100V Speakers and the GainClone Amp.

[McKiltie]

A few days ago white surfing the web I came across the website Decibel Dungon, which seemed devoted to a quality amplifier called the Gainclone. As a retired Chartered Engineer this site brought back happy memories of being a student engineer and building audio amps published in Wireless World. These were at the time massive 10 or 20 Watt units! How times have changed.

The amp in my local Church is about 25 years old and the hiss level is getting intrusive. I have been looking for a new high quality low priced replacement and I think the Gainclone may well meet our needs. However, all the loudspeakers in the church are 100V speakers. Now, at last, for my question...

Has anyone out there used the Gainclone amp to feed 100V speakers using a suitable transformer and if so how successful were you?

I would be pleased to hear feedback from anyone on the Gainclone and/or 100V speakers.

Ref

Decibel Dungon = http://myweb.tiscali.co.uk/nuukspot/...loneindex.html

The Old West Kirk, Greenock, Scotland =
http://www.owkgreenock.info

Thanks in advance,

[OzMikeH]

The hiss noise may not be your amplifier, it might be the way you are using the microphone preamp.

Increase the gain on your mics, reduce the gain on your amp to compensate. Mic gains should all be about 50% or higher, use the amp as the volume control. Get that intermediate signal up out of the noise.

Gainclone will work as well as any other reasonable amplifier, do you use your church PA for Music as well or just speech? does anyone sing through it?

There are some very low noise mic preamps about. I suggest looking there rather than the amplifier.

[McKiltie]

Thanks OzMikeH for your reply. The power amp is integrated with the pre amp section. However, I will experiment with the relevant controls.
The amp is used for 99% speech.

My concern about the suitability of a Gainclone was that it would have to feed an audio transformer then the signal distributed to 6 100V loudspeakers and I was concerned by the inductive load from the Transformers.

Thanks again for your feedback.

[OzMikeH]

The Primary winding on the output transformer may not be 8 ohms.
I have seen them as low as 0.3 ohms impedance. The amplifier was low voltage but very high current. You really need to have a good look at the circuit or measure it. Chances are yours would be the other way though, higher voltage and less current, less copper = cheaper transformer.
Don't worry too much about the inductance of the transformer.

[McKiltie]

Thanks again. Bye...

[richardash1981]

Provided you can get a big enough rating transformer for the step-up there shouldn't be an issue with going 8R -> 100V then 100V-> speakers. You still need to get the impedances right through, which is a bit complex because of the way they are specified.

Each of your speakers will have a power value in watts as well as the 100V on the back. The more watts it is rated to draw, the lower it's impedance will be. You can either calculate the impedance of each unit, work out the parrallel equivalent, and then work out the transformer you need, or you can cheat (the way it's normally done). The results are mathematically equivalent.

1) Find the watt rating of all the speakers on the system. Some may have multiple taps on the transformers, in which case you need to know the rating of the one in use.
2) Add these values up
3) You now need a source rated at 100V and the answer above or more watts.

To match up from an 8R amp, you can use a step-down transformer designed to go the other way, just find one with a primary tap rated for the power you calculated, and secondary for the rated load impedance of your amp. You can then just reverse it to do step up.
Canford sell a very expensive oversize step up that's rated at about 300W throughput, and I always wondered why, as typical taps are 30W or less, and the last unit I tested with a 10W tap was quite loud enough at about 4V in the primary (I was cheating, and using a standard 100W/4R MOSFET amp turned up loud to get the level as it was only for bench tests).

As far as the hiss goes I agree - input stages are probably the culprit. One option might be to build a better mixer for the job, and then feed it's output into the line input of the existing amp, if it has one that has lower noise on it. You then turn all the other inputs on the amp down to zero to loose their noise contribution.

[McKiltie]

Thanks for the helpful comments. I will study your input carefully. Bye from sunny Scotland

[gootee]

Or, if you already have a high-voltage supply in the system, maybe you could just use transistors, instead of transformers, maybe for less money.

But then you could probably just use a good opamp, instead of a power chipamp.

See AN-272 at http://www.national.com, or right-click and download the following:

http://www.national.com/an/AN/AN-272.pdf

You'd probably also want to look at AN18, at http://www.linear.com .

And at http://www.apexmicrotech.com , they have IC "power buffers" that can go WELL above 100v, on their own. They're a bit pricey, but maybe not compared to a transformer.

Sorry if I've totally-misunderstood what you are needing to do.

By the way, where do you think that hiss is actually coming from? In a system that's getting that old, and if it previously didn't have that much hiss, I'd start by looking at things like electrolytic capacitors, and microphones, etc.

- Tom Gootee

http://www.fullnet.com/~tomg/index.html