BC550C Balanced Pre

Alcaid · 13th November 2005, 01:43 PM

Hi,
What do you think about this preamp? Do I need to add a output stage with more current capacity, or will this do as a preamp? I was thinking of using it as an ubalanced to balanced preamp. Please give comments. It's a differential pair with CCS. Power ground is seperated from signal ground through a low value resistor.

AndrewT · 13th November 2005, 08:36 PM

Hi,
you have posted two single ended single transistor common emitter amps.
I think you will find problems setting the DC level and holding it. There appears to be no gain setting for either AC or DC. Have you thought about frequency response anomalies?

I think you would be better off looking at the various (many) discrete opamps around the web. Most of them could be adapted to balanced in/out.

Alcaid · 13th November 2005, 09:22 PM

Thank you for responding.
The DC is taken care of by the output caps, and the circuit does have AC voltage gain. I just want to build a unbalanced to balanced preamp because all my sources are unbalanced, and I want to build a balanced power amp. Any good sounding DIY designs you (or other) could recommend? BOSOZ may be a good candidate...

mod_evil · 13th November 2005, 11:18 PM

Can you send the complete schematic with the values of the components?

I realy like this design!

Thanks in advance.

Felipe Navarro.

AndrewT · 14th November 2005, 08:26 AM

Hi,

Quote:

There appears to be no gain setting for either AC or DC.

I did not say there was no AC gain.
Where is the control for your AC and DC gain? or is it completely dependant on hFE (Hfe) of the device?

Christer · 14th November 2005, 09:38 AM

The resistor between the emitters controls the gain, toghether with the collector resistors. However, I would suggest the more traditional diff pair topology, with one CCS and two emitter resistors, because now you must match the two CCSs, which is more work than to just match two emitter resistors. Of course, the BJTs in the diff pair must be matched in both cases.

Alcaid · 14th November 2005, 02:17 PM

Was afraid of having to match the CCS.

Maybe the BOSOZ with a CCS is a better solution?

Christer · 14th November 2005, 02:30 PM

But why use two in the first place? Split R1 into two resistors with half the value and use one CCS with twice the current.

Alcaid · 14th November 2005, 02:41 PM

The reason for two was symmetry and lower temperatures in the transistors.

13th November 2005, 08:36 PM	#2
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Hi, you have posted two single ended single transistor common emitter amps. I think you will find problems setting the DC level and holding it. There appears to be no gain setting for either AC or DC. Have you thought about frequency response anomalies? I think you would be better off looking at the various (many) discrete opamps around the web. Most of them could be adapted to balanced in/out. __________________ regards Andrew T.

13th November 2005, 11:18 PM	#4
mod_evil diyAudio Member Join Date: Dec 2004 Location: Rio	Can you send the complete schematic with the values of the components? I realy like this design! Thanks in advance. Felipe Navarro. __________________ Brazilian Tube Amp Builder.

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13th November 2005, 09:22 PM	#3
Alcaid diyAudio Member Join Date: Nov 2003 Location: Klepp	Thank you for responding. The DC is taken care of by the output caps, and the circuit does have AC voltage gain. I just want to build a unbalanced to balanced preamp because all my sources are unbalanced, and I want to build a balanced power amp. Any good sounding DIY designs you (or other) could recommend? BOSOZ may be a good candidate...

14th November 2005, 09:38 AM	#6
Christer diyAudio Member Join Date: Sep 2002 Location: Sweden	The resistor between the emitters controls the gain, toghether with the collector resistors. However, I would suggest the more traditional diff pair topology, with one CCS and two emitter resistors, because now you must match the two CCSs, which is more work than to just match two emitter resistors. Of course, the BJTs in the diff pair must be matched in both cases.

14th November 2005, 02:17 PM	#7
Alcaid diyAudio Member Join Date: Nov 2003 Location: Klepp	Was afraid of having to match the CCS. Maybe the BOSOZ with a CCS is a better solution?

14th November 2005, 02:30 PM	#8
Christer diyAudio Member Join Date: Sep 2002 Location: Sweden	But why use two in the first place? Split R1 into two resistors with half the value and use one CCS with twice the current.

14th November 2005, 02:41 PM	#9
Alcaid diyAudio Member Join Date: Nov 2003 Location: Klepp	The reason for two was symmetry and lower temperatures in the transistors.

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