Re: DOXA-70
Just for fun I looked up the BD245C here in the US. Digikey does not sell it and Mouser considers them obsolete. You'd have to update the BOM with modern parts to really build it, I think.
However, the circuit does have some merit, IMHO. I like the front end and the fact that this is a true DC amp, other than the one input coupling cap. No bipolar/'lytic cap in the feedback path. No miller caps on the Vas....No frequency compensation caps at all. No output zobel... No output inductor....hummmm. Not a big fan of pots, other than the pot in the Vbe circuit. P1 is probably a "zero-the-output" pot. Don't know what Q26, Q27 do either. Missing a few other parts to make it a "commercial" amp, IMHO.
It looks like a solid 70 WPC/8 ohms (+-38volts) and with 5 outputs per side, 4 ohms should be no problem and maybe 2 ohms wouldn't bother it too much.
I will input it into LT_Spice with modern SMT transistors and see how it works. Should answer any stability questions as well. Check back in a day or so.
Bill
Just for fun I looked up the BD245C here in the US. Digikey does not sell it and Mouser considers them obsolete. You'd have to update the BOM with modern parts to really build it, I think.
However, the circuit does have some merit, IMHO. I like the front end and the fact that this is a true DC amp, other than the one input coupling cap. No bipolar/'lytic cap in the feedback path. No miller caps on the Vas....No frequency compensation caps at all. No output zobel... No output inductor....hummmm. Not a big fan of pots, other than the pot in the Vbe circuit. P1 is probably a "zero-the-output" pot. Don't know what Q26, Q27 do either. Missing a few other parts to make it a "commercial" amp, IMHO.
It looks like a solid 70 WPC/8 ohms (+-38volts) and with 5 outputs per side, 4 ohms should be no problem and maybe 2 ohms wouldn't bother it too much.
I will input it into LT_Spice with modern SMT transistors and see how it works. Should answer any stability questions as well. Check back in a day or so.
Bill
Re: Doxa-70 Spice results
Not so good. When simulated this amp does not work as drawn. I think there are schematic errors. Look at Q21 and Q2. Q21 can sink current but Q2 needs a current source to bias it. Q4 and Q23 appear to be hooked up wrong too. Maybe the collector of Q4 should be connected to the base of Q2 and the collector of Q21 should go to the base of Q23??
Ideas???
Not so good. When simulated this amp does not work as drawn. I think there are schematic errors. Look at Q21 and Q2. Q21 can sink current but Q2 needs a current source to bias it. Q4 and Q23 appear to be hooked up wrong too. Maybe the collector of Q4 should be connected to the base of Q2 and the collector of Q21 should go to the base of Q23??
Ideas???
doxa-70
Searching the web via Google yields no new schematic, other than the same error filled one in this forum, IMHO, this amp is dead on arrival if you cannot find a "working" schematic to clone. Plus there are some many other well engineered clones that this one is kind of a don't care.
I am not going to waste my time fixing it or making it work. I do not care how good it sounds.
BK
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Searching the web via Google yields no new schematic, other than the same error filled one in this forum, IMHO, this amp is dead on arrival if you cannot find a "working" schematic to clone. Plus there are some many other well engineered clones that this one is kind of a don't care.
I am not going to waste my time fixing it or making it work. I do not care how good it sounds.
BK
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')Do you remember the Hannibal Lecter movie where Paul Krendler is made to eat some soup through a tube? He responds with; "Hey buddy, this soup is not very good". Let those word be the epitome of BD245/246 as a audio transistor. The only factor where it`s score is high, would be on the low price.
And, btw, this amplifier is a mechanical nightmare. On the iterations that utilize multiple output transistors, it is more than likely that some of these are not in contact with the heatsink at all. Borrowing some words from the Sex Pistols; "Never mind the bollock`s, stop beating a dead horse".
Regards
Roar
And, btw, this amplifier is a mechanical nightmare. On the iterations that utilize multiple output transistors, it is more than likely that some of these are not in contact with the heatsink at all. Borrowing some words from the Sex Pistols; "Never mind the bollock`s, stop beating a dead horse".
Regards
Roar
Hey Roar
Do you know that Doxa it is a Greek word writen with Latin characters?
Doxa ( ÄÏÎÁ ) it means "glory" in English. Doxa it is also the name of the local foot ball club of the town Drama (north Greece) where i live.
Doxa Drama, OLE!!!
This is the link:
http://www.doxa-dramas.gr/
BTW, except Sex Pistols i like very much Green Day, Dead Keneddys etc etc. Especially a song of Green Day of which i can't write its title to not missunderstund me our friends from America.
Regs
Fotios
Do you know that Doxa it is a Greek word writen with Latin characters?
Doxa ( ÄÏÎÁ ) it means "glory" in English. Doxa it is also the name of the local foot ball club of the town Drama (north Greece) where i live.
Doxa Drama, OLE!!!
This is the link:
http://www.doxa-dramas.gr/
BTW, except Sex Pistols i like very much Green Day, Dead Keneddys etc etc. Especially a song of Green Day of which i can't write its title to not missunderstund me our friends from America.
Regs
Fotios
Ahahahha...sorry dear Fótios, but it seems Alexander the Great
would be very happy with big Brazilian Bananas (those we cook and we eat them early morning with Cynamon and a little bit of suggar).
As i could see into the movie..heheheheh...he loved Bananas.
Ancient tradition maybe.... a great warrior..no doubts....also great banana eater.
regards,
Carlos
would be very happy with big Brazilian Bananas (those we cook and we eat them early morning with Cynamon and a little bit of suggar).
As i could see into the movie..heheheheh...he loved Bananas.
Ancient tradition maybe.... a great warrior..no doubts....also great banana eater.
regards,
Carlos
Attachments
Hi Roar, slightly OT:
You seem to be an experienced audio designer, and I would appreciate some advice.
I have decided to build a high quality power amplifier for my stereo/HT setup.
Today my setup consists of a Marantz SR-4200 receiver driving Focal Cobalt 816S fronts. Sources: Oppo DVD and Rotel CD.
To start with I will hook up the power amp to the pre-out of the receiver, and use it both for stereo and HT. Later on, I might add a separate preamp fro stereo listening.
As you may know, the Cobalt 816s are very detailed speakers, and my initial thought is to build a warm or slightly relaxed sounding power stage.
I have been studying some off PASS Labs class A DIY designs (Aleph 5), as well as the SKA designs.
I have some good powerful toroids and large electrolytics lying around, and the neccessary tools and instruments.
What are your advice and suggestions on which design to choose ?
Im thankful for any help
Bjørn
You seem to be an experienced audio designer, and I would appreciate some advice.
I have decided to build a high quality power amplifier for my stereo/HT setup.
Today my setup consists of a Marantz SR-4200 receiver driving Focal Cobalt 816S fronts. Sources: Oppo DVD and Rotel CD.
To start with I will hook up the power amp to the pre-out of the receiver, and use it both for stereo and HT. Later on, I might add a separate preamp fro stereo listening.
As you may know, the Cobalt 816s are very detailed speakers, and my initial thought is to build a warm or slightly relaxed sounding power stage.
I have been studying some off PASS Labs class A DIY designs (Aleph 5), as well as the SKA designs.
I have some good powerful toroids and large electrolytics lying around, and the neccessary tools and instruments.
What are your advice and suggestions on which design to choose ?
Im thankful for any help
Bjørn
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