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 NEW  Bruce Heran outlines the details and construction of his simple DIY 6DJ8 (ECC88) Tube Hi-Fi Headphone Amplifier Project.

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PostPosted: 06 Jun 2015, 06:18 
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Location: Athens-Greece
Dear friends

1. I was wondered if there is a drawing where I could combine an analogue mixer (stereo CD + universal preamp 4S input, mm cartridge turntable and pre-amp, ipod and tone control + 4S, AND MIC

This device should have a mic-preamp integrated, whilst all other equipment will be connected with their pre-amps in line.

The output of such device should be either for my tube amp : 6SN7-300B SE

or a proper one (maybe earphone output) , capable to drive and RF FM transmitter with 5763 tube at first stage

Is there something like this available or could it be designed ? Is it possible to combine different circuits?

Of course I am interested on using TUBES ONLY otherwise there are available mixers in the market. It looks a promising project

2. I have seen various pre-amps in DYI site, however, I could not find a device that could contain everything, eg MM-MC, ipod, CD, mic with proper selector and a number of output, either for amp or earphone, or RF transmitter input. It would not be a mixer but an interesting equipment for my "tubes family" . Any ideas on this?

Thanks in advance
Dimitris


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PostPosted: 07 Jun 2015, 11:53 
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There is a lot in your post but it is still not clear exactly for what you are asking. You have asked for a mixer but also want an integrated microphone preamp, an integrated phono preamp, a 4S preamp, a tone stack, and a headphone driver. What you are describing is a substantial piece of equipment. There is always a decision to be made when building equipment about how much will be integrated together. Each element added to a project brings with it challenges to system performance, physical size, layout, and construction. But with such a complex project, you will want to be very clear about what it is you want to build.

My suggestion is you start with a listing of exactly what it is you want to do with this equipment. Is it a preamp for music listening in your home? Is it a mixer to be used for DJ or broadcast work? Is it portable audio gear or will it fit on it's own shelf in a dedicated audio room? Then you need to list all the inputs and outputs that you require. Will you be driving a single amp or multiple amps? Will you be driving a monitor system (headphone, speaker, or both)? Answering all these questions will help you formalize exactly what you want.

I then suggest you draw a simple block diagram of what you think you need. Include in the diagram all the various audio blocks and all the various signal paths with which you'll be dealing. Once this diagram is complete, then you can begin to ask questions about the project you propose and it will be easier for people to post concise and helpful answers to your questions.

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PostPosted: 07 Jun 2015, 16:21 
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Joined: 25 Jan 2015, 11:51
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Don't despair Dimitris :)
I am pondering / dreaming of the same kind of monster to build.
I only would not put one tone-stack but a stack of tone-stacks like Fender, Marshall, Baxandall, James, Vox and others in a impressive array together with a nice double-deck switch to choose what stack will be used today.

Matt is right, as always.

Make things modular; all the separate stages like Phono, Microphone, guitar, Ipod/Android, Aux are projects on their own.
I am thinking about 2 mono-blocks that can be used for stereo hifi purposes together but also as a Microphone / Guitar amp, or a Guitar / Guitar amp, or whatever combination you need at the moment.
That is where the stack of tone-stacks comes in handy...
The power supply can be built 10 times; one for every module or you can invest in one big over-dimensioned PSU, capable of delivering different plate- and grid-voltages as well as filament current at 5V and 6.3V.
It will be a project in it-selves because you don't want the overall voltage to drop because the person on the left makes his guitar scream a little.

Yes,
It is nice dreaming of designing and building things like that.
I agree.

Mathieu


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PostPosted: 08 Jun 2015, 19:49 
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Joined: 01 Feb 2015, 13:41
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Location: Athens-Greece
Thanks for your comments. I attach herewith the diagram. A complex power supply is required but this is a nice challenge against humming etc.
Mixer is optional. What do you think? I could combine 4S with tone control, with oddwatt, adding tone control and volume control to this, plus mic pre amp and earphones section.
What do you think, any idea?


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PostPosted: 13 Jun 2015, 05:21 
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Joined: 25 Jan 2015, 11:51
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If I were an electron, i would instantly become agoraphobic looking at your block-diagram Dimitris.
After watching it for more then an hour i begin to see some structure there.

Why are there 2 times a block of Tone control ?

Mathieu


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PostPosted: 13 Jun 2015, 06:14 
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Joined: 01 Feb 2015, 13:41
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Location: Athens-Greece
Thanks Mathieu. The point is that so far I have followed a pre-amp drawing for CD/input from Matt that works quite well. This has a tone control incorporated in the circuit. Now, I am thinking to place in the same chassis a MM-phono pre-amp as submitted by Bruce (oddwatt) which is another circuit using 5 tubes. So I am not sure where to place the tone control and if could be a common one for both circuits without affecting their performance. You see, the initial version of 4S preamp uses one tube, and is fine with me, but the updated one with tone control uses two tubes (ref to other posts). Now, the question is,
if I use
the initial 4S pre-amp with one tube
and the MM-phono oddwatt circuit (that has no volume control)
could I have a common tone control at the output preserving good performance?

Last, I have another question; Bruce uses in his circuits 200VAC as the PT secondary. I have a good toroidal transformer 190-0-190 with adequate mAmps. Could I used It in order to have one transformer for both 4S and oddwatt?

Thanks to everybody


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PostPosted: 13 Jun 2015, 10:03 
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dimitris1811 wrote:
So I am not sure where to place the tone control and if could be a common one for both circuits without affecting their performance.
In this whole effort it is important to keep functional purposes in mind. Although we call both Bruce's Odd-watt circuit and the 4S "preamps" they actually have very different functions. The purpose of the 4S is as a traditional line preamp. This is to adjust line level signals for long capacitive lines, pad loss, equalization loss, and for driving low sensitivity equipment. Bruce's phono Odd-watt has the very specific purpose of matching the characteristics of the MM phono cartridge to a line level specification and to apply the correct RIAA normalization curve. These are very different functions.

There should be NOTHING between the Odd-watt phono preamp and the turntable output. No volume controls, no pads, and no tone correction circuits. The output of the Odd-watt is a proper line level signal. This signal should be considered in the exact same manner as the input from a CD player, tuner, or other line level output device. The Odd-watt will also be the most sensitive circuit in the unit so it will drive your requirements for shielding and filtering.

It looks like what you really want is 1) an Odd-watt phono preamp to get the phono signal to line level, 2) two tone control preamps (one for the phono and one for the CD/AUX input), 3) an integrated microphone preamp for a microphone (requirements TBD), 4) a line level three position selector, 5) three line level buffers to drive an off-board mixer, and 6) a headphone monitor amp. You can do this all in one chassis but it will be a very challenging build to get to operate properly. There will be MANY opportunities for hum, noise, and cross talk.

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Matt
It's all about the Glass!
http://www.CascadeTubes.com
Cascade Tubes Blog


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PostPosted: 13 Jun 2015, 12:58 
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Location: Arizona, USA
Hi, The 190-0-190 ought to be OK. The preamp needs about 225 on the final stage and about 10 volts less for each previous stage. The design is flexible enough to accommodate that without any changes. You encounter problems if you go much above the 225....say to 275-300. Then adjustments must be made to the cathode resistors and the voltage applied to the heater string from the B+ tap.

I have been following this thread for a while and my general comment is that this is a really ambitious project and unless it is undertaken with great care and planning by a skilled builder it will probably not achieve the desired level of performance. I hate to say it as I love tubes....but this would probably be a better solid state project with tube power amps to smooth out the sound. I would go for high performance ICs like the OPA2134 etc. It would be quieter, less prone to build problems and a lot less costly. Just my two cents.

Good listening
Bruce

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PostPosted: 13 Jun 2015, 13:42 
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Location: Athens-Greece
Matt if I understood welll do I need one 4s-tone control for cd input as I have now and one after oddwatt? I thought that oddwatt could be connected directly to my amp. If it is like this, can't I connect a selector switch to get input either from cd/ipod or oddwatt output?


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PostPosted: 13 Jun 2015, 13:50 
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Location: Athens-Greece
I think that I could handle humming since I use bigger chassis and first class material. My toroidal is capable to handle both circuits. Perhaps the EZ81 and 250 v could serve both circuits. If so in oddwatt i need to add the two blue lined boxes and the DC for the filaments. In 4S I will keep ac since it works well so far. With Big enough copper chassis I could place the tubes in order. Is it necessary to cover them with metallic sleaves? That destroys aesthetics I think. Bruce can I try having bigger distances with no sleaves?


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