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Old 15th February 2004, 01:02 PM   #1
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Question 150W Is it good?

I have found this schematic of a 150W amp
What do you think about that? Is a good amp?
-------------------------------------------------------------
This is one small description that I have found:

A really good amp with an outstanding bandwidth of 1.55MHz and slewrate of 80V/us
Output transistors have been changed to a type that can handle more power.
Also there has been added a separate powersupply for the input stages. This will increase power output for a given supply voltage significantly. A good tip is to separate powersupply for the input stages. You can just run the two powersupply inputs in parallel, and build a separate powersupply for the input stage in the future to acheive a higher power output. In any case the supply voltage for the input should be min. 5 Volts higher than for the output to acheive any real power increase. Run into a 4 ohm load the 150W amp will produce about 300Watts of continous output power. A really excellent amplifier!

-----------------------------------------------------------
Components:

0,33 9w R27-R30
1k R1
2k Pot2
2N5401 T3-T5, T7
2N5551 T1, T2, T6, T8, T9
2SA1358/MJE350 T11
2SA1553/2SA1943 T16, T17
2SA1837 T13
2SC3421/MJE340 T10
2SC4029/2SC5200 T14, T15
2SC4793 T12
3k9 R17
4,7F poly C2
4k7 R12, R13
10k R3
10 R5-R8, R31
15nF C10
15pF C7, C8
47 R23-R26
47F 25V C9
47F/100F 63V C3, C4, C11-C14
100k R2
100 R21, R22
100pF C1
200 Pot1
220 R19, R20
330k R4
330nF C5, C6
390 R14
470 R11
560 R18
680 R9, R10
Red D1, D2
100 R15, R16

regards
D.N.
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Old 15th February 2004, 01:08 PM   #2
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Default Re: 150W Is it good?

Quote:
Originally posted by m60gpmg
I have found this schematic of a 150W amp
What do you think about that? Is a good amp?



Very similar to the Rotel RB 980 BX...yes!! ....it's a good design!

It's a inverting amp!
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Old 15th February 2004, 01:24 PM   #3
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Arrow Commentable Thoughts

Good design but Inverting!
Excellent Current Amplification Factor using TRIPLET TRANSISTOR CONFIGURATION.
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AmPmAN
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Old 15th February 2004, 01:31 PM   #4
sreten is offline sreten  United Kingdom
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Just some minor points:

No protection against capacitive loads, either a series resistor
or an inductor, stability into these loads could be an issue.
(may be off the page to the right)

If seperately rectified and smoothed IMO the complication of
providing the extra 5V for the 60V rails is not worth the effort,
unless you can easily find a transformer with the right windings.

.
Quote:
In any case the supply voltage for the input should be min. 5 Volts higher than for the output to acheive any real power increase.
Doesn't make any sense to me, if anything going over 5 extra volts is pointless.

(Balancing of the input stages and VAS current value looks indeterminate to me.)

sreten
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Old 15th February 2004, 01:50 PM   #5
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There is a problem; in the schematic R15,R16 are 47Ohm but in the component list them are 100Ohm

Which value is better?

Regards
D.N.
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Old 15th February 2004, 01:57 PM   #6
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Quote:
Originally posted by sreten
Just some minor points:

No protection against capacitive loads, either a series resistor
or an inductor, stability into these loads could be an issue.
(may be off the page to the right)

(Balancing of the input stages and VAS current value looks indeterminate to me.)
About no series resistor or inductor...the stability issue is in my vue is very unlikely...because the output stage is a triple follower ..so the open loop input impedance will be very low.Then the phase shift caused by the capacitif load will be small.
A inductor or resistor at the output allways cause some sound quality degradation..
By the way ...the similar Rotel doesn't also use output inductor ( if memory serves)

About the VAS current value indeterminated...
The current in the LTP is defined by the CCS and cause a voltage drop in the colector resistor...this voltage drop define the voltage of the base of the VAS transistor...and that voltage define de current in the VAS by action of the emiter resistor of the VAS.
So i don't see any reason for this current to be indeterminated.
This kind of VAS biasing is a typical one!
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Old 15th February 2004, 02:03 PM   #7
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Quote:
Originally posted by m60gpmg
There is a problem; in the schematic R15,R16 are 47Ohm but in the component list them are 100Ohm

Which value is better?

Regards
D.N.
With 47 you have higher open loop gain and higher standing current in the VAS stage...whit 100 you have the oposite ,but with increased stability of operation points and more open loop linearity!
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Old 15th February 2004, 02:09 PM   #8
sreten is offline sreten  United Kingdom
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Quote:
Originally posted by Tube_Dude
By the way ...the similar Rotel doesn't also use output inductor ( if memory serves)
Yes, they used a series resistor instead, sreten.
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Old 15th February 2004, 02:12 PM   #9
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Quote:
Originally posted by sreten


Yes, they used a series resistor instead, sreten.

If they used it....my memory is not what it used to be...
Naim also use a resistor ...0,2 Ohms i think.
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Old 15th February 2004, 02:16 PM   #10
sreten is offline sreten  United Kingdom
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Quote:
Originally posted by Tube_Dude

About the VAS current value indeterminated...
The current in the LTP is defined by the CCS and cause a voltage drop in the collector resistor...this voltage drop define the voltage of the base of the VAS transistor...and that voltage define de current in the VAS by action of the emiter resistor of the VAS.
So i don't see any reason for this current to be indeterminated.
This kind of VAS biasing is a typical one!
Well the way I see it the VAS current affects the current sharing
in the LTP's or vice versa, neither the current sharing or VAS
current is fixed as I see it, which is why I said indeterminate.

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