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Tube DIY Asylum Do It Yourself (DIY) paradise for tube and SET project builders. |
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Tube DIY Asylum Do It Yourself (DIY) paradise for tube and SET project builders. |
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In Reply to: Very soft bass - scratching my head posted by single_ended on February 28, 2007 at 12:42:32:
Wow, many thanks for all the suggestions!I'll try to describe the circuit in more detail.
1. The interstage transformer (IT) is parallel feed so the BG coupling cap is used to remove DC from the primary. If I understand correctly, the RIT5-jr cannot have DC voltage on the primary or secondary.
2. In the secondary of the IT I am using a circuit from Asano's book. The "hot" leg of the secondary is connect to the grid of the 275A. The ground leg of the secondary is grounded through a 47K ohm resistor. A 1uf cap is connected from this point to the center point of the 1.21K cathode bias (I have a hum pot there). I understand this trick is from the WE amps (91B, 86B?). This change from connecting the secondary ground leg directly to ground did not affect the bass appreciably but made the midrange and high much nicer.
3. The power supply uses two stage choke input filter, each stage has 10H 100ohm chokes. I use a small 0.68uf cap on the rectifier output to tame the buzz on the first choke. A 20uf is between the first and second choke. The 47uf WKZ BG is after the second choke and goes to the output stage. Additional RC are used between the output and other stages. 18ga wire throughout.
4. One of the reasons I chose the 5K impedance IT is from reading the spec sheets for the Tango interstages. They show the response curves of the interstage transformer with different Rp. For instance, for a 10K 1:1.5 transformer, a 10K Rp gives the flattest high frequency response. A 7K Rp gives a high frequency bump. The bass penalty on the 10K Rp didn't seem significant enough to be consistent with what I am hearing. But I will try to replace the IT with a resistor and check out what happens. Is there anyway I can make the 5K IT work, perhaps a bass boost circuit? The reason I am asking is that I have engravings on the chassis that can't be changed.
Cheers
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Follow Ups
- Re: Very soft bass - scratching my head - single_ended 12:26:08 03/01/07 (11)
- I'd like to address 3) power supply....... - drlowmu 23:00:06 03/02/07 (9)
- Yes, let's address the power supply for a moment - Ray Moth 03:26:49 03/03/07 (8)
- Beg to disagree............. - drlowmu 08:18:46 03/03/07 (7)
- Not dogma, not bickering, not outdated. - Ray Moth 10:37:09 03/03/07 (6)
- PSU - Owen 01:43:46 03/05/07 (1)
- Bickbat theory? - Ray Moth 23:34:41 03/07/07 (0)
- Re: Not dogma, not bickering, not outdated. - NoWay 16:25:18 03/03/07 (3)
- I don't disagree. - Ray Moth 02:09:03 03/04/07 (2)
- Absorbing Modulations, AND the Music !! - drlowmu 11:17:08 03/04/07 (1)
- Re: Absorbing Modulations, AND the Music !! - Ray Moth 18:44:15 03/04/07 (0)
- Re: Very soft bass - scratching my head - J.Rankin 00:23:34 03/02/07 (0)
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