Recent content by Peter S

Slowly coming together! I have spent way too much time on this project! So many modifications to this amp. Initially I dipped the transformer 20 times in electrical vanish to stop the buzzing noise. Fans were replaced with quieter models. I abandoned the idea of making it passively...

With a little help from my friends, I was pointed to C8 on page 4. It is a 2.2 ufd film cap. I bypassed it with a 20 ufd film cap (sledge hammer approach). The response rose at 5 hz...this is probably dangerous! I will try 10 ufd. Could I use a good quality electrolytic rather than a...

On page 4 of the schematic, there is a SERVO/HIGH PASS section but I am unclear as to which cap (or resistor?) could be changed to remove or at least reduce the effect of the high pass filter. Thanks again for all your help.

The next dilemma is a built in high pass filter in the Crest. I have noticed a distinct improvement in the extreme low frequency response of a temporary replacement amp, a Peavey GPS3500. I measured the Crest CA-18 and the Peavey GPS3500 just to make sure I was not imagining things. I...

An update on the Crest catastrophe; The caps from China came in and of course they measure 15,000 ufd instead of 18,000. I could live with that but they are 130 mm tall and the ad claimed they were 118 mm. I was warned..... At the moment, the amp seems to run quietly with four 9,500 ufd...

What about removing / moving / changing the value of R 10 and R 12 on the fan driver board (page 2) The connection of Q 3 and Q 4 to the regulators via R 11 and R 16 (voltage divider) seems to reduce the effect of temperature change unless I misunderstand

So back to the fan issue. I have discovered the location of the temp sensors. The blank terminals must be for use with a different model. The LM35D temp sensor spec claims + 10 mV per 1 degree C. The sensor circuit seems to be working (to some degree, bad pun). Holding a soldering...

Getting in over my head---again. I have been using a Peavey GPS 3500 (about 600 WPC / 8 ohms) and it sounds great. Bass sounds deeper. I have discovered that the Crest has a non-switchable sub-sonic filter....This just won't do. I will have to reconnect the Crest with all the pieces out...

Hi Jim, they are 24 Volt fans but the series trick would still work. I have just discovered this morning that this amp does not have any temp sensing (see pics in entry #47 above). Maybe installing a sensor would solve the problem...No info yet on what sensor was called for.

J4 on the schematic is supposed to be connected to some sort of 3-pinned temp sensor presumably on the heat sink.

Further puzzlements, the manual says fans are governed by heat sink temperature but I have never heard the fans 'rev up' on start-up. Nor have I heard much change in fan speed, even after heavy use.

Too late, they're on their way...

That's funny Glen! But I have to confess that the clip lights have flashed on a few occasions. Pink Loyd on the 150" screen can get me carried away. Hi Jim, I bought the quietest fans I could find in that size about 7 years ago OK, further confession; I slowed the new fans a little more...

Thanks George. I have already ordered the 18,000 ufd caps from 'overseas' so I will wait for them to arrive to see if I have been bamboozled. I will keep that in mind. I suppose I could always phone Mouser or Digikey too. I have previously replaced the fans with quieter, lower CFM units...

Thanks, guys, I'm bracing myself for the disappointment. My meter can only measure capacitance up to 15,000 ufd, Hopefully it won't get a reading. I see mouser has 15,000 ufd 80 V caps that would fit. I was concerned about consequences of going from 18,000 (called for) to 15,000 ufd.