Hi mcc_2001,

J&K Audio is still in business.

https://www.facebook.com/share/p/15YgEZAGUp/

Johnny

Hi Karas,

Will you try to feed your PX25 amp directly from a DAC or CD player and see if there's any hum?

Johnny

有個低級問題想問下
部自己焊的單端(mh4+px25)發現 在沒輸入時有hum聲，short rca正負就會冇hum
電源接地已有ground loop breaker ， 應該係關輸入級事？
近排換前級才發現部機原來有hum

羅密歐兄，

不需要心淡， 其實技術方面。都係需要多交流。

例如這個貼。技術含量都好高啊。

#4392

其實我身邊朋友都有睇。祇不過他們沒有發表意見。

呢度R33依家变得冷清，週不時只見到幾個長命Thread 好似幾個朋友聊天group, 講及日常生活去到日本大媽女優，完全跟音响無關

有D係度提出問題，講兩下未到終點就消失咗唔知乜原因

又有D对技術研究語出驚人，但若果有人提出相反觀點就冇咗下聞

單端同好會由Michael 創立，有好多有經驗師兄分享技術，裡面有好多堅料，真係唔想以後冇咗

最後修改時間: 2025-03-11 19:16:03

Johnny兄，無需feel bad，不單止Facebook，這情況在review33這裏也比比皆是，發問的人信口開河，認真答的人往往熱臉貼著冷屁股，我慢慢也無心留戀了。眾人皆説，這討論區人氣越來越少，將其歸咎於年青人不再玩音響，其實是很多人，連討論區的基本禮貌都不懂。

From my experience, the mutual cancellation of the even harmonic harmonic to reduce THD isn't good at all. I have tried it in several SE amps few years ago but they sound weire and un-natural.

It is much better to keep each stage with minimum distortion. The final THD measurement would be higher BUT it sounds real good.

I found that most of the amplifier circuits would have high distortion at the driver stage.

Johnny

Hello 伏喱哩,

The Old Chen KT88 amp is not mine. I saw the post at Facebook asking for help. I spent sometime to provide him with all the information including the schematic etc. I asked him to check the B+ voltage and the value of those 3 cathode resistors. Too bad that he haven't respond since. I am just curious what happend to his amp.

Johnny

各級ECC99用唔同Harmonic Patterns, 用LTspice 好容易找到最optimum 綫性組合，相信stage harmonic cancelation 係主要，未有simulation 前只可以試焊跟住用Spectrum Analyzer 測試, 相當費時，甚至未必揾到最好parameters combination

1200V, 75mA, 出到A2 43W RMS at 5.4%THD



最後修改時間: 2025-03-11 17:09:06

回#4917
你陰極果3支並聯電阻應該變晒值.
KT88想唔燒都難.
依種碳膜皮電阻唔耐捱高熱.換第二種電阻啦

Hello Niceday009,

Yes, the LTspice is a damn good tool for analyzing the electronic and amplifier circuits.

With the distortion results from your runs, it is obvious that the THD at the final output isn't reflect the true performance of the amp.


Johnny

最後修改時間: 2025-03-11 01:39:28

Degeneration 27W output

CCS 27W output

Degeneration speaker output 1W

今日对無環路負回輸之失真數據又有新体驗

最近搞返好部史前Dell notebook computer, 去run個LT SPICE, 將我喜歡的ECC99 用各種configurations 去sim output data, 首先要感謝Jonny ECC99 data set 及Wilson 做介紹, 部Ultimate 845 前一及二級用ECC99 cascade 直結

過程中ECC99 試咗以下:

1. 普通Resistor load, Resistor 值若3.5至7倍of ECC99 internal impedance, 15mA，在冇任何低失真config, 普通电阻load失真可能較大

2. Degeneration 每section 2.5dB 分別係ECC99 一及二級，分別Idle current 8mA, 10mA

3. Degeneration 2.5dB 第一級ECC99 ，SS CCS cascade 第二級ECC99, 分別Idle current 8mA, 15mA


第一級ECC99 用2.5dB Degeneration 或CCS在此級中失真分別不太大，因為輸出只需2至3V RMS

第二級ECC99同樣2.5dB Degeneration 其失真係有戲劇性比較，當喇叭端出1W RMS時，第二級ECC99此級失真分別係0.08%(Degeneration 2.5dB)及0.06%(Cascade CCS), 喇叭輸出端大家也是約0.9%，其實係差唔多, 但當喇叭端出27W RMS時，第二級ECC99 的degeneration 係0.24% THD而CCS 係0.08% THD. CCS 失真在第二級低過degeneration 2.5dB 成三倍

而此時27W output 去分別量度喇叭端分別係5.6%(CCS果部)，5.77%(Degeneration 果部)，差不多而且每個order harmonic intensity 係好接近，咁明明係第二級ECC99 degeneration 果部失真高成三倍，但係在喇叭端大輸出27W 兩種結構係差唔多同樣失真，連各種harmonic order level都差唔多，其中級與級之間相信係存在harmonic cancelation





最後修改時間: 2025-03-11 01:24:51

cascode 通常係R1同R2去分壓給上面膽柵極做偏壓。

U3 接法和傳統cascode 不一樣。是少見接法, R7 是Feedback? R10接cathode 也是少見。



最後修改時間: 2025-03-09 08:26:34

Here is the Old Chen KT88 SE amp that I found and redrawn for simulation

A guy posted the following question at Facebook regarding his LoChen K1 KT88 SE power amp.

I would say having the technical support is very important in playing the Tube Amps. They need maintenance and service from time to time. Otherwise.....................

請問各位大老這個須要換掉嗎為什麼我的K T88 半年換二次
https://www.facebook.com/share/p/1GmQe2rfiP/