Using the THAT1646 As A Transistor Pre-Driver/Headphone Amp

Where we discuss new analog design ideas for Pro Audio and modern spins on vintage ones.
Post Reply
radiance
Posts: 46
Joined: Thu Jun 26, 2008 4:50 am

Re: Using the THAT1646 As A Transistor Pre-Driver/Headphone Amp

Post by radiance »

Thanks Wayne!
I've adjusted the bias so that I get 0,28V across both resistors 3R3. After that I measured 940mV at pin 4 of the 1646, slightly higher than what I had set earlier (850mV).

My DC offset is 5,8mV left and 7,8mV right. Also, I've clamped the heat sink to the chassis and now it gets mildly warm, actually not even that. Much better.

Thanks again for this nice amp!!
User avatar
mediatechnology
Posts: 5443
Joined: Sat Aug 11, 2007 2:34 pm
Location: Oak Cliff, Texas
Contact:

Re: Using the THAT1646 As A Transistor Pre-Driver/Headphone Amp

Post by mediatechnology »

Hey Radiance you're welcome!

Thanks for the data.

One thing I can't tell from the photos is whether or not the Vbe multiplier transistors are firmly attached to the heatsinks. Is it clamped somehow? Since it's on the backside I couldn't tell.
radiance
Posts: 46
Joined: Thu Jun 26, 2008 4:50 am

Re: Using the THAT1646 As A Transistor Pre-Driver/Headphone Amp

Post by radiance »

It's firmly attached on the backside of the heatsink. It was a tight fit as you can see.

Image
User avatar
mediatechnology
Posts: 5443
Joined: Sat Aug 11, 2007 2:34 pm
Location: Oak Cliff, Texas
Contact:

Re: Using the THAT1646 As A Transistor Pre-Driver/Headphone Amp

Post by mediatechnology »

OK, I see the pop rivet now. Thanks.

The BD139/140 I use are electrically insulated so I didn't have to use sil-pads.
radiance
Posts: 46
Joined: Thu Jun 26, 2008 4:50 am

Re: Using the THAT1646 As A Transistor Pre-Driver/Headphone Amp

Post by radiance »

Thanks Raf!
User avatar
mediatechnology
Posts: 5443
Joined: Sat Aug 11, 2007 2:34 pm
Location: Oak Cliff, Texas
Contact:

Re: Using the THAT1646 As A Transistor Pre-Driver/Headphone Amp

Post by mediatechnology »

So how does it sound radiance?
radiance
Posts: 46
Joined: Thu Jun 26, 2008 4:50 am

Re: Using the THAT1646 As A Transistor Pre-Driver/Headphone Amp

Post by radiance »

Yesterday, I spend some time listening to Miles Davis - In a silent way/ It's about time.
Man, I had a great time. It just sounded right! And it can do LOUD.
I can say this is a step up from my previous headphoen amp. That was a headphone amp in the monitor section from a Sony MXP2900 broadcast desk build with a 5216 (???) opamp set to +/- 18V.
User avatar
mediatechnology
Posts: 5443
Joined: Sat Aug 11, 2007 2:34 pm
Location: Oak Cliff, Texas
Contact:

Re: Using the THAT1646 As A Transistor Pre-Driver/Headphone Amp

Post by mediatechnology »

Thanks for the update.

I'm not a big headphone listener but I have a hard time taking them off when listening to it. I handed them over to my wife and had a hard time getting them back.

I'm glad the level is hot enough. Since it's unity gain it might need, with -10 sources, a little help up front depending on the 'phones. But it was certainly loud enough for me.
User avatar
mediatechnology
Posts: 5443
Joined: Sat Aug 11, 2007 2:34 pm
Location: Oak Cliff, Texas
Contact:

Re: Using the THAT1646 As A Transistor Pre-Driver/Headphone Amp

Post by mediatechnology »

Maybe it will develop into a DIY circuit board.
I was kind of hoping you would say that Roger.
radiance
Posts: 46
Joined: Thu Jun 26, 2008 4:50 am

Re: Using the THAT1646 As A Transistor Pre-Driver/Headphone Amp

Post by radiance »

If you're interested I can give you the gerbers of my attempt. They'll need some modefying to make them into a DIY project though....
Post Reply