Schematic shows two 10.000uFd caps in the power supply. Assuming this is ten-thousand, it seems "large" to me.
Yeah, without spitting hares, 300W in 8 Ohms.
Also the HA17741 is a laughable 2nd generation Hitachi op amp. 1 v/usec slew rate, likely to miss all the highs. No noise spec, likely to hiss like a boiler. For living examples, consider the first generation Peavey CS800 from 1980?. SC5278 op amp was really a LM355 or 741. Hissy, suitable for low frequency guitar source only very loud. Repair shops used these as door stops. By contrast a CS800x with NJM4560 or 4580 op amps is quite good sounding in hi-fi service.
About power claims. there are 1/10 second power claims, all over the internet. Lots of ali/ebay/amazon amps with tiny heatsinks. There are 24 hour 7 day a week power claims from manufacturers who have earned a reputation on the market for reliability. The latter are much better used & blown up than any new board rated for peak power. At least you get decent heat sinks already machined for ultra tough TO3 output transistors (originally MJ15024/25), and likely also a ball bearing fan.
About power claims. there are 1/10 second power claims, all over the internet. Lots of ali/ebay/amazon amps with tiny heatsinks. There are 24 hour 7 day a week power claims from manufacturers who have earned a reputation on the market for reliability. The latter are much better used & blown up than any new board rated for peak power. At least you get decent heat sinks already machined for ultra tough TO3 output transistors (originally MJ15024/25), and likely also a ball bearing fan.
Last edited:
Yeah, this seems inspired by a rather old design... nobody uses a 741 any more these days. Expect 40-ish nV/√(Hz). More recent designs have employed the likes of LM318, NE5534, µPC4570 or NJM4580.
The 50k pot and 680p input capacitance is perhaps not the most advantageous combination ... lacking some series R as well.
Even for a 250-300 Wpc amplifier, a gain of 40 dB seems like rather a lot. I don't think an input sensitivity of <500 mV is required for a power amp, even the pro audio guys will generally be shooting for 0 dBu (0.775 mV) only.
The 50k pot and 680p input capacitance is perhaps not the most advantageous combination ... lacking some series R as well.
Even for a 250-300 Wpc amplifier, a gain of 40 dB seems like rather a lot. I don't think an input sensitivity of <500 mV is required for a power amp, even the pro audio guys will generally be shooting for 0 dBu (0.775 mV) only.
Last edited:
hi indianajo
what is you opinion of rotel gear from the 80's/early 90's eg RB-850 & 870 ??
Why would you need anymore than 10kuF?
Crown with their 5kW amp only uses 12kuF and they sound phenomenal.
Rotel doesn't sell here, no opinion. At least that era gear will have leaded components you can solder with a $45 soldering iron. Not too many ribbon cables either which oxidize & lose contact on 2v signals in about 10 years.
Top 4 in PA market, Peavey, Crown, QSC, Yamaha. Repairmen on PA thread have recommended them. I own 3 Peavey's I bought used & repaired, they are tough and sound good. Don't buy peavey cs800 no suffix without the grill in the front panel (which is the cs800x). rev a,b,c anyway have those hissy 741's first op amp. PV-4c sounds great on HDTV source, cs800s is better. Saw a CS800x running here on craigslist (local pickup) for $100 in December. Bought PV-4c last spring on ebay for $20 "for parts or repair", including freight. $20 in output transistors, $30 in new filter caps, a few bipolar caps replaced, runs & sounds great. Some "for parts or repair" amps can require 130 parts like the PV-1.3k I bought & repaired. Roll the dice, take what you get. Fixing one, you learn a lot. Peavey gives away schematics & runs their own repair forum. Stocks weird unavailable parts.
Don't buy a crown DC300, it is designed to put out DC, which burns speaker coils. Was popular PA choice in 1976.
Church I tune pianos for has a QSC 1602, about 10-15 years old, running fine once a week. The sennheiser wireless mikes are *****ing out with old age but the amp runs on.
Another church I tune piano for has a 20 year old Crown, working great.
Another church I install organ parts for has a Peavey, 15 years old, works fine.
Alesis RA-100 gets a lot of recommendations on this thread, runs about $100 here in used running condition.
Last edited:
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.