- #4060 [johnnykmtang], 24-05-15 21:15
- #4059 [johnnykmtang], 24-05-15 18:27M7 schematic
- #4058 [johnnykmtang], 24-05-15 18:13Thanks for Wilson brought up the Miller Capacitance issue about the 12AX7 tube. This tube have been widely used in the high end audio amplifier for many decades.
I have a clone Marantz 7 phono + line preamp. I analyzed the phono circuit with the LTspice simulation. I had the NFB network cut out from the the circuit. The -3dB at the grid of the second 12AX7 is at 50kHz. If a cathode bypass capacitor is added to the 4.7K cathode resistor, the -3dB will be at 24kHz.
The original M7 phono circuit, the 2nd stage 12AX7 is having a 100uF capacitor.
The overall frequency response of the Marantz 7 preamp actually is real good >100KHz because it employs the NFB.
Johnny
最後修改時間: 2024-05-15 18:21:39 -
- #4057 [johnnykmtang], 24-05-14 07:09#4053, Hi Niceday,
I would say using the CCS-shunt voltage regulator makes the amplifier sounds more natural with very low background noises.
I like it.
Johnny - #4056 [niceday009], 24-05-14 00:11
- #4055 [niceday009], 24-05-13 23:46
中國制做,一貫風格,有型無.....
二次大戰日本人用嚟折磨囚犯
最後修改時間: 2024-05-13 23:49:04 - #4054 [niceday009], 24-05-13 23:12
Worth listening
300B single to drive the huge speakers
最後修改時間: 2024-05-13 23:13:37 - #4053 [niceday009], 24-05-13 22:18Johnny, How much difference when you add shunt regulator ?
- #4052 [niceday009], 24-05-13 22:15
- #4051 [johnnykmtang], 24-05-13 08:46This is the second pair of Mission 776 MC-Phono preamp with two 24Vdc CCS-Shunt regulator board.
The first pair phono preamp boards were given to my friend. He put them in a very nice chassis. He loves it a lot because it has very low noise, high gain, and most importantly very natural sound in comparison with this D3a LCR phono amp.
Johnny
最後修改時間: 2024-05-13 08:47:40 - #4050 [WilliamsonAudio], 24-05-10 01:12我都覺得Pathons會有足夠嘅頻寬。因為已經是一個產品。
我有時間再看清楚那一條公式。是否有一些特定條件。 - #4049 [niceday009], 24-05-09 22:04要drive 300B Miller Capacitance 一般推動胆內阻要20K内越少越好,12ax7 屏推300B唔得,用12ax7 接12au7 cathode follower, bandwidth 應該Pathos 考慮過屬於可接受範圍
- #4048 [WilliamsonAudio], 24-05-09 13:49
https://pearl-hifi.com/06_Lit_Archive/02_PEARL_Arch/Vol_08/Sec_31/2071_The_Miller_Effect.pdf
12AX7 -3dB =12.4kHz
但我用LTSPICE 去 Sim,
又沒有那麼低。 - #4047 [WilliamsonAudio], 24-05-09 08:10補上圖片
- #4046 [WilliamsonAudio], 24-05-09 08:10下面是臺灣張文俠的一段。
假設我們用一支p較高的真空管来推動300B,例如ECC83/12AX7,根擦真空管手冊得知ECC83/12AX7的屏
BErp在屏壓250V時篇62.5KS2。
-般三極的屏極負载電阻RL大多設定在屏内阻mp的3~7倍之間,我們取其中間值5倍爲屏極負載電阻,mp的
倍爲屏極負戴RL,即:
62.5K2x5=312.5K0
代入上式:
fc=159/RL{Cin+Cgp(1+A))
=159/0.3125{9415(1+3)]
=7.37KHz
----
如果屏阻用約100k, 頻應也有約20kHz - #4045 [WilliamsonAudio], 24-05-09 07:37#4043
我記得是12AX7 的頻應不高(沒有回輸),原因是內阻高和Miller effect.要用回輸來增加頻應。
所以後期的設計主流,就是用低內阻膽。當然沒有回輸設計也是主因之一。在無回輸情況之下,頻應也要足夠寬闊。在Low Tim 失真的石機設計。也是有這一條設計原則。
ARC, 開頭用12AX7.之后是6DJ8.現在是6H30
最後修改時間: 2024-05-09 07:42:59 - #4044 [johnnykmtang], 24-05-09 07:19In general, it is better to drive the Interstage transformer (IT) with low impedance. It is a lot easier to get better performance of the IT with lower inductance. Therefore, using the 6SL7 or 12AX7 isn't good with inductive load. The limitation is the IT.
Med/high gain triodes like D3a, C3g and 5842 which has low plate resistance would be nice to drive the IT or plate choke.
Johnny
最後修改時間: 2024-05-09 07:32:48 - #4043 [niceday009], 24-05-09 00:31Hi Wilson,
用12AX7 或6SL7 做differential stage 有一好處,一級电压放大已經達到合併机之增益,Pathos自己應該諗過呢個優點,但用AX7或SL7唔可以用PP牛load因為做唔到隻咁大电感牛比12AX7 load, 計過起碼要1200亨(60K(12AX7 內阻)x2.5÷(2x3.14x20)),只可以用CCS
Sim過12AX7 swing 到58V P to P(等於50W RMS output 幅度),失真其實好少,只有二次0.02%失真,三次order 以上harmonic 基本係冇乜
我完全相信你曾經講過,电压放大Triode 最好,电流放大石最好,失真已經證明到,而80年代其中一期MJ曾講過失真糸數係無負回輸下更有意義
最後修改時間: 2024-05-09 00:46:09 - #4042 [WilliamsonAudio], 24-05-08 22:57#4040
Hi Eric
Pathons 是用小九腳膽做推動。ECC83+ECC82
ECC83 就算用到舊裝金獅B759 或 Mullard 第一代炭黑屏。在冇回輸之下。開環的特性。是十分不理想的。冇回輸的設計,儘量避免用ECC83.
ECC82 的失真特性。也是比6SN7高。
ECC99 雖然係9 腳膽,但我見Lynn Olson 也推介用。應該是非常之綫性的膽。
最後修改時間: 2024-05-08 22:58:03 - #4041 [johnnykmtang], 24-05-08 02:52Hi Niceday,
Using Class A PP MOSFET stage works like a power buffer circuit. That means the output voltage is 1:1 between the gate input and output.
The electrical characteristic between Class A tube PP and MOSFET PP is a bit different. The tube PP would have a higher impedance than the MOSFET. The MOSFET class A would require a large heatsink.
I believe the MOSFET PP is something I would like to try too.
Johnny - 下一頁 (2 of 204)
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I don't think so. Even using parallel 6SL7 will provide sufficient drive voltage and extended high frequency bandwidth for the 300B.
Johnny