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Hiraga Le Monstre

Dan K said:
Are these any good?

http://rover.ebay.com/rover/1/710-5...0001&campid=5338728743&icep_item=112772158975
http://rover.ebay.com/rover/1/710-5...0001&campid=5338728743&icep_item=113079548115

Anyone used them?
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While they appear to use Dale and Wima parts, there are complaints regarding some clones that the boards actually supplied contain inferior substitutes. To be genuine, the semi-conductors (or some of them) would have to be NOS and are more likely to be fakes. So, if you want to take a punt be prepared to write £85 off to experience. Unless the pcb is of a very high standard, attempts to upgrade components will likely lift/break one or more tracks.
And btw a dubious pot I've chanced my arm on will arrive 'Wed, 08 Apr - Tue, 05 May'. Coronavirus is doubling waiting times, which are probably a guess at best, so don't hold your breath.
 
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I've a question about the proposed PSU for this amp. Actually it's a question about the power supply for any Class A amp:

The recommended supply (if you really must use the mains) was to use a single 60,000uF cap after the reg, then a 0.47 Ohm resistor, then a paralleled pair of 60,000uF caps - One of this combo for the +ve rail and another for the -ve.

Given that a Class A amp draws a constant current, what is the point of doubling the capacitance at the rail, ie why pair up those last 2 caps? Is there some additional attenuation of the 100Hz ripple from doing this? You would half the ESR at the rail, but you're still limited by the resistor and the ESR of the single cap. What's the reasoning?

Thanks all for your help :)

https://www.flickr.com/photos/152975944@N08/49540067607/

3/4 of the way down in this article:
https://sound-au.com/tcaas/hiraga3.htm
 
Dan K said:
I've a question about the proposed PSU for this amp. Actually it's a question about power supplier for any Class A amp:

The recommended supply (if you really must use the mains) was to use a single 15,000uF cap after the reg, then a 0.47 Ohm resistor, then a paralleled pair of 15,000uF caps - One of these comboc for the +ve rail and another for the -ve.

Given that a Class A amp draws a constant current, what is the point of doubling the capacitance at the rail, ie why pair up those last 2 caps? Is there some additional attenuation of the 100Hz ripple from doing this? What's the reasoning?

Thanks all for your help :)

https://www.flickr.com/photos/152975944@N08/49540067607/
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Class A amps are not that generic I'm afraid... neither do they necessarily have a constant current draw....

It's all down to PSRR at the end of the day. The simplest amps with least parts in them often have very poor PSRR and can need humongous and expensive PSU's to get the ripple low enough for a silent background whilst complicated amps with loads of feedback can have a silent background even with volts of ripple on the supply rails.
The PSU in question is an RC filter. The R needs to be a very low resistance in order to pass the current and this then means the C must be huge if it is to filter down at 100Hz and below.
 
sq225917 said:
Layout looks fine, doesnt tell you anything about the matching though.
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Indeed. Bit of a punt if it needs £200 of work spent on it (I can’t check for matching or scope for distortion).

Worth prodding the seller for some more details though.

Stacks of capacitance in the PS so one would hope it’s quiet?
 
Is that 0.08 THD or 0.08% ?

I reckon it will still have an annoying 100hz buzz through the speakers.

That PSU was never designed for Le Monstre, it's for the 25W amp. The 25W Hiraga amp has a resistor and a cap de-coupling the front end from the output and the rectifier
 
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Dan K said:
Is that 0.08 THD or 0.08% ?

I reckon it will still have an annoying 100hz buzz through the speakers.

That PSU was never designed for Le Monstre, it's for the 25W amp. The 25W Hiraga amp has a resistor and a cap de-coupling the front end from the output and the rectifier
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0.08% THD seems unlikely given the design, right?

How come the extra capacitance isn’t effective at reducing the ripple?
 
It's not the capacitors, it's the resistor. The amp wants to draw a lot of current and that means that the resistor has to be small. 100Hz is hardly attenuated at all by a large(ish) 10,000uF cap. Adding 0.1uF caps across each of the rectifier diodes will smooth the 100Hz saw tooth, but it will still be there. I've been through all this with my Bedini 25/25. The SLB PSU or cap multiplier is the way to go. At first I thought the active rectifier in the SLB was unnecessary, but Martin and experience have educated me. Active rectifiers in amps like these are a very good thing - less noise, less voltage drop, less heat. Its all +++
 
When you look at the ESR spec of a cap it's always stated at 100Hz because that's the frequency that the rectifier chucks out. If you use a bigger resistor then you get a voltage drop at the front end and a less dynamic amp. This is the reason that all Bedini and Dynavector amps normally put out a very faint 100Hz buzz through the speakers.
 
Dan K said:
It's not the capacitors, it's the resistor. The amp wants to draw a lot of current and that means that the resistor has to be small. 100Hz is hardly attenuated at all by a large(ish) 10,000uF cap. Adding 0.1uF caps across each of the rectifier diodes will smooth the 100Hz saw tooth, but it will still be there. I've been through all this with my Bedini 25/25. The SLB PSU or cap multiplier is the way to go. At first I thought the active rectifier in the SLB was unnecessary, but Martin and experience have educated me. Active rectifiers in amps like these are a very good thing - less noise, less voltage drop, less heat. Its all +++
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Think I get most of that! Thanks Dan.
 
I have a set that the chap from ebay and DIY audio matched (he's Igor) to as close as was possible. He has a few other sets. You would almost end up in a bidding war with each other for who wanted the closest matched MOSFETs and whether you wanted the lowest noise or the most gain. Easy enough to get the SLB board from the USA. Better to order an individual board and slip under the $50 duty threshold. Then just get the SLB BOM from DIY audio and click the Mouser order link.

I've all the bits, just need a case and a pair of traffos..
 
Dan K said:
I have a set that the chap from ebay and DIY audio matched (he's Igor) to as close as was possible. He has a few other sets. You would almost end up in a bidding war with each other for who wanted the closest matched MOSFETs and whether you wanted the lowest noise or the most gain. Easy enough to get the SLB board from the USA. Better to order an individual board and slip under the $50 duty threshold. Then just get the SLB BOM from DIY audio and click the Mouser order link.

I've all the bits, just need a case and a pair of traffos..
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What spec transformers are required?
 
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