stay at home type 69 project

[Ricardus]

I have some boards and just need to build them!

 

[fritzmyname]

I have some boards and just need to build one.

That's good cause I just sold my 4 spare boards to Janalex

 

[fritzmyname]

It's coming together!

Still waiting for knobs and mini pots, then I'm gonna do a final test fitting with the printed out faceplate and then I'm finally gonna order the faceplate.

 

[fritzmyname]

I got my frontpanel from Frank in the mail - solid work. I changed some dimensions and markings from @TwentyTrees design.

Most notably the mid frequencies.







I attached my final design, you just have to change .pdf to .fpd

Let's go!

 

[TwentyTrees]

Nice work! Did Frank do your bracket as well?

 

[fritzmyname]

Nice work! Did Frank do your bracket as well?

Thanks! Yes he did. Not sure if I really need it tho. It‘s also a bit to short, so I can’t use the 2 screwholes next to the card edge connector.

I will use it for some sort of protection, but I guess the front panel itself would be enough to hold everything.

 

[fritzmyname]

Alright, I finally got around soldering everything together and it passes sound. However it really distorts when putting stuff through from the DAW or it doesn't do anything (audible) when plugging in a mic.

Sending a track through it at line level sounds heavily distorted like a fuzzbox, the steps however seem to work. The PAD reduces the volume drastically so it's only audible when the gain is up. Then the distortion is enormous.
Plugging in a mic barely registers on the input meter in my daw.


It seems like all the controls work, but something in the amp circuit doesn't work as it should.

Where to start searching?

Thanks!

 

[TwentyTrees]

What level is the line signal you're feeding it? These modules don't have the high internal headroom of an API or similar, as they were designed to work in a console with lower working levels than we're used to these days, so I found that gain staging is more important than I was used to. A 0dBu (say -20dBFS, or lower) signal with the pad engaged and the gain knob set to +20 should be clear though. Are you getting unity gain in that scenario (gain +20, pad engaged)? I'm assuming that your pad is -20dB.

With mic signals, I likewise find I need to crank it a little hotter than I otherwise would to get a good signal into the DAW, or boost the signal afterwards (either an in-line compressor or in the box). Does that make a difference? Is your phantom power switch working?

I'm sure that if we break it down section by section we'll get it working.

 

[fritzmyname]

Thanks for your reply! I kept that in mind although I didn't think it would be so extreme.

I sent a vocal from my DAW through it at line level. I tried changing the output level from my interface and changing the input gain settings. It's always fuzzy to a degree, never really clear. I will investigate this further.

Where I'm really at a loss is when using a mic. I plugged in an SM58 and got nothing realy on my input meter.

My next step would be tracing the signal, but some reference measurements would help me a lot.

I will trace the phantom power - the switch works, I just need to confirm that it reaches the input.

 

[TwentyTrees]

Sounds like you've got something to start with. Try a known, calibrated line signal with peaks at or less than 0dBu, with pad engaged and gain set to 20, and let us know how you get on.

Do you have a condenser mic to try (or anything hotter than an SM58)? Leaving the input metering question aside, how does the recorded SM58 sound if you increase the clip gain to your normal levels - clean / distorted, any noise, etc?

It's worth keeping the HPF and EQ section disengaged during all this initial testing by the way, to simplify things.

 

[fritzmyname]

Sounds like you've got something to start with. Try a known, calibrated line signal with peaks at or less than 0dBu, with pad engaged and gain set to 20, and let us know how you get on.

Will do! Do you maybe have a picture where to put the stop pins in the grayhills? Didn't do that yet so it rotates all the way through.

Do you have a condenser mic to try (or anything hotter than an SM58)? Leaving the input metering question aside, how does the recorded SM58 sound if you increase the clip gain to your normal levels - clean / distorted, any noise, etc?

Yes I'll try it with a condenser - I didn't record any test yet because I assumed nothing got through.

It's worth keeping the HPF and EQ section disengaged during all this initial testing by the way, to simplify things.

Yes, I tested them tho and they seem to work (put through a 60 Hz sine wave that got affected by the HPF and the EQ did *something* to the signal atlthough I couldn't quite hear it in detail due to the fuzz.

 

[TwentyTrees]

Will do! Do you maybe have a picture where to put the stop pins in the grayhills? Didn't do that yet so it rotates all the way through.

Here you go:



Make sure the switch wiper is within the range you want, then pop one pin in the "zero" position and one in the appropriate hope for six or eleven stops. Caveat - check everything first, as those pins are very hard to remove if you get it wrong!

 

[fritzmyname]

Is this the same for all 4 grayhills? Put in 0 and then have 6 for gain and 11 for High/Mid/Bass?

Thank you so far for your help! I still need to wrap my head around grayhill switches...^^

 

[TwentyTrees]

Is this the same for all 4 grayhills? Put in 0 and then have 6 for gain and 11 for High/Mid/Bass?

Thank you so far for your help! I still need to wrap my head around grayhill switches...^^

Yes, should be the same for all 71 series Grayhills. I'd suggest testing with a bent paperclip or a sewing needle or something first, if you can. The datasheet for the switch series should help too.

 

[dogears]

The first thing I'd check is solder joints, and double-check that all your transistors are in the right spots. Its easy to put a PNP in for NPN (ask me how I know) haha. From the photos you posted everything looks ok, though.

If you have a scope, I'd start checking the signal one block at time.

first at the input between 8 and 10 on the card edge - start
at the pad switch
at pin 5 of the input transformer - before the first amplifier block
at H2 pin 1 - after the first amplifier block, before the hpf
at the connection of C10 and R25 - after the hpf
at pin 2 / common of the EQ cut switch - before the eq makeup amp
at the connection of C52 / R50 / R49 - before the output buffer
And then at the output between pins 2 and 4 on the card edge

if you don't have a scope, you can do the above with a mulimeter and a sine wave but you won't get as much out of it. try like 0.5 vrms at the input. I got a tiny handheld scope from amazon that works way better than it has any right to which is nice to have lying around.

double check also that the voltage at pin 3 of the regulator U1 is indeed +8 V over common (pin 2 of U1).

 

[oongbac]

I think I have quite similar symptom with @fritzmyname. I tried H9 and H9M, they all same. Feels like they only react with transient +distortion like old speaker or fuzzbox like shin-ei fy-6... I'll try suggestion above tomorrow... I tested both dynamic and condenser.

+voltage over pin2 and 3 is quite close with 8V.

 

[oongbac]

I follow the scope procedure, I found that there's a volume drop and slight distortion at pin2 of EQ cut switch. It's still shape of sign wave though, but two points after that I can see far distorted signal like old magnitude meter. Could you give me any suggestion? Thank you for your helping.

 

[dogears]

there will be a drop at the output of the EQ cut switch since there is a loss as it is a passive eq - thats normal. so that means your problem is in the makeup / output amplifier somewhere. i'd double-triple check solder joints, resistor values, transistor orientation in the areas around Q5, Q6, Q7.

 

[oongbac]

there will be a drop at the output of the EQ cut switch since there is a loss as it is a passive eq - thats normal. so that means your problem is in the makeup / output amplifier somewhere. i'd double-triple check solder joints, resistor values, transistor orientation in the areas around Q5, Q6, Q7.

Thanks!! I’ll check that points again!

 

[Cyril Jones]

Re. 16KHz mid boost. This was requested by Tony Arnold when I was rebuilding 2 Hellios consoles into one new frame at Heliocentic Studio. Tony had sold the old Helios modules in favour of his new trype. These lacked the former sound because new off the shelf mic tranformers did not have the correct sound particulaly at the top end. At Tony's request I added the necessary components.
Eventually when the stuidio closed and the console sold to USA I supplied 36 new Lustraphone tranformers to restore the correct sound response. These transformers will be on the market again next week from 8th Nov.
Basiclly repeating discussions from Forum yester year.
Cyril