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eBay mono LM1875 kit
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Old 23rd August 2019, 07:12 AM   #31
rabbitz is offline rabbitz  Australia
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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
Heatsink needs to be 1.5C/W minimum for 2 channels (ref ESP).

I use a Galaxy 288 2U (GX288) for my 3886 builds so would also suit this amp. Around EUR28 plus shipping from Modushop. Might be able to squeeze in GX283 but that's about the same price.
Galaxy Maggiorato GX288 230 x 280 mm

These cases also available at the diyaudio store.

Here's a pic of the Neurochrome 3886DR which has larger PCB and heatsink but gives you an idea. The transformer is a 160VA.
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File Type: jpg RZ_3886DR.jpg (193.3 KB, 215 views)
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Old 23rd August 2019, 07:23 AM   #32
rabbitz is offline rabbitz  Australia
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Originally Posted by Bare View Post
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..
The last PCB's I got from Canada were US$11 shipping.

I'm not trying to justify Rod's price but it is postage and handling which includes a padded envelope and his time. There is a US$7 option for under 50g which would cover a 75mm x 150mm PCB.
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Old 23rd August 2019, 09:01 AM   #33
chermann is offline chermann  Austria
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Quote:
Originally Posted by rabbitz View Post
Heatsink needs to be 1.5C/W minimum for 2 channels (ref ESP).

I use a Galaxy 288 2U (GX288) for my 3886 builds so would also suit this amp. Around EUR28 plus shipping from Modushop. Might be able to squeeze in GX283 but that's about the same price.
Galaxy Maggiorato GX288 230 x 280 mm

These cases also available at the diyaudio store.

Here's a pic of the Neurochrome 3886DR which has larger PCB and heatsink but gives you an idea. The transformer is a 160VA.
Thanks Rabbitz !

good to know that a 1,5C/W is suficient for both ....but i still not sure to use the case (cheap) like you propose with "internal" heatsink or use a small case with heatsink on both sides. ..anyway i have to look for the transformer size and CRC etc..for "designing"

1,5C/W is not expensiv:
%product-title% kaufen

%product-title% kaufen

thx
chris
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Old 23rd August 2019, 09:57 AM   #34
blackdod is offline blackdod  Europe
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Quote:
Originally Posted by rabbitz View Post
Heatsink needs to be 1.5C/W minimum for 2 channels (ref ESP).

I use a Galaxy 288 2U (GX288) for my 3886 builds so would also suit this amp. Around EUR28 plus shipping from Modushop. Might be able to squeeze in GX283 but that's about the same price.
Galaxy Maggiorato GX288 230 x 280 mm

These cases also available at the diyaudio store.

Here's a pic of the Neurochrome 3886DR which has larger PCB and heatsink but gives you an idea. The transformer is a 160VA.

I like how you set up your amplifier. I think Ill opt for the same configuration.

I have been using my amp for a month alternating headphones and monitors. I have both LM1875 attached to a single heatsink (10x6x2cms) and the temperature remains quite low at all times. Moreover, I think that the 337/317 of the PSU get hotter than the amplifier.
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Old 23rd August 2019, 02:23 PM   #35
rabbitz is offline rabbitz  Australia
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Originally Posted by chermann View Post
Just remember that the length of the heat sink in the spec is the vertical height when placed inside a case.

The width and height shown in the spec is the cross section and the length is how long it is when cut. So for a 2U case you need a length around 75mm.

To give you an idea the heat sink in the picture in my previous post is a Conrad MF15-75 with the length at 75mm which goes from the bottom of the case towards the top.
Conrad Heatsinks - Products
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Old 23rd August 2019, 02:33 PM   #36
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Moreover, I think that the 337/317 of the PSU get hotter than the amplifier.
I'm surprised you are using a regulated power supply as I just use a standard linear supply. They will get hot as I think the 337/317 are good for up to 1.5A unless used with a bypass transistor (never built one).
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Old 23rd August 2019, 02:45 PM   #37
rabbitz is offline rabbitz  Australia
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For reference, I've added a pic of the ebay module so readers know which one it is.
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Old 23rd August 2019, 04:10 PM   #38
blackdod is offline blackdod  Europe
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I'm surprised you are using a regulated power supply as I just use a standard linear supply. They will get hot as I think the 337/317 are good for up to 1.5A unless used with a bypass transistor (never built one).
Why a regulated PSU? Well, I think that as a headphones amplifier or monitors amplifier, you don't need much more than 1.5 Amp either: Its an LM1875 ... and IMO this amplifier is perfect for these things. If you need more power or you want to move bigger speakers you have other options within the Gain Clones family.

A PSU based on 337/317 is cheap and simple to get already assembled and allows you to play with the output voltage. In my case I have been altering the PSU voltage from +/-14Vdc to+/-19Vdc which has allowed me to check the performance of the amplifier.

Other reason is that a regulated PSU is silent enough so you can use headphones with high sensitivity.

Daniel in the thread "Beginner's Chip Amplifier, HiFi LM1875, The Amplifier Board" mentions the power of the transformer. If I remember correctly, talk about 1Amp

I have some measure done with headphones and I think it barely reaches 0.5 amps of maximum consumption per B rail with both channels connected (I have to check my notes).

This amplifier is so simple and so economical that I am simply dedicating myself to experiment and I recognize that it has been quite entertaining.

The only problem that I have encountered with the use of headphones iswith very sensitive headphones. You can hear the floor noise from a certain volume. The solution that I have found (without touching the gain) is to add a series resistance (50 to 100 Ohm) to the output.
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Old 23rd August 2019, 04:42 PM   #39
chermann is offline chermann  Austria
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Originally Posted by rabbitz View Post
Just remember that the length of the heat sink in the spec is the vertical height when placed inside a case.

The width and height shown in the spec is the cross section and the length is how long it is when cut. So for a 2U case you need a length around 75mm.

To give you an idea the heat sink in the picture in my previous post is a Conrad MF15-75 with the length at 75mm which goes from the bottom of the case towards the top.
Conrad Heatsinks - Products

AAAhhh. yes you are right...this heat sink are good for testing on the bench. but if it should in the case i have a "tower" of 100mm
your proposal is really nice thanks! MF15-75!

do you have a proposal for a nice small PCB or ready PSU board for this small amp. i have some board and can do point to point but for the final solution.

chris

Last edited by chermann; 23rd August 2019 at 04:55 PM.
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Old 24th August 2019, 02:19 PM   #40
rabbitz is offline rabbitz  Australia
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There are quite a few power supply boards on ebay and one is shown in the link in post #5. You don't need anything fancy but I make my own as I just Dremel the tracks as required on a blank PCB.

The pic shows the power supply I will be using on my build for when I finally receive the amp kit.

240V in through a IEC socket with fuse holder (1A slow blow.... 2A for 115V) > 6A switch for active wire only > 50VA 18-0-18 transformer > 35A bridge rectifier (10A would do) > power supply board with ground connected to mains earth > 3 pin XLR connector > umbilical cord to power amp with all wiring 7.5A.

The power supply board has the 2 inputs (+/-) from the bridge rectifier followed by two 4700uF 50V capacitors. Fuses (1.6A fast blow) are on each rail which then go to the output supply wiring to the XLR. The transformer centre tap is connected to the PCB at the output end with a machine screw and is wired to the earth connection. The ground is then connected to the output wiring XLR. There are 2 resistors on the output side of the board and these are for 2 LEDs with one for each rail. One is for the power board so I know power is on and the other for the front panel LED. All connections are via 6.4mm spades.

Tested today with a LM4780 module and no load gave me 28VDC rails and fluctuated between 25VDC to 27VDC under load. Nominal was around 26VDC and fell below 25VDC a few times during heavy passages.

Installed in a small plastic Hammond instrument case and nice not having to machine metal for a change.
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File Type: jpg RZ_LM1875_PS.jpg (199.8 KB, 174 views)
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Last edited by rabbitz; 24th August 2019 at 02:24 PM.
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