RUSSIAN GT308 BASS BOOSTER

[Renegadrian]

I saw this schem in the gallery and have some 308 in my bin, so guess I'd give it a try - maybe the rain made me dumb, what's that 4700 cap?! 4700pF (4.7n)?!

[DDD]

4700 = 4,7 n
The device is designed to produce a "click" at the attack portion of the bass guitar signal. Such a sound was widely used by the Soviet bass players in 1970-1980 years.
GT308 was chosen for it's good noise figures, nothing more.

[Renegadrian]

Dmitry, thx for your reply - care to explain better what you wrote about the "click"? Maybe you can post some youtube links so I can understand better what can I expect from this schematic...Thx again! 

[DDD]

Hi Adriano,
The circuit emphasizes the hi-frequency part of bass attack and makes the attack tight and bright. At the same time the low frequencies are cut off significantly hence you'll get the poor audible sustain of your bass.
I have to say the effect is pretty rare today, but the creative person can get some juice from it. The circuit is simple, so try it and you'll have some fun for sure.
The author mentioned Russian KT342A BJT (npn silicon, hfe up to 180) as a good candidate instead of GT308 if you don't want to have you power supply or battery to be "+" grounded. So you can use Philips BC548A-550A BJT.
Or, if you like Ge trannies, use GT308.
Pls note: this is linear device, so it will probably sound unpleasant if overdriven. But, who knows... ;-)
   

[Renegadrian]

Right, I made a vero layout to try it out - As soon it's verified I'll post it here - thanks again for your input! 

[svstee]

Hi Adriano,
The circuit emphasizes the hi-frequency part of bass attack and makes the attack tight and bright. At the same time the low frequencies are cut off significantly hence you'll get the poor audible sustain of your bass.
I have to say the effect is pretty rare today, but the creative person can get some juice from it. The circuit is simple, so try it and you'll have some fun for sure.
The author mentioned Russian KT342A BJT (npn silicon, hfe up to 180) as a good candidate instead of GT308 if you don't want to have you power supply or battery to be "+" grounded. So you can use Philips BC548A-550A BJT.
Or, if you like Ge trannies, use GT308.
Pls note: this is linear device, so it will probably sound unpleasant if overdriven. But, who knows... ;-)
   

That sounds really useful. I bet a decent player could use those dynamics to play a style like string bass with a different sound...

Looking forward to the vero! Any ideas where I could pick up a GT308? Already checked Ebay.

[DDD]

Why only GT308? 
You can use another low-power Ge transistor with hfe from 80 to 120 or more. Low-noise one is preferrable.
Or the silicon tranny as it described earlier in this topic.

[svstee]

Well, Ive had a lot of fun with GT313 transistors, and I have to keep the Russian mojo! 

[Renegadrian]

Right, this is the Layout I made for that bass booster...It is verified, I mean it works, but it doesn't work in a good way...It gives a poor trebly sound a lot below unity gain! It uses positive ground, I tried it with both gt308 and ac128. (keep in mind you have to twist gt308's legs to get it working, as it is BCE)

Dunno if I got something wrong, but I told ya the sound is coming out, but no good boosting I have...Sad me...

Sean, maybe you can check if my layout is correct!!!

[DDD]

Adriano,
it seems there's something wrong. The circuit should amplify but not attenuate the input signal.
I've asked Russian DIY community to help if anyone have some experience with the circuit.
So, pls be patient and wait a little bit.

[Spiteful]

 Layout seems right. Is transistor mounted right (dot on emitter)?
Cascade can be wrong biased... so what voltage is on collector?

[Renegadrian]

Yeah, tranny orientation is correct - it's EBC as you go down.
No way to track voltages, I dismantled it atm...

[svstee]

I compared the schem and the vero, no problems that I can see.   

[DDD]

Hi guys,
there are some news:
1. The schematic is right as well as the components' values. You can find the original schematic at
http://dvtube.w6.ru/schematic/OLD_BASS_BUST.jpg
2. As per original description (translation from the Russian book):
- frequencies from 30 to 100 Hz: approx. unity gain
- 200 to 600 Hz: attenuation
- 1500 Hz: hump
3. My software simulation results (with Si pnp BJT, hfe=120):
- 10 Hz: +2dB
- 63 Hz: 0 dB
- 100 Hz: -1,6 dB
- 200 Hz: -8,5 dB
- 350 Hz: -25 dB (notch)
- 500 Hz: -14 dB
- 1000 Hz: -6 dB
- 1500 Hz: -3,5 dB
- 3000 Hz: -1,5 dB
4. As you can see, the circuit behaves strictly as described and does what it is intended for. So, I guess there's something wrong with the Ge BJT since they are too sensitive to reverse voltage.
5. Here you can see Russian Ge BJT datasheet (GT308 and others):  http://lampilich.narod.ru/tr/small/gt308.html

[DDD]

I have to say the circuit handles up to 4V peak-to-peak input signal with Si BJT (my software simulator results) and clips asymmetrically at 2,2 Volts and higher.

[Renegadrian]

Dunno Dmitriy, I tried different 308s (got 3) and 128s (got 6) and I know they are quite good, and work well in the typical positive voltage configuration...

[DDD]

Some more info from the responsive Russian DIY guys:
1. Sound clip (actually a film soundtack, regretfully record quality is pretty poor):  http://www.youtube.com/watch?v=AMq7unC4vNk
2. They say the circuit works well, but with some audible loudness drop since a part of frequency range is attenuated. But the volume drop is not so considerable, it's not a problem at all.

[birt]

interesting sound

[wavley]

It's a Tic Tac bass!! Much cheaper than buying Danelectro Longhorn or Fender Bass VI.

[Nasse]

I did it on that vero layout, thanks, think it works now. Soldered it in low light and had few solder bridges so it took some time debuggin it, multimeter is your friend, socketed the transistor and fond some funny readings in the ohm setting between power terminals, and transistor socket pins. I used unselected AC128 straight from plastic bag. No bypass switch and tested with my shortscale bass with old flatwounds and crappy guitar practice amp and my precision copy is with the neighbour kid so not much to say about the sound but I think it does what is says in the plan

Have not boxed it, but I give it away anyway, another young bassplayer reaches 18 years today.

I think I do another for myself