Sunday morning chipamps…

It’s been some time since I did an ebay kit, but that doesn’t mean I have given up on them (in fact I bought plenty…) and a cheap kit is still a great thing to play with on a Sunday morning**

It’s a pair of power amps based on paralleled TDA7293 amplifier ICs in the correct “master/slave” configuration as per the data sheet (and this discussion on diyaudio). The TDA7293 and TDA7294 chips are among the few survivors of the “purge” of audiophile components and they should still be available. Unlike the LM38xx-series and its siblings, the TDAs have MOS-FET output stages which means they can run in parallel without resistors to limit current sharing between outputs. The parallel arrangement allows for more current into low-impedance loads, but as the TDA7293 will work on up to +/-50V rails having two ICs also makes for a fairly serious effective power output.

These kits are seriously cheap and although I’ve tried to use most of the components that came with the kit, some parts have been replaced for cosmetic reasons (because that matters to me, sorry!). Even with component replacements though, these kits are so cheap that there is no real excuse for not trying them – even if you don’t need new amplifiers at all 😉

No real sound impressions yet, but I know these chips can sound really good so I am looking forward to seeing how much of their potential can be unlocked for the same price as a takeaway meal 😉

**Yes I know it’s not Sunday today, but as Whit Monday is a holiday in Denmark it felt like Sunday morning 😀

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.

 

A Smaller Gainclone…

I have already done a couple of “gainclone”-type chipamp designs with the LM3875 amplifier IC, mainly here and here. Now there is a new one, this time based on the smaller LM1875 IC.

The smaller IC obviously means less voltage and less power compared to the LM3875 and LM3886 but unless you have a big room and/or very inefficient speakers (or you are having a party… 😀 ), the 20W or so that you can squeeze out of the LM1875 should still go quite far.

The circuit I’ve used is exactly the same as the standard one in the datasheet and also the same as the one used by chipamp.com in their kit. Some people might recognise the schematic as more or less a textbook example of how to make a non-inverting amplifier from an op-amp. That isn’t surprising though, because that is what the LM1875 really is – a power op-amp.

I have made the amplifier PCB as small as I could to make it possible to fit the amplifier either in a 1U enclosure or directly to a 50mm heatsink. The form factor of the board is a bit different than I originally intended, but layout-wise it’s obviously much better now than I could have managed by sticking to the original plan so that’s no big issue. In addition to the amplifier board I made a matching PSU board. This is a simple unregulated supply which is fine for this kind of application, but actually the current requirements of the LM1875 are approaching the range where regulation starts to be possible, so maybe I’ll do that some other time (in the future…).

The boards shown here are the prototypes with the mostly standard components I had available (and yes, the heat sink is for testing purposes as well). In the works is a more “boutique” version with better parts which is probably also the one I’ll end up putting in an enclosure. Testing confirms that it does indeed play music, but real listening tests I’ll hold off until I have the other prototype ready.

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: 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 🙂

Work in progress….

It’s been a while since I have posted here, but real life is still getting in the way of my build time. At the moment this means I am mostly starting up new projects, because for some strange reason I can always find time to start new projects – even when time to finish the old ones is nowhere in sight 😀

I have been shopping a little at diyinhk.com recently and bought several DAC boards and power supplies, so one a few DACs are in the cards for sure 🙂 Also, one or two gainclones might make an appearance as well at some point. One reason for this is that I rediscovered some pictures of the Audiosector “Patek” amp a couple of weeks ago, so guess who has been scouring ebay etc. for reasonably-priced copper bars lately? 😉

Lastly, the Borbely and the Le Monstre front/rear panels have arrived and I am pretty happy with those, so now I am just waiting for my transformer order and a free weekend and then at least that should be sorted out.

However, I have to say that even with not much new going on there are still plenty of people that find their way here. The blog was at 15k page views in the beginning of January and it is now over 21k views total – I can’t complain about that, so thanks a lot for stopping by 😀

Project files: LM3875 Gainclone and PSU

What is it?
These are the board files for the LM3875-based Gainclone amp and matching PSU described here.

How big are the boards?
Both boards measure 3.925″x1.5″ (app. 10 x 3.8cm)

What is the status of the boards?
The boards are both in version 1.2. I have built version 1.1 of both and corrected a couple of minor mistakes in the layout afterwards.

Does it use any special/expensive/hard-to-find parts?
Not really. The layout is quite tight though, so remember to check the fit/dimensions of your components before ordering.

Anything else I need to know?

  • Because I couldn’t get the ICs closer to the edge of the board I recommend that you use the LM3875TF (the isolated version) to be able to mount it flush against the heat sink.
  • The big caps on the amp board are supposed to be 18mm in diameter, but the two middle ones are so close together that 16mm caps are preferred instead.

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.

gc3875-1

A Gainclone with the LM3875 IC

I have built a couple of chipamps/gainclones before, but none like this. Firstly, it is my own PCB layout I am using and secondly it uses the LM3875 IC in a non-inverting configuration – pretty much the simplest GC there is.

For those not already in the know, “Gainclone” is a collective term for amplifiers built based on “power opamps”, mostly National/TIs LM38xx and LM47xx models, but also the TDA729x series and others. Since each chip is basically an opamp, the circuits are very simple. From a single chip you can normally get 30-60W class AB but depending on which chip is used, multiple chips can often be connected in parallel and/or bridge mode to get higher power levels.

The circuit I have used here comes from chipamp/audiosector and it is more or less the same that started the gainclone “revolution” (or “craze” if you want) on diyaudio and elsewhere around 10 years ago. The matching PSU board will take either four 18mm caps or one large 35mm snap-in cap per rail – I’ve used the Nichicon “Fine Gold” caps because I had them in the capacitor box anyway. There is some debate as to whether a Gainclone gets better or worse as the PSU capacitance is increased (I won’t take sides here 😀 ) but this board allows more or less all configurations to be tried, i.e. without the PSU board, with several smaller caps in parallel or with one big supply cap.

I have only managed a brief listen to this but it definitely sounds very promising – and extremely impressive considering the simplicity and low cost.