My synthesiser

[Dr.EM]

Hmm, can't get that to work. What I really need is a small webpage, for my various mp3 demos and pics etc. Anyone know of any free hosting, 10mb at least sort of?

 

[Nigel Goodwin]

Hmm, can't get that to work. What I really need is a small webpage, for my various mp3 demos and pics etc. Anyone know of any free hosting, 10mb at least sort of?

Doesn't your ISP provide some webspace?.

 

[Dr.EM]

Better late than never :lol:. I was searching for "optical compressor" because I remember Audioguru made some alterations to the circuit, simplifying it, but this is the only post my search returned. Anyhow, I found some free webspace, but have absolutely no idea how to make a page. Nonetheless, the mp3 should work, as should the picture:

**broken link removed**

If Audioguru still has the compressor diagram, I would be really grateful if he could post it/send it, I want to resvisit it with a 10000mcd LED :lol:
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[audioguru]

Hi Dr. EM,
Maybe you want this compressor circuit:

 

[audioguru]

Here's another neat circuit to try. Its output is supposed to follow an input frequency:

 

[Dr.EM]

Thats it, cheers

Have you tried either of these yourself? I just beadboarded chemelecs simple 10 watt amp and burnt my finger on a transistor :lol:. Don't know what I did wrong there, it made some very quiet output, so I went to touch the unheatsinked transistor, thinking it couldn't be very hot after just a few seonds, I was wrong...

 

[audioguru]

Hi Dr. EM,
I didn't try either one. Let us know how they perform. :lol:

Semiconductors quickly get mighty hot with linear power through them.
When I worked for a Japanese sound equipment manufacturer, I was asked to test an American name-brand competitor's high-power amp.
It smoked the entire test room in only a few seconds. Our amp had much more power, better specs and a lower price. It was designed for worst-case with a temperature-sensitive fan speed and could supply its rated power for weeks without any strain.
Actually, the only strain it caused was to the mains. It provides its rated power output with 120VAC input. My unloaded mains was 123V but dropped to 117V with the amp near full power. I had to turn-off the air conditioning to the whole building to keep the mains voltage high enough to test it properly. I'm glad I had its 1200W load outside. :lol:

 

[Someone Electro]

Meaby you had the transistor only slitly on.This proboibly coused an big voltage diference over it and therfore lots of heat.

 

[Someone Electro]

Did you use an speaker for the load?(If it was then it must of ben prety LOUD! :twisted: )

 

[Roff]

the wire knickers that so many people use.

Obviously this must have a different meaning in Canada :lol:

I think they're sorta like shorts, if you get my drift. :lol:

 

[Nigel Goodwin]

Thats it, cheers

Have you tried either of these yourself? I just beadboarded chemelecs simple 10 watt amp and burnt my finger on a transistor :lol:. Don't know what I did wrong there, it made some very quiet output, so I went to touch the unheatsinked transistor, thinking it couldn't be very hot after just a few seonds, I was wrong...

First thing! - if you're touching ANYTHING to see if it's hot, lick your finger first - the noise of the water boiling off your finger warns you BEFORE your finger gets burnt (within reason of course!).

As for the amplifer, there are many potential reasons, I imagine for a start that you didn't have the transistors mounted on substantial heatsinks? - bare transistors will overheat VERY quickly, and thermal runaway will keep them getting hotter. I'm also not a believer in using breadboards, they are far too restrictive - in your case the entire amplifier may well have being oscillating at ultrasonic frequencies?, which will rapidly cook the ampliifer.

Another strong possibility is the bias current, you may well have had it too high, again this would cause thermal runaway, and rapid overheating followed by destruction :lol:

 

[audioguru]

Hi Someone Electro,
We had subwoofer speakers that liked the 1200W from that amp. I frequently had the amps clipping when driving a pair during demo's.
The resulting 2400W didn't seem too loud since it occured only for a moment during the beat of the music. You could really feel the beat.
I wouldn't want to be anywhere near speakers that are being fed continuous sine-waves or pink noise (or rock "music") at such a high level.

Hi Ron,
Electricians use wire cutters to strip insulation instead of using wire strippers.
I call them wire nickers (spelling corrected) since the wire breaks at the nick when it is bent. Electricians are paid by the hour and like to see big sparks. It gives them more work with the resulting extra pay. :lol:

 

[Dr.EM]

Sound advice Nigel about the not touching things without a moist finger. Quite a lot of possible reasons for that excessive heat here. Any seem possible. I'm actually wondering if they are connected up right, the datasheet shows them (TIP120/125) with the base at the edge, not in the centre like usual. Anyhow, I dismantled it for now.

Audioguru, i'll let you know how the modified compressor works out, I used a 1458 dual 741 last time, so it should be quieter now. Only got a +/- 9v available for it though, so thats not ideal.

 

[Nigel Goodwin]

Sound advice Nigel about the not touching things without a moist finger. Quite a lot of possible reasons for that excessive heat here. Any seem possible. I'm actually wondering if they are connected up right, the datasheet shows them (TIP120/125) with the base at the edge, not in the centre like usual. Anyhow, I dismantled it for now.

TO220 transistors usually have the collector in the middle, as do most non-European transistors - base in the middle is actually pretty rare!.

 

[Dr.EM]

Ah, thats alright then. Can't have been that, must have been thermal runnaway or the ultrasonic oscillation then. I don't know if the transistors will still work, it kind of seems unlikely :lol:

 

[Nigel Goodwin]

Ah, thats alright then. Can't have been that, must have been thermal runnaway or the ultrasonic oscillation then. I don't know if the transistors will still work, it kind of seems unlikely :lol:

You can check them with a multimeter, if they have failed it will almost certainly be S/C.

 

[audioguru]

if they have failed it will almost certainly be S/C.

He, he. :lol: If they are S/C then they are melted inside! :lol:
You are lucky that your dry finger didn't melt.

 

[Dr.EM]

It was extremely hot, similar to when I accidently touched a soldering iron. The skin on my finger has gone all smooth where I touched it :lol: .

Audioguru, I tried the modified compressor with little success. It was impossible to get rid of the distortion that occured, and there was quite a buzzing (low output level). It also started boosting the high frequencies as I adjusted that 100k level pot. That said, I added in the FETs to convert it back to the original (and changed that 1M to 33k etc) and am still getting similar results. It has worked in the past, with the 1458, very well too, apart from the noise. I'll look over it in more detail, try changing the op-amp etc.

 

[Nigel Goodwin]

It was extremely hot, similar to when I accidently touched a soldering iron. The skin on my finger has gone all smooth where I touched it :lol: .

It'll grow back! :lol:

 

[audioguru]

I tried the modified compressor with little success. It was impossible to get rid of the distortion that occured

I see what you mean. The LED rectifies the input and isn't filtered so modulates the LDR with severe half-wave distortion. The circuit needs a rectifier and filter stage followed by an LED driver.

there was quite a buzzing (low output level).

The LDR is probably picking-up mains flicker from lightbulbs.

It also started boosting the high frequencies as I adjusted that 100k level pot.

The pot and output opamp have a frequency response down -3dB at about 16Hz and a flat response from 80Hz to about 8kHz with old opamps.
With a TL072 opamp its response will be flat up to 100kHz at full output and flat up to 3MHz at lower levels. I don't know what is boosting your highs.

I added in the FETs to convert it back to the original (and changed that 1M to 33k etc) and am still getting similar results.

I couldn't find the original article again but found this DIY site for stompboxes and things you might find interesting:
https://diystompboxes.com/