Quad 303 High End boards - Dada

[mikes08]

I bought these with a known fault of burnt out resistor on one board R122 - 10ohm...so replaced that but this board had a short across pins 2-6. A bit of investigation and replaced TR106 and TR105 and all good now. Before I fitted them I installed the regulator board and checked the voltage only to find it appears to be producing 82V instead of 67V I have set the trim pot to mid position now so will check again.

I have checked the component values against the original regulator board and all values check out OK so more investigation needed and will contact Dada if needs be.
This is more of an experiment to see if I can hear any difference and as they were half the price of buying new ones was happy to do that.
Once resolved I may leave them there or sell them on as fully working boards.

[Trevor]

Look to be of a good quality.

[mikes08]

Resolved now - i had swapped out TR 201 which was faulty for a BC461 as notated the board but then checked the transistor i had taken out - BC141-16. Replaced this like for like and now getting 67v as should be so going to fit the driver boards later check readings and then see how it sounds.
They are well built with high end components and neatly laid out compared to the original but we shall see if i can hear any difference.

[Boulevardier]

Just to be clear - are you saying TR 201 was wrongly marked on the Dada board as BC461?

[mikes08]

Yes - not sure if they changed the design but the annotation on the board says one thing and the TR is another.
Anyhow now that is resolved boards installed and quiescent voltage set and is merrily playing away now.
I switched on using headphones just in case as didn't want to blow my BC1's and I suspect the pop on turn on has also gone now - result.

[mikes08]

First listening impressions are good - cymbals seem more realistic through my BC1's (still not quite in electrostatic league if anyone knows what I mean) and vocals which the Spendor's excel on, are great. Brighter but not harshly so.
Not knowing the age or history of these do components need to 'burn in' or is that a complete myth?
Does anyone else on here go through their whole record or CD collection when they have changed something just to compare

[alanworland]

Not experienced the Dada high end boards but put mine through the standard upgrade and was amazed at how 'muddy' the sound had got without me realising, it was like the curtains had been removed from in front of the speakers.

Alan

[Silicon]

The standard BC461 is rated up to 60V.

If it is working at a higher voltage, you should check the breakdown voltage before soldering it into the PCB.

Some manufacturers (like Leak) needed to select suitable transistors in this way.

[mikes08]

Originally Posted by alanworland

Not experienced the Dada high end boards but put mine through the standard upgrade and was amazed at how 'muddy' the sound had got without me realising, it was like the curtains had been removed from in front of the speakers.

Alan

Hi Alan
It is like that and a bit more - I keep hearing things and think where did that come from.....
The BC461 seems to be what was originally fitted to the board and all seems to be working fine at present but understand what you are saying. Will keep an eye on it.

[nutteronthebus]

I have updated a number of 303 and some times they do sound dull and it's not just the caps causing this . I have found the transistors have epoxy rot where they go low gain HFE in the 10's not hundreds . I have also replaced the boards with kits from the bay ( pcb and components in kit but no transistors ) as the MK9 boards had been serviced with a poker and gas ring with print missing etc . The results were rather good with clear sounds

[Craig Sawyers]

Early epoxy potting technology for transistors often gave long-term problems such as described above.

Craig

[fetteler]

Hmmm... I hadn't heard of this epoxy rot before but now you mention it I'm wondering if it might be a good idea when refurbing the 303 and the 33 to go through and replace all the small signal devices on the assumption that they will all have suffered to some extent. The cost is minimal and it's a sort of 'might as well whilst I'm at it' kind of thing.


Steve.

[Ambientnoise]

If this effect is purely time dependent then you would need ensure that the replacements were of recent manufacture. This may not be easy. If say, it is an applied voltage effect then NOS devices will be ok. I would be interested to know more, must do some research !

[fetteler]

Yes, of course - I'm pretty sure that many if not all of the types needed are still in production (ISTR that the 33 is full of BC109s) and if not I can't see much of a problem finding replacements. I'll be looking into it. Using a component with an adequate voltage rating is a given.
This is in stark contrast to the output transistors though which modern equivalents cannot replace due to them being Expitaxial rather than the Homotaxial originals which have a relatively low ft. Being metal can types I guess that the epoxy rot will not affect these?

Steve.

PS edit - a quick look at the DaDa site (https://www.dadaelectronics.eu/faq) gives modern equivalents for the 303 but I note that they suggest a 2N3055 for the output which, if of modern production, is not ideal.

[Craig Sawyers]

Originally Posted by fetteler

Yes, of course - I'm pretty sure that many if not all of the types needed are still in production (ISTR that the 33 is full of BC109s)

Full of actually means 6 per channel. Two in the RIAA stage, one as a follower, and three in the tone control.

The circuit squeezes a lot of functionality out of those 6.

My kitchen system is a 33/303 and ceiling speakers. Fed by an FM4 fed by roof Ariel, and a D-A fed by optical from a wall mounted TV. Radio 1 and Radio 2 inputs.

Love it!

Craig

[fetteler]

Yeah, I love 'em too!

I agree about the functionality to transistor count ratio - it's a great piece of design all round.

Steve.

[Boulevardier]

Originally Posted by fetteler

a quick look at the DaDa site (https://www.dadaelectronics.eu/faq) gives modern equivalents for the 303 but I note that they suggest a 2N3055 for the output which, if of modern production, is not ideal.

Yes. Can't understand why Dada are recommending 2N3055s. The modern ones are known to cause serious problems. Have they modifed the circuit in some way to prevent these problems?

Mike

[nutteronthebus]

I use BC550 for the BC109 and MJ15003 for 2N3055 and the seem to work well

[mikes08]

Originally Posted by nutteronthebus

I use BC550 for the BC109 and MJ15003 for 2N3055 and the seem to work well

I have used the MJ15003's in one of my 303's without any issues - that was about ten years ago though I don't drive the amps to hard.

[Radio Wrangler]

MJ15003 looks like a very good idea. By going to a much higher voltage part, the Ft is brought down to something closer to an early 2N3055.

It'll also make the output stage a lot tougher. With these, there would have been no need for the regulated power supply.

The difficulty with modern power transistors is that thaey have got a lot faster since the late sixties. The devices used as drivers in the 303 have got faster too, but not by the same ratio as the TO3 sized jobs. Consequently the ratio between the Ft of the power devices and the other transistors in the triplets has reduced, narrowing the gap (in octaves). You could use faster power transistors, if you used similarly fast drivers to the point there the wiring to the remote TO3's becomes problematic.

Again, MJ15003 has an open ended Ft spec, >2MHz with no limit, but it's monolithic and not likely to have seen a step change like the early 2N3055.

OK, so there is a sound reason for that choice. Wildly higher voltage and current ratings, but it tames the Ft issue.

David