HE-569 pre/eq 500 series

[Whoops]

Thanks for explaining Cyril

 

[pahstah]

HI,

sorry for disappearing I was involved in another project.

To summarize ehatm is going on with this project, I have changed the layout completely and went for SMD, Cyril Jones transformer is fantastic! everything seemed fine and I thought this would be the final version but alas I now have problem with the 24v volt dc/dc regulator (worked fine in previous version) and after 7 revisions I am a bit tired of the project. I'm not perfectionist at all but I don't want deliver a malfunctioning product that's why I stopped update the project here on the forum, sorry for that but I was feeling really frustrated.
However I think I'm gonna resume the project with a new version. version 8.

Paolo

 

[TwentyTrees]

Welcome back Paolo! Everyone burns out on projects sometimes, don't worry at all about that - just glad to hear you're ok. Hope your other project was a success.

 

[pahstah]

Welcome back Paolo! Everyone burns out on projects sometimes, don't worry at all about that - just glad to hear you're ok. Hope your other project was a success.

Thank you! my other project was a success, more info here:API 1608 expander micro | Realgearonline

 

[Strat96]

Early Helios channels used the 2180 pre-amp,, followed by the switched passive bass filter which requires a high impedance follower, the EQ section requires a low impedance drive., the voltage follower provides both. Later modules incorporated the VF on large circuit boards using a 16 way connector. I have reduced to this design and thus lessen the cramped nature of components behind the front panel.
Here is a plea, for those constructing the early modules please use a small relay adjacent to the input transformer to change the microphone phase or move the phase switch to the top of the module. The module could be more stable at high gains if the microphone input cables and switching remain at the top of the channel away from high level signal levels..
Cyril

Hey Cyril,

Good to see you on here. I have some questions relating to the information you provided.

First question: I am incorporating the 0-40-80 bass filter on all my modules. You mention High and Low Impedance between different stages. Could you please give a little more information on that or clarify what kind of input or output these stages are looking for.

For example, my modules are utilizing 15C1 and the smaller 2128 cards. Those are 10K impedance correct? There are 10K resistors shunted on the back of the card at the output to ground. Would that be considered a High Impedance?

Second question is regarding the phase-reversal switch location and noise. On the old Helios modules, the transformer is at the bottom, closest to the phase switch, but furthest from the input selector switch. The switch would be adjacent but there is a longer line of cabling to the selector switch from transformer output and line input. Is that sufficient or should the output of the transformer and the line input leads be shielded or another solution? Also do you recommend twisted pair the transformer wires to switch, and from switch to the multi-connector.

Thanks

 

[InterstellarObscure]

I have a 2128 card and a 22113 card that both have a buffer circuit section added on. The same 1-transistor circuit is used on both cards. I’ve never known what the buffer was for precisely or why it’s only added on to certain preamp/post-eq cards And not others.

Could two of these circuits be used in Helios modules with Bass Filter? I wonder why it’s added onto both types of cards.

I also have another 16-pin Helios card, card 1447, with 2 separate 1-transistor buffers on the same card. The circuit is a little different than the 2128/22113 add-on.

 

[pahstah]

I think those buffers were used for HPF or Phase duties

 

[Winston OBoogie]

Paolo,
My post is in the wrong thread but I see you active here quite recently so...
Great job on Helios, much respect

I think you and I share similar passions regarding audio gear.
I have a proposition for you regarding Sound Techniques A range and getting you schematic info. I am bowing out of the group here but email me [email protected]
I'm busy now but I will help if I can, for you, the community or even just for future historians such as myself to get a schematic of ST A range into the world.
Later my friend,
John.

 

[oldskool1]

Paolo, that work you did on the mixer was amazing. did you ever get back to this Helios project?