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Old 18th October 2004, 02:30 PM   #1
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Default Calling Brian GT - Hybrid boards?

Brian,
I am not neccessarily a noobie, but have had tons of problems getting a TBIGC done right. I think the tube section along with grounding for three transformers are giving me the biggest headaches. Have you thought of doing boards for a hybrid. I know I would be very interested?

Thanks for any comments, Regards ...Lee
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Old 18th October 2004, 02:33 PM   #2
BrianGT is offline BrianGT  United States
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Default Re: Calling Brian GT - Hybrid boards?

Quote:
Originally posted by king30
Brian,
I am not neccessarily a noobie, but have had tons of problems getting a TBIGC done right. I think the tube section along with grounding for three transformers are giving me the biggest headaches. Have you thought of doing boards for a hybrid. I know I would be very interested?

Thanks for any comments, Regards ...Lee
Sounds interesting. What schematic are you using for it? Is it LM3886?

--
Brian
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Old 18th October 2004, 02:48 PM   #3
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Default Welcome to the ground loop club.

Quote:
the tube section along with grounding for three transformers are giving me the biggest headaches
Welcome to the VBIGC LM 3886 ground loop club.
Apart from making them moboblocks with separate tube stage and supply , I've been going crazy trying to solve the ground loop issues. It's possible that I'm missing the crucial simple solution because I'm looking too hard. The usual trouble shooting problem!
It is'nt desperately bad but it burns me up to see power supply charging spikes on the supply. Not to mention the strange reaction from the amp when you tap the speaker cone ! Did you try that ?
Cheers,
Ashok.
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Old 18th October 2004, 02:51 PM   #4
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While most of VBIGC here are based on Joe Rasmussen idea, and since he incorporates that in his commercial product, I don't think it would be appropriate to come up with such a board.

However, there is another proposition for VBIGC from Kuei, and he posted it here: http://ampchipdiy.com/phpBB2/viewtopic.php?t=85

Now, that is something I wouldn't mind to try
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Old 18th October 2004, 02:59 PM   #5
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I liked Joe's schematic due to the low voltages required for the 6922 tube. I will shoot him an email to see if he would mind.
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Old 18th October 2004, 03:05 PM   #6
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Default The feedback issue..............

Hi Peter,
Better you simulate such a circuit before trying it out. Also use an electrical speaker equivalent instead of a fixed resistor.
While the first loop is fine , the second one at the 1 ohm resistor will see a frequency dependant signal. So when the speaker impedance rises at HF it will have less fedback and thus have a rising HF response. As the speaker itself has been designed for a voltage source , it will cause a rise in the frequency response. It will also vary with speaker and crossover types.
Pandoras box ?

I tried the tube circuit with usual anode output , but could not hear any marked difference compared to a voltage follower. There may have been some difference , but it isn't too obvious.
Cheers,
Ashok.

King 30 : --- be careful with the 6922 in a real world circuit and low voltages . I have had problems with Electro Harmonix 6922 at +/- 35 volts. The Sovtek 6DJ8 worked better . Additionally the tubes supposedly can work at higher current at low voltage. I couldn't get that to happen. They worked only at 1 mA . I was told they should work at at least 5 mA. So a practical test is required. Simulation also works at 5mA but not the real tube.
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Old 18th October 2004, 04:13 PM   #7
r!sc! is offline r!sc!  Serbia
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Default Re: Calling Brian GT - Hybrid boards?

Quote:
Originally posted by king30

I know I would be very interested?


Me too


Boban
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Old 18th October 2004, 04:49 PM   #8
Nuuk is offline Nuuk  United Kingdom
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I don't know if it was 'beginners luck' but I have no hum problems with my VBIGC.

However, as good as it sounds, I have found a big improvement in using Pedja's Jfet buffer with an IGC. remember, Joe's design was a 'get you going' design that he kindly donated to the DIY crowd, and never intended to be the last word in Gainclones.
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Old 18th October 2004, 08:04 PM   #9
moamps is offline moamps  Croatia
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Quote:
Originally posted by Peter Daniel
While most of VBIGC here are based on Joe Rasmussen idea, and since he incorporates that in his commercial product, I don't think it would be appropriate to come up with such a board.
Hi,
I first saw this idea (buffer+GC) here
http://www.diyzone.net/diy/references/tube/

Regards,
Milan
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