Clone Modding

Open it up!

Last modified: 09-Feb-2007

Modding?

Ok, you just finished your clone and now what? First of all I would listen to it if I were you. And then? Is there a short track to the absolute audio nirvana? Well, not that I know of, but of-course it's quite good possible to enhance a basic version clone such as the GeenKloon to something more sophisticated.

Would you hear a difference? It probably depends on the rest of your set and the components used in your original clone. But on the other hand, once you've gone a long way building a clone with just a few high-end components why settle for less than the best components.

There are a few basic catagories for clone modding:

Change to an attenuator switch.
Change the power capacitors for better types
Use expensive resistors
Use a better input capacitor
Improve the wiring

Attenuator

First of all, if not already present I would recommend changing the volume control to a stepped attenuator. If you feel rich go ahead and buy a 24-step switch from Elna. If not, build a series or ladder atenuator such as descibed on the corresponding background page.

I built two versions of an attenuator for upgrade of the GeenKloon, both versions are described in some detail on the attenuator page in the example section. Bot make use of an open switch available from Conrad for just € 1.90 or € 3.22 for the double version. These switches are shorting types and need only a little modification after which they're usable for 12-position switches.

Version 1 : "Serious Serial"

The switch used here is available from Conrad (article nr. 709344-44, € 1.90) and is easy to work with. As you can see, with a little work it is possible to arrange the resistors such that the whole thing takes a minimum of space and there is no risk of shorting positions of the attenuator by accident. The total cost of this modification was 2 switches of € 1.90 each and 24 resistors of less than 2 cents each (I buy them in bulk) totalling to something in the order of € 4.25 ecluding labor of-course.

Technical details of this modification can be found on the attenuator background page in the Examples section.

Version 2: "Luxury Ladder"

An even "better" solutution would be an enhanced version over the GeenKloon version from a pair simple 2-deck switches available for about 3 euro a piece from Conrad. (The Conrad order nr is 709379-44, € 3.22 a piece). The version is making use of a 12-step rotary switch that was slightly modified in order to have a 0-position. The switch is a make-before-break (shorting) type although I initially thought it to be non-shorting. Therefore I built it as if the switch was non-shorting type, which is a safe decision should the switch wear out over time.

Non-shorting means that between two positions there is a short moment when the wiper does not have a resistance to ground (or signal) and thus the input of the amp will not be conneted to ground. Loud noises are the result which might possibly damage your speakers.

Of-course the most elegant and simple solution is to always buy a make-before-break switch but these are not sold in large volumes on the market except to audiophiles that like to spend big buck on HiFi. But there is a work-around by using a shunt resistor from wiper to ground and calculate the whole switch such that the resulting source impedance of the amp will still be the value that we like.

I developed a spreadsheet program for download that you can use to calculate your own ladder attenuator.

The result is a 12-position ladder attenuator with high-quality sound where always 3 resistors are in the input section and only 1 is in the signal path (unlike a series attenuator where for low volume settings there might be 12 resistors in the signal path).

And the winner is ...

I decided to give the serial version a permanent position in GeenKloon as it sounds very good and has exactly the steps in dB I like at low volume listening. The previous attenuator based on a Lorlin switch was doing OK, but I thought that the steps at low listening volume were just too coarse and I neede more attenuation at these levels as well.

Capacitors

In most gainclones there are only a few capacitors used:

In the power rails of the amp most people use 50V/1000uF electrolytic capacitors
In the rectifier section some use MKT type 22nF capacitors in order to get smoother rectification
In an inverted gainclone a 2.2 or 4.0 uF capacitor is used on the input in order to avoid DC on the output
In a non-inverted clone the same may be used or a 22uF elco is used to ground the feedback section.
And finally, a Zobel network at the output or a HF filter on the input may be present.

Since the mantra "less is more" is the blueprint for most gainclone designs, let's have a look at the first, third and fourth in this list as modification of these types probably delivers most value for money.

Black Gate

First of all I changed the Philips (BC Components) capacitors for Black Gate normal types. And while writing this text up I'm allowing the new caps to break in. Normally I do not expect components to take much time to break in (or my ears) but for Black Gates I make an exception. It indeed takes a few days before they give everything.

Resistors

I'm not the man with most experience in trying out all sorts of resistors in my projects. For my tube projects I work often with 1Watt Beyschlag resistors. For the gainclone projects I worked with Dale resistors, Caddock, Beyschlag and some other expensive types.

As far as I'm concerned Dale is worth the money but I wouldn't go much further than that.

Cosmetical enhancements

Apart from changing components it's always possible of course to change the looks of the amp. in my case I decided to put two blue LEDs in the GeenKloon. I know, additional components could possible introduce noise etc. to the sound, but I decided to do it anyway.

First of all, I use a din plug with 5 contacts which will eventually enable me to run the LED's on separate power. And secondly I do not believe 1 lowm power LED to degrade the sound anyway. There are a few things to take into account when doing trhese kind of LEDs right I think:

Use low power LED's (only a few mA)
When possible run the LEDs on their own power, for example by 10 additional turns of wire around the toroidal and using a diode.
Make a layout such that these components do not interfere with other components of the amp. In the picture of Geenkloon above it would mean to place the LED opposite to the power inlet of the amp and have the wire run at the right of the box (top of picture).
Compute the series resistor needed for the LED such that you stay on the safe side (and not vaporize the LED)

Latest BOM

In this section I'll try to put the latest Bill of Material (shopping list) for the GeenKloon. The will be changes to the amp over time and for those interested I'll give the state of the art material list so that copying the amp is easy for those not willing to experiment with all kinds of components and values.

GeenKloon
	Opamp: LM3875TF
	C1: 22uF Elco BC
	C2: 22nF Siemens
	C3, C4: 1000uF/50V Black Gate
	R1: 1k, 1%, 1Watt Beyschlag
	R2: 20k, metalfilm
	R3: 1 Ohms, Metalfilm
	R5: 1k Metalfilm 1%
	R4: Attenuator (22.729k imp)
	47 metalfilm 1%
	82 metalfilm 1%
	150
	330
	470
	820
	1430
	2400
	2200
	3300
	4700
	6800
	Box: Conrad 2x
	power transformer Amplimo 68015, 2x22V, 225VA
	D1-D4: HFA08TB60 Hexfret

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<< Page 3; Listening Impressions

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