Enhanced Pultec DIY

[9T9R]

nice project

[briomusic]

Ach... ich sehe gerade... ich hab garkeine BOM auf die Seite gepackt... das könnte natürlich davon abhalten das die meisten sich an das Projekt dranwagen. Very Happy

naja, wen das abhält - ich weiß ja auch nicht. in den pdfs steht ja alles drin. cool auch der link für den Induktor - da ich mir ein stereoteil bauen möcht werd ich mir das matched pair holen...

...
Beste Grüße
Max

hallo, ich mache mich nun langsam auf die parts suche für meinen dual pultec mit gyraf gainstage und NRG filterboard. wollte mal fragen ob es nun denn ein BOM gibt oder nicht? mit "in den pdfs" ist das pultecV15 pdf gemeint, also component placement, richtig? danke!

[nrgrecording]

wollte mal fragen ob es nun denn ein BOM gibt oder nicht?

Nicht!

Und ich will auch eigentlich garkeine machen.

Das hat verschiedene Gründe:

1. Eine BOM macht nur sinn wenn es eine komplette BOM ist. Wenn ich eine für Reichelt mache fragt der nächste ob es auch eine für Farnell gibt. Und der übernächste will eine für digikey.

2. Als ich damals das Platinenlayout gemacht hatte, habe ich mich an den lieferbaren Kondensatoren von Reichelt orientiert. Als ich dann ein Jahr später das Ding dann dochmal auch selber bauen wollte gabe es vereinzelte Kondensatoren nicht mehr. (2 oder 3 glaube ich). Es wäre also für den Erbauer von Nachteil wenn irgendwas nicht passt oder wieder mal ein Teil fehlt.

3. Ohne BOM ist die Wahrscheinlichkeit größer das die ganze Schaltung am ende funktioniert.

[seavote]

i'd like to make 2 channels. enhanced and mid pultec in one channel. can i connect one passive board directly to the other?
will one amp section per 2 board channel do or should i amplify befor sending the signal from one board to another?
thanks for any help. i may have been here for a while but i still have a great deal to learn.

[nrgrecording]

will one amp section per 2 board channel do or should i amplify befor sending the signal from one board to another?

I would do it like this. Make two seperate circuits... enhanced and mid pultec and connect the output of the first amp to the input of the second one.

You could also add a switch to seperate the two filters, or use a jack connector so that its possible to insert only one filter to a sidechain maybe.

I think its also easier to make two seperated circuits if you need to find any faults in the circuit.

[seavote]

great advice. more options .cant argue with that.
thanks for the advice

and thanks for sharing the project

[jensenmann]

i'd like to make 2 channels. enhanced and mid pultec in one channel. can i connect one passive board directly to the other?
will one amp section per 2 board channel do or should i amplify befor sending the signal from one board to another?
thanks for any help. i may have been here for a while but i still have a great deal to learn.

You have 15-18dB loss in each passive filtersection. This could be done with one amp but impedance matching of two passive filters in series won´t work. Each filter has 600 Ohm input and needs to see 10k at the output. If you´d connect them one after another the second filter input would shorten the first one´s output, causing low level, weird sound and filter misbehaviour of both filters.

[briomusic]

@Frank: mit BOM meine ich eigentlich nur eine auflistung der komponenten, ich weiss das sich das jetzt so mit bestellnummern eingebürgert hat, und diesbezueglich stimm ich dir zu das letzteres wirklich keinen sinn macht...

was allerdings supi wäre, wär ein schaltplan.....

ich möchte deine enhanced filterboards nämlich auch mit der G-Pultec Gainstage kombinieren und hätte gerne einen Filter-Bypass, wo das signal aber weiterhin durch die transen und röhren läuft. habe mal dein filterboard mit dem gpultec verglichen und da ist schon einiges anders, nicht nur die zusätzlichen Kondensator- und Induktorwerte. Wenn man sich folgendes Bild anschaut: http://gyraf.dk/gy_pd/pultec/gy_pd_sch.gif gibt es da noch ein paar widerstände (10k/1k) rund um den low-freq selektor. ich denke mal daß selbige wichtig sind damit der SW2 (bypass) funktioniert. sonst ist der eingang der gainstage direkt auf masse....

hat sich damit schonmal jemand beschäftigt? wäre für tips dankbar!

[nrgrecording]

@briomusic:

There is no schematic at the moment. But if you want to connect the filter to gyrafs SRPP gain stage you just have to connect it the same way. At the SRPP gainstage there are 3 pins gnd, in, out. Thats how it works.
If you want to have the tubes in the signal pass you have to bypass the filter. Then you will need a voltage divider to turn down the volume when the circuit is in bypass.
With the SRPP gainstage its much more expensive. You could make 10 pultec pcbs for the price of one pultec with SRPP because of the transformers, tubes, capacitors...

Frank.

[briomusic]

thanks for the advice. as I am looking at the gpultec filterboard in bypass they seem to have a 10:1 voltage divider (there are a few larger resistors in parallel to the 10k which might reduce the resistance a tiny bit. I guess the best way to try this out is to have a 10k trimmer as a voltage divider and find the setting with unity gain by trial and error.

as to the expense of the tube gain stage....
well you could get a lot of behringer composers for the price of a fairchild

[briomusic]

hi frank/group,
i am having troubles getting my enhanced tube pultec to work. I think my gainstages are fine, as they work as amplifiers and I can get them to unity gain with a simple voltage divider in place of the filterboard.
however, with the filterboard connected, I just get a ca 20dB amplifier with a tiiiiiinnny bit of hi boost working. all the other frequency bands have no effect whatsoever
it is a little difficult to troubleshoot this project as there is no schematic, so I tried to trace one myself from the pcb, and if I am not mistaken, there are some significant differences to the layout of the gyraf version (additional frequencies aside):

This is obviously an extremely simplified version with just one fixed frequency for each band. I found that apart from the 10k and 1k resistors missing on franks board, the caps for hi cut and lo boost are connected differently. Is this correct? or did I make a mistake tracing the pcb?
As I am having the same problem on both boards, I don't think that this is due to a solder bridge or similar. Any help appreciated!
Briomusic

[nrgrecording]

I can ony see 3 differences.. the two resistors... and the connection of the lowboost/highcut capacitors.

Which pcb layout do you use? The Gustav pcb? Any info on the version? pdf maybe?

However... I heard from different people that the circuits worked fine for them.
If you think there is an error... please add the 2 resistors, change the capacitor connection and let us know. If it still does not work - it might be another problem. What happens if you remove the 75R resistor?

Frank.

[briomusic]

Hi Frank,
thanks for your reply.
on the second filterboard I modified the circuit to be more like the gyraf one, but still the same result (only hi boost works, way too much gain).
I think my next step will be to build up one of the gyraf filterboards that came with the srpp gain stage boards in a minimal fashion (no rotary switches, just one frequency) just to see if that works. at the end of the day I am trying to merge two different circuits here, maybe I should also try making an op-amp gain stage to see if that works with the enhanced filterboard.
things got very busy on the engineering/producing side so this project might have to wait a week or two...
but like arnie says, I WILL BE BACK.

[Maarten]

Hi,

I would like to ask two short question regarding they Pultec PEQ’s Ultra Enhanced version (http://pagesperso-orange.fr/NBNS-Studio/ULTRAPULTEC/ULTRAENHANCEDPULTEC.gif).

In the drawing board at Prodigy Pro there’s a topic in which I’ve asked these question, but didn’t find an easy/uniform answer. Hopefully someone here will be so kind to answer it, as I think it’s a basic question for someone with extended knowledge.

The stock Ultra Enhanced Pultec has aprox 15dB of boost/cut range. I would like to downsize this to aprox 3-5dB of boost/cut range. Is there an easy way to implement this? For example by adding a series resistor before the treble cut pot? Or changing the treble boost pots resistance?

And if the range is successfully downsized, do you need to adjust the SRPP gain stage to maintain unity gain? If so, which resistor would this be?

Thank you very much for your time. Hopefully you are able to help me out. When all goes well, I will add the info to my website for future builders like I did for the Varimu.

Maarten van Helden
www.tubefreak.com

[nrgrecording]

The easiest solution is probably to use potentiometers with a different resistor value and two resistors at each leg of the potentiometer. It makes the same as if you would add two "end stops" to the potentiometers. You don't need to change the gain of the srpp gainstage then.
Iam curious about the reason why you want to have only 3dB if you can have 15dB?!

Frank.