Fotios
Lumba Ogir said:
Dear Lumba Ogir
The audio it is my occpation for 25 years. During these years mainly i am occupied with proffesional audio systems. I have builded enough P.A. amplifiers - only BJT - of enormous power. Usually the supply that i use it is from +/-80V and above, . As maybe you understand, in such power amplifiers (AB class) due to their dynamics the quality of capacitors lose his value. So the use of MKT or ceramic capacitors or a electrolytic in input does not matters in such type amplifiers. I have builded in the past 3 or 4 Hi-Fi amplifiers and due to this i have not so big experience with low power level (for domestic use) appliances. That is the reason for my ignorance about the difference in sound quality between KP or MKP caps. My scope actually of use special capacitors it is to cause impression. Anyway, thanks for the lessons. Fortunately i am good pupil and thus i am a quick learner. After 2 hours of searching i resulted in the use of MKP capacitors before J. Curl advice me the same.
Fotios
Hi fotios,
so you want to be an audiophile...
Audio is a special field within electronics. Beside the functional features, there is a delicate matter to handle: sound quality. You are approaching this in a confused manner and the more you know the more confused you get. (Unlike the ancient Greeks).
As all components will affect the sound to some extent, each one should be selected carefully. Their properties determine an upper limit: you can not use inadequate parts and still get nice sound. The laws of physics would never allow that.
I especially dislike ceramic capacitors, these are ugly types and should not be used in audio at all. Silver mica is not much better either.
Again, best sonic performance provide film capacitors with low dielectric absorption.
It is not possible to prove or disprove sound quality by measurements. When in doubt, please read the comprehensive documentation and even better, carry out listening tests.
so you want to be an audiophile...
Audio is a special field within electronics. Beside the functional features, there is a delicate matter to handle: sound quality. You are approaching this in a confused manner and the more you know the more confused you get. (Unlike the ancient Greeks).
As all components will affect the sound to some extent, each one should be selected carefully. Their properties determine an upper limit: you can not use inadequate parts and still get nice sound. The laws of physics would never allow that.
I especially dislike ceramic capacitors, these are ugly types and should not be used in audio at all. Silver mica is not much better either.
Again, best sonic performance provide film capacitors with low dielectric absorption.
It is not possible to prove or disprove sound quality by measurements. When in doubt, please read the comprehensive documentation and even better, carry out listening tests.
Lumba Ogir said:
You cannot give off blanket statements like that. There are many voltage regulators, for example, that oscillate with good quality film capacitors. They REQUIRE lossy caps like ceramics to function as designed.
Replacing the ceramics in such a place with films would be a huge step backwards.
There are more examples. You really need to know what you are doing.
Jan Didden
Lumba Ogir said:
Hi Lumba Ogir
Also me I don't like the abuse of use of ceramic caps, probably in a device of Hi-End class. Do you advice me the use of a polypropylene cap in the place of Cdom pole compensation? Instead a silvered mica? Sorry for my ignorance, but i am not sure that a KP or MKP cap has a satisfactory dV/dt part (in other words reaction speed) to suppress the fast oscillations (extended to the range of decades MHz due to the type of VAS transistor) caused from the Miller capacitance of the common emitter VAS transistor. Also I am some reserved and for the silvered mica type and i use it with big care.
If you have a better informing about this item will be appreciated from me.
Regards
Fotios Anagnostou
