Norge 1000 - Repairs and Modifications

[laksh]

Hello All,

I bought Norge 1000 amplifier and New Millenium speakers set last year Jan/Feb for around 27,000 Rs including remote. Connected to Phillips DVD Player it sounds good,clear and is a value for money product. I wanted a professional amp that sounded crystal clear at low volumes, had a hefty budget but settled for Norge.

Being electronically curious and hobbyist I had to open it to see why the heatsink got hot quickly and replaced it with a large 6mm thick copper plate, the length of the amp at the back to which I fused the aluminium heatsink with thermal paste and bolts. It works fine. The copper plate itself takes very long to get warm and I hardly keep the volume beyond 10 'O' clock as I have it in my bedroom. It only gets tested/noticed when old trance music is played.

Something has gone wrong with it now. The only incident I remember that happened was that the volume control was mistakenly turned to the max position and without noticing I had powered on the amp and with the DVD playing classical music, sent a blast of energy out of the speakers momentarily before I immediately shut off the amplifier. The volume control gave away long back as it sends background noise when turned.

After this episode, I noticed, the amp lost its balance and the left channel sounded more than the right channel. I had to wire and connect the tone defeat points on the pre-amp pcb to correct this. The bass control knob also appeared faulty as it lost its finesse when turned which I replaced with a locally purchased Rs.45 B100K pot. However the amp is not sounding the same but it plays.

I do not know how to check each component to figure out which one is faulty though I have a digital multimeter nor there are any visible faults/burns but I suspect something may have gone faulty in the power filter pcb or the pre-amp pcb.

I had ordered for 3 opamps LME49990 MA and a Bourns pot 1822848 (to replace the lesser bass pot) from kitsnspares today which I will get in two weeks time. I heard a lot of positive liking towards 49990 and hence wanted to try it on the pre-amp.

I am also considering to join a group buy for the Pass B1 preamp kit to replace the pre-amp section for much clearer and great music. It is a very exiting project and I keep reading about its progress on this forum. Great job all.

I can only find minimal time on weekends to support my electronics hobby.

I am thinking what else to do. If any one can please provide some advice, I would immensely appreciate your help.

Best Regards,
Laksh

 

[murali_n]

Hi laksh,

The 49990 OPAMP IC is a mono IC and is not a dropin replacement for the stock TL072 opamp IC in the Norge 1000, which is dual. If you want a big improvement in the sound quality, replace the stock pre-amp of this amp, with the Super simple pre-amp made by sachu_888 of this forum. I myself have done this to a couple of Norge amps and all the owners are more than happy with it.

Use the 49990(2 nos) with a adopter in the SSP Pre-amp, but you will lose the bass and treble controls on your pre-amp but the improvement in SQ is more than worth it.

N.Murali

 

[Audiodoc]

Yes changing or preamp helps. You can check rishiguru and my threads for Norge 1000 mods.

 

[laksh]

Thanks Murali. I did not know that these mono ICs cannot be simply replaced. On using an adapter, I ran across browndog adapters, links below, hopefully these are the ones you are referring to but I am not sure which one to pick and was also thinking if you know these are available locally to avoid international shipping charges. Else I may have to DIY this; quite tough?

1. DIP8 to SO8 Adapter (p/n 031101B)

2. Single-to-dual Op-Amp Adapter (p/n 020302A)

3. Single-to-dual Op-AMP Adapter - DIP version (p/n 021001)

Yes, thanks a lot for the direction. I will seek help from Sachin for the Super Simple Pre-amp. For powering the SSP, can I use the existing torroidal filtered power supply to the stock preamp? I think it is around 15 volts.

Also, do you think these 49990's with adapters (6 Nos) will work on the Norge stock pre-amp too?

Thank you AudioDoc. Your Norge 1000 mods are great, very inspiring.

Kind Regards,
Lakshmidhar

 

[murali_n]

Hi laksh,

Item No.2 will be suitable and I think they are readily available with sachin.

Contact him.

N.Murali

 

[laksh]

Thanks Murali. I have made contact with Sachin for the SSP kit.
If I wish to keep the tonal controls and change the opamps with 6nos
49990's using single to dual adapters will it still work on the Norge stock pre-amp? Would it be worth the effort/money?

Regards,
Laksh

 

[murali_n]

Hi Laksh,

Do not Change the opamps in the Norge Pre, just replace the Pre-amp ckt in total, the change you will get is more worth than losing the Bass & Treble control. Of course use 49990 in the SSP Pre-amp.

N.Murali

 

[laksh]

Agreed. The stock pre-amp anyways is an Elliot design, no offense. Once I recieve the SSP kit and opamps I will get going.

Also, I would like to put both these - Soft Start & Speaker Turn-On Delay and DC Protector Boards in my Norge 1000. Probably, these should have been there by default.

I found them on the DIYAUDIO store Soft Start & Speaker Turn-On Delay and DC Protector Boards (Set of 2 boards) - PCBs

but would like to know if there is one of our own versions used by anyone here?

@AudioDoc - I notice you have used a speaker protection board or which one is it?

Regards,
Laksh

 

[Audiodoc]

It is a cheap and effective solution from ebay for around 500 bucks, Lately Mr. Shyam Bajaj of Norge has incorporated a similar one by default in the new units.

 

[laksh]

Thanks AudioDoc. Please post link if you have.

Hi Murali: I heard from Sachin that the LME49990's may run very hot on +/-15volts supply. The SOIC adapter design I am receiving does not allow for tiny heatsink for the opamps. Can we reduce the voltage to say 9 volts? How would you deal with this? Also will the dual voltage requirement of SSP be taken care of?
I am ready to go for a separate power supply (transformer with filter) if required. Please advice.

Thanks,
Laksh

 

[Audiodoc]

The Norge has dual voltage requirements of its own. The transformer has separate secondary windings which go to the supply board and are regulated using 7815 and 7915 transistors giving a regulated +-15v. You can add a small PCB with 7809 and 7909 and a pair of capacitors to reduce it further to +-9v. Transformer, bridge rectifier will not be required as you can tap the same from the regulated supply.

 

[laksh]

After all the weeks and little time spent to fix this amp, I have been able to get it working with the SuperSimple Pre-Amp and a 50K pot. Thanks to Sachin for the kit and it still carries the scent of perfumed package.
Initially I used two 9 volt batteries but later I dared to connect 15volt secondary power supply from the toroid to the pre-amp and all has been working find till date with the LME49990 in all its splendour sounding excellent.

I still have to somehow figure a way to install the motorised pot that came with the Norge amp to the SSPreamp. I got lost in the pins and could not figure out correct connections to make this pot working. I would like to have this working because if it works I can use their remote to control volume and is very handy.
If someone can guide me pot pin to pcb hole (on the SSP board) in order, I would be able to make the connections accordingly and see if it works.

I am attaching pictures of my Norge 1000 Concerto Gold amp.