stay at home type 69 project

[mickdundee63]

Just to note that @pahstah had some issues with a Helios clone oscillating at high gain - turned out to be a duff transistor in the HPF in his case:

https://groupdiy.com/threads/he-569-pre-eq-500-series.72521/

interesting thank you! Will take a read

 

[dogears]

generally speaking it should get more stable with higher gain, not less. so i suspect build error, grounding / wiring, bad component, or layout in order of likelihood.

 

[mickdundee63]

generally speaking it should get more stable with higher gain, not less. so i suspect build error, grounding / wiring, bad component, or layout in order of likelihood.

Yeah probably build error. Same behaviour in both units so I'm thinking unlikely the same component went bad in both. If I trace the signal path with an oscilloscope to identify when the fault starts - this might be the best way to track down the issue?

 

[mickdundee63]

Yeah probably build error. Same behaviour in both units so I'm thinking unlikely the same component went bad in both. If I trace the signal path with an oscilloscope to identify when the fault starts - this might be the best way to track down the issue?

Ok so this was a layout error. When i removed the bottom board from the case the problem resolved. Still not sure what the issue was, possibly some conducting debris under the board. I thought the error was replicated in both units because the top was out of circuit - but it still was connected to chassis, I think through a switch, so maybe the fault was passing through there. Anyway nice clean noise floor through all ranges of gain now, time to put it back together!

 

[mickdundee63]

To close this off in case anyone has a similar issue - the solder had detached from the pad on the ground side of c51.

 

[fritzmyname]

Hello!
I'm quite interested in trying this project, thank you very much to @dogears for supplying the files and @TwentyTrees and everybody else who gave insights.
I have a few questions.
I have some DIY-experience (CAPI, AML and guitar tube amps and stuff) but never ordered a PCB. Do I just send the .zip-File to whoever produces PCBs and they just take all the info from that?
Are the PCBs in the dropbox link up to date? I read about some revisions, so I wanted to know if I could just use the PCB as is or if I have to modify something.

What exactly is the difference between the H9 and the H9M version? One has a buffer and one has a switch for line/mic? And also the input transformers are different? What benefits does the buffer have? I'm leaning towards the version with the line/mic switch so I can use it while mixing. What am I missing if I build this version rather than the M version?

Oh yes and where is the best place to buy the Sowter Transformer?

Does anybody have a template for the faceplate? Or at measurement for the holes?

Thank you very much! Looking forward to this project and learning new things

 

[TwentyTrees]

Hi! Great to hear you're looking at the Helios. I love mine. To answer some of your questions below (don't know about whether the dropbox files are current I'm afraid):

I have some DIY-experience (CAPI, AML and guitar tube amps and stuff) but never ordered a PCB. Do I just send the .zip-File to whoever produces PCBs and they just take all the info from that?

Yep! I used JLC PCB, I found the boards to be low cost and good quality. They've got guides on their site to walk you through the options.

What exactly is the difference between the H9 and the H9M version? One has a buffer and one has a switch for line/mic? And also the input transformers are different? What benefits does the buffer have? I'm leaning towards the version with the line/mic switch so I can use it while mixing. What am I missing if I build this version rather than the M version?

The buffer is pretty necessary in my view. The 2128 amp (used both for the preamp and post-EQ make-up in the early Helios modules, which this is based on) doesn't really have the necessary grunt to drive an output without a buffer, as the 0011 module was originally designed to feed the console's internal mix bus.

Oh yes and where is the best place to buy the Sowter Transformer?

You'd need to contact Sowter direct for the 7490E - SOWTER AUDIO TRANSFORMERS WORLDWIDE SHIPPING. I used Jensens in my builds for what it's worth.

Does anybody have a template for the faceplate? Or at measurement for the holes?

https://groupdiy.com/threads/stay-at-home-type-69-project.74779/page-5#post-989160

Thank you very much! Looking forward to this project and learning new things

You're welcome! Good luck and have fun, it's a great bit of kit.

Andy

 

[Cyril Jones]

TO https://groupdiy.com/members/fritzmyname.133302/It's a late reply unfortunately.

I f you are interested I developed /copied the original Lustraphone transformer which faithfully follows the frequency response of the transformer which according to over 50 users reproduces the old vintage sound.
I persuaded a lamination supplier to reproduce the identical specification performance and with careful transformer winding reproduced a faithful copy. The Sowter transformer was replaced with mine in over 44 cases

Regards. Cyril Jones

 

[fritzmyname]

Wow thank you very much for the warm welcome and the advice! I really do appreciate it!

So @TwentyTrees you‘re saying I shouldn‘t skip on the buffer or else I just don‘t get a strong enough output? Is there an easy way to incorporate the mic/line switch AND have the buffer? I‘d really like to use it while mixing so it would be nice not to have my mixes line output going into the mic pre (although I could deal with that).

@Cyril Jones thanks that sounds great! How much would you charge and do you have them in stock? I noticed while reading this thread that there were some supply and communication issues going on, so that‘s why I‘m asking Is your transformer the same footprint as the PCB? Meaning I can just drop it in?

Thanks ever so much and my apologies in advance if I‘m asking some obvious questions I‘m really impressed by the Helios plugins, so having the real deal would be amazing
While at it: do you get that resonant bump when switching in the bass frequency but without boosting yet? I noticed that is kind of a trademark thing and I really enjoy the 60 Hz but without boosting on guitar (even Andrew Scheps uses that and describes it as cabinet thump)

Thanks!

 

[TwentyTrees]

So @TwentyTrees you‘re saying I shouldn‘t skip on the buffer or else I just don‘t get a strong enough output? Is there an easy way to incorporate the mic/line switch AND have the buffer? I‘d really like to use it while mixing so it would be nice not to have my mixes line output going into the mic pre (although I could deal with that).

I'd have to look at the schematic to see exactly how that version does it, but the classic Helios approach to the line input is just to bypass the mic input transformer and go straight into the first 2128 amplifier, which is run at unity gain. You can achieve a similar gainstaging by just using an appropriate 20dB pad before the mic input transformer. Make sure you don't switch phantom power on when you've a line source connected, obviously! As to the question of buffer vs no buffer, there's lots of discussion out there if you go looking. I preferred the buffer in my builds.

While at it: do you get that resonant bump when switching in the bass frequency but without boosting yet? I noticed that is kind of a trademark thing and I really enjoy the 60 Hz but without boosting on guitar (even Andrew Scheps uses that and describes it as cabinet thump)

Yes, the minimum low boost is 2 or 3dB - the "Off" position on the low frequency switch is the only way to have a flat low end.

 

[Ricardus]

I still have yet to start building one of these.

 

[Whoops]

you‘re saying I shouldn‘t skip on the buffer or else I just don‘t get a strong enough output? !

Original Helios modules or consoles didn’t use output transformers, so if you want to add an output transformer you need a buffer circuit to be able to drive the transformer properly.
As no output transformers were originally used the original circuits also weren’t designed for that task

 

[fritzmyname]

I see, thank you!

I've settled with the version with the buffer. @TwentyTrees do you miss an output transformer?

Does anybody know where I could buy the Jensen (or Cinemag) input transformer in Europe? Or are there other matching alternatives (Lundahl? Sowter?)?

Thank you so much! I'm really looking forward to building this one and I'm gonna keep you posted. The PCB is already in production and I've finished the faceplate design (thank you @TwentyTrees for providing the pdf and fpd)

 

[TwentyTrees]

Great stuff! I'm afraid I don't have a European source for the input transformers, I got my Jensens from, well, Jensen. Don't think there are any other pin-compatible alternatives.

I don't miss an output transformer, no. I've got iron elsewhere that I can patch in if needed. I'm very happy with the sound as is, it's nicely balanced to my ears (and the original consoles had very few transformers in the signal path).

 

[Whoops]

Does anybody know where I could buy the Jensen (or Cinemag) input transformer in Europe? Or are there other matching alternatives (Lundahl? Sowter?)?

For the input transformer you can buy Lustraphone clone transformers from Cyril Jones,
those will be probably much closer to the original thing

 

[TwentyTrees]

For the input transformer you can buy Lustraphone clone transformers from Cyril Jones,
those will be probably much closer to the original thing

True, that's a very good option. Do they share the same pinout as the Jensens do you know, or can they otherwise be made to work with this PCB?

 

[fritzmyname]

True, that's a very good option. Do they share the same pinout as the Jensens do you know, or can they otherwise be made to work with this PCB?

Looks like the pinout is different :/

 

[dogears]

Sounds like you need to wire them in and use hot glue or a zip tie

 

[fritzmyname]

Sounds like you need to wire them in and use hot glue or a zip tie

Haha I hope not, but would the Sowter even work?

 

[fritzmyname]

I'm wondering if I could change the mid bands frequency selections by changing out the capacitor values. My electronics classes at university are not so long ago but I'm ashamed to admit that I don't know how to calculate this anymore. Gonna look up an online calculator Anything to watch out for?

I'm thinking of changing 2.9 kHz to 2.8 and also to ditch the 16 kHz and replace it with a lower frequency. I'm thinking of changing the 3 highest frequencies from 5K-6K-16K to something like 4.5K-5K-6K. What would be some tasty frequencies? Tbh I really don't use 6K on anything, so I'm actually contemplating 4.2, 4.5 kHz or something...hmmm

Thank you!