Hi Valo,
Nice amp you've made there. If I'm not mistaking, it is the original Crescendo from 1982.
I've build it myself to. My first prototype used fans also, but they where making to much noise on low level output. So I bought bigger heatsinks. I'm wondering if your heatsinks are big enough. My heatsinks (150x200x40mm, 0,4K/W) are heating up to about 65°C with a roomtemperature of 25°C.
How much VA is your powersupply, 4x300VA I guess? Did you use trannies with a secondary voltage of 50VAC? I've had to use two 55VAC secondary's to get a total of 148VDC
And out of what material is your frontpanel made? It looks cool.
What have you used for source resistors? Don't use wirewound resistors, the amp wil be oscillating than. I used 4 x 1ohm/1W in parallel.
It runs perfectly for about 3 years. Sound is good.
Pics of my amp, see:
http://groups.msn.com/BenJanssen/6kanaalsaudioversterker1.msnw?albumlist=2
Cheers
Ben
Nice amp you've made there. If I'm not mistaking, it is the original Crescendo from 1982.
I've build it myself to. My first prototype used fans also, but they where making to much noise on low level output. So I bought bigger heatsinks. I'm wondering if your heatsinks are big enough. My heatsinks (150x200x40mm, 0,4K/W) are heating up to about 65°C with a roomtemperature of 25°C.
How much VA is your powersupply, 4x300VA I guess? Did you use trannies with a secondary voltage of 50VAC? I've had to use two 55VAC secondary's to get a total of 148VDC
And out of what material is your frontpanel made? It looks cool.
What have you used for source resistors? Don't use wirewound resistors, the amp wil be oscillating than. I used 4 x 1ohm/1W in parallel.
It runs perfectly for about 3 years. Sound is good.
Pics of my amp, see:
http://groups.msn.com/BenJanssen/6kanaalsaudioversterker1.msnw?albumlist=2
Cheers
Ben
Hi Bensen
My heatsinks are ok, the temperature are aobut 60C, and the fan is not in use..
The›powersupply is 4x400VA, It is a overkill and i have problems starting up the amp, My spftsrater is to slow..
I also used 4x1ohm/1w for source resistors.
Frontpanel was med of plexiglass, and I painted it black on one side, gives me the electrocompaniet look
Sorry for My bad English
My heatsinks are ok, the temperature are aobut 60C, and the fan is not in use..
The›powersupply is 4x400VA, It is a overkill and i have problems starting up the amp, My spftsrater is to slow..
I also used 4x1ohm/1w for source resistors.
Frontpanel was med of plexiglass, and I painted it black on one side, gives me the electrocompaniet look
Sorry for My bad English
Attachments
a Crescendo problem
I builded my crescendo, the 1982 one from elektuur already two times, but always have the same problem. The crescendo works but after a couple minutes there exist a noisy sharp sound that rises up. and then after about 5 minutes collaps C14 or C15(the big Elco's on the PCB's) only one will explode.I checked the polarity for mor than 100 times, but still have this problem, can anyone help me. I think is't something stupid,
Is there maybe a fault in the chematic that i don't have? I think sombody told me ones there was a fault in the chematic, is it true am I the problem.
I hope somebody can axplain my problem, because I builded it complete and it looks very ok, only the sound don't works.
I'm from Belgium.
I builded my crescendo, the 1982 one from elektuur already two times, but always have the same problem. The crescendo works but after a couple minutes there exist a noisy sharp sound that rises up. and then after about 5 minutes collaps C14 or C15(the big Elco's on the PCB's) only one will explode.I checked the polarity for mor than 100 times, but still have this problem, can anyone help me. I think is't something stupid,
Is there maybe a fault in the chematic that i don't have? I think sombody told me ones there was a fault in the chematic, is it true am I the problem.
I hope somebody can axplain my problem, because I builded it complete and it looks very ok, only the sound don't works.
I'm from Belgium.
Re: a Crescendo problem
Or could be thermal runaway, if not all relevant components have thermal contact. Transistors or diodes for the bias setting often need to be thermally connected to the same heatsink as the power stage or even directly to the power transistors.
Sounds like oscillation. Maybe some of the information here is useful. The Crescendo seems to easily become unstable, when the bias setting is not correct.WimVL said:
Or could be thermal runaway, if not all relevant components have thermal contact. Transistors or diodes for the bias setting often need to be thermally connected to the same heatsink as the power stage or even directly to the power transistors.
I've commented on this amplifer before, but here goes again.
This is a 1980's design and back then the philosohy was in general the higher the loop gain the better. Nothing wrong with that point of view, but then you have take some design precautions to ensure the amplifer behaves.
There is no dominant pole compensation so the amp perfomance is overly sensitive to layout, component tolerances, EMI ingress etc. On top of that, Mosfet suppliers are notorious for reducing chip size on a regular basis (to remain competitive) and this often affects key parameters like input capacitance etc. On this design, that will impact the stability.
This amp could do with miller caps between the VAS Cascode collectors and the bases of the VAS transistor (sorry, cannot read the references on the posted copy - they are a bit blurry).
Maybe Bob or Glen want to comment.
Anyway, good luck with your amp - if you can get it stable no doubt it will sound good.
(My first Elektor amp was the 'Equa' - I think it was about 1978 or 1979 - if anyone has a copy of the schematic, I'd really appreciate it if you would post it).
This is a 1980's design and back then the philosohy was in general the higher the loop gain the better. Nothing wrong with that point of view, but then you have take some design precautions to ensure the amplifer behaves.
There is no dominant pole compensation so the amp perfomance is overly sensitive to layout, component tolerances, EMI ingress etc. On top of that, Mosfet suppliers are notorious for reducing chip size on a regular basis (to remain competitive) and this often affects key parameters like input capacitance etc. On this design, that will impact the stability.
This amp could do with miller caps between the VAS Cascode collectors and the bases of the VAS transistor (sorry, cannot read the references on the posted copy - they are a bit blurry).
Maybe Bob or Glen want to comment.
Anyway, good luck with your amp - if you can get it stable no doubt it will sound good.
(My first Elektor amp was the 'Equa' - I think it was about 1978 or 1979 - if anyone has a copy of the schematic, I'd really appreciate it if you would post it).
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