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Crest 8001 - Value

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levyte357- View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote levyte357- Quote  Post ReplyReply Direct Link To This Post Topic: Crest 8001 - Value
    Posted: 21 February 2017 at 1:30am
Been offered 20 year old version of one of these, wonder what the people here think it is worth !?

Told years ago, certain version  is headache to repair/service, assuming it's the older one?

Confused
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Post Options Post Options   Thanks (0) Thanks(0)   Quote B_Bender Quote  Post ReplyReply Direct Link To This Post Posted: 21 February 2017 at 5:15am
A 20 year old power amp. £100...? 

Full re-cap would be required, major cleaning job as well.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jbl_man Quote  Post ReplyReply Direct Link To This Post Posted: 21 February 2017 at 9:06am
Price entirely dependent on condition Lev,is the same with a 20 or even 30 year old Crown,a lovely clean one will appeal to the hifi bods and make a good price,a scruffy one,well,as mentioned above,£100-ish.
Be seeing you.
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levyte357- View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote levyte357- Quote  Post ReplyReply Direct Link To This Post Posted: 21 February 2017 at 10:03am
Thsnks guys.

Wouldn't even consider it, if it wasn't 8001.

Wondering if it will be money pit, like buying classic car.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote U.Viktor Quote  Post ReplyReply Direct Link To This Post Posted: 21 February 2017 at 12:31pm
Most of you thinking about only Electrolyte capacitors what seriously defines lifetime of power electronics (amplifiers).

Unfortunately this is not so simple in practice, power semiconductors also have "wearing out " effect which depends on how many and how big heating up and cooling down cycles received.
In the analog amplifiers the dissipated energy of the power semiconductor is modulated by twice of the frequency of the amplified signal. Sharp temperature changes in the junction layer making some changes in the crystalline structure of the semiconductor, which may results failure sooner or later.
This effect is present in switching-type of semiconductors (sw MOSFET, IGBT) too , but their structures have been designed to better handle this issue.
Sorry to say this but the time has well went over the type of dissipative circuitry (analog, AB, classH), their linear transistors have never evolved to those levels like the switching couterparts.

It means that the available low number of linear power devices are lagging ~20years back of today's "conventional"  power switching devices, in terms of power cycling capability, reliability, maturity of crystalline structures.


Edited by U.Viktor - 21 February 2017 at 12:34pm
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levyte357- View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote levyte357- Quote  Post ReplyReply Direct Link To This Post Posted: 21 February 2017 at 12:44pm
Originally posted by U.Viktor U.Viktor wrote:

Most of you thinking about only Electrolyte capacitors what seriously defines lifetime of power electronics (amplifiers).

Unfortunately this is not so simple in practice, power semiconductors also have "wearing out " effect which depends on how many and how big heating up and cooling down cycles received.
In the analog amplifiers the dissipated energy of the power semiconductor is modulated by twice of the frequency of the amplified signal. Sharp temperature changes in the junction layer making some changes in the crystalline structure of the semiconductor, which may results failure sooner or later.
This effect is present in switching-type of semiconductors (sw MOSFET, IGBT) too , but their structures have been designed to better handle this issue.
Sorry to say this but the time has well went over the type of dissipative circuitry (analog, AB, classH), their linear transistors have never evolved to those levels like the switching couterparts.

It means that the available low number of linear power devices are lagging ~20years back of today's "conventional"  power switching devices, in terms of power cycling capability, reliability, maturity of crystalline structures.


Mein Gott, I 100% agree with one of Victor's posts!!! LOL


Edited by levyte357- - 21 February 2017 at 12:45pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Earplug Quote  Post ReplyReply Direct Link To This Post Posted: 21 February 2017 at 3:33pm
"Mein Gott, I 100% agree with one of Victor's posts!!! "

Now that is worrying!   LOL


"Sorry to say this but the time has well went over the type of dissipative circuitry (analog, AB, classH), their linear transistors have never evolved to those levels like the switching couterparts."

That's quite a sweeping statement. I still have amps made from/around the old Maplin/Hitachi MOSFET modules working fine after 30 years, never mind my Crests, etc. One guy I know recently got rid of his Ram Audio lightweights and replaced with 8001's. He's never been happier.

And how would you define something like Lab Class TD - analogue or 'digital'?

On the subject of the 8001, one thing you could do is stick a multimeter on the output and see if there's any (DC) drift. That is quite a good signal of the health of the amp.





Edited by Earplug - 21 February 2017 at 3:34pm
Earplugs Are For Wimps!
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U.Viktor View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote U.Viktor Quote  Post ReplyReply Direct Link To This Post Posted: 21 February 2017 at 7:28pm
The Crest 8001 is a 2x 1200W (4Ohm) amplifier as far as I remember. May deliver 1800W peaks on 4R load for short periods... Its weight is ~40kg, consumes 3 or 4 rack unit spaces, has terrible power factor, poisoning mains with injected current peaks, its power valid only rock solid 220Vac due non regulated power supply..
Despite its large number of output transistors, did not perform very well on certain speakers because the output stage did not like largely shifted output current vs. voltage due heavy dissipation in the endstage.
As I remember it has a momentary U*I dissipation protection per output transistor arm and causes terrible sound effects when acted sometimes ;_)
So let us say the linear amp has made to deliver 50A peaks but if you have just half the output Voltage the output momentary current shall not exceeds 25A, which is typical with resistive loads.
Unfortunately the real speakers like to act as motors//generators so sometimes the maximum source and/or sinking current capability of endstage is required not only at time of peak Voltage events..
Here most of the linear amplifiers fall and properly constructed class-D win, which can deliver (or sink) its nominal output current at ANY output Voltage without the risk of exceeding momentary dissipation limits of the output power devices. This small trick is the secret sauce of good speaker control, what nobody tells you.
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Post Options Post Options   Thanks (1) Thanks(1)   Quote nickyburnell Quote  Post ReplyReply Direct Link To This Post Posted: 21 February 2017 at 8:47pm
This is brilliant. You keep up all the negativity and persuade the sheep they are all useless now. The rest of us will then rejoice is a market flooded with £100 8001's and PPX's etc.  Good job, keep up the good workThumbs Up

Wow, sound must have been shit for the last 20 years
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Post Options Post Options   Thanks (0) Thanks(0)   Quote luton_soundman Quote  Post ReplyReply Direct Link To This Post Posted: 21 February 2017 at 9:28pm
From the guy who loves pkn
Sound Hire/Sales new/used equipment.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote kedwardsleisure Quote  Post ReplyReply Direct Link To This Post Posted: 21 February 2017 at 10:16pm
Parts for those old crests are getting dear now.

A set of electrolytics could be as much as £450. You will find out if they've failed when they spurt boiling electrolyte all over the board in the middle of a bass drop.

K. Edwards Electronics Engineers

North Staffordshire

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nickyburnell View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote nickyburnell Quote  Post ReplyReply Direct Link To This Post Posted: 21 February 2017 at 10:39pm
Better start a Crest breakers yard then :)

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