Thanks, good information!
If the audio output chip needs 8 vdc to produce 410 mW/channel, would it produce proportionally less power on 4.5 or 3 vdc?
For mono, can you tell if the channels are shorted together before or after the amp, and are both channels connected to the single speaker in most ULR's, or just one channel of the amp?
I seem to get some noise or distortion if I short the stereo headphone output for mono, connected to an external mono amp, but much more if I tune an FM station in stereo. [I am not surprised]
On the DSP CR-1100 large portable, it does have a line output jack, and shorting that for a mono amp is cleaner sounding than shorting the headphone output. Same result with the SONY ICF- 7600G.
Thanks to your information, I tried some non-powered stereo computer speakers on the PL-310. I got pretty clean sound on FM stereo, but had to set the volume around 20, instead of around 10, to have the same volume in the room. On the CR-1100, I guess it has a more powerful headphone amp, or the 6 vdc gives louder room volume on the computer speakers. I checked those speakers with an Ohm meter, and each one measures just above 8 Ohms.
It sounds like any of my DSP ULR's will drive a pair of 8 inch Jensen, EV or Altec PA speakers as well as the PL-390. As soon as I can rig a patch cord, I'll try that out. That was my original goal.
For driving a mono amp, I might order one of the ground loop isolators used in car stereo. They are an isolation transformer for line level audio I think, and may prevent the channels from actually shorting. Anyone already tried that idea?
Thanks for all the help.- FARMERIK
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--- In ultralightdx@..., Rick Robinson <w4dst@...> wrote:
On 12/24/2010 5:22 PM, farmerik wrote:
Could any one who has a PL-390 answer a few questions for me? Does the line input jack work as a line output jack as well? [my CR-1100 seems to].
What impedance are the speakers inside?
How many mW output/channel?
Does the headphone out use a small 20-40mW amp, or just connect the stereo head phones in place of the speakers?
I am thinking of buying one to use more as a table radio with larger, but highly efficient speakers, or driving a stereo amp with the PL-390.- FARMERIK
Farmerik and others,
I've been hacking into all my ULRs and have found the same audio output
chip in all of them. My CCrane SWP, G8, PL-310 and PL-380, and I assume
about any small Chinese made portable, use the same CD1622CD audio
output chip. This is a 16 pin 2 channel output SMT IC rated at 410mW
per channel into 8 ohms with a maximum VCC of 8VDC. The headphone
output appears to merely take the place of the internal speaker or
speakers, when plugged in. I think it's a safe bet that the PL-390 is
not different from any of the other ULRs as far as the audio output chip
used. From what I can tell about the Si473X family, they output both
of their audio channels as mono unless stereo is detected in the FM
band, in which case the output is stereo. There are a lot of "smarts"
in the Si473X chips, but another processor is used to drive the LCD, and
input the parameters such as selectivity, frequency changing, memory,
etc. to the Si473X. Does anyone know what processor is used to drive
the Si4734?
These CD1622CDs are most likely the source of white noise which folks
find objectionable in their ULRs. The CD1622CD is by no means an
audiophile chip, it is merely a small low cost SMT device made for the
portable radio industry. In fact, the only data sheet I have been able
to locate for the CD1622CD is in Chinese. The specs do use English so
it does make it easy to interpret the parameters. Just because the
specs call for an 8 ohm impedance for speakers, doesn't mean the
speakers in the ULRs are 8 ohms. It just means they will drive an 8 ohm
speaker to a maximum of 410mW. There could be 32ohm speakers in some of
these ULRs, who knows?
Burkhard Kainka, the designer of the Elektor DSP receiver uses 2 LM386 8
pin DIP amplifier chips instead of the CD1622CD. This is an improvement
over the CD1622, still not audiophile quality but a significant step
forward. He also uses the well known and easily programed ATmega 168
microprocessor to drive the Si4735 in the Elektor DSP receiver. His
ATmega interface is almost identical to the Arduino Duemilanove board.****
****
Rick W4DST
