SEWA - Seven Watt Amplifier - Page 12 - diyAudio
Go Back   Home > Forums > Amplifiers > Pass Labs

Pass Labs This forum is dedicated to Pass Labs discussion.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 1st May 2006, 12:01 PM   #111
Tyimo is online now Tyimo  Hungary
diyAudio Member
 
Join Date: Nov 2002
Location: Hungary
Default 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
  Reply With Quote
Old 1st May 2006, 08:13 PM   #112
Mad_K is offline Mad_K  Norway
diyAudio Member
 
Mad_K's Avatar
 
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
  Reply With Quote
Old 2nd May 2006, 05:16 PM   #113
Tyimo is online now Tyimo  Hungary
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
  Reply With Quote
Old 2nd May 2006, 08:38 PM   #114
Mad_K is offline Mad_K  Norway
diyAudio Member
 
Mad_K's Avatar
 
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
  Reply With Quote
Old 3rd May 2006, 06:55 PM   #115
Tyimo is online now Tyimo  Hungary
diyAudio Member
 
Join Date: Nov 2002
Location: Hungary
Hi Mad!

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
  Reply With Quote
Old 4th May 2006, 06:17 AM   #116
ACK2005 is offline ACK2005  Taiwan
diyAudio Member
 
Join Date: Feb 2006
Location: Taiwan
Default Zener Proctection

Hi

Don't forget to add the protection Zener diodes
  Reply With Quote
Old 4th May 2006, 04:37 PM   #117
Tyimo is online now Tyimo  Hungary
diyAudio Member
 
Join Date: Nov 2002
Location: Hungary
Quote:
Don't forget to add the protection Zener diodes
Who? Where? Why?
  Reply With Quote
Old 8th May 2006, 07:10 AM   #118
Mad_K is offline Mad_K  Norway
diyAudio Member
 
Mad_K's Avatar
 
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
  Reply With Quote
Old 8th May 2006, 07:43 AM   #119
jleaman is offline jleaman  Belgium
Banned
 
Join Date: Apr 2002
Send a message via AIM to 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.
  Reply With Quote
Old 8th May 2006, 08:38 AM   #120
ACK2005 is offline ACK2005  Taiwan
diyAudio Member
 
Join Date: Feb 2006
Location: Taiwan
Default Speakers

You may need high efficient speakers to match this amp...
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Tube Pre Amplifier for SEWA 7 Watt ClassA MOSFET lineup Tubes / Valves 278 2nd June 2009 05:44 PM


New To Site? Need Help?

All times are GMT. The time now is 11:21 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2