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Chip Amps Amplifiers based on integrated circuits

eBay mono LM1875 kit
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Old 21st August 2019, 09:13 AM   #21
chermann is offline chermann  Austria
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Quote:
Originally Posted by kurtvisti View Post
Hi Chris
I generally agree with your advice about the 25V POWERAMP LM1875 PSU, but my question was about the quality of the 15V PREAMP PSU-addition shown at LM1875_20W_diy_haoDIY.
Is that PSU-addition (used for powering a preamp) ok for hifi?
Ahh...sorry....i overread this.
generally a voltage stabilizer with zener diode is the simplest way to reduce 25V-15V. resistor and zender diode are"noisy" . so for a pre amp its important to use a very low noise psu. usage of a linear regulator + 7815 / -7915 minimum setup.
its needed to know how much current/power your preamp needs and with some margin you can search for a low noise/ultra low noise regulator (TPS7A4700)which can handle your current and the peaks.


chris

Last edited by chermann; 21st August 2019 at 09:17 AM.
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Old 21st August 2019, 01:45 PM   #22
rabbitz is offline rabbitz  Australia
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Yes, forget about that pre amp supply in the link and as mentioned above use a 781x / 791x depending on what output voltage you are after. Better still is the 317 / 337.

Have a look at ESP P05 (all versions). You can take off DC from the 25V rails from the amplifier supply so you don't need the rectifier diodes.
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Old 21st August 2019, 03:40 PM   #23
Bare is offline Bare  Canada
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Erm.. Actually one does not require a Pre amp.
This being well into the 21st century, most sources output a directly usable voltage.
That can one feed directly into a power amp .
A simple Dact type stepped attenuator serves well, being more transparent than even the best silly priced preamps.
Despite their maker claims.
Try it ? It's a very simple experiment.
IF there are impedance issues (flat sounds) a Passdiy.com B1 buffer $50$.. Ably does the matching task.
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Old 21st August 2019, 03:56 PM   #24
Bare is offline Bare  Canada
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I'm putting My faith in Rod Elliot's Circuit .
His work has proven Perennially good.
Others ? less likely so. Or at least with a lesser track record.

Despite Rod's claim (he needs make an income) his is an easy Perfboard build
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Old 21st August 2019, 05:12 PM   #25
kurtvisti is offline kurtvisti  Denmark
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I had the feeling, there were more to it than just 2 zener-diodes.
Think I'll go for Rabbitz's advice with the ESP P05.
For reference the 15V linear PSU is not for a preamp but for powering an active crossover for the chipamps.
Any suggestions for a good sounding diy 2-way opamp version?
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Old 21st August 2019, 08:20 PM   #26
Bare is offline Bare  Canada
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Crossover? suggest :-) a ...Passive... line level Crossover which uses NO op amps, No power supply
Because of that it's simple and V inexpensive to experiment with and to build.
Calculator is here;
TLS.org | Passive Line-Level Crossover

Imo even that is overkill / inappropriate given the size/range/quality of speakers an 1875 amp chip can successfully drive.
Small, and ironically as there are few made: High 80's low 90's db efficient ~4" full rangers).
Just saying .

Last edited by Bare; 21st August 2019 at 08:23 PM.
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Old 22nd August 2019, 01:40 PM   #27
rabbitz is offline rabbitz  Australia
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Quote:
Originally Posted by kurtvisti View Post
For reference the 15V linear PSU is not for a preamp but for powering an active crossover for the chipamps.
Any suggestions for a good sounding diy 2-way opamp version?
Have a look at Rod Elliott's. Boards are available and with the low AU$ reasonably priced.
ESP Projects Pages - DIY Audio and Electronics
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Old 22nd August 2019, 01:52 PM   #28
chermann is offline chermann  Austria
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Hi

any recommendation for a size of amp housing or heat sink size for this amp?
As i rad at dunk02 thread his housing was very tight
i will not install a preamp section. no knob

thx
chris
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Old 22nd August 2019, 09:59 PM   #29
Bare is offline Bare  Canada
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Originally Posted by rabbitz View Post
Have a look at Rod Elliott's. Boards are available and with the low AU$ reasonably priced.
ESP Projects Pages - DIY Audio and Electronics
Yesss... but I balked at buying... as the cost of Postage, even for a 'Quite Small' PCB is a flat 14U$. Offputting to my sensibilities.
My currently 'Iffy' Canada Post charged 7$ Cdn (5 U$)to air parcel under 100 gms to Aus .. I sent 6 postcard sized pcbs there .. under 1/2 the weight limit..
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Old 23rd August 2019, 05:43 AM   #30
chermann is offline chermann  Austria
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Originally Posted by chermann View Post
Hi

any recommendation for a size of amp housing or heat sink size for this amp?
As i rad at dunk02 thread his housing was very tight
i will not install a preamp section. no knob

thx
chris
hi

iam looking at this thread - post 56 + page 2 - and "estimating" the dimensions:
LM1875 Amp layout

the LM1875 is about 18mm (Datasheet last pages) high and 20mm extra is the high of the aluminium plate what dunk02 use for mounting on the heatsink. the pcb is 46mm long and if i look at the pic its about 4-5X the lenght

so the heatsink is about 40 x 250mm for both channels.

chris
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