Simple Killer Amp - Introductory Offer!

mgalusha · « **Reply #40 on:** 4 Feb 2006, 04:13 am »

Quote from: BradJudy

Sounds like you've got a good plan going Mike. I hope it turns out well. Perhaps I'll even get to see/hear it.

You're always welcome Brad. Maybe once the amps are up and running we can get a few guys together for a listening session. I'll post some photos and such as they come together.

amplifierguru · « **Reply #41 on:** 4 Feb 2006, 07:13 am »

Way to go Mike, I'll be watching for that.

Maybe I could start an Australian DIY amplifier camp - 1 week intensive and everyone comes away with an amp built from scratch and the skills honed? Summer meltdown or winter chill?

Cheers,
Greg

audiojerry · « **Reply #42 on:** 4 Feb 2006, 07:29 am »

Thanks for introducing a new product and a great looking offer, Greg.
Thanks for being an early US pioneer on one of these amps, Mike. Please keep us posted.

amplifierguru · « **Reply #43 on:** 4 Feb 2006, 08:22 pm »

Hi audiojerry,

Thanks. You know the response has been overwhelming and I'm running out of these kits faster than expected.

Cheers,
Greg

JoshK · « **Reply #44 on:** 5 Feb 2006, 12:14 am »

I got asked by someone if your modules would support 4 ohm loads well or not. Thought it was a good question, since it doesnt seem to be answered on your site.

mgalusha · « **Reply #45 on:** 5 Feb 2006, 01:49 am »

Quote from: audiojerry

Thanks for being an early US pioneer on one of these amps, Mike. Please keep us posted.

Jerry,

I'll post some photos and details as things come together. My initial build will be in a old pair of Parasounc HCA-1201 chassis. These were the chepies sold by Audio Advisor about 5 or 6 years ago. The power supply has the correct voltage but only a 280VA transformer, so it won't be able to reach full power, especially into 4 ohms. I figure this will give me a good handle on the sound and if I like it enough I can always put them in a larger chassis and use a stiffer power supply. The upside is my initial cost will be low and my speakers are about 91dB sensitive, so I don't need huge amounts of power.

amplifierguru · « **Reply #46 on:** 5 Feb 2006, 06:53 am »

Hi Josh K,

The larger amp, the GB300D, is rated 300W into 8 or 4 ohms. This means, as a dedicated 4 ohm amplifier it should run from a suitable power supply for maximum 300W with (nominal) 4 ohms. That's a peak 49V, so +/-55V quiescent supplies is optimum. For the same at 8 ohms requires a peak 69V so a supply of +/-75V is needed. This is detailed in the instructions.

For general 4/8 ohm usage a +/-65V quiescent supply with typically 300VA transformer should suffice with an adequately large heatsink (0.3-0.4C/W). Clearly, thrashing the amplifier on this supply into 4 ohms (like a hard driven sub) would certainly put a strain on reliability.

For sub use I would recommend supplies be run at least 5V lower than full range for the same impedance, with larger than average heatsinking.

mgalusha's power supply sounds about perfect.

Good luck.

cheers,
Greg

ctviggen · « **Reply #47 on:** 5 Feb 2006, 01:54 pm »

Oh I see -- current goes up, so voltage goes down, therefore the smaller valued voltage rails.

amplifierguru · « **Reply #48 on:** 5 Feb 2006, 08:47 pm »

That's right Bob,

I once did a commercial audiophile amplifier design that used 4 secondary windings either series or paralleled (by a rear panel octal plug/skt) for 4/8 ohms or 1/2 ohms. So supplies were +/-68V or +/-34V.

99% of owners used the higher setting only.

Cheers,
Greg

rez · « **Reply #49 on:** 6 Feb 2006, 12:25 am »

into the deep end - taking the plunge with the GB150D and GB150ABS.
Greg you've got paypal mail.
Roman

KLe · « **Reply #50 on:** 9 Feb 2006, 04:22 am »

Hi Greg
Its an excellent VASless design (unless, its hiding?), and, I have placed my order for a pair of your GB300D (300W Class AB MOSFET) amplifier module kits.

Is a 300VA transformer, and +/-70V supply rails, per channel sufficient/ok

I know of a nice +/-60V SMPS? Perhaps, I could change the PS to it at a later date.

thanks again
KL

amplifierguru · « **Reply #51 on:** 9 Feb 2006, 07:41 am »

Hi KLe,

Thanx for your order.

I am very happy with this unique amplifier design. Wasting the Vas was the big step forward! The use of a 250MHz Class A EF driver stage instead allowed me to bootstrap the input stage gain up to 80db and reduce it's distortion by 2 orders of magnitude. Then with the 30dB of output stage gain in common source mode the MOSFETs have negligible output stage/power supply losses so the amp requires a smaller Ps and is leaner, cleaner (typ 0.005% 2HD at 10W), and GREENER.

The GB300D will run up to +/-75V for 300W into 8 ohms or 55V for same into 4.

SMPS - I've never tried, but the higher PSRR of the topology goes a long way towards reducing spurious intrusion from the supplies, so I don't see a problem with your +/-60V SMPS. I'd be interested in hearing the result.
If there was ever an amp that should go well with an SMPS , this is it.

Good luck with it.

Cheers,
Greg

KLe · « **Reply #52 on:** 10 Feb 2006, 07:23 am »

Hi Greg
Just a few questions

1. It looks like the amp has a differential input stage with a complementary output stage. Is that correct

2. Do the input stage bipolar's need to be matched

3. Do the output stage mosfet's need to be matched

4. Complementary output stages are noted for having excellent local feedback, which provides for low distortion, but, are not noted for handling difficult loads, such as <4 ohm loads. How is the GB300D in this area

5. It would also appear that no special classA biasing circuit is required. Is that correct

6. I know the design is simple, and as a result is low cost and excellent value, but, the power supply needed appears to be smaller than others with the same power rating. Is that correct

7. So for the GB300D, what is the smallest size transformer that you would recommend

thanks

amplifierguru · « **Reply #53 on:** 10 Feb 2006, 09:46 pm »

Hi KLe,

I answered you in the other forum you posted to, but will copy here for general interest.

1. The amplifier is complementary throughout. The input differentials are complementary BJT, the driver stage is complementary Class A 250MHz BJT, and the output stage is complementary common source MOSFET. Even the input stage current sources and thermal comp are complementary. Sexy, hey?

2. The input BJT pairs are matched to 5% on current gain to minimise DC offset particularly in DC couple mode.

3. The output MOSFETs are matched in a custom jig to 10mV on Vgs on to facilitate equal sharing of load current in conjunction with their internal resistance.

4. The amplifiers are designed to function on nominal 4-8 ohm loads and are Vgs limited to limit maximum currents in untoward situations.

5. The amplifier has been optimised for low bias Class AB operation with residual distortions well contained below 0.005% and inaudible at normal levels, but can be biassed up to Class A operation of 1/3 the power rating on suitable lower continuous duty supplies for those who need it. I have not experienced any audible benefit.

6. The topology with the power efficient common source output stage can swing to within 2V of the supply rails so, in conjunction with the high PSRR of the design , can perform with lower supply voltages and capacitance for a given power output over conventional designs. The difference is typically 30% - making this a very lean, green performer.

7. 250VA for the GB300D is about the minimum I would suggest for full output on one channel, typically 300VA. If the power output is reduced this could be reduced further without detriment.

Hope that helps.

Cheers,
Greg

amplifierguru · « **Reply #54 on:** 11 Feb 2006, 07:47 am »

'todays' new owner review -

http://www.diyaudio.com/forums/showthread.php?postid=842783#post842783

cheers,
greg

KLe · « **Reply #55 on:** 13 Feb 2006, 09:19 am »

Quote from: amplifierguru

Hi KLe,
I answered you in the other forum you posted to, but will copy here for general interest.

1. The amplifier is complementary throughout. The input differentials are complementary BJT, the driver stage is complementary Class A 250MHz BJT, and the output stage is complementary common source MOSFET. Even the input stage current sources and thermal comp are complementary. Sexy, hey?
2. The input BJT pairs are matched to 5% on current gain to minimise DC offset particularly in DC couple mode.
3. The output MOSFETs are matched in a custom jig to 10mV on Vgs on to facilitate equal sharing of load current in conjunction with their internal resistance.
4. The amplifiers are designed to function on nominal 4-8 ohm loads and are Vgs limited to limit maximum currents in untoward situations.
5. The amplifier has been optimised for low bias Class AB operation with residual distortions well contained below 0.005% and inaudible at normal levels, but can be biassed up to Class A operation of 1/3 the power rating on suitable lower continuous duty supplies for those who need it. I have not experienced any audible benefit.
6. The topology with the power efficient common source output stage can swing to within 2V of the supply rails so, in conjunction with the high PSRR of the design , can perform with lower supply voltages and capacitance for a given power output over conventional designs. The difference is typically 30% - making this a very lean, green performer.
7. 250VA for the GB300D is about the minimum I would suggest for full output on one channel, typically 300VA. If the power output is reduced this could be reduced further without detriment.

Hope that helps.
Cheers,
Greg

Thankyou Greg
Sorry for not replying sooner, but, I have been down with the flu. Real bummer actually, but, the answers are terriffic

It amazing that you can get away with a 300VA PSU. It is quite small, but, the PSR is 10 times better than usual, so ...

I will probably have a few more questions for you, if that's ok

, when I think of them?

thanks again
KL

KLe · « **Reply #56 on:** 13 Feb 2006, 09:23 am »

Hi Greg
PS: I am Looking forward to receiving my pair of GB300D (300W Class AB MOSFET) amplifier module kits.

KL

jdybnis · « **Reply #57 on:** 13 Feb 2006, 10:01 am »

Can I use the power supply from the Leach Amp to power a pair of GB150D's? My transformer is rated 500VA. Supply outputs (+-57V).

http://users.ece.gatech.edu/~mleach/lowtim/pwrsply.html

KLe · « **Reply #58 on:** 13 Feb 2006, 10:39 am »

Hi Greg
Actually, I have thought of another couple of questions ...
1. What is the GB300D's rise time

2. What is the GB300D's damping factor

thanks again
KL

amplifierguru · « **Reply #59 on:** 13 Feb 2006, 08:22 pm »

Hi jdybnis,

At a stretch you could use the GB150D on a stiff +/-57V. but only with light duty 8 ohm use. I would add an RC component to each power supply so it fell a little under load ( and delivered lower ripple as a side benefit).

However the larger GB300D would be fine on this supply for all 4-8 ohm loads.

Hi Kle,

Good to see

you off your death bed!

Rise time is limited by the 160KHz input filter to 6uS , without it the amp does <1uS dictated by the small lead C in the FB network.

Damping factor I can't measure easily - must be greater than 500 at 20-50Hz. Certainly an order of magnitude better than needed.

cheers,
Greg