stay at home type 69 project

[TwentyTrees]

Yep, that's absolutely possible, an RLC calculator will get you there. Be aware that changing the capacitance without changing the inductance or resistance will change the bandwidth of your filter. That said, 2.9kHz to 2.8kHz won't be a major difference (and your 2.9 might actually be 2.8 depending on tolerance of the components).

 

[fritzmyname]

Yep, that's absolutely possible, an RLC calculator will get you there. Be aware that changing the capacitance without changing the inductance or resistance will change the bandwidth of your filter. That said, 2.9kHz to 2.8kHz won't be a major difference (and your 2.9 might actually be 2.8 depending on tolerance of the components).

Thanks for the heads-up. How would I go about checking that?

 

[fritzmyname]

What's your opinion on the input transformer? The Cinemag one is considerably cheaper than the Jensen one. Both these companies seem solid, so I'm wondering if there's a reason not to pick the Cinemag one?

 

[ruffrecords]

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!

Yes, you can make smallish frequency changes by altering the capacitors. It is a series LC resonant circuit so the frequency is given by 1 / (2 * PI * SQRT(L*C)) but there are plenty of on line calculators that are a lot easier to use.

As I said small changes of frequency are OK as these will not alter the Q of the resonance too much.

Cheers

Ian

 

[TwentyTrees]

I tend to use these calculators: Filter Design and Analysis

Re input transformer, they're both excellent and high quality pieces. I used Jensen as in my experience they're very transparent as far as transformers go, but Cinemag will also doubtless sound great (as would the Lustraphone with zip ties and hot glue!).

 

[Cyril Jones]

Hi There, the 16KHz frequency was added requested by Tony Arnold because the Sowter transformers lacked the correct high frequency response at 26 to 27KHz response top end - a 10to 12dB lift and tonal qualities. The Lustraphone I produce has it and faithfully replicates the original.
Whish you well with the mid .frequency selections.

Cyril Jones

 

[fritzmyname]

Perfect, thx @TwentyTrees then I‘ll go with the Cinemag!

ad frequencies: good to know, thx @Cyril Jones for that insight and thx @ruffrecords and @TwentyTrees for the help. My reasoning is, that IF I boost that high up, it‘s mostly a high shelf using an SSL type EQ starting at 8k. So I really don‘t need a bell boost at 16 kHz, I‘m not a dog LOL. (Also I’m planning to use the Helios on guitars, so having more options from 1-5 k is handy). So my thinking is, to move the 5 and 6 k points „one up“, ditching the 16 and making 6 the highest. The three top bands are all at the 0.1 H tap of the inductor. 5 and 6 k are already there, I‘m just moving them, so there should not be any concern regarding the Q. That leaves the 3rd highest frequency point free, so I would put something in the 4k area in there. Having the 0.1 H tap, I just need to figure out the proper C value.
Do I have to worry about the Q? I mean if 5 k is ok with the 0.1 H tap, why shouldn‘t 4.1 or 4.5 be?

Thank you very much for the help so far, this community and especially you is very helpful and I really appreciate it.

 

[fritzmyname]

Hi There, the 16KHz frequency was added requested by Tony Arnold because the Sowter transformers lacked the correct high frequency response at 26 to 27KHz response top end - a 10to 12dB lift and tonal qualities. The Lustraphone I produce has it and faithfully replicates the original.
Whish you well with the mid .frequency selections.

Cyril Jones

That‘s very interesting! Would you mind sharing a datasheet of your transformers?
How much do you sell them for?

 

[ruffrecords]

My reasoning is, that IF I boost that high up, it‘s mostly a high shelf using an SSL type EQ starting at 8k. So I really don‘t need a bell boost at 16 kHz,

I am going off shelving EQs. My problem is their out or band response. A shelf that boosts 10dB at 8KHz is still adding 10dB boost at 20KHz and most probably at 40KHz too. Instead I now use a low Q bell curve that looks very similar to the shelf where it starts, but it has the advantage of dropping steadily above 20KHz.

I think this is even more import for LF shelving boosts which usually boost right downwell below 20Hz, Again I now use low Q bell's to produce the same basic shape but with a falling response below 20Hz.

Cheers

Ian

 

[fritzmyname]

I noticed that RL1 is 255K according to the schematic but it says 150K in the BOM. Does anybody know which it is?

 

[TwentyTrees]

I think that depends on your input transformer. 150k is the value recommended in the datasheet for the Jensen JT-115K.

 

[fritzmyname]

Hello thanks for the reply! I see.

I'm building the M-Version, so the question is JT-110K-HPC vs. CMMI-10APC.
In the schematic for H9M RL1 is 255k, however in the BOM it's 150k. The datasheet for the JT-110K-HPC says there is a 100K resistor on the secondary with a 30.1K and 56pF parallel to that.
The Cinemag datasheet doesn't have such a schematic.
Jensen:


I'm just wondering where the 255K in the BOM comes from?

@dogears explained the effect of RL1 on the input impedance to me (thank you!), so I'm wondering what a good value to aim for would be. Assuming I understood it correctly, using the Cinemag input transformer with RL1=150K would give me an input impedance of 1.5K. Is this ok (Neves usually have 1200 or 300 Ohms) or should I goo higher?
@TwentyTrees what did you use for RL1?

Thank you everybody!

 

[TwentyTrees]

I'm building the M-Version, so the question is JT-110K-HPC vs. CMMI-10APC.

Of those, the Cinemag is I believe closer to the original, which has a 1:10 ratio. In theory this should present a standard 200R microphone source as closer to the optimum source impedance of the 2128 amplifier than the 1:8 Jensen, meaning the Cinemag should result in less noise (and slightly more gain). An RL1 value of 150k should be fine in that case, unless the transformer datasheet suggests a specific value.

 

[fritzmyname]

Of those, the Cinemag is I believe closer to the original, which has a 1:10 ratio. In theory this should present a standard 200R microphone source as closer to the optimum source impedance of the 2128 amplifier than the 1:8 Jensen, meaning the Cinemag should result in less noise (and slightly more gain). An RL1 value of 150k should be fine in that case, unless the transformer datasheet suggests a specific value.

Alright, thank you! Then I'm gonna with 150K

 

[fritzmyname]

First step: got the PCBs in the mail! I have 4 left, so if anyone in the future needs some for this project, feel free to contact me, I will ship them to you non-profit (hope that this is ok, but then again I think it's better if I offer potential builders these pcbs instead of people going through the hassle of having them manufactured)!
Edit: they‘re gone!

 

[Janalex]

Due to that recent post from Cyril on this thread really had the hope of getting through and ordering some Lustraphones. Tried multiple email addresses. Cyril if you read this please check your inboxes.

Jan

 

[Whoops]

First step: got the PCBs in the mail! I have 4 left, so if anyone in the future needs some for this project, feel free to contact me, I will ship them to you non-profit (hope that this is ok, but then again I think it's better if I offer potential builders these pcbs instead of people going through the hassle of having them manufactured)!

Are those boards the one that Dogears designed?

 

[fritzmyname]

Due to that recent post from Cyril on this thread really had the hope of getting through and ordering some Lustraphones. Tried multiple email addresses. Cyril if you read this please check your inboxes.

Jan

I went with the Cinemag

Are those boards the one that Dogears designed?

They are from the dropbox link so I guess yes!

 

[Whoops]

They are from the dropbox link so I guess yes!

Thanks,
I’m a bit outdated on this thread, I lost track of it at some point.
I have to read everything from the beginning again to know how this turned out

 

[fritzmyname]

Thanks,
I’m a bit outdated on this thread, I lost track of it at some point.
I have to read everything from the beginning again to know how this turned out

Yes, it's literally the link in the first post in this thread