[AVAILABLE] TTSH V4 Build Thread

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I have another question concerning the ADSR/VCF. I'm not sure if it's my inexperience with the TTSH (or synths in general as I'm not a keys player) but I sometimes seem to get 'thumps' if the ADSR is set a quick-ish attack/decay and I have the ADSR control more than halfway up in the VCF. I can usually dial this out by lowering the amount of ADSR control into the VCF or playing around with attack and decay times. Is this normal? Thanks!

[KSS]

Yes, it's normal. <--If normal means many TTSH and even many 2600s exhibit it. Which they do. But does it have to be normal? No. But that's a bigger answer, and can be found deep in the existing TTSH build threads. Below is a condensed summary.

Basically for a start, the VCA needs the best adjustment you can give it. Fine tune your VCA first.

Unfortunately there was a mistake made in the original ARP2600 PCB layout which limited the range of the adjustment you could make. ARP chose never to fix the problem and instead chnged the service manual to say turn this VCA trim all the way to its end and leave it there. <--Sometimes this works, sometimes it doesn't. Half the intended trim is missing due to the mistake.

It also has to do with transistor matching in the 4019 VCA, and a few other things there. To deal with this, one means of minimizing its effect is to insert 3 or 4 DC blocking caps as provided for on the TTSH PCB at the VCF input mixer. These are optional, and I suggest that -if you do this- you leave the Ringmod input to the filter uncapped in this way.

The alternative is to fix the VCA mistake and enhance its operation. Another alternative is to learn a few patching tricks to minimize or eliminate the effect. Changes to the ADSR can make this easier to do, at the expense of some sounds.

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The alternative is to fix the VCA mistake and enhance its operation. Another alternative is to learn a few patching tricks to minimize or eliminate the effect. Changes to the ADSR can make this easier to do, at the expense of some sounds.

Thanks! What is the fix to the VCA or the ASDR? I've already added the AC coupling caps as well as calibrated the VCA's linear gain and control reject as much as possible..

I've also tried bypassing the VCA by raising the VCF slider in the mixer (and lowering the VCA slider) and I still hear the popping on some settings. That said, I'm able to work around it for the most part by tweaking settings to minimize the thump.

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Here's the thump I am experiencing. I've also attached a screenshot of the settings on the TTSH. Unfortunately it's recorded with the TTSH's built-in speakers with my iPhone but you should get the general idea. The thump presents itself as a bassy thump depending where you put the decay slider. The sound of a capacitor discharging is obvious and not subtle. I've attached mp3's of both the VCA and VCF output of the mixer.

Is this normal? Envelopes on the output of the ADSR look correct on the scope.

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Can anyone comment if the mod to the reverb recovery amplifier circuit proposed by Nordcore using the NE5534 is worth the effort? Does it drastically reduce hiss when using the reverb?

[LED-man]

Before you start this reverb mod do this:
- remove the internal powersupply (DC-DC) and just use a linear psu solution with external transformer
(https://www.dsl-man.de/display/DSO/Bipo ... upply+BIPO)

- use high quality triple shielded RCA cable

This improve the total performance, no bleed or hiss from a dc-dc converter or hum from a internal transformer.

[bemerritt]

General question about building the case. Do most people build the traditional style case due to being true to the 2600, or because the increased space inside the cabinet is beneficial for the power supply and reverb tank?

I am thinking of going more eurorack style and being just a plain box.

[kristop]

Got replacement 5460s finally and my ADSR works!

[KSS]

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Got replacement 5460s finally and my ADSR works!

That's great.. I'm curious if you get the same thumps as I do with some attack/decay settings and with the ADSR control turned up in the VCF.

It's the only thing on my TTSH that annoys me. For me the fix is lowering the ADSR control level in the VCF. See my post a few posts up in the thread. No one has commented since so I'm assuming this is normal for a TTSH/2600.

I'm aware of the VCA thumping but I get this even when I patch the VCF directly into the mixer. (coupling caps are installed in the VCF as well)

[KSS]

No one?

The trim the service manual says to putt fully one direction needs its gnd end changed to -V. That puts its adjustment in the middle instead of the end. then you can adjust the VCA properly. <--Assuming all the other things I listed are already taken care of.

Edit: Did you use tantalum caps for the EG timing? What type caps did you use for the ADSR and VCA decoupling? If elcaps, did you parallel a smaller cap along side the x10 cap that 'replaces' the 1uF,35V tants?

Edit2: Just listened to your audio files. Go through the VCF cal again too.

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* dupe *

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No one?

The trim the service manual says to putt fully one direction needs its gnd end changed to -V. That puts its adjustment in the middle instead of the end. then you can adjust the VCA properly. <--Assuming all the other things I listed are already taken care of.

Thanks KSS. I did everything you mentioned and everything is calibrated correctly as far as I can tell, including the VCF.

I guess my confusion is that this 'thump' I'm experiencing happens even when routing the output of the VCF directly into the mixer which leads me to believe something is amiss in the VCF or ADSR

Edit: Did you use tantalum caps for the EG timing? What type caps did you use for the ADSR and VCA decoupling? If elcaps, did you parallel a smaller cap along side the x10 cap that 'replaces' the 1uF,35V tants?

I would have to check but I'm assuming you mean C1 and C2 in the AR are the timing caps? I believe they are 1uf tantalums.

As for the decoupling caps, I'm talking about the 4 caps in the VCF that require cutting the traces. I installed 4 1uf film caps here (cut traces)

Are you referencing some other decoupling caps?

[KSS]

The four 1uF fim caps are for the VCF inputs? If so, they're likely too small. Take -at least- one out and jump the cut trace. Using only that input, does your thump go away? I suspect it will. And these would be 'coupling' caps rather than DE-coupling. Because they 'couple' various stages together by eliminating -or vastly reducing- the DC element in a mixed AC-DC signal.

Decoupling caps generally means power supply in ARPs. These would be the original power supply distributed input filter or bypass caps. They are all 1uF,35V tantalums in the original. They are replaced with 10uF elcaps in the TTSH and should also have a small -like 1nF- cap in parallel. <--Don't need the 10x or the parallel cap if you use tants.

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The four 1uF fim caps are for the VCF inputs? If so, they're likely too small. Take -at least- one out and jump the cut trace. Using only that input, does your thump go away? I suspect it will. And these would be 'coupling' caps rather than DE-coupling. Because they 'couple' various stages together by eliminating -or vastly reducing- the DC element in a mixed AC-DC signal.

Excellent, I will give this a try first in the next few days and see if it lessens the thump I'm hearing. That said, what value would you suggest here? Aren't their purpose to eliminate thumps? I do understand these are 'coupling' caps. Sorry, it was a typo!

Decoupling caps generally means power supply in ARPs. These would be the original power supply distributed input filter or bypass caps. They are all 1uF,35V tantalums in the original. They are replaced with 10uF elcaps in the TTSH and should also have a small -like 1nF- cap in parallel. <--Don't need the 10x or the parallel cap if you use tants.

I'm using 1uf caps as silkscreened on the PCB and specified in the Synthcube BOM (and fuzzbass build guide) for all of the power inputs to each module/section (the caps next to the power headers). They sent 1uf electrolytics, and that's what the silkscreen indicated, so that's what I used! Ha! There is no provision for a cap in parallel with these though. Could this be an issue? Should I replace these with 10uf and strap a 1nf across the terminals since there's no pads for these? Or just replace these with 1uf tantalums?

You're right, the TTSH schematics do show 10uf's for the input filter caps with a 100nf in parallel but again, would this cause what I'm hearing?

Thanks again, very much appreciated.

[KSS]

Yes, kind of. They're there to eliminate DC bias. Which is *then* less likely to cause thumps in following circuits. Like the 4019 VCA.

But, they're capacitors. Which means they're affected by frequency. <--Otherwise they couldn't block the DC.

So you'll want to look at the equation for frequency as it applies to caps -easily found online- and read up.

I've seen caps as high a 33 or even 47uF in some 'upgraded' 2600s by notable Techs. <--Elcaps, 50V

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1uF elcaps are not going to give enough filtering. That's the problem when someone updates old circuits without understanding the component choices and their effect on the result. I'm not a tant hater, but many still are. Your suggested courses of action would be fine. Follow the TTSH schematic, or use tants.

Yes, in the big picture having 1uF elcaps will have an effect on some patches and sounds. Especially if the PSU is SMPS. As the elcaps by themselves are not very responsive to higher frequency noise. I'm frankly surprised that on V4 this is still showing 1uF and suggesting elcaps.

[Jaytee]

Shouldn’t it be simple enough to just look at the signal with a scope and see if the DC offset is gone?

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Shouldn’t it be simple enough to just look at the signal with a scope and see if the DC offset is gone?

I thought the same. I saw very minimal DC on the output of the VCF when scoped and was able to adjust any that was present with the offset trimmer . When calibrating the VCF according to the Service manual (Section 2.9.3, steps 7-9), I'm able to adjust DC offset to 0 and if I slide the resonance slider to the right, I see less than .5V of DC on the scope. I'm pretty sure that's within spec, unless I'm missing something?

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Edit: Did you use tantalum caps for the EG timing? What type caps did you use for the ADSR and VCA decoupling? If elcaps, did you parallel a smaller cap along side the x10 cap that 'replaces' the 1uF,35V tants?

I misspoke earlier.. I just took a look and the 1uf timing caps in the ASDR are indeed electrolytic as well! For some reason I though I remembered soldering in some tantalum caps but I was incorrect. All of the 1uf caps provided for my build were electrolytic.

Should I replace the timing caps in the ADSR circuit with 1uf tantalum caps?

Thanks!

[KSS]

Should I replace the timing caps in the ADSR circuit with 1uf tantalum caps?

I would. And do. But others will disagree.

I don't think that's going to have much to do with your thump, but it will give more accurate-to-the-original operation.

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So I'm still not clear on what the issue with my build is. I can't tell weather it's the ADSR or the VCF that is giving me grief but I'm leaning towards the ADSR. I'm trying to narrow it down but still can not for the life of me figure out what's going on. I don't think it's the coupling caps in the VCF audio mixer. This is what I can do to reproduce the thumping.

All VCF mixer sliders down
Freq slider to the right
Resonance set on the edge of self oscillation
ADSR CV on the VCF fully up
ADSR triggered by the S&H clock
Play with Attack and Decay setting on ADSR
VCF output into the mixer

Here's a pic of the front panel (vcf slider was raised in the mixer when recording was made) and I included an audio file of what I'm hearing when randomly adjusting attack and decay sliders.

I will also note, if I plug another CV source (S&H for instance) into the CV control of the VCF, I do not get any odd noises or thumps. It's only the ADSR that causes this. The ADSR output looks normal on my scope. I'm truly at a loss.

[KSS]

First eliminate the VCA as the problem.
By directly patching SIN from VCO2 into VCA's VCF normalled input jack.
Then patch VCO1 square wave into the ADSR normalled CV jack (4th of 4 in the VCA). Set VCO1 to LF. Raise the VCA slider of the mixer.

The ADSR and VCF are now bypassed and the VCA is set up for a stress test as it's getting the 0-10V on-off of the VCO1 SQ as CV. In its most senstive CV input. Set VCO2 to some reasonably pleasant frequency and and slowly raise the 4th -ADSR CV- slider of the VCA.

Does it thump?

Play with the patch to learn about your VCA. Once you've explored the SIN as input, swap to VCO2's Pulse. Start with it as a a square and then play with adjusting the width.

Then patch the pulse from VCO2 into the voltage processor mixer and apply a negative 5V bias to approximately center the pulse so it goes from -5 to 5+ instead of 0-10V. Still going into the input of the VCA.

Now you're hitting your VCA with a worst case bipolar signal in place of the formerly worst case unipolar signal. And you're slamming the VCA on and off HARD. If it's going to act up these tests should will show it.

You'll want to use the 3rd jack of the VCA also. But this linear CV input is less likely to thump comapred to the expo CV input of the 4th ADSR normalled jack. <--Remember, we're NOT using the AR, ADSR OR VCF at all. VCO1's square is still applying a hard 0-10V tremolo CV to keep the VCA stress level high.

Let us know what your results from this are and then we can look at the VCF and ADSR -again separately- if needed.

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Well... The LM301 strikes again!

Replaced the one on the 4012 with one from another batch and things seem to be working!

Odd thing is, that was one of the first things I tried and it didn't like the 2nd one I tried so I didn't even give it another thought!

I appreciate everyone's help. I owe you a beer KSS!

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