I know of no other amp with a device like this and already
recommended reinforced resistors for R7 and R8.
As far as I know the "crowbar" was inside from the beginning and
considered to be useful together with their electrostatic speakers.
recommended reinforced resistors for R7 and R8.
As far as I know the "crowbar" was inside from the beginning and
considered to be useful together with their electrostatic speakers.
Do you think you discovered the fault while desoldering in readiness for the spare board or like me you are just happy that the blanket approach brought the desired result?
I cannot advise on the crowbar circuit, it does offer some protection. Many people bin them and fit speaker protection boards, Velleman are a popular choice.
Well, I read it of course. But there appear filaments or wires protruding from the goo?
Best regards!
Best regards!
The crowbar was fitted after about 12 months of production As I have stated earlier quad got hit with a no of damage claims with the 405 burning out voice coils on the woofers it was well known at the time
The crowbar was a brilliant low cost fix Does not do much for the amp but it will save the woofer
Trev
The crowbar was a brilliant low cost fix Does not do much for the amp but it will save the woofer
Trev
This is the usual look of a 405 transformer.
The screwdriver was stuck in the goo before.
#47 Sorry that they did not fit it in any other Quad amp as far as I know.
I have seen amp channels destroyed by the crowbar.
I have seen amp channels destroyed by the crowbar.
In theory the crowbar should take out the supply fuses on the card but to be honest by this time the output devices will have been destroyed The Vi current limiters should protect under normal conditions
My comments are for the 405 amplifiers only As I have said the crowbar is to protect the speakers not the amp
Trev
My comments are for the 405 amplifiers only As I have said the crowbar is to protect the speakers not the amp
Trev
Seriously, I have not seen any speaker damage with my converted 405s in 40 years.
When changing to useful output binding posts the crowbar is thrown away.
When changing to useful output binding posts the crowbar is thrown away.
i was a young engineer at the time and the mk1 quad had a no of problems the resistors feeding the op amp would open circuit the amp went dc on the output and the voice coils on the speakers burn in seconds
I would never leave a 405 on unattended nice amp spoilt with cost cutting
Trev
I would never leave a 405 on unattended nice amp spoilt with cost cutting
Trev
I can confirm that R7 and R8 feeding opamp and zeners
have to be replaced regardless of the age of this amp.
have to be replaced regardless of the age of this amp.
Again the wonderful encapsulated transformer ! These used to mechanically hum and buzz
changed loads of them at the time
I used to hold quad in high esteem the 405 changed that for me the quad 2 brilliant design
the 303 never had one go wrong until they reached a grand old age
The 405 changed all that
The mk 1 about 30 watts into 4 ohms blowing spk up and buzzing a nightmare to sell
I can remember having to do a 200 mile round journey to repair one the problem a loose tag on a supply cap
Trev
changed loads of them at the time
I used to hold quad in high esteem the 405 changed that for me the quad 2 brilliant design
the 303 never had one go wrong until they reached a grand old age
The 405 changed all that
The mk 1 about 30 watts into 4 ohms blowing spk up and buzzing a nightmare to sell
I can remember having to do a 200 mile round journey to repair one the problem a loose tag on a supply cap
Trev
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