Building a symmetrical PSU B1 buffer

[Salas]

1 or 2 sec are enough. Use a real darlington.

 

[KatieandDad]

I was using the TIP122 a "REAL" darlington but the results were exactly the same.

For some reason or other the BC550C isn't acting as I would expect it to. Its perfectly OK and has been swapped with a new one.

I'm not familiar with the maths of working out how the BC550C should act in this configuration. If I were to swap it with a virtual zener, what voltage should the zener be ?

I'm not suggesting that I will substitute a zener, I am just trying to appreciate what is happening in this circuit. Or NOT in my case.

 

[udailey]

did you use the right value cap? In delay circuits usually a cap charges, fires a transistor which turns another one in in a way that it stays on and in firing the second it allows electricity to the relay. Google 'latching circuit.'
So value of cap is critical.

 

[KatieandDad]

First cap was defective. The one in circuit now is behaving as one would expect.

 

[udailey]

That would do it.

 

[buzzforb]

I'm having a bid of a headache with the delay section.

How much of a delay should this circuit provide ?

For some reason or other the base of my Relay Driver isn't reaching ON for about 10 minutes. If I omit the BC550 I get virtually no delay. I can work around the problem if I could figure out how long the relay should be de-energised for.

The junction of the timing R & C are rising to 12V as I would expect. The issue seems to be the use of the BC550C as a Zener to de-sensitise the relay driver.

I'm not using the BC517 I'm using 2 x BC550Cs connected as a darlington.

Are you running stock values?should be about 10 seconds.

 

[KatieandDad]

I've just "Bitten the Bullet" and ordered a pile of BC517s just to see if that works.

Unfortunately I made the PCB to accept the TIP122 so I'll have to bend the legs around a bit.

The HM 2xBC550C should equate to to the BC517 though.

Everything else is STOCK.

 

[KatieandDad]

How ODD.

I've replaced the BC550c with two 1N4148s in series (ie a 1.4V zener) and used the TIP122 as the relay driver and it works perfectly.

It just didn't work with the BC550c acting as a zener.

There's nothing wrong with the BC550c's that I was using, they both test correct.

 

[KatieandDad]

Odd thing though.

Measuring the Base drive voltage of the TIP122 with the BC550c using a DMM caused the relay to oscillate.

Nothing made sense. It's perfectly OK with the 2 x 1N4148.

I'm just wondering if it might be a bit quick though. the relay operates after just less than 2 seconds.

 

[KatieandDad]

Its coming to life

The DCB1 is slowly coming to life.

Just waiting for a few components to finish the build.

Those of you that are real "spotters" will notice that the board isn't fully drilled yet. The BC560s need a few more holes.

 

[KatieandDad]

The TIP122 for the relay drive is under the board as it didnt quite squeeze past the timing cap on the top of the board.

 

[buzzforb]

You have a greater Vbe drop vs that of the BJT, i think, and this is reducing turn on time. I believe a larger cap will slow it down. 220uF. I could be wrong.

 

[Salas]

The BC550 zener effect as used in the original scheme lies higher at about 6.3V. For variations of lower threshold the time capacitor's value has to grow accordingly, but 2 secs are enough to avoid power up thump on audio outputs.

 

[KatieandDad]

I might try a bigger cap in order to increase time delay.

 

[Salas]

Since you established a working variation and the relay clicks alright you are ready to go. Time delay is up to you. Just look to have no audible power on thump and a rapid power off relay release.

 

[dvb projekt]

Spooky hum problem

Hi all,

i have a funny problem with my DCB1.
Since i have finished my F5 on sunday, i have disconnected my 300B mono's and now the F5 runs with the DCB1.

Now the following happened:
If i connect only the right channel from the DCB1 to the F5, all is dead silent.
When the left channel followed i have a hum on both channels.
If i disconnect the right channel, the hum stays on the left channel.

All that is intependend to the connected inputs and the mains cable...
Yes, if i disconnect everything including the mains, the problem stays!

Very crazy... Perhaps someone has a good idea...

 

[Salas]

Oscillation? Do you use same long cables as it was for the 300B amps?

 

[dvb projekt]

Oscillation? Do you use same long cables as it was for the 300B amps?

Hi Salas,
Yes, the same cables. I have tried some other Nordost Tyr i have with the same result.
BTW, it's a deep hum but not loud...

 

[Salas]

Did you try the F5 with another preamp in the same system configuration?

 

[Salas]

Stick a capacitor between them to see if its some bad dc interaction also.