x-can V1 V2 psu problems

[bullpup]

Morning all

In the past I have taken advice from here in relation to various power supplies for my Samwha'd V1 and as a temporary measure bought a 3 amp supply from Maplin:

www.maplin.co.uk/Search.aspx?criteria=l54br&source=15&SD=Y

However yesterday I discovered this thread:

rockgrotto.proboards39.com/index.cgi?board=q&action=display&thread=1196272010&page=1

where another member - allenf found the same power supply runs at 14.2v unloaded but in my case drops to around 12.5-13v when loaded ( with a 12 volt halogen bulb)

Maplin tested the unit and maintain the unit is in tolerance and compared it with another unit with identical results and indeed a 1 amp which measured 14.1 v with no load and 12.4 with the same load.

The question is are these characateristics normal for this type pf supply and more importantly on the basis that the supply voltage drops under load is it safe to continue to use it until I can justify buying a Little Pinkie psu?

If not does anyone have a standard or Rapidonline unit I can buy please? In fact this looks remarkably similar to the Rapidonline unit:

cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&rd=1&item=260200312516&ssPageName=STRK
Many thanks

[Deleted]

bullpup
Did you measure the actual voltage while it was working ?
SandyK

[bullpup]

SandyK

Thanks for your reply. The short answer is no. To do this I assume I would need to slide the covering tube off the amp and put the probes across the incoming supply and test with the amp actually driving some Headphones?

Many thanks

Bullpup

[Deleted]

bullpup
Yes,but it shouldn't matter about the headphones.
BTW,many valves are rated to work on a nominal 12.6V AC supply for the heaters. 6.3V and 12.6V AC are among the more common valve heater voltages. It is not uncommon to have 2 valves with their 6.3V heaters connected in series, and working off a 12.6V AC supply, either.
SandyK

[bullpup]

Thanks I will give it a go this evening after the little horrors have gone to bed.

[XTRProf]

Hi there,

It should be quite normal for the supply to drop under load. However, the main thing is not whether that drop or not but whether that dropped voltage still meets the requirement of the V1 and V2. Is your input supposed to be 12V for the V1 and V2?

[allenf]

bullpup said:

Morning all

In the past I have taken advice from here in relation to various power supplies for my Samwha'd V1 and as a temporary measure bought a 3 amp supply from Maplin:

www.maplin.co.uk/Search.aspx?criteria=l54br&source=15&SD=Y

However yesterday I discovered this thread:

rockgrotto.proboards39.com/index.cgi?board=q&action=display&thread=1196272010&page=1

where another member - allenf found the same power supply runs at 14.2v unloaded but in my case drops to around 12.5-13v when loaded ( with a 12 volt halogen bulb)

Maplin tested the unit and maintain the unit is in tolerance and compared it with another unit with identical results and indeed a 1 amp which measured 14.1 v with no load and 12.4 with the same load.

The question is are these characateristics normal for this type pf supply and more importantly on the basis that the supply voltage drops under load is it safe to continue to use it until I can justify buying a Little Pinkie psu?

If not does anyone have a standard or Rapidonline unit I can buy please? In fact this looks remarkably similar to the Rapidonline unit:

cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&rd=1&item=260200312516&ssPageName=STRK
Many thanks

Mine didn't volt drop when loaded with my V2, and bearing in mind the heat issues I've quietly dropped the idea for now.
My Pinked-up V2 continues to sound fantastic enough for me for now with the standard supply, besides I've just bought another car so I'm skint anyway

[sometrolls2]

From memory, on the V1 the supplies to the components on the amp board go through regulators and the valve heaters take voltage from the side. People use all sorts of wrong voltages on the heaters and get away with it, a lot of russian tubes want 6.3V not 12V. The regulators are there to deal with this kind of issue.

[Deleted]

sometroll2,Allenf,bullpup

The X-Can V1 takes its filament power from a couple of 1,000uF electrolytics ,via D6, BEFORE the regulators. Another diode could always be tried in series with D6 (1N4007) in this unit.
A 1N4004 would suffice, and may be easier to obtain.
SandyK

[sometrolls2]

I never understood the need for those big caps for the heater, or do they need to 'move with the music' with the rest of the components?

[Deleted]

Sometrolls2
They are there to provide filtered DC for the heaters, as this normally reduces/eliminates any potential hum problem due to AC on the heaters.

SandyK

[sometrolls2]

Does it matter much if there is noise on part of the circuit that is separate from the bits that matter, they could have used a smaller cheaper cap?

[sometrolls2]

Does it matter much if there is noise on part of the circuit that is separate from the bits that matter, they could have used a smaller cheaper cap?

[Deleted]

sometrolls2
The beancounters wouldn't let them use anything bigger, or more of, than necessary to meet design specifications. You wouldn't want an amplifier with an annoying low level 50HZ hum!

SandyK

[PinkFloyd]

The stock 500mA MF wallwart measures between 13.2V - 13.9V under no load. I have probably measured over 50 of them over the years and have yet to see one anywhere near the 12V mark.

As a matter of interest the regulators in the X-CANS amp are AN7815 / AN7915 which are 15V regulators.

[bullpup]

Afternoon All

I have now had a chance to measure this psu both connect to the X-Cans and without.

It measures 14.7v unconnected and 14.3v connected. Is this acceptable please?

[Deleted]

bullpup
It's still higher than I personally would like. It may sound great, but you run the risk of greatly shortened valve longevity.
SandyK

[allenf]

I guess the reason a standard psu gets so hot is that it is on its limit powering the x-can; the voltage drops just enough under load to run the valves at the voltage specified by the amp designer.
Which is a cheaper option for the OEM than specifying a high quality psu regulated at a comfortable 12 volts, fair enough.

Next time I disassemble my V2 I'll meter the standard psu under load to test this theory.

[Deleted]

Also to be remembered, is that when a valve with a 12.6VAC filament is heated by D.C. , that the DC voltage for the same heating is more likely to be around 9V DC. ( I hope I got that right ! I think I need another cup of coffee.)

SandyK

[PinkFloyd]

The 500mA stock walwart may sometimes run hot when it's struggling (a teacup of current) swap her out with a swimming pool of current PSU and the components may actually get what they need and you'll find the PSU runs relatively cool but certain components in the amp get warmer..... this is NORMAL

[allenf]

allenf said:

I guess the reason a standard psu gets so hot is that it is on its limit powering the x-can; the voltage drops just enough under load to run the valves at the voltage specified by the amp designer.
Which is a cheaper option for the OEM than specifying a high quality psu regulated at a comfortable 12 volts, fair enough.

Next time I disassemble my V2 I'll meter the standard psu under load to test this theory.

Hah - standard supply is 13.4V open and 11.9V loaded with the V2.

[bullpup]

admin said:

The 500mA stock walwart may sometimes run hot when it's struggling (a teacup of current) swap her out with a swimming pool of current PSU and the components may actually get what they need and you'll find the PSU runs relatively cool but certain components in the amp get warmer..... this is NORMAL

Hi Mike I guess I am being a touch thick here - my psu is ok?

Many thanks

[allenf]

Slightly OT, but I've just had an Ei ECC88 valve go in the V2.

Rats..