stay at home type 69 project

GroupDIY Audio Forum

Help Support GroupDIY Audio Forum:

dogears

Well-known member
Joined
Nov 15, 2017
Messages
507
Location
Texas
So I decided to do a stay home project, to ease some anxiety.  Helios type 69, with some guidance from Ian's brilliant project for the EQ.

Here’s a link to a folder with everything needed.

https://www.dropbox.com/sh/bubik24c260aji1/AADFpRVm4H_Oposg5k_VItb6a?dl=0
 

ruffrecords

Well-known member
GDIY Supporter
Joined
Nov 10, 2006
Messages
14,770
Location
Norfolk - UK
Couple of technical points.

The use of a tap on the secondary for the -20dB pad position on the mic input always was a dubious idea. Probably better to replace this with a balanced pad at the transformer input.

The gain make up amplifier has limited headroom. It is not really meant as an output amplifier. Probably better to replace it with the proper Helios line output amp.

The additional very high frequency selections in my design were not in the original. The Carhnill inductor used can give some odd out of band behaviour at these frequencies which are probably due to parasitics in the components. You might like to review the inclusion of these extra frequencies.

Cheers

Ian
 

dogears

Well-known member
Joined
Nov 15, 2017
Messages
507
Location
Texas
Thanks Ian!

I think I'm going to make a version with an 8 pin footprint for the input transformer.
 

Tubetec

Well-known member
Joined
Nov 18, 2015
Messages
4,168
I dont mean to be unkind or to dampen your spirit , but +1 on the thread name change. 
 

dogears

Well-known member
Joined
Nov 15, 2017
Messages
507
Location
Texas
I didn't mean it in any sense other than - something to do while I'm stuck at home. Sorry for any disturbance caused.
 

dogears

Well-known member
Joined
Nov 15, 2017
Messages
507
Location
Texas
I made a couple different versions if people would like to build.

One is true to the original schematic, with only minor changes, using the Sowter in 500 series.

The second is the same card but with molex connections to rack mount. Gives flexibility with input transformers if you want.

The third uses a "US-style" 8 pin input transformer (like a Cinemag CMMI10 or a Jensen 110K) with a switchable pad as Ian recommends, and uses a two transistor output buffer to up the output drive a bit.  Also 500 series.

All boms, gerbers, etc can be found in OP link.
 

ruffrecords

Well-known member
GDIY Supporter
Joined
Nov 10, 2006
Messages
14,770
Location
Norfolk - UK
Are you sure R55 is the correct value  at 6.2 ohms?. There is roughly one diode drop across it which according to my calculator is 100mA. Seems a little on the high side. Or have I missed something?

Cheers

Ian
 

dogears

Well-known member
Joined
Nov 15, 2017
Messages
507
Location
Texas
You know, that came from the buffer that was supposedly added to Lenny Kravits desk by Dave Amels...shared by Winston here:

https://groupdiy.com/index.php?topic=1222.msg930095#msg930095

He did mention a heatsink is required, but I can't see why you'd need 100 mA for this job. 20R  / 30 mA should be plenty I'd think. 18 dBu peak into 600 ohms...?

Ah he was driving a 1:2. Without the transformer we shouldn't need nearly as much.
 

ruffrecords

Well-known member
GDIY Supporter
Joined
Nov 10, 2006
Messages
14,770
Location
Norfolk - UK
dogears said:
You know, that came from the buffer that was supposedly added to Lenny Kravits desk by Dave Amels...shared by Winston here:

https://groupdiy.com/index.php?topic=1222.msg930095#msg930095

He did mention a heatsink is required, but I can't see why you'd need 100 mA for this job. 20R  / 30 mA should be plenty I'd think. 18 dBu peak into 600 ohms...?

Ah he was driving a 1:2. Without the transformer we shouldn't need nearly as much.

Even with a 1:2 you should need no more than half that tops.

Cheers

Ian
 

Rocinante

Well-known member
Joined
Jan 17, 2014
Messages
1,132
Location
Minnehopeless
Dogears; this is an amazingly comprehensive redesign on the original. I'm going to try it out when i can but it looks very promising.
 

Tubetec

Well-known member
Joined
Nov 18, 2015
Messages
4,168
Makes me wanna put on mid to late 60's records REALLY LOUD !,
like Marshall stack loud ,and blast the whole town with sounds
lets dial in some extra THD for good measure  :D
 

Whoops

Well-known member
GDIY Supporter
Joined
May 9, 2008
Messages
6,992
Location
Portugal
yesterday I started thinking what could I do to help dogears  "stay at home type 69 project",
as I think it's a great idea.

I was able to find my full Tech docs of the Helios Musicland Console.
I spent the evening scanning the files and processing them.

I'm uploading them individually to the technical docs section.
If anyone wants the compilation in pdf format just pm me your email.

Wish this is useful for this projects and future projects
 

Whoops

Well-known member
GDIY Supporter
Joined
May 9, 2008
Messages
6,992
Location
Portugal
ruffrecords said:
Couple of technical points.

The use of a tap on the secondary for the -20dB pad position on the mic input always was a dubious idea. Probably better to replace this with a balanced pad at the transformer input.

The gain make up amplifier has limited headroom. It is not really meant as an output amplifier. Probably better to replace it with the proper Helios line output amp.

I totally understand your technical points Ian, and I understand the urge to overcome the original circuit technical limitations.

But in my personal opinion, not coming from someone that designs great circuits like Ian does, couldn't those technical limitations be part of the Helios sound?
Could they be part of the reasons we also like the sound of the records  that are associated with Helios?

There's probably a lot of different ways the circuits could be improved but personally I already have a lot of different mic pre and circuit designs, with some circuits with high headroom and flatter frequency response, to build an Helios Type 69 module or circuit I would prefer to keep it as much as possible close to the original circuits.

I mean no disrespect to your opinions Ian, quite the opposite, it's just a different opinion.

Checking the Musicland schematics for the input modules , there's 3 versions:

Version 1 - uses 15C1 as the mic pre and  15C1 as the eq makeup (probably used Lustraphone input tx)
Version 2 - uses 2128 as the mic pre and  a "modified 2128"  as the eq makeup (probably used Lustraphone input tx)
Version 3 -  uses a different transformer, it's a Beyer, and  2128 as the mic pre and 22113  as the eq makeup

For the info I gathered on Helios the version 3 doesn't seem to be the most common one, most of the consoles of the records I like seem to be either version 1 or version 2

on this Musicland console,
MMC1 seems to be the bus output amplifier and 15C1 (V1 and V2)  and 22113 (V3) seem to be used also has the Fader amplifier,
with all 11 outputs (8 multitrack outs, Echo1 send, Echo2 send and Foldback out) having unbalanced outputs.
Master L+R use 22117/8 as the output amp with unbalanced out also.
If I'm not seeing something right please correct me

 

lestatdog

Member
Joined
Jun 14, 2016
Messages
15
dogears said:
I made a couple different versions if people would like to build.

One is true to the original schematic, with only minor changes, using the Sowter in 500 series.

The second is the same card but with molex connections to rack mount. Gives flexibility with input transformers if you want.

The third uses a "US-style" 8 pin input transformer (like a Cinemag CMMI10 or a Jensen 110K) with a switchable pad as Ian recommends, and uses a two transistor output buffer to up the output drive a bit.  Also 500 series.

All boms, gerbers, etc can be found here:
https://www.dropbox.com/sh/c9bpexgojyhycke/AAA9Qdhxy3iulcDAsCeTTL6Qa?dl=0

I have not built or tested this, so there may be errors! Use at your own risk.

Any chance of an OEP footprint for the input transformer? Those Lundahls are expensive.
 

Latest posts

Top