PRIMARE A35.8 Power Amplifier User Guide

: June 9, 2024
: PRIMARE

Table of Contents

A35.8 Eight Channel Amplifier
Power Supply Section
Control from Input to Output
Circuit Layout
System Configurations
A35.8 Specifications
References
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A35.8 Power Amplifier
User Guide
Primare A35.8 Design Brief
PRIMARE A35.8 Power Amplifier

A35.8 Eight Channel Amplifier

The A35.8 is Primare’s most powerful and flexible multi-channel amplifier, designed to serve the needs of virtually any high-performance two and multi- channel system through its ability for each pair of its eight channels to be bridged to mono for an incredible level of power delivery, up to 1500 watts in total.

8 channels, 150 watts per channel (all channels driven)
Output stage based on Hypex NCore500 amp modules
XLR and RCA inputs
Each pair of channels is bridgeable to mono

Power Supply Section

Given the total power output of the A35.8 a switch mode power supply was the only choice in that it allows for rapidly varying demand, providing much more stable voltage, with ancillary capacitive storage to meet peak transient burst requirements.
To meet the need, a completely new power supply, the most powerful we have made, was designed to deliver the electrical power needed for the eight amplifier modules to produce the immense amount of musical power of which it is capable. For a point of comparison, the 200-watt per channel rated A35.2 uses a 900-watt power supply while the 1500-watt full output rated A35.8 uses a 1500-watt supply, effectively delivering more than 60% more power to the output modules. Dual outputs from the power supply mean that each group of four amplifier modules are provided with more direct and consistent power delivery by the shortest power path.
This newly developed Active Power-Factor Correction (APFC) supply is as much as 5% more efficient than past supplies and comprises dual PFC converters 180 degrees out of phase from each other. AFPC is used to avoid input current harmonics, thereby minimizing interference with other devices being powered from the same source. This reduces the total current ripple and improves EMC (Electromotive Compatibility), while current ripple at the output of the PFC converter is also reduced, which decreases stress within the circuit for prolonged life. Additionally, the supply operates in what is called “transition mode”, minimizing switching losses and improving overall efficiency in delivering power to the UFPD 2 amplification module.

Control from Input to Output

A35.8 features ultra-short signal path circuit design:

four-layer circuit boards employed throughout to shorten signal path
SMD devices used whenever possible to shorten signal path and avoid solder as electrical conductor of signal (large scale devices used when necessary)
power amp module output directly connected to five-way binding posts without solder for shortest signal path and most efficient transfer of power
Utilizing eight Hypex NCore500 class D output modules, with operation based on a non-hysteresis 5th order self-oscillating control loop taking feedback only at the speaker output, providing extraordinarily musical power delivery.

RCA and XLR balanced inputs options are offered for each channel and bridging capabilities for each pair of channels, with maximum power output of 1500 watts, providing the capability of delivering 185 watts at 1KHz of peak power per channel, all channels driven.

Power output is rated as 150 watts into 8 ohms, 300 watts into 4 ohms, and 400 watts into 2 ohms at 1kHz.
Each pair of outputs can be bridged, capable of producing 740 watts into 8 ohms (clipping protection limited), 750 watts into 4 ohms, and 450 watts into 2 ohms at 1kHz.

Circuit Layout

PRIMARE A35.8 Power Amplifier - Circuit Layout

The modular design of the heatsink and paired output circuits assembly, utilize a multi-pin connector and secured by four screws, allowing for easy field replacement should service be required.
The Hypex NCore output module’s standard aluminum heat sink plate is removed for direct connection of the amp module to the heatsinks for more efficient heat transfer. The heat sink arrangement provides shielding of amp sections for lower noise, meaning that the amp module is shielded from the power supply and the input module from the amp module while maintaining the shortest and most direct signal and power path.
To achieve the shortest signal path, a channel is cut out from the bottom of the heat sink to allow for direct circuit board connection from input to amp module and then from amp module to output stage without the use of signal carrying wires that might otherwise introduce noise and distortion.

System Configurations

The bridging capabilities of the A35.8 allow it to be used in a variety of system configurations, with or without the addition of a stereo amplifier, to suit most multi-channel system requirements. A few examples:

5.1 Channel System – bridge three pairs of outputs for Front Left, Right, and Centre speakers, with the remaining two outputs for a pair of rear speakers.
7.1 Channel System – bridge a pair of outputs for the Centre channel with remaining outputs for the remaining six speakers
5.1.2 Channel Atmos System – bridge a pair of outputs for the centre channel with remining outputs for the remaining six speakers
5.1.4 Atmos/DTS:X system – adds an A35.2 stereo amplifier for the Front Left and Right speakers, while using one bridged pair of outputs from the A35.8 for Centre, and the remaining outputs from the A35.8 for Surround Left and Right, Front Height Left and Right, and Rear Height Left and Right speakers.
7.1.2 Channel Atmos System – adding an A35.2 stereo amp for Front Left and Right speakers, bridge three pairs of outputs of the A35.8 for Centre, Rear Right and Left speakers, with the remaining pair of outputs for a pair of height speakers
7.1.4 Channel High Power System – three bridged A35.2 amps for Front Left, Right, and Centre speakers, and A35.8 for Rear, Surround, and Height speakers.
9.1.6 – two A35.8 amps, one pair of outputs bridged for Centre speaker, and remaining outputs for Rear, Surround, and Height speakers.
13.1 Auro 3D system – uses two A35.8 amplifiers, with bridged pairs of outputs for the Front Left and Right speakers, and the remaining 11 outputs for the Centre speaker, Front Left and Right Height speakers, Surround Left and Right speakers, Middle Left and Right Height speakers, Rear Surround Left and Right speakers, Rear Left and Right Height speakers, and Top speaker.

And for an extraordinarily powerful two channel bi-amplified system, one A35.8 all pairs of outputs bridged providing peak power of 4 x 375 watts or 750 watts per pair per channel at 8 ohms in a stereo system.
Additional convenience features include auto-sense turn-on from standby and autostandby after an absence of input signal for twenty minutes, which can be turned off by holding down the front panel standby switch for five seconds allowing the A35.8 to remain on indefinitely.
At start up, eight internal red LED lamps, one for each channel’s amp module, will light up inside the chassis confirming that the clipping sensing system is operational. These lights will extinguish once the unit goes into standby and is ready for operation. These LEDs will flash should clipping conditions occur, visible when looking from above into the amplifier through the top cover openings.
Additionally, an eight LED warning system is located under the top cover at the front of the amp that will indicate the following:

On – DC is detected on the related amp module
Flashing – overheating on the related amp module
All lights cycling – power supply unit overheating

The A35.8 provides immediate and sustained high power output with very low distortion, instantaneous rise time and linear amplification across the entire bandwidth. This results in a naturally fast, clean, and agile sound over an ultra-wide frequency range and with exceptional headroom, capable of bringing to life even the most sophisticated systems, both multi-channel and bi-amped stereo.

A35.8 Specifications

PRIMARE A35.8 Power Amplifier - Figure 1

Amplification
Amplifier module: Hypex NCore500
Power supply: Primare APFC
Inputs per channel:

1 x RCA (L&R)
1 x XLR (L&R)

Input Impedance: RCA 15kΩ; XLR 36kΩ
Input Sensitivity: RCA 150W 8Ω = 1.7V; XLR 150W 8Ω = 3.4V
Gain: RCA 26dB; XLR 20dB
Output impedance: <0.02 Ω
Number of channels: 8, with each pair bridgeable
Output Power

Single channel – 1500 watts maximum total output all channels driven
o 400 watts at 2 ohms
o 300 watts at 4 ohms
o 150 watts at 8 ohms
Bridged channel – 1500 watts maximum total output all channels driven
o 450 watts at 2 ohms
o 750 watts at 4 ohms
o 740 watts at 8 ohms
clipping protection circuit limited

Frequency Response: 20Hz – 20kHz +0.2/-0.5dB
THD + N: < 0.005%, 20Hz – 20kHz, 10W AES 17at 8Ω
Signal to Noise: >115 dB

General
Control: