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Old 20th January 2009, 10:06 AM   #1
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Talking Looking for 6AQ5 audio preamp schematic!

Hi,
I'm new to this forum and only 17 years old. I'm just wondering if anyone has, or can write up a very SIMPLE audio amp schematic using a 6AQ5 tube for a preamp and 1 6CA7 for the power amp. and I mean really simple, im looking for 1 input 1 output, maybe a single pot for Gain.


I have at my dispossle:

1 breadboard.
many assorted wires.
2 6CA7 power tubes.
1 6AQ5 tube
Many assorted resistor's, capacitor's,
switch's and diodes.
1 speaker,
1 microphone.
1 1m pot
1 10k pot
1 100k pot
2 1/4 inch female plug's

Ill be using any and all safety precautions when building this, im just looking for the simplest design for a audio amp curcuit.

I want to start out with just a preamp first and get the curcuit operational before adding in the 6CA7 tube, As I've read a single 6CA7 can produce 11 watts which should be sufficent

Any help with this little project would be GREATLY apreciated!!

Thank You,
Weston
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Old 20th January 2009, 10:26 AM   #2
SY is offline SY  United States
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Do you have a power transformer and an output transformer? Those are generally the biggest-ticket items.
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Old 20th January 2009, 10:30 AM   #3
Stuey is offline Stuey  Australia
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Not sure how simple you want, but look at the Moebius for a preamp.
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Old 20th January 2009, 03:41 PM   #4
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You will need more 6AQ5's, but they can be had for a relatively low price. This is the Moebius that was suggested above.

http://www.audiotropic.net/Projects/...inePre6AQ5.gif

For more 6AQ5's check here:

http://www.surplussales.com/

I would check this tread out too since the 6AQ5 is more or less a 7-pin 6V6.

6V6 line preamp

As for the 6CA7's, may I suggest the Tubelab Simple SE. A simple design with a full PCB available and lots of support from DIY Audio, both from builders and from the designer himself. You would have to invest in a 12AT7 but they are fairly cheap. If you hit surplus and garage sales you can probably find some, I picked some up for $0.25 each not to long ago. The 12AT7 can also be bought new for around $7 to $10. The 5AR4 rectifier is optional as the board also has previsions for SS diodes, but a new stock 5AR4 would run about $10 to $15. The majority of the parts can be ordered from Digikey or Mouser and there is a full build manual with parts list on the Tubelab site. All in all, using Edcor output transformers (the $20 ones, don't let the price fool you, great transformers), this amp can be built for around $200. Check out Allied for the power iron and some of the parts as well. It is also very friendly to tube rolling, with some tweaks it can use just about any octal out there.

http://www.tubelab.com/SimpleSE.htm

Could also go the other way, pick up some more 6AQ5's, and build this:

http://homepage.mac.com/planet10/for...3jun06-map.gif

Great little amp that again would weigh in at around $200 mark, give or take, depends on what you already have.

Cheers

James
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Old 20th January 2009, 11:57 PM   #5
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The Moebius looks very inticing, I think I will go for that.
I've changed my plans for this little project, since I own and run a recording studio out of my home I think ill try and make just a preamp for the microphones, no power amp. which means I wont need the 6CA7's. Anyone know where I can get 4 mounts for the 4 6AQ5's?

Oh and before I go for 6AQ5's im wondering if I should go with better tube's? perhaps some 12AX7's? Any suggestions on better preamp tubes?

I'll also need this to have balanced inputs & outputs aswell.
How can I add in transformer balancing to the in's and outs on the moebius schematic? What transformers will I need?

And thank you for helping me out here, I appreciate it!
Weston
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Old 21st January 2009, 01:48 AM   #6
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Hi Lightning,
Is that your sail number?
Thanks, Victoria
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Old 21st January 2009, 02:14 AM   #7
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Default och the noo...

ummm, with all the little changes you suggest, suddenly you don't have a moebius any more... I think you need to more clearly define your design goals. Either this project is aimed at maximising the use of available parts, or you ar eprepared ot start from scratch. Either it is a pre- for a specific use (a microphone being substantially different to a CDP as a source) or its an integrated for pleasant noodling. Good luck - and welcome to the DIY toobies dillema!
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Old 21st January 2009, 04:11 AM   #8
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I don't know much about mic preamps so can't help you there. However if this will be used for mics I would shy away from the 6AQ5, Poinz (and I am sure others) found them to be microphonic in the Moeb preamp, now he is playing with 6T4's. If this will be used for home audio and you need balanced you could try something like this:

http://www.nutshellhifi.com/Raven-MarkII.gif

Transformers from Lundahl but Sowter also makes some specifically for this line amp.

Like I said, for mic I can't help much, but I can say you could look to Lundahl for mic iron too. Also Electra-Print, great iron and custom wound to whatever you need; Jack is a great guy too, just an added bonus. If you have 12AX7's great, but they are a "hot" tube so NOS prices are sky high. Luckily they are also still made by lots of tube companies. 12AT7's deserve a look, along with maybe 12AZ7's, 12AY7's, 6SL7's, EF86's, 6J7's...all medium high to high gain triodes and petodes. 6J7 for example was used for years by RCA in high gain low noise photo input sections on theater amps. The EF86 is kind of a continuation of this tube, different specs and 9-pin, but still low noise high gain. NOS EF86's command high price points, but are also still made today. (I may regret saying this, but it seems this tube is fairly undiscovered, or maybe disliked, IDK) NOS 6J7's can still be had on the cheap, the down side is a cap to deal with, but no worries, it is just a grid cap. I would go out on a limb and say that the 6J7's bests the popular 6SJ7.

Cheers

James
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Old 21st January 2009, 09:55 AM   #9
Stuey is offline Stuey  Australia
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Apex Jr has the seven pin sockets for only 0.35c.
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Old 22nd January 2009, 06:17 PM   #10
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Hi, Thanks for all the info everyone!

Victoria:

Sail number? huh?


aardvarkash10:

Well, my design goal did change I was just planning on tinkering iwth some tubes, but i figured if I can manage to build a preamp for $200, I would do that, since I need preamp's in my studio for recording and most preamp's that are 100% tube are anywhere from $500 to $7,000. The "Moebius" looked like a good schematic I just figured that I could add to it and make it have balanced in's and out's since that is a requirment since studios need 100% hum/noise-free conditions. I am more of starting fom scrap parts, I would like to find out what else I need and how much it would cost to build a modified Moebius.


JPeitzman:

Thanks for the heads up on the 6AQ5's, however the Raven is a bit more complex I dont think im skilled enough to build something like that. and im not sure about using different tubes in the "Moebius"? Not sure about compatibility. Like I said im new to this forum and am fairly new to tube circuit designs.
What would you suggest for a better audio qaulity tube that is compatible with the "Moebius"?


Stuey:
Thanks!

Thank you all for your help!
Weston
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