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Old 4th June 2007, 08:37 PM   #1
fusion is offline fusion  United Kingdom
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Default Cambridge Audio A1 Gainclone Conversion

Hi, as someone who has not built a gainclone as of yet I will be purchasing BrianGTs Stereo Kit with one Power Supply and Two Amp boards.

Now, Ive got a Cambridge Audio A1 in perfect working condition, but I do not really use it and do not like the lack of bass, etc. although the quality is ok.

I was wondering if a gainclone would fair better or worse? I would guess better.

Another question is wether I could use the existing torrodial power transformer that is in the case. When powered up the output measures 20.9 (21) V. Would this be suitable as an input to the gainclone or not?

I believe this would be useful because I could use the input stages built in.

Any ideas or feedback very VERY appreciated.
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Old 5th June 2007, 07:07 AM   #2
space is offline space  Norway
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A +/-20V supply will make a very cool running GC. The output power will be abit limited though. (About 2*30W into 4ohms and half of that into 8ohm.) I think that most use about +/-25 to 30V for 4 ohm and up to 35V for 8 ohm.


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Old 5th June 2007, 07:24 AM   #3
Nuuk is offline Nuuk  United Kingdom
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A lot depends on how easy your speakers are to drive. For a similar project, take a look here .

If you find the A1GC lacking in power, you should have plenty of space to fit a larger transformer later!
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Old 5th June 2007, 01:07 PM   #4
fusion is offline fusion  United Kingdom
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Thanks ALOT you 2. So 50V on the rails would work for a GC running 8 ohm speakers? no loss in sq?
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Old 5th June 2007, 06:28 PM   #5
Minion is offline Minion  Canada
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Are you measureing the AC voltage off of the Transformer or the DC Voltage after the rectifier (or regulators) ??

Because 21V DC Might be a Little bit low but still quite useable even into 4 ohm loads, but 21v AC will be about 28v-30v DC which is plenty for a Gainclone....

You should also check that the Xformer supplies enough Current for the gainclone...... You will need close to 2Amps of current at 28v DC for a single LM3886 Chip or about 80vA......


Cheers

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Old 10th June 2007, 12:12 PM   #6
Ponz is offline Ponz  United States
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21VDC sounds a bit low and the output power might be limited.
i suggest you to buy a transformer about 100VA rating and
has a pair of 20-0 transformer sec. wiring.
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Old 17th May 2015, 12:34 AM   #7
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Sorry to resurrect what looks like a very dead thread, But I am thinking of doing practically the same thing. funnily enough. I have an A1 Mk3 SE, with the optional phono stage fitted.

I have decided to launch my new DIY hobby in a very simple way, by trying to build a basic LM3886 based stereo chip amp (2 x channel boards, with a singular tranfo).

I did originally think about starting off by building a pair of the ACA's, but, I only have a couple of sets of decent speakers, Both of which, have a minimum amp requirement of 15wpc, and not great sensitivity. I decided against this as I'm already pretty broke, and don't want to have to replace woofs and tweets if I can help it. (I have however totally abosorbed and understood the principles behind the ACA, even though this is no substitute for the actual experience of a hands on build.

I did want to start off with something discrete, (i think I'd learn more) but for now, I would just enjoy the satisfaction of having built a nice amp, and get my sound system running again. So I've settled on a gainclone type deal.

I am actually an absolute beginner however, so, I hope you guys are ready to answer (what you think) are probably dumb questions, HOWEVER, I can show some initiative, and I'll try not to ask a question if a google search could easily reveal the answer.

So here is the plan:

What I would like to do, is build a custom chassis, and to START with the torroid that came in the amp (with a view to replacing it with a bigger tranfo/pair of tranfos when I have the fundage.)

What I'm most confused about, is, how easy would it be to use the input and channel section that came in the amp. All I really want, is the input sockets, input selector, phono stage, (although i'm guessing that this would complicate matters) and the volume control.

It seems straightforward, but lots of things do until you actually make a start!

Any help would be much appreciated, hard to find google results because it's such a specific project.

Thanks in advance!
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Old 18th May 2015, 09:14 AM   #8
AndrewT is online now AndrewT  Scotland
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Build a Mains Bulb tester.
Use it to power ON every new mains powered project.
Use it to power ON every modified project.
Use it to confirm the wiring of any unknown mains transformer.
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Old 20th May 2015, 10:36 AM   #9
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You want specific advice, but instead I'm going to make some general comments that might or might not be informative.

If I understand, essentially you want to junk the A1 Mk3 SE except for the chassis (for now), the power transformer, and a few hardware items.

<< What I would like to do, is build a custom chassis >>

Poke around here and elsewhere and you'll see some very, very nice chassis. But of course the chassis is of zero significance as long as it's made of metal, to provide RF (radio frequency) shielding.

<< START with the torroid that came in the amp (with a view to replacing it with a bigger tranfo/pair of tranfos when I have the fundage >>

Some say toroid power transformers are critical to high fidelity. Others, such as me, say they're just a fashion created by advertising with no real-world advantages. The really significant consideration with power transformers is that they be capable of supplying at least twice the amplifier wattage, three times is better. For practical purposes watts = volts x amps = VA.

<< I have decided to launch my new DIY hobby in a very simple way, by trying to build a basic LM3886 based stereo chip amp (2 x channel boards, with a singular tranfo). >>

Remember that the ratings you see around here are real watts, not the fictional "music power" advertised by manufacturers. 100 watts (two LM3886 channels) will serve a small auditorium of a couple-hundred people, it's not really needed in a living room.

You might be better served by the 40 watts (two 20 watt channels) of the LM1875--which itself will blow the windows out of your living room. A real advantage is being able to use a smaller (less expensive) power transformer. The factory schematic (almost identical to the LM3886) is on page 2 of the data sheet: http://www.ti.com/lit/gpn/lm1875

<< What I'm most confused about is how easy would it be to use the input and channel section that came in the amp. All I really want is the input sockets, input selector, phono stage, (although i'm guessing that this would complicate matters) and the volume control. >>

Getting to the meat of things, I did a very quick google but didn't find a schematic of your amp. So making some assumptions...

The input sockets are just hardware.

An input/channel selector is commonly just a rotary switch, nothing special about it. All it does is connect the desired input socket to the single amplifier input. It might or might not ground the unused input sockets. Usually you just...connect it.

By phono stage you mean RIAA equalization? Presumably the RIAA circuit you have now is a section of the large circuit board in the A1 Mk3 SE. Somehow removing this section and connecting it to a new amp board sounds very difficult, and also pointless. It would be much easier to build a new one. Do you actually play vinyl records?

A volume control is commonly just a dual (for stereo) potentiometer, $3 from USA shippers, $1 from Asia. Unless you have some kind of superduper digital volume control then it's just a component, nothing special about it. Certainly you don't need anything special for a chip amp/gainclone.
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