SEWA - Seven Watt Amplifier
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 1st May 2006, 12:01 PM #111 Tyimo   diyAudio Member   Join Date: Nov 2002 Location: Hungary preamp question Hi Mad! I am looking for a good tubpreamp and need your suggestions. What parameters has to be the preamp? I know the SEWA V1 requires a preamp that can swing +/-10-12V, but I don't know how is this have a relation to the gain/dB parameters. I don't understand (how to calculate) the gain/dB connection. I mean: many times I see for example the gain of the preamp is 7, but how many dB is it? Or, I see the gain is 20dB, but how many amplification is this? So, how should be a perfect preamp for the SEWA V1? Greets: Tyimo
 1st May 2006, 08:13 PM #112 Mad_K   diyAudio Member     Join Date: Sep 2002 Location: Norway BOZ or BZLS or one of it's iterations are good candidates for SEWA Rev.1. I suspect a good tube pre will be excellent also. As it has a input impedance of 330K, one can use almost any preamp that can swing the required voltage. For a SEWA with 30V V+, you need a preamp that can swing +/-15V. The gain calculations are simple. 10X (10 times) are in dB: 20*log 10=20dB. From dB: 10^(20/20)=10X. more examples: 4X=20*log 4=12dB 12dB=10^(12/20)=4X. So if you use a typical MM preamp with 100X gain from a typical MM pickup with outputvoltage 5mV, you have a source with 0,5V output to your preamp. The preamp then needs to have 15/0,5=30X or 31,6dB gain. __________________ Mads K
 2nd May 2006, 05:16 PM #113 Tyimo   diyAudio Member   Join Date: Nov 2002 Location: Hungary Thanks Mad! You help me a lot to learn! What do you think, is it worth to use 2SK216 instead of the IFP610 in the BOZ? Greets: Tyimo
 2nd May 2006, 08:38 PM #114 Mad_K   diyAudio Member     Join Date: Sep 2002 Location: Norway You're welcome I wouldn't do anything to the BOZ... I would explore other designs, like Bipolar, JFET, TUBE or maybe the OPA2227? __________________ Mads K
Tyimo
diyAudio Member

Join Date: Nov 2002
Location: Hungary

Quote:
 I would explore other designs, like Bipolar, JFET, TUBE or maybe the OPA2227?
Me too. I am in the search for a good competitor, but it is not easy to find a good preamp what is sufficient for the SEWA V1.

I thought on the Threshold NS10 clone, but it has only 10V output....

I will tell you if I find something interesting.

Is it worth to try by the BOSOZ to decrease the
value of R15 to 0 ohms, the gain will approach 50 (34 dB)?

Greets:

Tyimo

 4th May 2006, 06:17 AM #116 ACK2005   diyAudio Member   Join Date: Feb 2006 Location: Taiwan Zener Proctection Hi Don't forget to add the protection Zener diodes
Tyimo
diyAudio Member

Join Date: Nov 2002
Location: Hungary
Quote:
 Don't forget to add the protection Zener diodes
Who? Where? Why?

 8th May 2006, 07:10 AM #118 Mad_K   diyAudio Member     Join Date: Sep 2002 Location: Norway If R15 is the 100R Source resistor, you can not simply delete it as it sets the bias. You can reduce it (if you re-adjust the bias) to get more gain. I encourage you to try the BZLS, especially if you put in a active CCS (like the X2r1) __________________ Mads K
 8th May 2006, 07:43 AM #119 jleaman   Banned   Join Date: Apr 2002 This looks like a nice simple amplifier. I think i should try one. Since i'm running a 15-20watt class a and hardly use all of that power. I think i should try this one.
 8th May 2006, 08:38 AM #120 ACK2005   diyAudio Member   Join Date: Feb 2006 Location: Taiwan Speakers You may need high efficient speakers to match this amp...

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