SEWA - Seven Watt Amplifier

[Tyimo]

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

[Mad_K]

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.

[Tyimo]

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

[Mad_K]

You're welcome I wouldn't do anything to the BOZ... I would explore other designs, like Bipolar, JFET, TUBE or maybe the OPA2227?

[Tyimo]

Hi Mad!

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

[ACK2005]

Hi

Don't forget to add the protection Zener diodes

[Tyimo]

Don't forget to add the protection Zener diodes

Who? Where? Why?

[Mad_K]

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)

[jleaman]

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.

[ACK2005]

You may need high efficient speakers to match this amp...