I wonder if they do it intentionally or maybe they just don't know what they're doing  :duh
Anyway, I'll be using the first transformer I've shown in the other thread since the amp's main purpose is for practicing guitar with distortion, although it won't happen anytime soon. I'm having a hard time creating a layout for the P27 preamp. I don't consider buying a pcb from australia since customs and shipping fees are a considerable increase.

I just put a dedicated faston terminal in the star ground for the speaker return, another one for the transformer's 0 volts.

Here's my power amp and ps almost ready for testing. Power amp is exactly from ESP Project 72, PS used 2 caps 2200 uF 35v only since it's what's available in my storage. I won't be using my newly purchased transformer since I don't trust it's rating, so I think I'll stick with the transformer I showed in the first page.

I just bought a transformer made here in the Philippines. It's 220vac to 18-0-18vac and rated at 2 amperes. (i don't know why they don't use va for transformers rating here)
I'll be using it for a power amp (Rod Elliott's Project 72) which asks for at least 50VA. Problem is I don't trust its rating since it's on the small side. Photos below shows the laminations' dimensions. Can anyone confirm if it really is 2 amperes (72VA for 18-0-18)?

without Rod's reply yet and having just read about the zobel, I computed the resistor needed for my LM1875 amp. The Red White and Blues has an Re of 6.42 so multiplying it by 1.25 gives me a value of 8.025. Therefore, I'm gonna use a 10 ohms resistor for the zobel. Confirmed?

PS: Since the Philippines' electrical system doesn't have grounding (true earth) after entering residential meters (i heard that one of our two prong outlets is actually grounded but not sure which one), if I am to just let my circuit's common float, of course common to chassis connection is a BIG NO. Aside from that, do you have any suggested modifications, additions or other reminders for a floating ground circuit? I still have a plan to add true grounding in the future if it's safer.

Quote from: phatt on April 24, 2016, 07:52:31 AM
Arrh ,, Why don't you Email Rod and ask him for confirmation? Looks like a typo error. :tu:

ah maybe, I'll just ask him then

Quote
Those little 1 watt smokey amps through a quad box are quite loud.  8|
Phil.

Yeah, and this is how it would look like if I'm the one building it  8|

okay I have started the LM1875 already but I have some questions:
1. Rod Elliott's schem shows R6 as 10 (10 ohms maybe?) (Encircled PURPLE)

but in the following text, he stated that the 1 ohm resistor (R6) should be a 1 watt type. So what really is the value of R6? 10 ohms or 1 ohm? (Text is highlighted in the next image)


2. Also, I don't know what came to my mind in creating the layout. Rod's schem doesn't have a 10 ohm resistor in between the common of the input and the common of the power amp (Traced RED in the first image). But I decided not to directly connect the two traces and then provided holes for a 10 ohms resistor, which I have seen in most LM1875 gainclone projects.


this is my actual pcb, components are not yet soldered

should I put a 10 ohms resistor? what difference would it make? (NOTE: The amp is to be used as a power amp for guitar, coupled with Rod's P27 preamp)

3. Lastly, Rod warned not to connect the speaker return to the amplifier's earth bus, coz it will get oscillation. My actual pcb above has a 2 contact terminal block on the right for speaker out (+ and -), well I think it can be seen that the (-) goes to the middle of the 3 contact terminal block, which will return to my star ground located near the filter capacitors of the PS. However, that speaker return is connected to the amp's earth bus, will it be ok since the other signals' paths are not that large to allow the speaker return current to pass through easily? Or should I just connect the speaker return directly to the star ground, or use a 5 watts 0.1 ohm resistor on the way back to the star ground?
Can I use the schem below for the speaker returns? One goes to the amp's ground, another goes to 0R1 5W resistor then to star ground?

I'm envious 
I haven't even finished my LM1875 amp yet because of family problems.
Although, my first project, the Ruby amp is already done and working, yet uncased. I just finished it yesterday.
It's hard to finish a project when you don't have a personal power drill. I hope I'll be able to buy it soon.

Anyway, your build looks great. I really am envious  :dbtu:
+1

well, i just thought the regulators would be better   :loco
but thanks for the info

I'm building this http://sound.westhost.com/project27.htm as preamp for an LM1875 power amp.
Since I don't think this preamp will require current above 1 Ampere, can I use LM7815/7915 voltage regulators instead of the zener diodes?
Also, what other things do I have to change to match the output of the preamp to the input of the LM1875 power amp?

Quote from: J M Fahey on March 27, 2016, 01:38:06 PM
Ouch!! that "free" Fritzing software is f***ing EXPENSIVE!! :loco

:lmao:
I actually considered their Fritzing Fab service but it really is soooooo...... expensive

Quote
Check that you can "export" or save the final design as a printable *graphic*  file (.gif / .jpg / .bmp / etc.) so you can print it on paper (or transparent/drafting paper)  and use it as a real size guide to make your own PCB

Yeah, fritzing has options to export as PDF (actual size), SVG and Gerber.

Quote
Or use pedal maker oriented http://diy-fever.com/software/diylc/  which is simplest and fastest to learn.
It also designs perfboard and Veroboard, besides etched PCBs.

I also have this, the old and the new versions. I used it already for some of my pedal designs. I downloaded the old version to be able to view those old layouts compilation. So I guess I just have to find its users' community for parts. Thanks.

Thanks Phil. BTW I'm using Fritzing for designing the PCB and I'm having a hard time designing coz I don't have the LM1875 part. And I also didn't know what components should be far from each other. But your post helped me a lot.
+1 

i wasted about 5 hours today trying to figure out (draw) how to make a layout for my lm1875 amp based on ESP Project 72. i looked at the national datasheet and found only small difference in the schem. Someone mentioned that the bypass caps and the zobel should be as close as possible to the chip but how far is not advisable?

Phil, I've seen your lm1875 layout where the chip is separated from other components of the power amp. Is it okay if the chip is a bit far from those bypass caps?
Also, which traces or wires should I avoid getting close to each other?

Hey Phil, in your LM1875 layout, I see that you had a separate pcb for the chip. Besides the chip, what components are also located in that pcb?