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HouRman9 7th September 2003 12:06 PM

GainClone not Loud
I've just completed an Inverted Thorsten's Gainclone channel. The problem is it does not play loud, but play's music at about 50db or so. (audible and good sounding, but not loud). I've tried different speakers and different sources but the amp doesn't seem to want to put out more than a fraction of a watt.

However, when we disconnect the RCA ground (RCA jacket connected to source ground), there is a very loud HUM/BUZZ that sounds like when you touch the end of a guitar signal cable that's plugged into an amp (maybe 80-90db @ 1 meter). I put on a 75k resistor between the signal (Center pin of RCA jack) and the source ground and it lowered the volume of the hum/buzz considerably but it was still there.

The two 1000uf capacitors are connected to the diodes P2P, yet are wired fairly far from the chip. I didn't think this would affect the volume but I plan to move these caps closer to the chip in the final build.

I've used hot solder joints for almost everything, and it's been double checked. I am however using 3 separate aligator clip wires to connect the grounds together.

Nothing gets hot, the transformer is an Avel 2x22v secondary 160VA unit for the channel. I measured the power supply output (after bridge rectifier) to be 30V and -30V for the other bridge which is right. The diodes are MUR860. A single Blackgate 4.7uf cap, and panasonic 1000uf power source caps are used.

I use a 216kohm resistor between pin 8, and the "+" speaker terminal binding post instead of a 220kohm, but that should be fine.

The 110V IEC AC receptacle used is wired as follows: The Negative "N" pin is only connected to the two negative 110V primaries blue and violet. All the other power and source grounds connect to the "Earth" ground pin on the IEC receptacle.

I plugged the GainClone into a surge protector that is also plugged into a front projector. This surge protector is plugged into another power strip that is plugged into a Mac G4 and all it's peripherals. This Mac strip is then plugged into another surge protector that is filled and connects to an imac and various powered appliances. This strip is plugged into another surge protector that connects to the lights in the room, and that strip plugs into the wall. So that means the gainclone is plugged into the wall through 3 filled surge protectors (some with 8 sockets), which then plugs into the wall. I think it is nuts to have 3 strips daisy chained but it's not my house and gainclone. I'm just trouble shooting it for a friend. :)

The interal wiring is scrap wire taken out of a broken PC power supply.

If you have any questions, i can post more details and even pictures of the test channel rig. (or would you like to see the power strip daisy chain madness).


jcactaur 7th September 2003 08:22 PM

the signal is passing through both the interting and non-inverting terminals

HouRman9 7th September 2003 08:59 PM

That would explain the low volume because it would be like running an inverted GC and a non-inverting GC at the same time. One of them is supplying a slightly weaker voltage so it's not as strong of a signal. So we'd be hearing the stronger "inverted" one.

I guess this should have been posted in the Chip amp forum.

I'll fix it today and I'm about 95% sure that it will work flawlessly.

BTW, as a tip, check polarity on the capacitors because if wired wrong, it will explode and spray everything. I forgot that one of the caps had to be wired in reverse polarity because it was hooked to a Negative lead and lost a $3 cap.

These things can be nerve racking

Greg Erskine 7th September 2003 11:54 PM

Another possibility
I also made a GC that played softly but sounded good.

I had the feedback resistors reversed.:o

ronc 8th September 2003 01:51 AM

Ahhh grege one of those polorized resistors huh?LOL. No i have learned (the hard way) to measure the ohms right before i solder the things.

Greg Erskine 10th September 2003 03:11 AM

Yeah Ron,

I always check, and double check as well.

Unfortunately, the PCB had the two reversed. It even made mention in the instructions that the PCB was wrong but somehow I compensated twice and got it wrong. It wasn't until I built another p2p GC that I realised the first one had a problem. After building a few of them now it seems really obvious but hey, I have to make a mistake at least once in my life.;)

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