This is not just another gainclone

[JDeV]

Yesterday when replacing OPA549 with LM3875 , I accidentally caused a short between V- and pin 8 , Input, on LM3875 - without noticing. When I switched on the amp the 1 channel was causing alot of high frequency sound and other channel was dead. I started to test and soon find problem, this short, and also that this side's speaker was now measuring only 1ohm, oops! Luckilly the amp was connected to a set of cheap speakers of which I got 6 from a guy that chukked them away. BTW, I can actually start noticing differance between 2 IC's, LM 3875 sound much more likeable - and to close for comfort to my Aleph30

1.)Could this short between V- and In caused the speaker to pop?
2.) Can 1 protect your speakers against such faults without causing any degrading in sound quality?

[Peter Daniel]

If you supply around 25V DC to the speaker, you shouldn't be surprised that it pops. As to the protection circuits do a search under "amplifiers and speakers protection circuits". There is a whole thread dedicated to that.

[JDeV]

Originally posted by Peter Daniel
If you supply around 25V DC to the speaker, you shouldn't be surprised that it pops.

Sorry , the short was between pin 8 and V-, I editted origenal post.

[Philo]

JDev,
1) Yes, 18-24VDC directly to your speakers is bad.
2) Yes, don't short your legs That and there are other circuits you can add in that protect your speakers but they are actually larger than the entire gainclone circuit. One is a "crowbar" circuit. Consisting of a diac, a triac, a Zobel circuit, a few diodes across the power rails, an RC circuit and a shunt cap across the speaker leads . It also adds an inductor in the path. My suggestion is just to keep your path as short as possible without shorts
Once you close up your final assembly they are so cheap you can build a prototype to mess around with and not worry about losing some music time.

[massimo]

Hi Peter!

Are you sure the Motorola MUR1520 is a schottky?
Not according the data sheet of the series MUR1520-1540-1560 where these diodes are simply Ultrafast Rectiers (not even soft recovery, just ultrafast).

I spent nearly a fortune to order some expensive IR Hextfred at Digi Key, while I have plenty of MUR1520.........

I'm glad you liked them in the gainklone anyway: at least if I'll make it I already have some suitable components.

[Bricolo]

Peter: I bought parts for my gainclone yesterday, the shop hadn't 3875 nor 3885, so I use two TDA7296


Now, I've seen your shematic, and I just realised you suggest 1W 10kR and 1/2W 220kR resistors, but I use classical 1/4W metal film ones

Is this a problem? I don't see the use for such powerfull resistors, can you please explain why you use those?

[Peter Daniel]

Originally posted by massimo
Hi Peter!

Are you sure the Motorola MUR1520 is a schottky?
Not according the data sheet of the series MUR1520-1540-1560 where these diodes are simply Ultrafast Rectiers (not even soft recovery, just ultrafast).

I also thought it's a ultrafast diode, but in Digi-Key katalog it's listed under schottky http://dkc3.digikey.com/PDF/C031/0511.pdf
unless I got it wrong (top left). The one I'm using is from IR.

[Peter Daniel]

Originally posted by Bricolo


Now, I've seen your shematic, and I just realised you suggest 1W 10kR and 1/2W 220kR resistors, but I use classical 1/4W metal film ones

Is this a problem? I don't see the use for such powerfull resistors, can you please explain why you use those?

Nothing wrong with different parts. It's just that I used the listed ones and they make the amp sound really well.

[Bobken]

Hi Peter,

Thanks a lot for sharing your findings on the differences in diodes, which make interesting reading.

This list of preferences will be most useful for many DIYers who maybe don't have the chance to make these comparisons.

I did a lot of similar listening tests maybe 10 years ago, and I came down heavily in favour of Shottkys then, but there have been a lot of developments/improvements in diodes' specs since that time.

Like you, I found them all to be very directional!

You will doubtless get a lot of "try this and try that" now you have published your results, but if you do get the chance, it might be worth having a listen to some of the Ixys HiPerFRED diodes, DSEP 9-06CR.

Todd Krieger said some glowing things about them on AA in Nov. 2001, when he compared these with both Hexfreds and Harris Ultrafasts, but I still have been unable to find anyone who I regularly deal with who will let me have a few to try.

I'll still keep on looking, though.

I hope the GC business is taking off well.

Regards,

[UrSv]

One has to be careful with these:

Fairchild: MUR1520 is a 15A, 200V Ultrafast Diode
IR: MUR1520 is a 200V 15A HEXFRED
Onsemi: MUR5120 is a 15A 200V Ultrafast Rectifier