I got a Crown D-150A for $40, there are not too many modifications out there, the only thing about to upgrade is the op amps
The original op-amps are the ua739PC
according to this video the tech used
https://www.ebay.com/itm/2838610294...IH1Z77Mr+2n8gej56r15kc3g==|tkp:Bk9SR9SKmrz1YQ
this adapter and the 5532 op amp, however he did not get good result and went back to the originals
Anything else I can use that will yield better results ?
The original op-amps are the ua739PC
according to this video the tech used
https://www.ebay.com/itm/2838610294...IH1Z77Mr+2n8gej56r15kc3g==|tkp:Bk9SR9SKmrz1YQ
this adapter and the 5532 op amp, however he did not get good result and went back to the originals
Anything else I can use that will yield better results ?
Ua739 is NOT a standard op-amp. It is an old design that used external compensation, in this case tuned to be part of the power-amp. An op-amp like 5532 has internal compensation designed for unity gain by itself, and not well suited to be part of a power amp. It may be possible to modify the circuit to work with 5532 etc, but expect to fight with stability problems. This is an old question. See https://www.diyaudio.com/community/threads/ua739-op-amp-replacement.86796/
If you are not happy with the original DC150, I would replace the entire amplifier module(s).
If you are not happy with the original DC150, I would replace the entire amplifier module(s).
Power rails are +-45 vdc. There is no DC on speaker protection, and there are output offset pots which are a known failure point if the pot wiper loses contact. I'd salvage the power supply heat sinks & fan, ditch the boards. There appear to be a single pair of output transistors quasicomp. The schematic says the crown has motorola 2n5631 outputs which was really along time ago.
Diyaudio honeybadger is +-60. Those boards are kind of big even if it would work. Triple parallel output transistors.
Single IC amp ST TDA7294 could work. See if you can buy it with a board. Specified for maximum +- 50 vdc.
Here is a quasicomp 2sc5200 single output amp schematic somebody posted years ago. You already have the output transistors on the heatsink. Don't believe the 150 w title out of a pair of 2sc5200. For 10 seconds maybe. The crown already has the output inductor parallel a 2 w resistor to keep AM/CB/police/fire radio from feeding back from the speaker wires. The 2sc5200 schematic doesn't have speaker ringing back diodes across the output transistors, add them. No, 1n4148 and 1n4003 aren't big enough. Use 3 amp or bigger anti-ring diodes.
Diyaudio honeybadger is +-60. Those boards are kind of big even if it would work. Triple parallel output transistors.
Single IC amp ST TDA7294 could work. See if you can buy it with a board. Specified for maximum +- 50 vdc.
Here is a quasicomp 2sc5200 single output amp schematic somebody posted years ago. You already have the output transistors on the heatsink. Don't believe the 150 w title out of a pair of 2sc5200. For 10 seconds maybe. The crown already has the output inductor parallel a 2 w resistor to keep AM/CB/police/fire radio from feeding back from the speaker wires. The 2sc5200 schematic doesn't have speaker ringing back diodes across the output transistors, add them. No, 1n4148 and 1n4003 aren't big enough. Use 3 amp or bigger anti-ring diodes.
Attachments
Last edited:
Yes. diyaudiostore is a usually reliable source. Their only other choice I can see is a 10 watt class A project which would be total wimpdom in my music room. With 98 db 1w1m speakers I run 1/2 watt usual which only gives 40 db available for music which can have 55 db peaks on LP, 72 db for CD.
Honeybadger boards are pretty huge, won't fit in any of my donor amp chassis.Honeybadger output transistors line up down one edge, which won't fit a $25 (for parts) PV-4c chassis but will fit those $300 chassis available on ebay with 2X $80 heatsinks down both sides.
I'm happy with a 72 w/ch amp (5 seconds at a time) which I built from Apex AX6. https://www.diyaudio.com/forums/solid-state/236256-retro-amp-50w-single-supply-42.html Single pair quasicomp outputs, but it uses 70 v rail, which would be +-35 v if one left out the center tap of a transformer. AX6 does come with auto-DC protection in guise of a $3 3300 uf cap series the speaker. I'm using MJ15003 equivalents, (NTE60) which may have a little more SOA than 2n5631.
Last edited:
The last version of the DC300A Series II used an LF357H for the opamps. The DC150 circuit is pretty much the same. Not sure if it's feasible to retrofit them if you could find some.
Craig
Craig
One thing that can be done with ANY of those old class B amps is to convert the output stage to complementary and increase the bias to at least 3mA per output transistor. You can usually get away with more, but not always up the the usual 30mA without adding fans. A higher bias does sound better if you don’t make an oscillator out of it. The full comp output stage is more STABLE, and therefore able to deal with a wider range of bias. Although on one this small QC is not usually an issue like when running big parallel banks on the edge of voltage oblivion.