OTA - One Transistor Amplifier

[Mad_K]

Thanks Steen 😉

Tyimo; I like it a lot compared to other Zen amps
Compared to Zen it has better bass control, and I think it leaves very little of it's own signature on the signal when played at normal listening levels. My favorite is the new SEWA (Rev.1) which is like this one (OTA3,5) but with a 7W output and a active current source. This 3,5W version is getting a little stressed at party levels 😉 My old SOZ (the one you know about) has become my testbed for prototype designs, so in a way I'm still listening to it. 😉

 

[Tyimo]

Thanks MadK!

Did you write already about how to make a SEWA (Rev.1) from a "simple" OTA 3.5W?

Sorry for the stupid question.... 🙂

Tyimo

 

[Mad_K]

SEWA Rev.1 is coming shortly. No such thing as a stupid question 😉

 

[Tyimo]

Thanks !
I will waiting for.

I forgot to say: nice design and amps you built! Congrats!

Greets:

Tyimo

 

[Mad_K]

I will waiting for.

Tyimo

The waiting is over 😉 http://www.diyaudio.com/forums/showthread.php?postid=846775#post846775

 

[Tyimo]

Hi Mads K!

Thanks for the fast and good news!! You are great!

One more question: why do you prefer the new version of SEWA more than the old SEWA? Is it only because the CCS is more comfortable to operate or it has nicer sound?
Until know I prefer my ZenLite's sound (with "power-bulbs") more than another Zen's with CCS.

Greets:
Tyimo

 

[Mad_K]

I prefer SEWA for both reasons actually 😉 I haven't tested a OTA version with the same power output though. I can't comment on Zen vs Zenlite, but I have tried Aleph with both CCS and ACS and various SOZ versions. From them I clearly preferred SOZ, but I think SEWA is better still..

 

[Tyimo]

O.K. so you are saying there is some sonic difference between the SEWA and SEWA-V1?
Can I drive the amp with a normal BOZ?

Tyimo

 

[Mad_K]

I'd like to call the one with just one transistor (SEWA Rev.0) OTA and the one with CCS SEWA (Rev.1). Yes, there is quite some difference in sound between these. BOZ is like the perfect pre for these amps 🙂 Please use the SEWA thread for further discussion on that design. Sorry for the name shifting, but I just like the name that much..

 

[Tyimo]

Thanks! I see now.
Should I use IRFP044 Fets for the OTA?
Can I use 2 way speaker (with Xover) with the amp?

Tyimo

 

[Mad_K]

IRFP044 would be nice. As long as you don't ask it to deliver more than 3,5W you can use any speaker you like. Speaker sensitivity in the upper nineties is preferable 😉

 

[john-china]

hi Mad_k

what speaker do you use to match your OTA now.

i am going to build Zv8 which is also little amp like your OTA, so
i am now considering what speaker should i use?


i am sorry if i ask a question that some one had asked?
i am so lazy to recheck this thread or others.

 

[Mad_K]

Klipsch RB75 😉

 

[JRKO]

How would a 15inch Tannoy Dual Concentric @ 93dB do?

It sounds great with a little Sonic Impact digi amp with 6watts (going downhill with a tailwind!)

 

[Mad_K]

I think I would give it a little more than 3,5W 😉 It strongly depends on your listening habits though. My RB75's are 97dB/W and I feel that 3,5W is not enough, but 7W is 🙂

 

[JRKO]

I generally listen at low levels in the late evening.

As you know with your RB75's big drivers and large cabs can bring out all the detail without the need for mega watts

 

[Mad_K]

Yup, and what's even nicer is that if you build OTA 3,5 and find you want more power, you can simply swap in a SEWA as they have the same PSU/heatsink demands 😉

 

[JRKO]

I thought that the SEWA was a current source amp, kind of like Nelson Pass' F1 & F2 and that they dont react so well with speakers that have a crossover?

Maybe I'm wrong😕 😀

 

[Mad_K]

No, it's a "normal" voltage source amp 😉

 

[JRKO]

Hehehehehe😀

I am trying to get to grips with NP's article on crossovers and current amps that I downloaded from the FirstWatt site.

Still Charles Mingus will sound great (i'm sur) with 3.5w and then as long as I am not electrocuted I'll try the SEWA😉