Cary呢隻interstage 設計有失販地方，用300B 接interstage 又同時用coupling cap load 隻220K, 佢隻interstage頻率响應係咪唔掂？

而實際上interstage 比輸出牛難做好多係事實，interstage 初及次級都是幾千圈，电容量很難搞，要interstage 性能好最好使用貴價permalloy 或Cobalt Based Amorphous 或Nano Crystalline





最後修改時間: 2025-03-23 13:29:14

Traced the CARY CAD-805RS 211/845 Mono Power Amplifier circuit. Here's the schematic I would share with you.
Note: The two 6SN7GTB tubes' filament share the same power supply with the 300B. Therefore, the 6SN7GTB filament is at ground potential.

NFB or Non-NFB

With NFB, the THD figure can be reduced significantly. However, it will creat wide spread high frequency harmonics. Here's one example I ran the simulation of the CARY CAD-805RS power amp to show the difference.

Johnny

Hi WilliamsonAudio

已搵到noise的原因來自條ｒｃａ線及未完成的diy前級；
RCA短路或斷開，ｍｖ都接近０或至0.6 左右。
ｍｈ４燈絲冇接地，直接４ｖａｃ



壞的那條ＲＣＡ度不到mv, 我用手機測的



最後修改時間: 2025-03-18 16:26:39

Hi Karas,

先把後級看成一個unit， 如果把"後級"RCA 座，短路(輸入短路)。輸出噪聲是多少？又或者是否正常？

另外假設你 MH4 的燈絲有接地。(因為沒有完整電路圖，所以這一點不能確定)

頂 搞搞下，原來係條rca線問題
一頭冇駁 一頭駁amp 就噪，點解呢？
他過條線又冇short，線又冇傷

我重新焊過條line input部份 做回100k input，同執執ground loop breaker, 無左噪聲了


johnnykmtang

Yes, this is the board I bought. I asking the shop what status in "0 and mute".

Found this TVC relay control board

https://www.aliexpress.com/item/1005005647465831.html#nav-specification

Dear Karas,
When the volume control is at 0 or Mute, the RCA output should be shorted. I think it is the problem is with the connection at the relay control board.
I don't have any information of the board. Therefore, I have no idea how to fix the problem.

3 Hum 應該是來自前面（前級）。因為short RCA 沒有。

關於前級，可能我會講到有d亂，而我都係第一次接觸TVC
1. 新前級係Khozmo 新TVC relay式遙控，有volume 0同mute，用佢聽歌係全段都冇問題既，mute的時候 阻值接近0
係甩 rca線時會有噪

2. 之後我又買左日本24級finemet core Tvc，夾淘仔24級relay板去用，個24段都係無問題，
個問題又係0及mute時，會發生甩rca線咁有噪，
發現呢塊板mute的狀態是正負斷開當mute


所以rca short埋係正常定唔正常？

WilliamsonAudio

1. 可以排除由第一級的柵電阻感應。 100K 是可以。電學原理是電阻越大，noise 越高。也容易pick up noise.
原來如此

2. 可以排除燈絲入，因為有接地和VR 可調
我昨日才發現圖的mh4燈絲都有vr, 這個我沒裝 不是直熱裝vr 才有用？

兩款網屏都有，但始終ac/hl最正

Hi johnnykmtang
Thank you for the simulation.
The actual b+ doesn’t very high. Around 390-400v for px25.
The R4 replaced a choke load. May I revise the value in drawing later?

MH4 最早期是網屏，師兄有否試過?

＞＞＞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＞＞＞

3 Hum 應該是來自前面（前級）。因為short RCA 沒有。
4 換了前級才有，所以也是指向前級問題。
5 後級Gain 約在10(粗略心算)。是合理，例如Gain = 60,就會把前級noise 放大60倍。

基於提供的資料，初步分析方向是前級。

最後修改時間: 2025-03-17 08:17:24

The hum buzzing noise could be cause from the faulty connection from the preamp to the power amp. Check the connection for both signal line and ground between the two. If it is OK, check if the noise is from the preamp itself. You could try to feed a DAC or CD player directly to the power amp to verify there's noise or not.

Also, you may use other line amp for the testing too.




最後修改時間: 2025-03-17 07:28:16

2. 可以排除燈絲入，因為有接地和VR 可調

#4398

＞＞＞試左唔插mh4 就得番燈絲hum聲 = 平常噪聲
可能我果input電阻100k太細? 換左470k好似細聲d
手頭未有1m電阻可試….＞＞＞

1. 可以排除由第一級的柵電阻感應。 100K 是可以。電學原理是電阻越大，noise 越高。也容易pick up noise.

最後修改時間: 2025-03-17 07:07:49

The output waveform and FFT spectrum at full output.

Here's the simulation of the MH4-PX25 SE amp.

The MH4 provides very clean signal for the PX25. Great.

I would prefer changing the PX25 cathode resistor from 560 to 500 ohm. The idle current would be 57.2mA.

Johnny

There isn't much information about the MH4 and ML4 tubes.
I checked the plate curve graph of both tubes.
MH4 gain : 45, Ra : 11K
ML4 gain : 12, Ra : 3.7K
PX25 gain : 9.5, Ra : 1.26K

Both MH4 and ML4 max anode voltage is 250Vdc.

Hi Karas, my understanding is you are using the MH4 to drive the PX25, right?

Johnny




最後修改時間: 2025-03-17 02:58:19