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Old 3rd October 2006, 04:10 PM   #1
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Default Transformer for Greg Ball Kits

Hi guys, i purchased 5 kits from Greg, (3x300w and 2x150w) i need to purchase the transformers right now.

I call some stores and they told me that have the following products.

Toroidal 300VA with Electrostatic Screen 100u$s
Toroidal 300VA without Electrostatic Screen 92u$s
Toroidal 500VA (Compact) with Electrostatic Screen 160u$s
Toroidal 500VA (Compact) without Electrostatic Screen 140u$s

Normal 500va $85u$s


Is ok to use one 1000VA or 1200VA for this amp? i want to build an 5 channels amp for my HT, i really dont want to get noise, i want an GOOD HQ amp, and i read nice comments abt the Greg Amps dont want to **** it with strange tranformers, what can i do?

Thanks
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Old 3rd October 2006, 04:18 PM   #2
djQUAN is offline djQUAN  Philippines
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if they use the same rail voltages, then it would actually be an advantage to use one big trafo than many small ones.
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Old 3rd October 2006, 04:28 PM   #3
AndrewT is offline AndrewT  Scotland
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Even better to use VERY short speaker cables and locate each amplifier right next to the speaker terminals.
This layout requires 6 monoblocks. Now that is performance!
300VA to each gb150 and 500VA to each gb300. What happened to the point one of 5.1?
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Old 3rd October 2006, 04:52 PM   #4
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mmm ok, with one 1kva or 1.2kva 40-0-40 will be enough for the 5 kits?

is or if is not an Toroidal one?

About the 5.1, the 1 is the subwoofer that have his own Amp, (300Watts). i will build another soon, with an ClassD UCD700
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Old 3rd October 2006, 04:56 PM   #5
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Wow the Monoblocks will be a lot of money in transformers

300VA is not too much for an 150GB?

Can i use 200VA for each 150GB and 400VA for each 300GB?

i will heard some diference using that monoblocks?

Can i use normal transformers? or need toroidal ones?
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Old 3rd October 2006, 05:20 PM   #6
djQUAN is offline djQUAN  Philippines
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non toroidal trannys are fine. just that they have more leaking magnetic flux that can introduce noise into other parts of the system. then toroidals are more expensive but smaller.
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Old 3rd October 2006, 05:23 PM   #7
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and is not possible to create an shield or something that stop the leaking magnetic flux?
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Old 4th October 2006, 09:11 AM   #8
AndrewT is offline AndrewT  Scotland
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Hi,
there is a copper shield that you can fit around an EI transformer.
I have seen it done in a number of websites.
I cannot comment on how effective it is.

I realise my short cable suggestion is much more expensive (but you save on cable costs) but it gives an idea of where you can aim if you want to go that type of route.

Ampguru has specifically designed his GB amplifiers to have very high PSRR. This feature should make them less sensitive to PSU fluctuations. Ampguru recommends a wide range of amplifiers ratings for his amps, as designer he is aware of the limitations.

My size suggestion is on the basis of a "normal" ClassAB power amplifier requirement of about 1.5times the maximum power output and is recommended by many commentators. I find it works well in practice.

I also know that running a group of amplifiers from a single transformer can manage with less than the sum of the individual requirements IF the signals to each are DIFFERENT. If all the amplifiers are playing the same bass notes to the same level, then they will all be drawing the same current at the same time.
But there is a significant economy to be had here. Just make sure each amplfier has it's own rectifier and smoothing bank.
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Old 4th October 2006, 09:43 AM   #9
AndrewT is offline AndrewT  Scotland
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Hi Sams,
the 40-0-40Vac transformer sounds a little bit high for the gb150.
Ampguru specifies +-55Vdc from the PSU.
40Vac (when driven from the specified input voltage) will give about 58Vdc to 60Vdc depending on regulation and quiescent currents.

gb300 can easily cope with the higher voltages when driving the higher impedance loads but needs a lower voltage PSU when using 4ohm loads.

I am using a 230Vac to 35vac 300VA transformer (effectively 36.5Vac when on 240Vac mains) and it produces +-52.8Vdc into the running amplifier (when on 240Vac and shorted input RCA).
This will/does rise to +-56Vdc when the mains incomer is +6%.
This short term overload is just about acceptable for 7ohm or more and probably OK for 6ohm as well (4 to 8ohm speakers during a party night with everything blaring and mains @ +6% might be going a bit too far, particularly if the heatsink is getting a bit hot)! Could this set of circumstances ever apply to you?
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Old 4th October 2006, 10:29 AM   #10
KLe is offline KLe  Australia
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Hi samsagaz
I use a single 500VA, 42-0-42, torroid tranny to power 2 x 300D modules (ie. a stereo 300D).

hope this helps
KL
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