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Mikael Abdellah 27th July 2006 11:41 AM

Hybrid bass/guitar preamp
I decided it was time to leave Zafira's thread alone. I aplogize for the massive hijacking.

My preamp now consist of a tube gain stage with a Svetlana 6N1P, wich will probably be connected to my BUF634 buffer through a potentiometer so I can set the level into the buffer. A little addition I thought up yesterday is a vu meter. I will use 3 pcs of LM3915. Since my preamp will be capable of fairly large output voltages I would like a way to:

1. Find a normal 0dB point
2. Know when I have overdriven the buffer into clip level

Do you think I should use 2 different meters or can I find a way to combine everything in one 30 led array? What should I use as 0 dB if i want it to be compatible with other gear?

Mikael Abdellah 29th July 2006 08:37 AM

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I have finished my eagle schematics. Im still not sure about the values for P1 and P2, escpecially P2. I have run some tests where I had a 100k pot insted of 500k and I cant notice any difference. The cap banks C3 and C4 is made up of small tantalum bypassed by ceramic and will be placed VERY close to the buffer. Please let me know what you think.

Mikael Abdellah 29th July 2006 11:58 AM

Is there any advantages with a B+ of 400VDC instead of 250VDC? Im fiddling around with duncan psu designer. Im going to order mains transformer and one or maybe two chokes soon. When it comes to the chokes... is it better with a higher inductance rating?? I have measured the current and its only 3.04mA so I have been looking at a 20H hammond choke that is very cheap.

Mikael Abdellah 12th August 2006 04:47 PM

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I have been modelling a few different HV PSU's for the tube and I think I have come up with something really good. The ripple is EXTREMELY low in simulation at least. Are there any drawbacks with this kind of PSU design?

Mikael Abdellah 13th August 2006 09:15 AM

Ok, I really need your opinion on something now. On the pcb I only have room for one cap immidiately next to the power supply legs of the BUF634. Should I go with tantalum or ceramic?

Mikael Abdellah 13th August 2006 07:52 PM

maybe this thread should be moved to solid state instead. could a moderator please help me with that?

SY 14th August 2006 01:27 PM

Moved, with a redirect left behind, just in case.

Mikael Abdellah 19th August 2006 05:50 PM

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Today I have finished the CRCRCRCRC-filter PCB and I have tried it with my new Hammond 260A transformer. My voltmeter changes between 249 and 250 VDC so I am very pleased with the result. I have not made any ripple measurements but I think it should be somewhere near what I have simulated since everything else seem to match.

I have also soldered a few caps to my big PCB that will contain my buffer stage and VU meter complete with rectifiers and voltage regulators and all.

Mikael Abdellah 19th August 2006 05:52 PM

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The picture quality is rather poor since I took them with my cell phone. I will try to get better pictures later.

Mikael Abdellah 15th February 2007 05:06 PM

Project progress
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I have just started to drill holes and such in the chassis. Here is a little pic of the work so far. I will probably have two large knobs for input and outout level on the sloped face plate, and the input connector on the front part of the chassis. The idea is to have a 20 LED vu meter in the middle of the face plate.

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