A preamp designed for the minimalist, and having no frills at all is the design goal for this project. 一个前置放大器设计简约,没有虚饰完全是为这个项目的设计目标。It was originally designed as a preamp for the Death of Zen (DoZ) Class-A power amp (Project 36), and has very low levels of noise and distortion, in a minimum component count, fully discrete circuit. 它最初的设计是一个前置放大器的死亡,禅(打)甲级功率放大器(项目36),已经非常低水平的噪音和失真,在最小的组件数量,完全离散电路。The Revision-A version dispenses with the single 30V supply, and can be used with the P05 power supply, or any other supply with low ripple and noise. 修订过的版本无需单30 v电源,可以用P05电源,或任何其他供应与低纹波和噪声。Operation is permissable with supply voltages up to ±20V, allowing additional headroom.可允许的操作与供应电压±20 v,允许更多空间。

This gain module can be used as the basis for any preamp - performance is exemplary, with low noise, wide bandwidth, and it sounds extremely good indeed.这个增益模块作为基础任何前置放大器-性能是模范,噪音低,宽的带宽,这听起来非常好的确。

You can add as many inputs as you need, and the only controls are volume and input selection. 您可以添加尽可能多的输入,因为你需要,唯一的控制是体积和输入选择。A power switch is also a good idea, but if you wanted to you could leave the preamp running all the time. 一个电源开关也是一个好主意,但是如果你想要你可以离开前置放大器运行所有的时间。This is not necessary, as it will reach a stable operating condition within a few seconds, and will not change its characteristics to any audible degree.这是没有必要的,因为它将达到一个稳定的操作条件在几秒钟内,不会改变它的特性到任何声响程度。

The preamp can also be used with other amplifiers, and can drive an impedance of 3k Ohms with ease. 这个前置放大器也可以用于其他的放大器,可以驱动一个3 k欧姆阻抗与缓解。As shown, frequency response is absolutely flat from 10Hz to 100kHz, without any frequency stabilisation required. 如图所示,频率响应是绝对平从10赫兹到100赫兹,没有任何频率稳定要求。The table shows the rated performance of the gain module.上表显示了额定性能增益模块。

#p#分页标题#e#Performance is almost identical to the original P37 published way back in 1999. 性能是几乎相同的原始P37早在1999年出版。The primary difference is that the new design can be used without any output capacitors, although I recommend that they be used anyway. 主要的区别在于新设计可以在不用任何输出电容,虽然我建议他们无论如何被使用。Having any DC - even a few millivolts - across the volume pot will cause noise when the pot is rotated, and the caps ensure that this is eliminated. 有任何DC -甚至几毫伏——整个体积罐会导致噪音当锅旋转,帽确保这是消除。The main output coupling cap should be a bipolar (non-polarised) electrolytic, and the optional film bypass cap can be included if it makes you feel better (it won't affect frequency response though).主要的输出耦合帽应该是一个双极(非极端)电解,和可选的电影旁路帽可以包括如果能让你感觉更好的(它不会影响频率响应虽然)。

The circuit for the left channel of the preamplifier module is shown in Figure 1, and as can be seen is very simple. 这个电路用于左声道的前置放大器模块如图1,可以看到非常简单。The PCB is recommended, as it makes construction very straightforward. PCB是推荐的,因为它使建筑非常简单。This preamp relies on a completely hum free power supply, as it is not an integrated opamp, and cannot reject supply noise as well. 这个前置放大器依赖于一个完全哼免费供电,因为它不是一个集成opamp,也不能拒绝供应噪声。This is not to say that the power supply rejection is especially bad, just that it is not as good as an opamp.这并不是说供电抑制尤为糟糕,��是说,它不是一个opamp一样好。

Figure 1 - Gain Module图1 -增益模块

Q2 and Q4 form a current source providing a bias current of about 7mA. Q2和第四季形成电流源提供一个偏置电流约7马。This stage is not an amplifier, but an active (and very linear) load, allowing the amplifying transistor Q3 to provide a high gain with excellent linearity. 这个阶段不是一个放大器,但是一个活跃的(和非常线性)负载,允许放大晶体管Q3提供高增益和线性度好。Feedback is applied through R6, with R5 setting the AC feedback ratio and thus the voltage gain of the amp. The transistors Q2 and Q3 operate at about 100mW and will get slightly warm in operation.反馈是应用通过R6,R5设置交流反馈系数和因此电压增益的amp。晶体管第二和第三季度约100兆瓦,操作会稍微温暖的操作。

The trimpot VR1 is used to set the voltage at the collectors of Q2 and Q3 to as close to zero volts as possible - this is easily measured at either end of R10. 这个trimpot VR1用来设定电压在收集器的第二和第三季度为尽可能接近零伏特——这是容易衡量在两端R10。Each amplifier has its own independent adjustment. 每个放大器有它自己的独立的调整。The bias current for each preamp module is bypassed to ground using C2 to help eliminate noise. 为每个前置放大器的偏置电流模块是绕过地面使用C2帮助消除噪声。If you really don't want to use a multi-turn pot, there is provision on the PCB for a conventional horizontal mounting single-turn trimmer. 如果你真的不想使用多罐,有提供PCB上的传统卧式安装单匝微调。This will make setting the 0V level more critical, but if the output caps are retained a small DC offset is not a problem. 这将使设置0 v水平更重要,但如果输出帽是保留一个很小的直流偏移不是一个问题。When the pot is adjusted for 0V at the collector of Q3, there will typically be around 4.7V across C2.当锅调整为0 v在第三季度的收藏家,通常约为4.7 v在C2。

The distortion of the preamp is reasonably consistent with both output level and frequency, and is typically less than 0.01%. 前置放大器的变形是相当一致的两个输出级和频率,和通常不到0.01%。I measured about 0.0075% - this is just above the residual of my signal generator (0.006%), so it is presumably much better than this, but I can't measure it. 我量大约0.0075%——这是略高于剩余的信号发生器(0.006%),所以它大概是比这做得更好,但我不能测量它。A rough guess would be the difference between the two, giving 0.0015%, but I prefer to err on the side of caution. 粗略估计将两者的区别,给0.0015%,但我更喜欢宁可失之谨慎。Noise is also extremely difficult to measure - there simply isn't enough of it to obtain an accurate reading with my equipment.噪音也很难衡量——因为根本没有足够获得一个精确的阅读与我的设备。

Frequency response is flat to within -0.1dB from 10Hz to 100kHz, and even at 100kHz, square wave performance is almost perfect, showing slight rounding and no ringing or instability of any kind. 频率响应是平的,在-0.1 db从10赫兹到100赫兹,甚至在100 khz,方波性能几乎是完美的,显示出轻��的圆,没有任何形式的铃声或不稳定。Measured output impedance is 200 Ohms, and the circuit can drive 6 Volts RMS into a 3k Ohm load easily. 测量输出阻抗是200欧姆,电路可以驱动6伏RMS到3 k欧姆负载很容易。These are excellent figures, considering the simplicity of the circuit. 这些都是出色的人物,考虑简单的电路。The gain is nominally 3.2 (10dB) as shown, and is easily changed by varying R5 - increase the value to decrease gain and vice versa. 名义上的获得是3.2(10分贝)如图所示,可以容易地改变通过改变——将该值增加到R5减少增益,反之亦然。The PCB is 75 x 50mm, and has two complete amplifiers on the board.在PCB是75 x 50毫米,有两个完整的放大器在黑板上。

As many preamp modules as needed may be used. 根据需要尽可能多的前置放大器模块可以使用。For example, you may use one module before the volume control, and another after it to provide some additional gain and present a low impedance to the outside world. 例如,您可以使用一个模块在音量控制,另一个在它提供一些额外的增益和现在的一个低阻抗到外面的世界。In many cases, the module will provide the only gain stage, and may be bypassed for high level signals (such as CD players) that have enough signal to drive the power amp directly. 在许多情况下,模块将提供唯一的增益阶段,并可能绕过针对高水平的信号(如CD播放器),有足够的信号驱动功率放大器直接。This is a great advantage for those who want the minimum number of components in line with the signal. 这是一个很大的优势对那些想要最低数量的组件符合信号。The circuit cannot be direct coupled, however, since it has an inherent DC offset at the input. 这个电路不能直接耦合,然而,因为它有一个内在的直流偏移的输入。Polyester (or polypropylene if you must) caps can be used at the inputs, but for low impedance outputs, a bipolar electrolytic capacitors is recommended. 聚酯(或聚丙烯如果你必须)帽可以用于在输入,但是对于低阻抗输出、双相电解电容器是推荐的。These may be bypassed with 100nF polyester caps, but the frequency response is not altered to any significant degree (not measurable at 100kHz), and there is no measurable decrease in distortion with the bypass caps.这些可能是绕过100 nf聚酯帽,但频率响应是不改变任何重要度(没有可测量的100千赫),而且没有可衡量的下降与旁路帽。扭曲

Figure 2 - Preamp Wiring Suggestion#p#分页标题#e#图2 -前置放大器布线的建议

Figure 2 shows one channel of a suggested wiring for the preamp. 图2显示了一个频道的一个建议的布线前置放大器。This is duplicated exactly for the other channel, and the switch and volume control are common to both. 这是完全的复制其他渠道,开关和音量控制是共同的。The CD input bypasses all electronics and is applied directly to the volume control, and the low level inputs use the gain of the modules to bring their level up to that of the CD player. CD输入绕开所有电子和是直���用于音量控制,和低水平输入使用获得的模块将他们的水平的CD播放器。This introduces a bit more switching, but many audiophiles will prefer this method. 这引入了更多的开关,但是很多发烧友会更喜欢这种方法。Note that when switched to CD, the input of the preamp is earthed to prevent any noise pick-up.注意,当切换到CD,输入的前置放大器是接地的,以防止任何噪音拾音器。

The switching requires a 4-pole, 5 position rotary switch for both channels, and a dual-gang pot. I strongly suggest that a linear pot is used, with the resistor as shown. 开关需要一种,5的位置旋转开关两通道和一个双帮派锅。我强烈建议使用一个线性锅,电阻器如图所示。Although this produces a variable impedance to the source, it is a better approximation of a log pot than those you can buy at normal outlets, and has much better tracking between channels. 尽管这会产生一个可变阻抗源,这是一个更好的近似的日志锅比你可以买到在正常的商店,有更好的跟踪频道之间。If you can get a conductive plastic logarithmic pot, do not use the resistor, as these are generally much better than the normal carbon film types, and the resistor will ruin the log curve.如果你能得到一个导电塑料对数锅,不要使用电阻器,因为这些通常要比正常的碳膜类型,和电阻器将毁掉日志曲线。

In some cases - due to an amplifier with unusually low input sensitivity for instance - an output gain stage might be needed. 在某些情况下,由于一个放大器有着异乎寻常的低输入灵敏度例如——一个输出增益阶段可能需要。This would typically use another gain module using the circuit above, but generally with lower gain. 这通常使用另一个增益模块使用电路以上,但通常较低的增益。It is expected that a gain of 2 (6dB) will be enough for any amplifier, since this will provide an output of 4V RMS for a CD players typical 2V output. 预计上涨2(6分贝)将足以让任何放大器,因为这将提供一个输出4 v RMS对于一个CD播放机典型的2 v输出。I have found that with typical sources, a preamp gain of about 10dB is sufficient to drive a typical power amplifier, so the additional gain will probably not be needed.我发现,与典型的来源,一个前置放大器增益的大约10分贝是足以驱动一个典型的功率放大器,因此额外获得可能不需要。

The photo shows what the new board looks like when fully populated according to the construction details.这张照片显示了新董事会看起来像当完全填充根据施工细节。

The power supply must be free from hum and noise, and the circuit shown in Project 05 (Rev-B) is highly recommended. 电力供应必须摆脱哼和噪音,和电路显示在项目05(启b)高度推荐。A discrete circuit could also be used, but P05 is a far better proposition. 一个离散的电路也可以使用,但是P05是一个更好的命题。The variable regulator ICs have extremely low noise. 变量调节器ICs有极低噪声。A single P05 will easily power about ten P37-A boards ... 一个P05将容易功率大约十P37-A董事会……more than anyone is likely to need.比任何人都可能需要。