Hamlet Delay and Preamp: Schematic, build doc, layouts, and demo

[Brossman]

Im relatively new to delays, so excuse my ignorance... I see you mentioned this is compatible with the taptation controller. Taptation's documentation states a delay time up to ~1100 ms. Does that mean it can essentially double the delay time on the PT2399? Or would this require using two 2399s?

[midwayfair]

Im relatively new to delays, so excuse my ignorance... I see you mentioned this is compatible with the taptation controller. Taptation's documentation states a delay time up to ~1100 ms. Does that mean it can essentially double the delay time on the PT2399? Or would this require using two 2399s?

The taptation uses a 100K digital pot; since the PT2399 works by more resistance = more delay, using a larger value pot (with no limiting resistor like I use here) will mean more delay.

In reality, I've never heard a PT2399 that can get above about 800 milliseconds.

I'm not the right person to ask about the taptation, though. I suggest finding the thread in the digital subforum.

[Brossman]

I was honestly after Taptation for the modulations it can provide for the delay repeats.  However, it seems that the singing/ringing quality obtained by your extensive filter removal can be mildly close to that, albeit lacking "swirl", yes? Conversely, I suppose I could experiment with running a phaser of some sort AFTER the Hamlet, thus modulating the repeats, no?

[midwayfair]

I was honestly after Taptation for the modulations it can provide for the delay repeats.  However, it seems that the singing/ringing quality obtained by your extensive filter removal can be mildly close to that, albeit lacking "swirl", yes? Conversely, I suppose I could experiment with running a phaser of some sort AFTER the Hamlet, thus modulating the repeats, no?

You couple splice in an effects loop on the repeats (taken after the decoupling cap on Q2) if you want some strange form of modulation on the repeats like tremolo or phasing. If you want the normal vibrato effect of modulated delay, you would just add an LFO modulation circuit on the delay pin. There are many, many examples of delay modulation for the PT2399 if you search for them.

The filtering of the repeats here does not create modulation.

[Jazznoise]

Sounds great! Nice guitar playing too! 

[Brossman]

Okay, gonna try to add an LFO to my build on perf. 

I'd like to know if you think this build would be seriously hindered by NOT using film caps and metal oxide resistors? I've been wondering because the electronics store in town has Mylar caps, but I can get WIMA/CDE metal films from Mouser (cheaper), and I have Carbon film resistors, so buying metal oxides would be another throw down. I mean, this is a really cheap build (maybe $50), factoring in buying MULTIPLES of all components, enclosure, etc. I could cut my cost, etc etc by buying from Mouser...

Bottom line, how would the fidelity of this be affected based on the choice of cap and resistor materials?

Thanks

[midwayfair]

Okay, gonna try to add an LFO to my build on perf. 

I'd like to know if you think this build would be seriously hindered by NOT using film caps and metal oxide resistors? I've been wondering because the electronics store in town has Mylar caps, but I can get WIMA/CDE metal films from Mouser (cheaper), and I have Carbon film resistors, so buying metal oxides would be another throw down. I mean, this is a really cheap build (maybe $50), factoring in buying MULTIPLES of all components, enclosure, etc. I could cut my cost, etc etc by buying from Mouser...

Bottom line, how would the fidelity of this be affected based on the choice of cap and resistor materials?

Thanks

You should be able to build this for less than $35, probably closer to $25 including the PCB if you paint your own enclosure and get parts from Tayda.

I would use metal film for R3 at least. You probably won't notice a difference for most of the other resistors in this build. The other one that matters, the drain resistor on Q2, is a trim pot, though you could replace it with a fixed metal film and maybe reduce a very tiny amount of noise. But this isn't a high-gain effect, so unless you've just got horrible parts, the dry path will be fine, and nothing to do with resistors and caps will make a PT2399 less a less noisy chip except more filtering (i.e., the tone control).

Caps are caps, with a couple exceptions: As noted in the build document, the 10uF filtering cap on the PT2399 should ideally be tantalum for best performance (this is explained in the build document), and the 100nF from +9v to ground should be film because film is best at filtering very high frequencies (that's why it's there in the first place). Many of the caps in this build are not part of the audio path. It's nice to use box film caps because they're 5% tolerance.

Have you looked at Tayda?

[Brossman]

Thanks for all of this... Im looking at about $30 for the build, but Im buying pt2399 in bulk, extra charge pumps and JFETS, and extras of most of the resistors and caps while im getting a few... I like the idea of tight tolerances and being able to hand pick parts if I so desire. The other things are also considerably harder to source locally, not to mention more expensive. I should not have to pay $2 for an NTE equivalent JFET single... thats absurd.

Not sure if you know, but Mouser has a cheaper residential shipping op thats like... $5-6, so for small orders, Im still paying about 1/3 of what I could locally. Mind you, I get dealer-break prices at the shop cuz they know Im hard up and Im a frequent customer so...

I also planned on using WIMA films for the tolerance and size.  

Thanks for the tips!

EDIT::  I had a look at Tayda lastnight... wow. They've got almost everything!! And for really good prices too.  Can't beat 50x 2n3904s for $1

[Brossman]

Hey Jon,

Im trying to squeeze this build into my (pre-drilled) enclosure and ai noticed im having trouble with larger pots... Ive looked at Tayda for the Mix and Tone controls (both external is the goal). Tayda only has 20ka pots - will using these adversely affect my range of control..?  Thanks.

[midwayfair]

Hey Jon,

Im trying to squeeze this build into my (pre-drilled) enclosure and ai noticed im having trouble with larger pots... Ive looked at Tayda for the Mix and Tone controls (both external is the goal). Tayda only has 20ka pots - will using these adversely affect my range of control..?  Thanks.

20k should be fine for the mix. Use one of the 30k trims for the tone (I do), or go with a 50k if you're making it external. Bigger value = more available rolloff.

[midwayfair]

Did a small redesign on this after learning a few things from the Cardinal V2.



(10K for the bias trim might be overkill.)

Kinda neat that you can share the collector of a BJT with the drain of a FET. The biasing is more complicated but it can be dialed in by ear by moving the trims a little at a time, and you get a little more overall control over the maximum volumes of each. I also added an optional second base resistor, which would let the same layout use any type of transistor.

This also gets rid of the slight signal loss that came from mixing the signals after the decoupling caps in the older version.

I haven't fully tested it and I don't really have time to do so at the moment, but a preliminary test sez it's sound.

[maoriente]

I just finished building version 1.2 on vero.

I'm getting strange noises when in the tails bypass mode, the delay and tone knobs affect the noise.

Seems like the PT2399 doesn't like FS1 hanging open.

I was able to eliminate the noise while in tails bypass by grounding FS1. I tried grounding FS1 with the stomp switch but had a pop echoing whenever the switch was opened or closed. 

I eventually gave up the tails and went with true bypass and so far everything seems fine.

Any suggestion on how to get the tails bypass quiet?

[midwayfair]

Dunno. I've built a dozen of them on PCBs are perf board without it and this is the first I've heard anyone having the problem.

The source and PT are usuallypretty close in voltage but ground is way different, hence the pop. There are other ways to do tails, like swithing in a very large resistor instead of fully disconnecting, or switching a gigantic cap to ground at pin16 so you just don't get sound but don't DC ground it.

If I think of something else I'll let you know but the oscillation mint indicate some other problem. Is the veto layout you used verified? Which layout is it?

[PRR]

> share the collector of a BJT with the drain of a FET.

"Plate mixer". RDH 3rd.

It's a pretty sad thing with vacuum triodes. Better with pentodes, but that spoils the cost and simplicity. Ought to work great with BJT or FET. Using both (and especially with the variable bias on BJT) may be more clever than elegant or mass-repeatable.

[midwayfair]

> share the collector of a BJT with the drain of a FET.

"Plate mixer". RDH 3rd.

It's a pretty sad thing with vacuum triodes. Better with pentodes, but that spoils the cost and simplicity. Ought to work great with BJT or FET. Using both (and especially with the variable bias on BJT) may be more clever than elegant or mass-repeatable.

Ah. I neglected to update this thread. I remembered over at Madbean: That experiment was a bust. It sounded fine when clean but when pushed even a little bit, it was just terrible.

It does work great with only FETs (which is what I did in the Cardinal), and this design can be built with two of them if one is willing to sacrifice some input headroom and redirect the 4M7 to ground. You get far more accurate high frequency response in exchange for the headroom. Ironically it ends up sounding less like the (FET-based) EP3 that inspired it than the BJT version. I didn't feel the need to change anything in the end.

Two BJTs with their collectors joined is equally awful. I also tried MOSFETs but that didn't work out at all.

[Transmogrifox]

> share the collector of a BJT with the drain of a FET.

"Plate mixer". RDH 3rd.

It's a pretty sad thing with vacuum triodes. Better with pentodes, but that spoils the cost and simplicity. Ought to work great with BJT or FET. Using both (and especially with the variable bias on BJT) may be more clever than elegant or mass-repeatable.

Ah. I neglected to update this thread. I remembered over at Madbean: That experiment was a bust. It sounded fine when clean but when pushed even a little bit, it was just terrible.

It does work great with only FETs (which is what I did in the Cardinal), and this design can be built with two of them if one is willing to sacrifice some input headroom and redirect the 4M7 to ground. You get far more accurate high frequency response in exchange for the headroom. Ironically it ends up sounding less like the (FET-based) EP3 that inspired it than the BJT version. I didn't feel the need to change anything in the end.

Two BJTs with their collectors joined is equally awful. I also tried MOSFETs but that didn't work out at all.

I never noticed this project (but started a few years ago)...Kudos Jon, really nice work!

I have played around with this mixing scheme in simulation and implemented a variant of it in a stereo-to-mono mixing box for an old tube audio receiver.

What worked out acceptably well for the stereo-to-mono mixer was to use the Sziklai pair to compose a "super transistor", and of course a healthy-sized (4.7k) emitter resistor on each node.  From a 15V rail I was able to achieve about 6Vpp clean headroom which is about double what I needed to drive my mono receiver at maximum volume.

Using the Sziklai configuration the "collector" voltage has much less effect on the overall gain of the stage so the distortion is very low until the point that it actually starts clipping.  Because of this the inter-modulation between the two separate signals is much lower up until the point at which it starts clipping.

It wasn't phenominal but not bad in simulation.  I was simulating something like 70 dB signal/distortion ratio on the 6Vpp sum, which amounts to 0.03%. I avoid using the term "THD" because I was measuring 2 different signals mixing at a common node so the distortion figure includes both harmonic and inter-modulation distortion.

To my ears it was perfectly acceptable, and probably a lot lower distortion at the actual levels I was using to listen to music.  I would guess for more practical levels the distortion was below the specs on my mp3 player output.

Anyway if you get bored and want to take this a step further you might try cooking something up with some Sziklai pairs.  You can also couple N-ch JFET with PNP BJT if you want the convenience of ground-reference biasing -- which actually works really well with a JFET because it's operating much closer to pinch-off, which drives the source voltage much higher so you can handle larger input signals.

[maoriente]

Thanks Jon, I designed the vero myself.

http://guitar-fx-layouts.42897.x6.nabble.com/Hamlet-Delay-by-Jon-Patton-td32472.html

I had 1st tried the perf layout (my 1st attempt at perf) didn't go well. Low output and the tone control created smoke. Didn't attempt to troubleshoot as I found the perf process frustrating.  (I'm a long time vero builder)

Anyway, I'll go over the vero layout again to see if something is amiss. Somehow it sounds fine with true bypass.

And I'm sure you've heard this many times, thanks again for all the great videos and designs.     

[maoriente]

Turns out, the tone control (and playing) was masking the noise.

I am getting the oscillation with the effect engaged, without playing, even without the charge pump installed.

Most noticeable with the tone control and mix on full. It sounds like a clock or LFO type noise. The delay control effects the noise, almost sounds like dialing in a old radio or CB.

Won't be able to troubleshoot until tomorrow...

[midwayfair]

Check that Q1 isn't backwards. The pedal will oscillate if it is.

[maoriente]

I was hoping that was it, but no. Q1 oriented correctly.

Went through the layout and version 1.2 build doc and they seem to match. I couldn't find any errors with my populated board either.

Audio probe at PT2399 pin 15 sounds fine, pin 14 has the noise.

It seems the noise appears when not playing and with delay resistance above 40k. Delay fully CW the noise sounds like motorboating. 7 of 8 PT2399s have the same noise (2 or 3 suppliers). Some have noise with the delay knob turned all the way down too.

Is that a clue or does this indicate 7 bad PT2399s? 

1 of the 8 PTs has much less noise, only a slight motorboating at full CW. I think if I go with a 50k pot and no parallel resistor, it may be suitable.