[PinkFloyd]

Yes Folks! It's the worlds first under the bonnet preview of the £29 B-Tech BT928 "Headphone Pro Amp".

I bought it for TV use but it turns out it's got capabilities that extend beyond speech, quite a musical little amp as well. A cracking amp for the money and highly tweakable.

I've already replaced the caps with some ELNA's

and I've only had the amp since this morning! I'm going to change the 5532 Op amps with another type. Does anybody know if there is a better replacement than the OPA 2134PA ??

You can view the **** here: http://freespace.virgin.net/rock.grotto/index2.htm

Look for the B-Tech link and please wait till the page fully loads as there are quite a lot of pictures.

 

[Budgie]

Wow, Pinkie, that looks like a great platform to tweak and modify. Just enough room in there, and a simple opamp design. Good find!

I (personnely) have not found a dip 8 package chip that I like better then the OPA2134. Some, like the OPA627, sound different, but not better, in my opinion. I am sure others here, will have ideas.

 

[PinkFloyd]

Quote:

Originally posted by Budgie Wow, Pinkie, that looks like a great platform to tweak and modify. Just enough room in there, and a simple opamp design. Good find!

It sure is a great platform to tweak and modify Budgie! There is even enough headroom to piggyback a PCB onto the main board.
The casework is nothing short of miraculous for the price, very solid and well built... you could even justify £29 for the case alone!

£29 is the retail price of this amp and not a knock down price. The B-Tech website is http://www.b-tech-int.com/

These guys http://www.btech-usa.com/bt928.htm charge $79 for it in the USA but I'm sure you could get hold of it for its retail price if you shopped around. That's about £49 in the USA... robbers!

Pinkie

 

[PinkFloyd]

It may be of interest to point out that this £29 B-Tech uses the exact same potentiometer that the Creek OBH 11 uses. It also employs the same headphone socket as the Creek.

In fact, it even sounds like the Creek in certain respects! It's been playing for a few hours now and its sound is really beginning to open up. It'll be interesting to hear the changes in sound after it has been left on for a week or two.

If you're looking for a decent sounding £29 amp you won't go far wrong with this little beauty!

Pinkie

 

[PinkFloyd]

The pic I just attached was the inside of the Creek OBH 11 to show the identical potentiometer and headphone socket!

To see the same items on the B-Tech http://freespace.virgin.net/rock.grotto/index2.htm

Pinkie

 

[wordsworth]

Thanks PinkFloyd for the pics of the B-Tech innards.

I saw this sometime before christmas and like you though it would be terrible and as I didn't need a tv amp didn't buy it but from your description it sounds well worth £29 and I think richersounds sell them so I might have to go there tomorrow and have a look. I'll be interested to here how it sounds after it has been burned-in.

Wordsworth

 

[PinkFloyd]

Quote:

Originally posted by wordsworth Thanks PinkFloyd for the pics of the B-Tech innards. I saw this sometime before christmas and like you though it would be terrible and as I didn't need a tv amp didn't buy it but from your description it sounds well worth £29 and I think richersounds sell them so I might have to go there tomorrow and have a look. I'll be interested to here how it sounds after it has been burned-in. Wordsworth

"well worth £29" is an understatement wordsworth. I'm listening to it now and they really have done it injustice referring to it as a TV headphone amp.

The Op amp is a NE 5532 which is a well known "dog" and warrants replacement with the highly rated OPA 2134PA (£2 from RS components)

The caps I replaced have already started to bring about a very nice sound and I expect an Op amp replacement and resistor upgrade would bring this amp up to something comparible to a Creek OBH 11.

There are two aspects of this amp I find particularly annoying, The "tone control" and the 3.5mm additional headphone socket are silly features and serve no purpose (unless you like messing about with tone controls which are about as subtle as Bernard Manning)

The tone control has to be fully clockwise to sound "flat". Turning it anti - clockwise strangles HF and midrange detail. Very odd design indeed! I'll whip the tone control out of the circuit ASAP! Having said that... if you leave it in the fully clockwise position it's ok.

The secondary 3.5mm headphone socket is also a bit of an odd (unnecessary) feature but.............

At £29 who's complaining?

The casework is superb, the potential for tweakers / modification is immense, the potentiometers are good quality, the sound is nothing short of unbelievable for £29.

I'll certainly be busy with this amp for the forseeable future and will upload all my tweaks and modifications to http://freespace.virgin.net/rock.grotto/index.htm as per usual!

Anyone reading this in the UK who is looking for a good starter amp with a view to throwing say £15 worth of components in to the B-Tech's innards should order one now.

All the best.

Pinkie

 

[PinkFloyd]

Sorry! wrong URL

Should have read: http://freespace.virgin.net/rock.grotto/index2.htm

 

[wordsworth]

Have given some though to DIY'ing an amp but there are some good pre built ones out there, however this could be the perfect oportunity as for £29 you can't really lose. I will be eagerly awaiting your tweak results.

BTW might want to move this thread to the DIY forum or the amp forum as it fits those better than being in cables, etc forum and would get more exposure to those looking for a cheap DIY amp.

Would love to know how the finish B-tech modded amp would sound against a meta 42? Though a meta is said to be better than a Creek OBH 11 so it might be a bit of the meta's performance.

Wordsworth

 

[PinkFloyd]

Originally posted by wordsworth
"Have given some though to DIY'ing an amp but there are some good pre built ones out there, however this could be the perfect oportunity as for £29 you can't really lose. I will be eagerly awaiting your tweak results."

I'll deliver the goods fast! keep an eye on http://freespace.virgin.net/rock.grotto/index2.htm as you say "£29 you can't really lose"

"BTW might want to move this thread to the DIY forum or the amp forum as it fits those better than being in cables, etc forum and would get more exposure to those looking for a cheap DIY amp."

I'm happy here and really aint looking for "exposure" I'd prefer to keep this between you and me if you don't mind!

"Would love to know how the finish B-tech modded amp would sound against a meta 42? Though a meta is said to be better than a Creek OBH 11 so it might be a bit of the meta's performance."

Will keep you posted for sure.

All the best.

Pinkie.

 

[PinkFloyd]

The pictures of the PCB's on my website are to scale (actual size) and will give you an idea what you can fit in. http://freespace.vi....grotto/B-tech.htm

Further to yesterdays capacitor upgrade I've ordered the following:

1 x OPA 2134 PA Burr Brown RS part number: 285-8069 £2.03
10 x 47R 0.5W metal film resistors RS: 149-638 £0.50
10 x 10K 0.5W Metal film resistors RS: 149-818 £0.50
10 x 2K2 0.5W Metal film resistors RS: 149-739 £0.50
10 x 100K 0.5W Metal film resistors RS: 149-925 £0.50
Total: £4.03

These should arrive tomorrow and I'll fit them, take pictures and upload to my website tomorrow evening sometime. I took a chance on the 0.5W resistors but maybe should have gone for 0.125W or 0.4W varieties... anybody got any comments on this, will the 0.5W values be ok?

All the best.

Pinkie