Project files: LM1875 Gainclone

What is it?
The project files for my mini gain clone with the LM1875 IC as described here. The download file includes both the amplifier board and the matching PSU-board.

How big are the boards?
The amplifier boards measures 1.8” x 1.3” (app. 33 x 46 mm.)  and the PSU board measures 3.9” x 1.8” (app. 99 x 46 mm.)

What is the status of the boards?
Both boards are v1.0. I have built a working prototype, but detailed testing is on hold until I have build another set that I want to turn into a finished amplifier. All I know is that the design plays music just fine on the test bench 🙂

Does it use any special/expensive/hard-to-find parts?
Not really, unless you choose to go overboard with expensive boutique parts, such as premium capacitors and fast rectifiers. You can, but you don’t have to… 😀

Anything else I need to know?

  • The boards are intended to be used in dual-mono configuration with one supply board per amplifier. Take the speaker output from the amplifier board and the speaker ground connection from the spare ground terminal on the PSU output connector. It is of course also possible for two amps to share a PSU, but you may struggle with wiring everything with reasonably thick cables.
  • If you want to mount the amplifier in a 1U/40mm heatsink you need to keep the capacitors on the PSU board below app. 30mm in height and the amplifier board mounted perpendicular to the heatsink. If you have more space it is possible to mount the boards directly to a 50mm heat sink (parallel to the heat sink with the IC mounted from the underside). This would however mean you have to bend the pins of the LM1875 to fit yourself, because there is no standard pin configuration that supports this way of mounting.
  • You can mount R4 either on the top or the bottom of the board. I’d recommend that you use the opposite side of where the amplifier IC is mounted for easiest access.
  • There are more versions of the LM1875 IC depending on how the leads are shaped (straight and two different bend patterns in both 90deg and 180deg versions). From the datasheet I honestly can’t determine the correct order code for this board, so you’re on your own here… 😉

Downloads:
Download design files here

Related information:
Note: Always read the “intro post” for additional important information about my designs.

Read the LM1875 datasheet for more information. I’d also recommended the chipamp.com kit manual as a good source of information.

 

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Past projects: Old ICEpower Amps…

I’ve built quite a few ICEpower amplifiers over the years, but many of them were built and sold before I started this blog. Recently I actually saw an amp for sale that I am pretty sure I built and so I started looking to see if I had any pictures of these amplifiers. Mostly I don’t, but I did manage to find a few:

The first amp is a small amp based on a 200ASC-module with a 200AC hanger. Unlike the ASP and A-series, the amplifier sections on the AC/ASC are the same so it is possible to build a (deceptively compact) stereo amplifier this way. I used this amplifier in my office system before I eventually replaced it with the B1/125ASX combo.

The second amp is a full-size amp based on 2 pcs. 1000ASP-modules. At the time, this was intended to be my own reference amp, but firstly I preferred the sound of the 500ASPs I were using before and secondly I got a very good offer on it so I decided to sell it soon afterwards.

The last amp is a three-channel model with a single 500ASP and a pair of 200AC hangers. The amplifier I used for a couple of years to power the center and rear channels. As the front amplifier I had two stereo amplifiers with dual 500ASPs wired in bi-amp mode, which made for a very compact surround system with plenty of power – around 3kW into 4Ohms – on tap :D. I eventually sold all these amps and started using the 6-channel 50ASX instead.

Cloning a classic…

I have been looking at class AB amp designs for a while, trying to find a “compromise” between my low-power (but very large) class A and high-power (and compact) class D builds. For some reason very few among the class AB designs managed to “stand out” to me with the right combination of simplicity, compactness and reputation. It’s not that I really had anything specific in mind, I just kept looking at stuff and thinking “naah, that’s not what I want” 🙂

However, one design that did keep cropping up was Rod Elliot’s “Project 3A” (or just “P3A” for short). This is a discrete amplifier with a reasonable power level for normal use and a very simple design. There’s plenty of evidence out there to support that the performance is good and even a way threads to evolve the design (search the “solid state” forum on diyaudio.com)

Rod sells PCBs for the P3A and that would of course have been the easy route, but because I had a specific form factor in mind I decided to “roll my own” 🙂 The end result is app. 70mm square (flat mounting on a 75mm heatsink were one of the key design criteria) and quite compact. My only concession over the original is that I removed the input capacitor. Well, I didn’t actually remove it on this version since there is space for a bipolar electrolytic from Muse or Blackgate, but the main version is intended for having the input cap off-board.

As I wanted a matching power supply I “recycled” the last Gainclone PSU I did but added a second capacitor bank (which just fit on a board that is still constrained by me using the free version of Eagle). Since the P3A runs on 35V rails it is possible to use 50V capacitors and then a reasonable capacitance is still feasible with this PSU footprint – especially in a dual-mono setup. Of course the board has space for normal 35mm snap-in caps as well, but that’s so boring 😀

I have only done this test version of the amp so far and confirmed that it works and that it plays music. (This is also the reason for the transistor pins not being trimmed properly – bias adjustment). That said, I do have a couple of case ideas in mind for this one where the lower heat of a class AB amp will be welcome (or should I say “required”) 😀

Woodface…

Yes, I know it’s the title of a classic album from Australian group Crowded House but it is also an occasionally very popular way of finishing hifi products 😀

European (or at least Scandinavian) readers may recall the now-defunct Danish “Holfi” brand from a decade or so ago. Here, thick cherrywood fronts were the norm and as usual with these things, that made the opinion of the brand more based on looks and perception than on sound quality (comments along the lines of “I don’t want something I have to paint every year to keep it from rotting” were frequent…).

However, wood also has a number of benefits, mainly that it is easier than metal to work with for most average diy’ers, and so when I stumbled upon some suitable wooden panels I started planning to give it a go as well. The wood is an unknown “exotic” (for a Scandinavian at least) species that I purchased in Japan last year. The boards are cut to 5mm by 50mm dimensions that are perfect for front panels for Modushop cases and that is honestly why I bought them**.

What am I doing with them? Good question and I am not quite ready to show that yet, but it will be a small pre- and power amp combination (because I definitely need more of those – groan! :D)

**Sidenote: I am sure many of the readers here recognise the feeling of looking at something and realising that it can be used for an audio project – if that rings a bell, I can only warn you against going to Tokyu Hands (especially their main branches in Shibuya and Shinjuku) and visiting the DIY-supplies section 😀

woodface-1

Amp Camp Amp

Here is another one of Nelson Pass’ brilliant designs, the “Amp Camp Amp” or ACA for short, that I managed to put together (halfway at least – as usual…).

First launched a couple of years ago, the ACA was developed by Nelson for an “amp camp”, an audio maker event and the schematic since posted as a project article on his website firstwatt.com. The ACA is a very simple and easy to build class A amplifier that produces around 5W (which goes surprisingly far in most “at-home” applications). To make the ACA more “beginner friendly” it is designed to work off a 19V switching adapter from a laptop computer. This makes it cheap to build and ensures that an inexperienced builder does not have to worry about mains wiring etc.

For this build, I have used the “official” boards from the diyaudio store. There is also a very sexy looking custom chassis for the ACA in the diyaudio store, but since they would be shipped from the US and I would be hit with well over 30% extra in VAT, import duty and brokerage fees I elected not to go that route.

Instead I found some special heat sinks from ebay to brighten up an otherwise black chassis 😀 The main argument for choosing these was otherwise that they are 80mm long as opposed to the more commonly available 75mm ones which would be just a tad small for the ACAs recommended mounting. The quality is decent although the colour washed off a bit while I was threading them (using lots of spirit for lubrication). The aluminium alloy is also a bit softer compared to the Fischer or Alutronic heat sinks I normally use, but that isn’t necessarily a problem.

As usual with the Pass designs, the components for the ACA are completely standard “off the shelf” types and the only part that could be difficult to obtain is the 2SK170 input JFET. There are a few alternatives though (the 2SK246, 2SK369 and LSK170 should all work if you just respect the pinout) so even that should not deter prospective builders.

The original ACA design used external switching supplies but I prefer to keep the PSU internally in the chassis, because the laptop supplies are a bit impractical. Instead, I have got a standard “industrial grade” 20V/100W SMPS from Mouser in a 3″x5″ open-frame format.

Looking forward to the Xmas holiday where I should be able to make some more progress on this one 🙂

Project files: The ManyCaps PSUs…

What is it?
A little sideline project one might say :). For one of my other (upcoming) projects I needed to buy quite a few Panasonic FM series capacitors in one specific value. As is sometimes the case, buying 100 wasn’t much more expensive than just buying the 35 I needed and so I ended up with a question: What can you do with the rest?

In theory, paralleling multiple small capacitors gives you lower ESR/ESL and higher ripple current than a single big cap. However, due to the physical distance required between the many small caps some of the benefit is negated and overall I am not sure I dare say that one approach is inherently better than the other – that depends on what you are trying to achieve I think.

However, as I already had the capacitors I might as well try it. Obviously, something as groundbreaking as this needs to have a suitably audiophile-sounding name, so without further ado allow me to introduce the “ManyCaps”(™) audiophile PSU boards 😀

There are two versions, single and dual, with space for either 2×12 or 1×15 13mm radial capacitors. The most obvious application for these is probably gainclones and smaller class D amplifiers but they can be used anywhere where an unregulated supply is OK. The boards can of course also be used with a DC input, either with the rectifier in place or with the rectifier bypassed.

How big are the boards?
The single board measures 3.8″ x 2.0″ (app. 97 x 51 mm) and the dual board measures 3.925″ x 3.2″ (app. 100 x 81 mm).

What is the status of the boards?
Both boards are in v. 1.0. They are simple designs, so I didn’t need to make any changes and they worked the first time round 🙂

Does it use any special/expensive/hard-to-find parts?
Nothing really stands out:
  • The main capacitors are 13mm max diameter and voltage obviously depends on the application.
  • Rectifier is GBU-type and should probably be rated at least 6-8A.
  • The decoupling capacitor should be around 1.0 uF MKP or MKT. The lead spacing is 22.5mm on the dual board and 15mm on the single board.

Anything else I need to know?
Can’t think of anything 🙂

Downloads:
Download design files here

Related information:
Note: Always read the “intro post” for additional important information about my designs.

Project files: Mini JLH1969

What is it?
This is the project files for my version of the JLH1969 amplifier as shown here. The files for the matching PSU will follow shortly.

How big are the boards?
The board measures 2.25″x2.3″ (app. 57x58mm).

What is the status of the boards?
The board is in version 1.0. I have built and tested a couple of prototypes (as described in the original post) and although they play music just fine, you should still consider this a “work-in-progress”. I would be especially concerned with confirming the thermal stability of the amp because of the compact dimensions, so if anyone decides to build this please share your results 🙂
EDIT 17th Jan. 2016: Added v1.1 of the files in a separate link below. Minor tweaks to the board and the download now includes a basic BoM as well.

Does it use any special/expensive/hard-to-find parts?
No. I have used MJL21196 output transistors because I had them, but versions of the MJE/TIP3055 should be OK as well as long as they are in suitable (meaning TO-247 or TO-264) packages. Do not be tempted to use faster transistors such as the MJL/NJL3281-types as the amp will most likely not be stable with these. Have a look at the TCAAS page on transistor substitutes for more info.

Anything else I need to know?

  • The only change I have done from the original schematic is to replace R5 with a 200k trimpot to make it easier to adjust the operating point. Oh, and I’ve made up designators for the parts that don’t have a number on the original schematic 😉
  • In my opinion the output cap should be 4700uF or larger, even with an 8 ohm load. Even if the supply voltage is 27V, I’d be comfortable with using a 25V cap in this position. All the other electrolytics should be 35V or higher.
  • Heat sink T3 as it might get hot. You’ll probably not be able to find a standard heat sink that fits. so my recommendation would be a small piece of bent aluminium or copper with a hole tapped in it for easy mounting.
  • Raise the R2 resistor 5-10 mm above the board for cooling (I haven’t done this in the prototype version but it gets quite hot).
  • The footprint for the input transistor is for a 2N3906 as described in the original BoM, but other types can be used as well. An easy to get choice is a BC560C which needs to be turned 180 deg. in order for the footprints to match.

Downloads:
Download design files here (v1.0)
Download design files here (v1.1 – added 17th Jan. 2016)

Related information:
Note: Always read the “intro post” for additional important information about my designs.

As usual, both TCAAS and this diyaudio.com thread contains lots of worthwhile information.

minijlh1969pcb-1

JLH 1969 revisited…

Finally a bit of progress around here 😀

Even though I have already built a Linsley-Hood JLH1969 clone and another is in the works, I still wanted to make my own layout for this classic amplifier – and here it is!.

The board measures measurements are 2.3″ by 2.25″ (app 57×58 mm.) and as usual the layout is as tight (some would say “cramped” as I could make it. The transistors used are based on Geoff Moss’ recommendations. I actually have some NOS 2N1711, but the BD139-16 actually measures better (higher hfe). The output devices are MJL21196 because I had them available and because the larger TO-264 package is nice.

The board will be powered by a regulated PSU (hopefully ready shortly – the last parts are in the mail) based on a normal 3-pin regulator as shown in the 1996 JLH article (if all these references seem a bit like you have to be “in-the-know” to keep up, I suggest you start reading the pdf-articles here instead 🙂 ).

Now, I haven’t really done much with this beyond testing that it plays music, but when the PSUs are up and running I’ll look into more testing. In terms of value-for-money this isn’t likely to compete with the cheap ebay-kits, but hey – if I wanted to save money I wouldn’t be building amps I would just buy one that worked! 😀

Project files: New gainclones

What is it?
These are the board files for the gainclone amp and PCBs posted here. They (sort of) supercede the original files from this post – at least the PSU.

How big are the boards?

  • Amp: 2.4″x1.5″ (app. 61×38 mm)
  • PSU: 3.925″x1.95″ (app. 100×50 mm)
  • Bridge: 2.55″x1.6″ (app. 65×41 mm)

What is the status of the boards?
The boards are in version 1.0 or higher. They have all been built and tested.

Does it use any special/expensive/hard-to-find parts?
Not really. You can do what I did and splash out on 0.1% resistors and audiograde caps, but it definitely isn’t necessary.

Anything else I need to know?

  • The LED on the amp board is connected rail-to-rail which means that in a typical application it will drop around 70V, so it should be rated 1W.
  • If you use film caps thicker than 3mm for the bridge board, you may have problems mousing the diodes completely straight (as I had on the one I built)

Downloads:
Download design files here

Related information:
Note: Always read the “intro post” for additional important information about my designs.

You can find additional information about the LM3875 gainclone in the LM3875 build guide over at audiosector.com.

 

New gainclones…

At the start of the year I promised that I was working on some new gainclones – and here they are 🙂

Actually, it is only really one new amp (and it is “only” a mono-version of the one I’ve already published. The amp design is faithful to the original non-inverting GC circuit that is still used by Audiosector. Along with it is a tweaked version of the original PSU design I did and a new rectifier bridge PCB if you want to stick to the “original” gainclone concept and only have relatively small capacitors in the PSU.

My test-implementation here is a little bit “over the top” as I have used 0.1% Vishay RN55 resistors and Nichicon KZ and KG “Gold Tune” audio-grade caps. Not sure if it makes a difference, but it does look nice I think (and that matters to some people – me included :D). I have also assembled the diode-bridge and I plan to (at some point) make up another set of amp boards and try the minimalist implementation with only 1000-2000uF of capacitance on each PSU rail and see if I can hear a difference.

The assembled set of boards will be used as a dual-mono amp with two 150VA transformers (on order) and the boards are mounted to 25x50x100mm pieces of aluminium for heat sinking (we’ll see if that is enough, but it should be).

The project files will be published soon – I just need to make a few final tweaks to them first 🙂