A21 vs A51

[silverfox]

I am currently powering a Paradigm Studio v3. compliment (100s, CC570, ADP470s) using an A51. A good bit of my listening is 2-channel without a sub filler. I am thinking about potentially adding an A21 as dedicated amplification for the Studio 100s. All equipment is currently powered via 3 dedicated 20 amp circuits.

Can someone please
(1) lay out the differences between the A21 and A51 (besides the fact that one is a 2 channel and the other a 5-channel unit ) and
(2) comment on whether it makes sense to add an A21 and whether there would be any material benefit by doing so.

Thanks much

[mike c]

I know little about parasound, but wouldn't you benefit more if you went for dual JC1's?

[silverfox]

I know little about parasound, but wouldn't you benefit more if you went for dual JC1's?

You're right that would be more of an upgrade, however, I unfortunately do not have the rack space, nor the budget for 2 JC1s :cry:

[mike c]

im just saying that between the a51 and a21 ... there might not be too much of a difference if there is any. unless you bi-amp?

[Chris D]

No, there is a difference, albeit not night-and-day. If I remember, Peter Nielsen had particulars. To start, though, take a look at the back panel and you'll see a difference in some features, such as the gain knobs for the A21.

Hi, Silverfox, and welcome to the Guide and Club Parasound! :banana:

[silverfox]

No, there is a difference, albeit not night-and-day. If I remember, Peter Nielsen had particulars. To start, though, take a look at the back panel and you'll see a difference in some features, such as the gain knobs for the A21.

Hi, Silverfox, and welcome to the Guide and Club Parasound! :banana:

Thanks, Chris.

Peter, I gather you are the resident expert here. Any thoughts?

[Peter Nielsen]

There is a big technical difference between the two amps. The circuit board layout of the A21 is such, that the capacitor bank of the power supply can be shared by the two channels. The A51 uses separate circuit boards for each channel, and the capacitors are not nearly as closely coupled.

My experience is that the A21 is capable of outputting more current than the A51. If you have demanding speakers, you will actually notice a big difference between the A21 and A51 if you drive them close to their clipping limit. The A21 is much more powerful in this area.

If you have 4 ohm speakers, then I would strongly recommend the A21 instead of the A51. With 8 ohm speakers, the difference is probably less noticable.

Peter

[silverfox]

There is a big technical difference between the two amps. The circuit board layout of the A21 is such, that the capacitor bank of the power supply can be shared by the two channels. The A51 uses separate circuit boards for each channel, and the capacitors are not nearly as closely coupled.

My experience is that the A21 is capable of outputting more current than the A51. If you have demanding speakers, you will actually notice a big difference between the A21 and A51 if you drive them close to their clipping limit. The A21 is much more powerful in this area.

If you have 4 ohm speakers, then I would strongly recommend the A21 instead of the A51. With 8 ohm speakers, the difference is probably less noticable.

Peter

Thanks.

[silverfox]

Feedback from Parasound on my query

(1) the technical differences between the A21 and A51 (besides the fact that one is a 2 channel and the other a 5-channel unit )

- A21 has about twice as much capacitance per channel
- A21 has more available power from larger transformer
- A21 has much larger heat-sink surface to run cooler under harder loads
- A21 has higher pure class A operation (about 12-15 watts compared to 7- 8 )
- Gain controls on the rear panel

(2) would there be any material benefit to powering the Studio 100s via an A21 vs. an A51.

-There is definitely some benefits to the greater power capabilities of the A21. Basically more power in reserve and more total power. Sonically at lower volumes they may be difficult to tell apart. The circuit design is very similar.

Peter, this appears to corroborate your findings about the A21s ability to better drive more difficult loads.

(3) From what I understand, the circuit board layout of the A21 is such, that the capacitor bank of the power supply can be shared by the two channels. The A51 uses separate circuit boards for each channel, and the capacitors are not nearly as closely coupled. As such, the A21 is capable of outputting more current than the A51. Is there any validity to this statement?

-The capacitor banks are not shared between the channels. Power supply is completely independent including power supply windings. This way, one channel can't take power from another. The higher current is because of the bigger transformer, larger output transistors and bigger heat sinks.

[Peter Nielsen]

A21 has about twice as much capacitance per channel

Correct. 50,000µF vs 32,800µF.

A21 has more available power from larger transformer

The A21 has a 1200VA transformer and the A51 has a 2400VA transformer. This really does not make a difference in practice, as it's the capactors that need to handle the peak power requirement.

A21 has much larger heat-sink surface to run cooler under harder loads

Correct. The A21 has double the cooling area (4 transistors/heatsink vs 8/sink in the A51).

A21 has higher pure class A operation (about 12-15 watts compared to 7- 8 )

Correct, but those wattage figures are off. In 8 ohms, the A21 switches @5W/channel and the A51 @2W/channel. (In 4 ohms the figures are 2.5W and 1W respectively). Parasound has confirmed these figures. (Sounds like whoever you talked to did not have their numbers right).

Gain controls on the rear panel

Yeah, that's the only thing I don't like about the A21. Those gain controls need to go away! They present an obstacle in the signal path and most people don't need them. Worse, the gain control potentiometer is an electro-mechanical component that will not age well...

The capacitor banks are not shared between the channels. Power supply is completely independent including power supply windings.

Oh, I have to admit that I did not know the A21 was a dual mono design. I just looked into this, and it appears that the A51 also is using separate windings for each channel. This really explains the difference between the A21 and the A51 when it comes to the ability to deliver power. So, the A21 really only has 50,000µF capacitance available (per channel) and the A51 has only 32,800µF.

IMHO it is a bit misleading when Parasound says the A21 has 100,000µF and the A51 has 164,000µF... They should advertise the per-channel figures since the capacitance is not shared.

The higher current is because of the bigger transformer, larger output transistors and bigger heat sinks.

The output transistors are the same type and same quantity. Both the A21 and A51 have 8 transistors/channel. Both models use the same 15 amp, 60 MHz bipolar output transistors The difference is the higher power supply capacitance in the A21 that helps provide higher current.

Bigger heat sinks, true! This gives the amp a better ability to dissipate heat. In effect, it allows Parasound to yank up the idle current bias for more power in Class A. More heatsinks also lets the amp take more long term abuse. However, it does nothing towards peak power. Neither the transformer plays a role here. It is the capacitors that need to provide the peak current.

Peter

[Grzywa]

Different versions of A21

Great info.

I have similar situation but inverted. I will have new cinema space and less space for equipment. So My current config with A21 for mains and other parasound amps for other channels needs to be compacted to two "slots". Two amps max to handle 11 channels (7.4.4 to be exact).

Since what I can see on the Parasound web A21 has now 88,000µF, I wonder if there is new design since 2006 when you have discussed this. An I'm not talking about new PLUS (+) version, but last before they released A21+.


Edit: I just noticed that my signature is decate out of date... I will correct it next time I'm here... Sorry.