Opinion

I have problem with my Quad 405-2 transformer where humming occur inside the amplifier but not effet sound. i decide to replace Old transformer with new transformer using toroidal transformer. All otai outsider please help me about all metters below:

1. Suitable power such as VA, Ampre, Volt.
2. Possible to re-cap main capacitor? now 10,000uf 63V. how the value can i upgrade for better ractifier?
3.other question is what are the difference if i change Op Amp IC? what the best code number?

I really wat to know about transformer then the rest..

Thanks coz sharing experience with.

rgds,

Azrul

Hi Azrul,
1. I had the same problem with 405-2, I changed to toroidal transformer 300VA, 0-230V Primary, 2x 0-35V Secondary, I found the sound very slightly "thinner" compared to using original transformer, but acceptable to me.
2. The main cap I changed to 12,000uf 63V. But from my experience my 405-2, I did not hear sound quality improvement after changing main cap.
3. Op amp. Yes, when changed to other op-amp I hear the difference immediately, original op-amp on my unit TL071 was soldered to the pcb, so I unsolder & solder on an IC socket, then you can easily swap op-amp. I had tried OPA134 & OPA604 & also NE5534 ... in the end I like the NE5534 sound... & it is the cheapest among the op-amps... I still have the OPA134 & OPA604 if you interested, can sell to you cheap cheap...
BTW where are you located ? I am in Segamat on weekends..
Regards
Cham

The 405 need somewhat 50VDC at the B+, maybe you're not having the desired DC voltage there thats impeding the performance somehow. The 405 schematic can be found on the internet. 10,000uF to 12,000uf will NOT make much difference. I know to some point that simply increasing filter capacitance is NOT always beneficial in some amplifiers, moreover can make the sound different but not neccessarily better.
BTW, its not always a good thing to "socket" an opamp permanently. Sockets introduce extra and unnecessary capacitance and can induce noise especially in sensitive stages. Perhaps once you've settled on a preferred opamp for its SQ, solder it permanently.

Hi cmboy,
The transformer spec secondary 2 x 35V refer to AC rms 35Vrms, when it is rectified will be DC about 49.5 VDC, which is close enough to the original 50VDC IMHO. Good suggestion about soldering the opamp permanently after deciding on which opamp to keep, but mine still with the socket, after finding the right sound for myself, lazy to open up the amp again, but that's just me....
Kind regards

Hmmm...all this remind me to dig up my 33 and 405 andmuck around with it. Its been so damn long in hibernation.

Hi Chamts1,

Thank for your valueble information. after you mention transformer spec I searh through internet and I found Match transformer as you mention 300Va, 35V from Rs Component.

http://malaysia.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=2238235#header

But I'm very curious about how good this transformer. it is enough Ampre fo the amp? need magnetic shield or not for this transformer?

Changing Transformer consider Upgrade or downgrade?

cmboy wrote:The 405 need somewhat 50VDC at the B+, maybe you're not having the desired DC voltage there thats impeding the performance somehow. The 405 schematic can be found on the internet. 10,000uF to 12,000uf will NOT make much difference. I know to some point that simply increasing filter capacitance is NOT always beneficial in some amplifiers, moreover can make the sound different but not neccessarily better.
BTW, its not always a good thing to "socket" an opamp permanently. Sockets introduce extra and unnecessary capacitance and can induce noise especially in sensitive stages. Perhaps once you've settled on a preferred opamp for its SQ, solder it permanently.

thanks for your advise... will take note for further upgrade.

If the ori mains transformer is defective, why not rewind it? I've heard of good rewinders to be found here in KL, but don't ask me who or where. I know of one somewhere in KL but never used that services. A good rewinder can replicate any mains transformer windings properly if very experienced. Rewinding valve output trannys is another thing and story altogether. A transformer hums mainly because the lacquer that secure and hold the windings together have deteriorated seriously over the years. Internal shorting or electrical resistance leakage in the windings can also cause hum. A full rewind is the only recourse if kept to original. I sometimes think the Americans make better quality, more reliable and resilient transformers, can stand higher temp than the Brits.

Hi Shamjohor,
Ya that is the transformer I used (RS component). When I was looking for transformer for the 405-2, Dada Europe got one used unit, but too costly to ship in (heavy & I was not very sure if will kena tax so...that is history), the spec I used suggested by kind gentlemen running Dada. I think it has enough current (ampere) for the 405-2. I also did not do any special shield. I am not sure what is the original transformer spec, the one I used is 300VA, so not sure if upgraded/downgraded. Important thing is the amp is running without transformer vibration/humming.

cmboy wrote:If the ori mains transformer is defective, why not rewind it? I've heard of good rewinders to be found here in KL, but don't ask me who or where. I know of one somewhere in KL but never used that services. A good rewinder can replicate any mains transformer windings properly if very experienced. Rewinding valve output trannys is another thing and story altogether. A transformer hums mainly because the lacquer that secure and hold the windings together have deteriorated seriously over the years. Internal shorting or electrical resistance leakage in the windings can also cause hum. A full rewind is the only recourse if kept to original. I sometimes think the Americans make better quality, more reliable and resilient transformers, can stand higher temp than the Brits.

Cmboy,

I heard about guys that expert in rewinding transformer but dont have a contact. But for sure cost for rewinding more expensive compare to buy new transformer. My quad actually produce humming but not to loud. does not effect the sound quality. but so sad becous spend rm2K++ for this amp and this amp give some unsatisfied humming. but lucky becaus all component is still original.

In the long past I've rewinded 2 transformers for 2 different tube amplifiers, one power amp and one pre, cost me somewhere RM200 for each. Moreover, I had no blinking idea what the voltage nor current output was and depended on the rewinder to sort them out, especially the preamp. The half wave rectifier circuitry had shorted out causing the tranny to smoke. It all worked after the rewind. I've not heard any complaints to date since it was all settled. Sorry, me don't do these things nowadays. For convenience, I think I can trust local rewinders in the business for years and doing up mains transformers. Its no more complicated than to rewind sizeable single phase or 3phase motors. I only hope they use reputable quality copper wires and lacquer insulation during the rewind. OK.,,thats all I know for now.

that great story cmboy. Thanks a lot for both of you Hifi Otai.. i'm very appriaciate your advise. may be we can minum kopi together one day.