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Old 20th June 2012, 04:48 PM   #21
Vostro is offline Vostro  South Africa
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This is the progress of circuit 2.
Ive learned much, adding to circuit one thing at a time,
still so much to learn
I need advice please,
Q12,3,21 Any advice on which transistors to use here,
The ones shown are Vce=120V and wont do.
Ill still make some changes and tweak some values.
Here is circuit and pcb, pcb needs more work.

Regards
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Old 20th June 2012, 04:53 PM   #22
AndrewT is offline AndrewT  Scotland
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Remove RV2. Remove 3pr of output devices. Reduce the supply voltage to about +-35Vdc.
Don't fit CF1, nor C2, nor C16. Leave the pads in the PCB in case you need them for compensation.
Now you have a much simpler circuit and PCB to work with and more likely to understand what you measure on the working amplifier.

With the lower rail voltage, you don't need any high voltage transistors and that makes sourcing all your transistors easier.
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regards Andrew T.

Last edited by AndrewT; 20th June 2012 at 04:55 PM.
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Old 20th June 2012, 05:36 PM   #23
Vostro is offline Vostro  South Africa
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Thanks the reason for higher supply was in the hope for louder, crazier saturdays
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Old 6th July 2012, 03:37 PM   #24
Vostro is offline Vostro  South Africa
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Havent had much time but I just want to ask if this is a better layout,

Im also asking for advice on what I'm doing wrong on the pcb layout.

Ive built up the old pcb and it works reasonably well, just a small bzzz sound when you place your ear closer than 50cm to tweeter.
Pot body is metal and grounded.
Also have main ground to earth.
I have a pot on input, the bzz does not get any louder, when pot is at min or max, with input floating.
At max volume it delivers the full 100W, and plays Bass to High nicely.

Thanks
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File Type: jpg 1old.jpg (113.7 KB, 331 views)
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Old 6th July 2012, 08:40 PM   #25
amptech is offline amptech  Scotland
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@Vostro, your decoupling caps at the supply line don't need to be a 1000uf per rail..most amps use say 100uf to 220uf's.. followed via 220nf's.

An idea would be to add a speaker protection relay to soft start and this will stop the on/off thumps plus the circuit will cut off amp from speaker in case large dc is found on the o/p..

Just one question, what is your ac voltage reading on the o/p before clipping kick's in??
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Old 6th July 2012, 10:25 PM   #26
Vostro is offline Vostro  South Africa
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Thanks for reply, the two caps are 10000uf and is intended as main smoothing,
Just bridge and transformer off board.
My board is sadly lacking in decoupling.

In initial testing with the first board from previous post,
I was running from a 30V-0-30V 300VA transformer,
When running a 1kHz sinewave into 8R resistive load the amp started clipping
at about 77Vp-p out, 27.2Vrms giving 93Wrms into 8R.

Im now running it from a 35V-0-35V 500VA transformer, aloowing amp to deliver
over the 100W in original design goal.

I have some transformers not in use, so I just used them here to test.

Regards
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Old 7th July 2012, 02:19 PM   #27
Vostro is offline Vostro  South Africa
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I have one Sansui S-900G (sample pic added) here that I use to test amplifiers with.
Its the remains of a component Sansui system that blew up and took out its speakers with it, all three speakers in the one box was destroyed, along with the tweeter and mid in the other one, just leaving the 10in bass. The owner decided its to costly to repair and replace, so he left the speaker with me.

I used two Audiopipe ATX-3720(mine with MKT caps not electrolytics as in sample pic) to replace the blown mid and tweeter with, producing nice speaker box that I don't mind to thump.

I connected this amp to this speaker today and Im surrpised with the sound,
its not bad at all, driving the 10in bass to the max and still giving a
clear and crisp signal to the tweeters.

Im going to build up this circuit which is similar just with upgrades, (edit: Im also changing VAS to darlignton)
so hopefully by next weekend I'll see if I can hear the difference between the two.

Regards
Attached Images
File Type: jpg SANSUI_S-900g.jpg (23.4 KB, 116 views)
File Type: jpg audiopipe.jpg (18.2 KB, 109 views)
File Type: jpg 1bcct.jpg (275.2 KB, 174 views)
File Type: jpg 1b.jpg (161.8 KB, 144 views)

Last edited by Vostro; 7th July 2012 at 02:32 PM.
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Old 8th July 2012, 10:50 AM   #28
amptech is offline amptech  Scotland
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@Vostro, just notice on your foil patten that c3 is not connected on one side of it's leg but in the circuit diagram it is connected between collector and base pins.
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Old 8th July 2012, 11:04 AM   #29
amptech is offline amptech  Scotland
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Also power out in to 8 ohms is 93w and into 4 ohms comes out at 27.2 divided by 4 ohm gives 6.8 amps times by 27.2 = 184.96 watts. nice circuit.. just add v-limiter circuit in there and this will steal the drive voltage away from the o/ps in case of short circuit to the o/p.

if linked in bridge mode your have roughly 370w @8 ohms.
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Old 13th July 2012, 05:42 PM   #30
Vostro is offline Vostro  South Africa
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After final checks I made some changes, Ill build when I get the chance.

I have some more questions on other design,

(#1) I would like to know where I should ground these two points on PCB,

The simulation with the "darlington VAS" caused Q3 to saturate badly,
so I added Q22, in simulation it seemed to work.

(#2) Id like to know If I added Q22 corectly, not totally sure about R17.

Thanks
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