Why Bose?
 

Dave Plowman (Nutcase & Moron) wrote:


---------------------------------------

** Bose did not sell an PA amplifier in the early 70s.

I've no idea of the number, but I can describe it.

In a vinyl covered case (similar to a guitar amp, etc). Rack width, and
with the equaliser mounted in the box too. About 4U high and roughly
square. Pretty heavy so likely had a decent size transformer. Cooling fan.
Odd thing was the speaker output connectors were 1/4" jacks - same as the
speakers. Whole lot clearly labelled Bose. Of course it could have been
something cobbled together by the UK importer.

Not the sort of thing you'd do for a domestic amp. Designed for being
moved around - it even had a lid and carrying handles.



** Bose sold a model 1801 amplifiers for *domestic use* with 901 speakers.

It had NO fan, weighed 37kgs and featured large inverted VUs on the front.

Jacks sockets for input and binding posts for output.

Possibly available in the UK from 1975.

Front view:

https://i.ebayimg.com/00/s/NzY4WDEwMjQ=/z/AdwAAOSwax5Yp1v-/$_86.JPG

Back view:

http://product-images.highwire.com/5475850/bose1801.jpg

Domestic hi-fi, not PA gear.

The model 1800 was the later PA version with no VUs.

Both models suffered from serious design flaws, they would go DC full rail at any time, cease to work if you operated the power switch during loud use and had the poorest reactive load driving ability of any power amp ever sold.

A perfect match for Bose's overstuffed little boxes.

Bose are for Bozos.


..... Phil

Why Bose?
 

On 20/07/2017 11:58 AM, Phil Allison wrote:

Bose are for Bozos.

**Emphatically agreed. Back when I had my retail store, a client walked
in, looking for a system. He said that he had been listening to some
'high end' speakers in a flat-mate's system, but he was prepared to
compromise. Turns out they were Bose 901 speakers (around $2.5k back
then). I said "No problems". I connected a nice pair of Mordaunt Short
speakers (around $600.00), a Sansui AUD33X amp, a Dual 505-3 and a
Nagaoka cartridge. Total value, less than $2.5k. The guys was,
predictably, stunned that the system sounded much nicer than his mate's,
much more expensive, system.

The Bose 901 has not been a viable product for a long time. Hardly any
are sold in Australia (I know at least one Bose dealer that has not sold
a pair in several years) and very few anywhere else. Bose keeps them in
production, because not to do so would be an admission that the product
always was a seriously flawed design.

I, too, have worked on some 1801 amps. Burned PCBs, smoked outputs, etc.
Horrible design. That said, I have found a couple of Nice Bose products:

https://www.bose.com.au/en_au/produc...ver_anz_in_uae

A really nice $50.00 computer speaker.

https://www.bose.com.au/en_au/produc...lo_5_black_anz

Reasonable sound and easy to use,

Of course, both products are nonsensically over-priced.


--
Trevor Wilson
www.rageaudio.com.au

Why Bose?
 

Trevor Wilson wrote:

--------------------

Phil Allison wrote:

Bose are for Bozos.

**Emphatically agreed.

I, too, have worked on some 1801 amps. Burned PCBs, smoked outputs, etc.
Horrible design.



** Did you see failures of the soft start resistor ??

If the amp is ever switched on with strong audio signal present at the input, the combination of a huge transformer & filter capacitor inrush plus audio power to the speakers at that moment smoked the 8 ohm, 10W resistor.

Happened to *every* Bose 1800 owned by the hire business I did repairs for.

Main cause was the LACK of input mating at switch on.

As the amps built up more hours, the hot running 3k/2W carbon comp resistors on the power boards fell in value to under 1kohms casing their associated 15V zener to fail short. This meant the op-amp at the input lost one rail and sent the output stage to full DC !!!!

The VI limiting circuit for the output transistors was super fast and overcooked. With even a mildly reactive 8 ohm load, +/- full rail spikes appeared on the output at less than rated power.

Oh, and if the AC supply went even a little high, the amp hummed.

My schem is marked with simple fixes for all the above.



...... Phil

Why Bose?
 

On 20/07/2017 1:58 PM, Phil Allison wrote:
Trevor Wilson wrote:

--------------------

Phil Allison wrote:

Bose are for Bozos.

**Emphatically agreed.

I, too, have worked on some 1801 amps. Burned PCBs, smoked outputs,
etc. Horrible design.



** Did you see failures of the soft start resistor ??

**Possibly, but I don't recall. I've only worked on a couple of the
damned things and it has been awhile.


If the amp is ever switched on with strong audio signal present at
the input, the combination of a huge transformer & filter capacitor
inrush plus audio power to the speakers at that moment smoked the 8
ohm, 10W resistor.

**Now that fault I have seen, but in other amplifiers. The big ME power
amps (5.5kVA transformer + 310,000uF) were susceptible to such a fault,
except the resistor was a 4.7 Ohm 50 Watt ceramic type. Replacing with a
100 Watt aluminium clad or an NTC resistor (an array, actually) solved
the problem.


Happened to *every* Bose 1800 owned by the hire business I did
repairs for.

Main cause was the LACK of input mating at switch on.

As the amps built up more hours, the hot running 3k/2W carbon comp
resistors on the power boards fell in value to under 1kohms casing
their associated 15V zener to fail short. This meant the op-amp at
the input lost one rail and sent the output stage to full DC !!!!

**Ouch!


The VI limiting circuit for the output transistors was super fast and
overcooked. With even a mildly reactive 8 ohm load, +/- full rail
spikes appeared on the output at less than rated power.

**That much I noted under test. Disgusting.


Oh, and if the AC supply went even a little high, the amp hummed.

My schem is marked with simple fixes for all the above.

**How did you fix the hum?


--
Trevor Wilson
www.rageaudio.com.au

Why Bose?
 

Trevor Wilson wrote:

------------------------

Phil Allison wrote:

Bose are for Bozos.

**Emphatically agreed.

I, too, have worked on some 1801 amps. Burned PCBs, smoked outputs,
etc. Horrible design.



** Did you see failures of the soft start resistor ??

**Possibly, but I don't recall. I've only worked on a couple of the
damned things and it has been awhile.


If the amp is ever switched on with strong audio signal present at
the input, the combination of a huge transformer & filter capacitor
inrush plus audio power to the speakers at that moment smoked the 8
ohm, 10W resistor.

**Now that fault I have seen, but in other amplifiers. The big ME power
amps (5.5kVA transformer + 310,000uF) were susceptible to such a fault,
except the resistor was a 4.7 Ohm 50 Watt ceramic type. Replacing with a
100 Watt aluminium clad or an NTC resistor (an array, actually) solved
the problem.


Happened to *every* Bose 1800 owned by the hire business I did
repairs for.

Main cause was the LACK of input mating at switch on.

As the amps built up more hours, the hot running 3k/2W carbon comp
resistors on the power boards fell in value to under 1kohms casing
their associated 15V zener to fail short. This meant the op-amp at
the input lost one rail and sent the output stage to full DC !!!!

**Ouch!


The VI limiting circuit for the output transistors was super fast and
overcooked. With even a mildly reactive 8 ohm load, +/- full rail
spikes appeared on the output at less than rated power.

**That much I noted under test. Disgusting.


Oh, and if the AC supply went even a little high, the amp hummed.

My schem is marked with simple fixes for all the above.

**How did you fix the hum?



** Change 20kohm to a 30kohm ( add a 10kohm in series) that biased the base of the current source transistor for the class A stage.

Having too much current ( over 20mA) put the preceding diff pair and cascode class A pair out of balance.

The +/-DC rails on 1800s I saw was 96V instead of the schematic's 84V.

The other fixes all involved resistor changes or additions.


..... Phil

Why Bose?
 

Trevor Wilson wrote:

------------------------

Phil Allison wrote:

Bose are for Bozos.

**Emphatically agreed.

I, too, have worked on some 1801 amps. Burned PCBs, smoked outputs,
etc. Horrible design.



** Did you see failures of the soft start resistor ??

**Possibly, but I don't recall. I've only worked on a couple of the
damned things and it has been awhile.


If the amp is ever switched on with strong audio signal present at
the input, the combination of a huge transformer & filter capacitor
inrush plus audio power to the speakers at that moment smoked the 8
ohm, 10W resistor.

**Now that fault I have seen, but in other amplifiers. The big ME power
amps (5.5kVA transformer + 310,000uF) were susceptible to such a fault,
except the resistor was a 4.7 Ohm 50 Watt ceramic type. Replacing with a
100 Watt aluminium clad or an NTC resistor (an array, actually) solved
the problem.


Happened to *every* Bose 1800 owned by the hire business I did
repairs for.

Main cause was the LACK of input mating at switch on.

As the amps built up more hours, the hot running 3k/2W carbon comp
resistors on the power boards fell in value to under 1kohms casing
their associated 15V zener to fail short. This meant the op-amp at
the input lost one rail and sent the output stage to full DC !!!!

**Ouch!


The VI limiting circuit for the output transistors was super fast and
overcooked. With even a mildly reactive 8 ohm load, +/- full rail
spikes appeared on the output at less than rated power.

**That much I noted under test. Disgusting.


Oh, and if the AC supply went even a little high, the amp hummed.

My schem is marked with simple fixes for all the above.

**How did you fix the hum?



** Change 20kohm to a 30kohm ( add a 10kohm in series) that biased the base of the current source transistor for the class A stage.

Having too much current ( over 20mA) put the preceding diff pair and cascode class A pair out of balance.

The +/-DC rails on 1800s I saw was 96V instead of the schematic's 84V.

The other fixes all involved resistor changes or additions.


..... Phil

Why Bose?
 

In article ,
Phil Allison wrote:
In a vinyl covered case (similar to a guitar amp, etc). Rack width,
and with the equaliser mounted in the box too. About 4U high and
roughly square. Pretty heavy so likely had a decent size transformer.
Cooling fan. Odd thing was the speaker output connectors were 1/4"
jacks - same as the speakers. Whole lot clearly labelled Bose. Of
course it could have been something cobbled together by the UK
importer.

Not the sort of thing you'd do for a domestic amp. Designed for being
moved around - it even had a lid and carrying handles.



** Bose sold a model 1801 amplifiers for *domestic use* with 901
speakers.

It had NO fan, weighed 37kgs and featured large inverted VUs on the
front.

Jacks sockets for input and binding posts for output.

Possibly available in the UK from 1975.

Then that's not the one I described. Perhaps you could get your nurse to
read things out to you?

--
*Why do overlook and oversee mean opposite things?

Dave Plowman London SW
To e-mail, change noise into sound.

Why Bose?
 

Dave Plowman (News) wrote:



Not the sort of thing you'd do for a domestic amp. Designed for being
moved around - it even had a lid and carrying handles.



** Bose sold a model 1801 amplifiers for *domestic use* with 901
speakers.

It had NO fan, weighed 37kgs and featured large inverted VUs on the
front.

Jacks sockets for input and binding posts for output.

Possibly available in the UK from 1975.

Then that's not the one I described.




** What you described was no Bose amp ever made..

I posted pics of the Bose 1801 to prove that point

You did not describe the speakers at all.

So probably not Bose either.

FFS look up the Bose 800 model.

Then go **** yourself.




..... Phil



..... Phil

Why Bose?
 

In article ,
Phil Allison wrote:
Dave Plowman (News) wrote:



Not the sort of thing you'd do for a domestic amp. Designed for
being moved around - it even had a lid and carrying handles.



** Bose sold a model 1801 amplifiers for *domestic use* with 901
speakers.

It had NO fan, weighed 37kgs and featured large inverted VUs on the
front.

Jacks sockets for input and binding posts for output.

Possibly available in the UK from 1975.

Then that's not the one I described.




** What you described was no Bose amp ever made..

ITYM one you've never seen. A very different matter.

But carry on enjoying your own little world.


Perhaps you might ponder on why Bose would make speakers specifically for
PA etc use - vinyl covered with lids - but not a matching amp? Especially
since those speakers need an active equaliser to give their best?

It's quite possible the one I'm referring to is an amp sourced from
elsewhere, but built into the case and simply badged Bose. I neither know
nor care.

--
*If you can't see my mirrors, I'm doing my hair*

Dave Plowman London SW
To e-mail, change noise into sound.

Why Bose?
 

Dave Plowman (Nutcase and DAMN LIAR ) wrote:



Not the sort of thing you'd do for a domestic amp. Designed for
being moved around - it even had a lid and carrying handles.



** Bose sold a model 1801 amplifiers for *domestic use* with 901
speakers.

It had NO fan, weighed 37kgs and featured large inverted VUs on the
front.

Jacks sockets for input and binding posts for output.

Possibly available in the UK from 1975.

Then that's not the one I described.




** What you described was no Bose amp ever made.

ITYM one you've never seen.


** Nor anybody else.

The ONUS is 1000% on you to prove otherwise.

Plenty on the net about Bose amps.



Perhaps you might ponder on why Bose would make speakers specifically for
PA etc use



** In fact just a simple modification to the existing 901 model.

8 x 16ohm cheap 4inch woofers instead of 9 x 8ohm ones *rammed* in a tiny wooden box that sound like pox.

http://i.ebayimg.com/00/s/MTE5NVgxNjAw/z/37YAAOSwwNVTsw2n/$_3.JPG


It's quite possible the one I'm referring to is an amp sourced from
elsewhere, but built into the case and simply badged Bose. I neither know
nor care.


** It ****s up your entire bull**** story.

Cos the PA system was not made by Bose.




...... Phil