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Old 21st January 2007, 05:36 PM   #1
mikee55 is offline mikee55  United Kingdom
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Default catapillar to butterfly

Hi all, sorry about the tacky title.

I was told once to take the parts from a dead amp and make a new amp. I have 3 dead (two and a half, one is half working) amps. Three big trannies and some boards, what do I need to do?

Curious Mikee55
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Old 21st January 2007, 05:43 PM   #2
jaycee is offline jaycee  United Kingdom
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What specifically do you have in parts?
How much experience do you have?
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Old 21st January 2007, 07:06 PM   #3
mikee55 is offline mikee55  United Kingdom
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Default Parts

Hi jaycee,

I have a 2 x 45v (2 x 5 amp) Toroidal transformer. The guts of a JVC AX-2 amp, with a 2 x 40v (2 x 1.5amp) transformer. Technics SU-V2 amp which has STK blocks, this amp is dead on one channel and I don't care for STK blocks but its got a big trannie. And I have a Realistic amp in the loft which has a big trannie. So basicaly I'm looking at a Power supply with a handfull of Smoothing caps, and bridge rectifiers, oh and some heatsinks. Erm... transistors are no good and like I said, don't like STK blocks, oh and the circuit boards too.

I have just completed a Linkwitz Transform for my sub. I'm using the one channel of the Technics as the amp for this sub. So I'd like to build a mono block for it. I'd like to make something of the Toroidal, which I bought to replace the one in the JVC, it cost me 30. It was probably the 5v difference that killed that amp, I don't know, but with a split rail of 45volts at 5 amps would give 90 volts at 10 amps = 900 watts. So could something like a 200 watt amp be made? I don't want to max out the psu because of the nature of gain in the Linkwitz Transform.

What do you think?

Cheers mikee55
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Old 21st January 2007, 09:40 PM   #4
mikee55 is offline mikee55  United Kingdom
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Default Anybody

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Old 21st January 2007, 10:06 PM   #5
jaycee is offline jaycee  United Kingdom
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If you want it for driving a sub I'd say Elliot's P68. You need good heatsinking though. You will want to use 4 pairs of output devices. That should get you roughly 200W into 8 ohms, and more into a 4 ohm load.

For your power supply capacitors you are going to need capacitors that can handle more than 63V. My guess is the caps from what you have will be 63V max. I would suggest looking on eBay for some 80V or 100V parts.

One of the STK's on the Technics is probably fried which is why one channel is dead. Agreed, the extra voltage (63V versus 56V) is probably what killed it, although it depends on what STK modules were being used. You may well have fried the PSU caps in this unit, too.
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Old 21st January 2007, 10:35 PM   #6
mikee55 is offline mikee55  United Kingdom
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Default Got it open in another window

Hi jaycee,
Looking at project 68, it looks a beast of a design, I take it I just assemble Figure 1 - Basic Amplifier Schematic? I shopped at Maplin for the parts to my Linkwitz Transform. They're not as good as they used to be. I paid 13p for a resistor, then you got to buy 10 minimum, so if you want 1 resistor it'll cost 1.30. Thats mad. This amp will cost a packet with 20 odd resistors. Where else can I shop? RS requires an account, I don't have a business and when I've been able to take a sneaky peak at a price list, they seemed more expensive compared to Maplin. Mind you, last time I looked was 5 or 6 year ago. And what about Trannies? Wheres best place to get them from?

Cheers Mike
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Old 22nd January 2007, 09:55 AM   #7
jaycee is offline jaycee  United Kingdom
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Basically yes, although you will want the extra transistors shown in figure 1a.

I would recommend you order the PCB from Rod. As the article says, there is no way you can safely construct this amp on something like Veroboard, you need a proper PCB.

Forget Maplin. I didn't even know they'd started selling resistors in 10's. That used to be the only reason i'd buy anything from them.

RS will now let individuals purchase things through their website. They do charge a fair bit for shipping though, and this isn't cost effective for a low-cost order. Similarly Farnell will also deal with individuals, but they have a 20 minimum order.

Rapid are quite good, they have a lot of stuff, more like how Maplin used to be. www.rapidonline.com

For the power transistors used in the P68, you might want to try getting these as samples from OnSemi directly. Explain that you're building a DIY amplifier and they should be fine with this.
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Old 22nd January 2007, 11:11 AM   #8
mikee55 is offline mikee55  United Kingdom
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Default PCB issue

Hi jaycee,

Would it be costly to ship Rod's PCB over? Buying abroad has always been off-putting due to ship costs,currencey conversion etc.(15 appx for the board)
Do you think the board would have a particular layout? Would I be able to make my own?

Oh I dunno, could buy a ready made job from BKtronics.

What do you think?

Cheers Mike
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Old 22nd January 2007, 11:44 AM   #9
Bone is offline Bone  United Kingdom
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Default P68 - Rod Elliott

Mikee,

I live just up the road from you in Blandford. If you want any help let me know. I've bought boards from Rod before and paid by Credit Card.
The exchange rate at the moment is about A$2.5 to the pound and he would charge $12 for shipping and $32 for the board. Which would make it about 18 or less. You'd also have to pay a currency exchange fee.
He has an encrypted order form which safeguards the card number or alternatively you could pay through Paypal. Although this would cost a little more.

If you need help my email is tony dot harker (at) lineone dot net. Replace the dot with . and (at) with @.

Regards Tony.
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Old 22nd January 2007, 11:49 AM   #10
AndrewT is offline AndrewT  Scotland
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Default Re: Parts

Quote:
Originally posted by mikee55
Hi jaycee,

I have a 2 x 45v (2 x 5 amp) Toroidal transformer. ......but with a split rail of 45volts at 5 amps would give 90 volts at 10 amps = 900 watts. So could something like a 200 watt amp be made?
something is not adding up here.

2 x 45v ? is that 45-0-45Vac or is that +-45Vdc?

(2 x 5 amp) is that 10amps from each secondary winding or is that 5amp from each winding or is that four secondary windings, each rated at 5A?

If the transformer is 45-0-45Vac then one will get +-66Vdc to +-67Vdc from it when the amp is on low quiescent current. Use 75V or 80V capacitors (75V leaves 12% spare for mains supply overvoltage).

The same transformer, 90Vac centre tapped and rated at 5A from each secondary, will equate to 450VA. this must be reduced by a factor of 0.7 when feeding a capacitor input filter (the smoothing bank capacitors). you will have about 300W to 350W available to drive the amplifier. However a ClassAB is only about 70% efficient so for good performance you can expect as little as 200W or stretch this to 300W if you design the PSU to maximise good quality power.
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