Group Buy: Mauro Penasa MyRef Rev C kit

[gobble]

Hi guys

We've populated one board. Pic is enclosed. Shiva was kind enough to provide a diagram and has marked the changes.

Mathew Syriac, was has helped me by assembling the amp is our forum member is an experienced DIYer, having designed and developed his own 7 channel amp.

They have initially connected the amp to a 12-0-12 V trafo to avoid frying the amp in case of any wrong connections. Not finding any issues, (heating/hum etc) we decided to connect the amp to the main trafo 24-0-24 200 VA and to small bookshelfs.

What?!! No amp fry?!! :licklips: Oh well I will settle for Bangdaa fry then ...

Again no issues and hence we have connected to the source, Marantz CD6003. Played a track or two. It played on nicely.

We then connected to Torvin Two way tower. Tremendous slam, the amp was playing very cleanly upto 40% volume beyond which, there was some distortion. We then connected it to a Oscilloscope. We have noticed clipping
of signals with bass heavy content after about 40%.

Took it home and connected to the APs and my towers. One thing I noticed is this amp excels in lows with even drum sounds having much more texture, mids are a little lean, highs are ok. Ofcourse, my listening time was very limited. I'll post a detailed writeup sometime later.

Did you try this with a preamp? Mybe it wont clip at 40% then ... The good thing about your description of the SQ is that I am searching for more texture in the low mids ... hyeah: For getting highs I will connect to the Chillum instead :licklips:

Cheers

 

[gobble]

if your application is low voltage dc(like 24v-36 for the amps and other hobby electronic circuits), better option is to go for a continuosly variable dc powersupply in which you can adjust both voltage level and also have a variable current limit . Variac is usually useful for testing equipments working directly on line.

Only DC ? What about AC? I want this to test the amps I build before I connect to the speakers, using a dummy passive speaker load circuit.

Thanks

 

[keith_correa]

Cap'n what pot/attenuator/preamp was used?

 

[gobble]

Cap'n what pot/attenuator/preamp was used?

Pot? Yeah, I want to know if it will go down well with my chillum ... :licklips: hyeah:

 

[borg]

Only DC ? What about AC? I want this to test the amps I build before I connect to the speakers, using a dummy passive speaker load circuit.

Thanks

i meant the dc supply voltage of amp,you can connect at the output of rectifier, with current limit on, if anything wrong(like wrong cap polarity, ic pin reverse etc) it will protect by shutting down,
i thought this is your application, if you want for something else please ignore
with variac there is no current limit and might be difficult to realise the mistake in time

 

[stereorules]

For getting highs I will connect to the Chillum instead :licklips: Cheers

you're too good :lol:

 

[Hiten]

We then connected to Torvin Two way tower. Tremendous slam, the amp was playing very cleanly upto 40% volume beyond which, there was some distortion. We then connected it to a Oscilloscope. We have noticed clipping
of signals with bass heavy content after about 40%.

Hello Captain,
From what I read from the various forums mauro's amp is stable and clean sounding and should not distort. There are many factors which may be the reason specially when DIYing. I can think of one possible cause would be a low value volume control (Pot for Gobble ).
Regards

 

[gobble]

i meant the dc supply voltage of amp,you can connect at the output of rectifier, with current limit on, if anything wrong(like wrong cap polarity, ic pin reverse etc) it will protect by shutting down,
i thought this is your application, if you want for something else please ignore
with variac there is no current limit and might be difficult to realise the mistake in time

Yeah I figured but still being a noob at electronics decided to ask and confirm. so how much is this VariDC kit for? Looks more sensible than a Variac.

Thanks

 

[linuxguru]

We then connected to Torvin Two way tower. Tremendous slam, the amp was playing very cleanly upto 40% volume beyond which, there was some distortion. We then connected it to a Oscilloscope. We have noticed clipping
of signals with bass heavy content after about 40%.

The speaker load is 8 ohms minimum, right?

Not sure if this is due to the trafo or the caps - I'd probably upgrade the caps to 10,000 or 12,000 uF first. If the clipping persists, replace the trafo with an EI trafo of identical rating and test again.

 

[borg]

Yeah I figured but still being a noob at electronics decided to ask and confirm. so how much is this VariDC kit for? Looks more sensible than a Variac.

Thanks

i dont know if there is a kit available,once you decide the specs,it is quite possible to design/find from net a reference circuit and assemble in a common pcb

OR you can buy something like this for 89$
Linear DC Power Supply HY3003D

 

[gobble]

i dont know if there is a kit available,once you decide the specs,it is quite possible to design/find from net a reference circuit and assemble in a common pcb

OR you can buy something like this for 89$
Linear DC Power Supply HY3003D

Thats a steep discount. A DIY PCB thingie will not have LCDs and knobs like that one Tempting .. Isnt there an Indian version form Vartech and likes? They do make clones of Mastech ... some searching is in order ...

Cheers

 

[captrajesh]

For getting highs I will connect to the Chillum instead :licklips:

Chillum will only get you high, not highs. You have to try harder for 'highs' I guesshyeah:

Cap'n what pot/attenuator/preamp was used?

I think it was 35K pot. Will confirm tomorrow.

From what I read from the various forums mauro's amp is stable and clean sounding and should not distort. There are many factors which may be the reason specially when DIYing. I can think of one possible cause would be a low value volume control (Pot for Gobble ).
Regards

Hiten, my post was too preliminary. There could be things that we could've overlooked.

But IMO, since this is a Class AB amp, it is bound to distort after a point right?

The speaker load is 8 ohms minimum, right?

Not sure if this is due to the trafo or the caps - I'd probably upgrade the caps to 10,000 or 12,000 uF first. If the clipping persists, replace the trafo with an EI trafo of identical rating and test again.

The speakers were 8 ohms; as I said before, there could be some issues here. Will post a detailed review after sorting out issues like heatsink, chassis etc etc.

 

[captrajesh]

The speaker load is 8 ohms minimum, right?

Not sure if this is due to the trafo or the caps - I'd probably upgrade the caps to 10,000 or 12,000 uF first. If the clipping persists, replace the trafo with an EI trafo of identical rating and test again.

I forgot to add in my previous post. With the music running, we checked the voltage at the caps to see if there would be a drop in voltage. I believe the voltage would drop whenever the amp is required to play bass heavy content and if the caps are smaller but there was no drop. (Similar to your reading light getting dimmer when you crank the car engine / lights dimming when you switch on the A/c) (most of the older low/mid-end flats do not have separate wiring for A/c and geysers)

@Linusguru, is is not normal for a Class AB amp to start distorting beyond 40% I'm told it is normal. If not, at what level should we be experiencing it?

 

[borg]

this drop in voltage cannot be measured with dmm, try with scope, since you have access to it

 

[nshankar]

AFAIK, Class AB amps work like class A amp upto a certain point after which the switching of transistors cause some distortion.

Not sure what that 'point' is though!

 

[captrajesh]

this drop in voltage cannot be measured with dmm, try with scope, since you have access to it

Hi Borg,

I have limited knowledge with regard to technical aspects of the functioning of the Amp. All tests and measurements have been done by Mathew Syriac and his father using equipment available with them. They own a Electronic Servicing agency in Chennai.

I guess 'dmm' means Digital Multimeter. AFAIK, it was not DMM but AMM (Analogue Multimeter) According to them, if the Amp requires bigger caps, the needle pointing to a certain voltage would oscillate; however, the needle was rock steady even when some really bass heavy content was played.

 

[borg]

Hi Borg,


I guess 'dmm' means Digital Multimeter. AFAIK, it was not DMM but AMM (Analogue Multimeter) According to them, if the Amp requires bigger caps, the needle pointing to a certain voltage would oscillate; however, the needle was rock steady even when some really bass heavy content was played.

yes i meant Digital Multimeter,interesting method you mentioned above,
i havent seen an AMM since i left college

however i am not sure you can accurately observe the dynamic response of powersupply with this method.

We are looking for the effect of possible poor load regulation of tfr /insufficient cap value so need to look at the powersupply ripple to confirm

 

[captrajesh]

We have since populated the second channel also. The amp is now fixed onto a breadboard. I'm posting the pic.

The amp sounds nice and has terrific slam.

 

[gobble]

We have since populated the second channel also. The amp is now fixed onto a breadboard. I'm posting the pic.

The amp sounds nice and has terrific slam.

Nice! Where did you get the HS from? How much? dimensions? fin size?

More about the SQ please?

Cheers

 

[grubyhalo]

Hey cap'n! Looking good, there. How does it compare with the 'D'?