DIY'ers...Improve my Helios

Er...you're already over my head

Guess that's the original...

i have no doubt svart could design/modify your HO to give you that head room, but with mods come changes in tone, the Helios character is very cool sounding with it's design and it's limitations.
 This is totally not like me, and I know this will come as a shock to you, but i suggest leaving it alone, they are what they are, and Amazing sounding at what they do, get the staging right, and move along, nothing to see here....

JMO 

Looks like this is the line amp cards in the schematic.. www.danalexanderaudio.com/OutboardPic/HeliosInputSchematic.jpg


And yes, that's NEGATIVE 24VDC.. 

So gain is managed by using C5 as an AC bypass through a variable external resistor.  This changes the AC gain while leaving the DC gain set.  It's pretty standard stuff, although I don't personally like doing gain like this.

I recall David Kean talking about modding and running the old modules at -36 instead of -24. That will not happen in a 500 series rack. John, you should message David on FB and invite him over. He is very knowledgeable on the vintage Helios stuff.

Up the rails to -30 or even -40 volts. Check the voltage ratings on the caps to be sure they can handle it. You may have to adjust a couple of resistors to match the current draw. Those transistors can also be replaced with low noise types like 2SA1084 PNP's and 2SC2545 NPN's. Use a scope to examine sine waves to determine if one stage clips before the other. Once you figure that gain staging out you can adjust the gain of each stage so clipping is evenly spread out.

Get an adjustable DC single ended power supply and test it all out. Installing sockets for the transistors will allow trying different types. Forget 500 supplies, this will be a custom job, if you want to expand the capabilities.

We do carry supply an update for the Standard Size T-69 using a small Piggy-Back PcB

but due to space on the 500 series T-69 its not been easy but I'm working on it John.
We are bringing out our own Rack that will take both the Standard Size Helios products
as well as the 500 gear, it will be much stronger as it will be in Flight Case Format.

Paul of Millbrook is having five made in NY for some of our US clients

.
Kind Regards 
Tony
Tony Arnold (Director) 
Helios Electronics Ltd 
&
Arny's Shack (Recording). 
Ampex UK (Sales, Parts & Service) 

Sorry John this is going to be a long reply but those suffering with insomnia might find it useful
But here Goes

First there are a few things to make note of:

We have sold well over 500 X the 500 Series Type-69 and only a handful of complaints about headroom problems
First there are a few things to make note of:

We have sold well over 500 X the 500 Series Type-69 and only a handful of complaints about headroom problems

The same applies to the Standard Size Helios Type-69, in fact even owners of the original Helios Consoles have sold their console as they have found our Helios Type-69 reissue quite satisfactory for their needs:
ie Ethan Johns, and two others who wish to remain anonymous.

But we do understand that many of our clients are used to using the Helios Type-69 and take all the precautions it demands, also in the original consoles they were used as a direct output, but in most cases they went via another Pre-amp before arriving at either the Final part of the Tracking busses or the Mix-Busses..

The reason you had a problem with yours is the same reason that Paul of Millbrook Studios NY (Knobtwiddler as he's know by GS)

It was discovered that to output pot was only 1k and the PSU was not sufficient, once that was rectified Paul ordered more & more Helios Type-69's he has over
16 now as well as two of our Helios F760's

After we completed the design of the Helios F760 one of the Helios Engineers involved, designed a small Pre-amp which was part of the Helios F760 Push-Pull output, we had 100 little PCB's made up and posted a couple of Type-69's to Paul with these tiny Push-Pull Pre-Amps piggy backed onto these two T-69's this was for Paul to compare, with his Standard Type Re-Issues

He felt that it changed the sound slightly and decided not to have his 16 Helios Type-69's updated with this adjustable up to 10dB Pre-Amp.
But
At the same time we posted one of our own Lunchboxes to Larry at Silvertone Mastering

LINK
www.gearslutz.com/board/high-end/745434-should-i-get-helios-69-mic-pre-eq.html

Note the line:
Tony also sent the Type 69 with the hotter output... what a great pre-amp

So this goes to show that "One mans meat is another mans Poison"
as Larry liked the Hotter output produced by our Piggy Back Pre-Amp. but Paul preferred not to use it.

The problem is, the 500 Series T-69 is so tight for space we can't see where we can Piggy-Back this tiny six Transistor Pre-Amp, but, what we can do is bring out an even smaller one exactly as the original Helios Line-Amp 15-C1, as used in the very early Helios Consoles, this only has three Transistors and also considering that there was never a complaint about a sound difference when the user of these consoles sometimes went direct from the T-69 Mic-Pre or whether the sound caught a bus to go via the 15-C1 Line-Amp.

When Richard & I first decided to bring out a Re-issue it was never intended to be used as a stand-alone unit, it was to upgrade the many Helios Consoles that only had 16 Channels and even some of the 24 Channels Consoles were being overstretched.

It also has to be considered that most engineers gear these days runs on a Duel PSU Rail, with a balanced DC of a Plus and minus Voltages which, can be from +12V & -12V up to as much as +18V & -18V both with an earth running as a centre rail. this in can greatly improve the Headroom up to as much as 36dB. where as discrete Pre-Amps run on a single rail and on a good day can only achieve max 18dB adding that added to the fact that the Helios Type-69 is totally passive and is only OVU output = .775mv instead of our moderne gear running at +4dB = 1.23V, furthermore the EQ being totally Passive, so with this in mind, one has to be very careful how they use the Helios Type-69.

So in order to help the those who find it difficult to manage the headroom we have now decided to Re-Issue the original 15-C1 Line-Amp, when we took over Helios Electronics Ltd we adopted over 200 of these little cards as either M.M.C. 1 or as the 15-C1 either can be used for a Line Amp, we have maybe just over
100 left for sale if anyone wants to experiment with these by fitting them in their racks.

The Push-Pull PCB is available F.O.C, to owners of the Standard Helios Type-69 reissue, but if they want the components to fit DIY then there is a small charge of $20 USD, if they would like them Populated or
(Stuffed which I understand is the US term) then they are $75 USD each

Kind Regards

Tony
Helios Electronics Ltd
&
Arny's Shack (Recording).
Ampex UK (Sales, Parts & Service)

Four original Helios Pre-Amps as used in their Lustraphone Type-69 but,
also used as a Buffer Amp or Line-Amp.


Here is our Variable up to + 10dB Piggy-Back Pre-Amp for boosting the output
of our Standard Helios Type-69, the lower one is unpopulated with components.


This picture show the size Differance and this being the case we may be able to
Piggy this onto the Type-69 x 500 Series

a