Low noise, high voltage input trannies...

Shaun Onverwacht · 26th March 2001, 04:41 PM

Hi

This is my first post. I've designed and built an amplifier based around Douglas Self's "Load Invariant" amplifier. My problem is that it is (relatively) very noisy! I wonder if anyone can suggest high voltage, low noise input transistors. I'm currently using MPSA42/92. The supply rails are 62V.

I must say that this amp is very beefy, and quite easily drives the 3ohm voice coils of my 12" Earthquake Magma sub. It also sounded very good with my first speaker project... miles better than with my Elektor Mini Crescendo.

mlloyd1 · 26th March 2001, 05:10 PM

Shaun:

Congrats on the project and your first post!

Look at these devices: PNP -> 2SA872 or 2SA872A, NPN -> 2SC1775 or 2SC1775A. For PDF datasheet, go here:
http://semiconductor.hitachi.com/2s.html
Look for the part numbers. The "A" suffix means 120V breakdown, instead of 90V.

Good general purpose, high gain, low noise. Available cheaply at most parts houses that stock Japanese semiconductors (e.g. Dalbani, etc.).

These are small signal (less than 20mA Ic) devices

I've used 'em for YEARS. They work well.

Lower on the choice totem pole (to me anyways - lower gain, lower breakdown voltage, lower fT, etc.) are the ON Semiconductor (was Motorola) MPS8099 and MPS8599. One is PNP the other is NPN; I don't remember which. Data at the ON Semi web site.

By the way, are you sure your noise isn't due to some non-audible high frequency oscillations?

Michael

Shaun Onverwacht · 27th March 2001, 03:46 PM

I can't confidently state that it's not caused by hf oscillation. I've scoped it, and the signal looked free from oscillations. However, I must concede that development is not complete. I have a friend who has some distortion measuring equipment, and he is building up a pair of the modules for evaluation.

Thanks for your help.

rborer · 7th May 2001, 09:25 PM

Would anybody happen to have the Spice models for these Hitachi devices (2SA872/A, 2SC1775/A)?

RBorer

mlloyd1 · 8th May 2001, 07:45 PM

Just for grins, I did a quick search via http://www.google.com for "spice model for 2SA872"
The only hit was here: http://www.labcenter.co.uk/index.html?/support/
Maybe you can download one of the trial programs and find the models in the libraries?

If you found them elsewhere, I'd like to know. I'd like the models myself :-)

Michael

Hoffmeyer · 9th May 2001, 05:36 AM

Hi fellas.
send me a mail at hoffmeyer@aub.dk , and I'll send You the Spice models this afternoon.
They are part of the japaneese bipolar library from Orcad Pspice.

26th March 2001, 04:41 PM	#1
Shaun Onverwacht diyAudio Member Join Date: Mar 2001 Location: Cape Town, South Africa	Hi This is my first post. I've designed and built an amplifier based around Douglas Self's "Load Invariant" amplifier. My problem is that it is (relatively) very noisy! I wonder if anyone can suggest high voltage, low noise input transistors. I'm currently using MPSA42/92. The supply rails are 62V. I must say that this amp is very beefy, and quite easily drives the 3ohm voice coils of my 12" Earthquake Magma sub. It also sounded very good with my first speaker project... miles better than with my Elektor Mini Crescendo. __________________ shon

27th March 2001, 03:46 PM	#3
Shaun Onverwacht diyAudio Member Join Date: Mar 2001 Location: Cape Town, South Africa	I can't confidently state that it's not caused by hf oscillation. I've scoped it, and the signal looked free from oscillations. However, I must concede that development is not complete. I have a friend who has some distortion measuring equipment, and he is building up a pair of the modules for evaluation. Thanks for your help. __________________ shon

9th May 2001, 05:36 AM	#6
Hoffmeyer diyAudio Member Join Date: Dec 2000 Location: Önnarp, Söderslätt	Hi fellas. send me a mail at hoffmeyer@aub.dk , and I'll send You the Spice models this afternoon. They are part of the japaneese bipolar library from Orcad Pspice. __________________ Regards Hoffmeyer ;0)

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
High(er)-voltage, low noise v-reg?	Khron	Power Supplies	9	12th November 2012 02:28 PM
high voltage input opamp	sunrise	Chip Amps	7	9th April 2007 06:54 PM
6BY5 High Voltage & High Current Choke Input Design P.S.	snoopyma	Tubes / Valves	7	28th June 2006 01:32 PM
How can I calculate input noise voltage and current?	thanh	Solid State	0	8th July 2004 04:34 AM
Choke-Input: How do I calculate the right snubber for high-current-low-voltage	Blitz	Solid State	20	24th March 2004 08:37 PM


	Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving

26th March 2001, 05:10 PM	#2
mlloyd1 diyAudio Member Join Date: Feb 2001 Location: illinois	Shaun: Congrats on the project and your first post! Look at these devices: PNP -> 2SA872 or 2SA872A, NPN -> 2SC1775 or 2SC1775A. For PDF datasheet, go here: http://semiconductor.hitachi.com/2s.html Look for the part numbers. The "A" suffix means 120V breakdown, instead of 90V. Good general purpose, high gain, low noise. Available cheaply at most parts houses that stock Japanese semiconductors (e.g. Dalbani, etc.). These are small signal (less than 20mA Ic) devices I've used 'em for YEARS. They work well. Lower on the choice totem pole (to me anyways - lower gain, lower breakdown voltage, lower fT, etc.) are the ON Semiconductor (was Motorola) MPS8099 and MPS8599. One is PNP the other is NPN; I don't remember which. Data at the ON Semi web site. By the way, are you sure your noise isn't due to some non-audible high frequency oscillations? Michael

7th May 2001, 09:25 PM	#4
rborer diyAudio Member Join Date: May 2001 Location: São Paulo, Brazil	Would anybody happen to have the Spice models for these Hitachi devices (2SA872/A, 2SC1775/A)? RBorer

8th May 2001, 07:45 PM	#5
mlloyd1 diyAudio Member Join Date: Feb 2001 Location: illinois	Just for grins, I did a quick search via http://www.google.com for "spice model for 2SA872" The only hit was here: http://www.labcenter.co.uk/index.html?/support/ Maybe you can download one of the trial programs and find the models in the libraries? If you found them elsewhere, I'd like to know. I'd like the models myself :-) Michael

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read