caruso preamp blog on vinylike.com

[flozki]

hello everybody.

i finally managed to put some information about the caruso preamp on the vinylike site... like partslist with mouser order-numbers, mods, schematics....

it is a blog and from now on you will find all information i have so far there.
http://vinylike.de/index.php/carusopreamp/

i also did a quick test with the grampian head because there are a few people using that amp with grampian...
tests where done only on my lab desk. no cutting yet...
and it would be nice if grampian users can verify this...

thanks
f.

[markrob]

Hi Flo,

The link to the schematic is broken on the blog. Based on the block diagram and your comments on setting up for the Grampian, I think you may be missing needed dominant pole compensation to close the loop properly. In the case of a moving coil head, there is no need for this (in fact a bad thing). But with the Grampian it is required if you want to avoid that nasty high frequency oscillation. Both the RA7 and Gotham amps had this built in as they were purpose built for this head. If you fix the bad link, I may be able to suggest a mod to add the proper loop compensation to allow for more stable operation of the head using your pre-amp.

Mark

[flozki]

uup fixed the link.
anyway i did yesterday a quick test.
nasty feedback comes when too much feedback. but before its is very stable..


but i think the maximum you can gain on grampian is compensate loss in low end (3-6 dBs) when if i remember right?

all ideas wellcome.grampain users would like to know best values.
and i dont have the time and need to figure out better...

f.

[Nickou]

hey flo

super cool !! c est le projet le plus interessant depuyis 10 ans !!!

ok , how I can log , do I need a wordpress account ?

I tried with no success

[markrob]

uup fixed the link.
anyway i did yesterday a quick test.
nasty feedback comes when too much feedback. but before its is very stable..


but i think the maximum you can gain on grampian is compensate loss in low end (3-6 dBs) when if i remember right?

all ideas wellcome.grampain users would like to know best values.
and i dont have the time and need to figure out better...

f.

Hi,

3-6db iof feedback is way too little. It will not completely flatten the head's low frequency response and, as much as this type of head can, improve distortion (only at low frequencies as you mention). The problem is that when you try to close the loop on this head with the pre-amp as designed, you are reliant on some uncontrolled roll-off in the system to reach the unity gain crossover. By adding a controlled -6db/oct roll-off at the midband, you force the open loop response to crossover unity gain at a much lower (and controlled) frequency. I suggest this roll-off at around 2-3Khz. This allows 20db or more of feedback and results in a flat head response from 20hz-20Khz.

Looking at you schematic, this can be easily done by playing with the components in the summing stage. As I see it, this is what would be required:

Remove C403 Note: there are two?? C403's on the schematic. This clearly an error. The device I'm talking about is the 100pf value

Remove C404 and C405.

Replace R406 with a jumper

Remove R408

Remove R606 (sets SSM2019 gain to unity)

Replace R405 with a 150K resistor

Replace C403 (the 3.3nf unit) with a 390pf capacitor

The combination of R405 and C403 results in a simple single pole low pass in forward feedback loop. The break point is :

F = 1/ (390e-12 x 150e3 x 2 x PI) = 2.7Khz

The 150 K value provides a gain of about 10 as seen by the feedback. Depending on the sensitivity of the power amp, you may need to adjust this up or down. If you change the resistance value, make sure you change the capacitor to keep the break point the same. Also make sure you get the feedback polarity correct or you will make an oscillator.

I don't have this pre-amp to test, but based on my experience building a similar summing amp, I belive it will work fine. This design is nice compared to mine becuse the RIAA is built in and it is easy to adapt to the moving coil heads.

Hope this is of some help.

Mark

[maniman]

Aha , MarK considerations about adapting with the Grampian gonna taked in care for me , maybe a document about use the board with the Grampian can be do it , not ?

For me its a very long term project but someone with better skills (and more instant results wanted ) can be useful.

Seeinng the old "Jamaika Style" sheet I must assume the new board follows that idea ? (not ?)

I'm totally new to electronics , and is more for plasure than per function , try to do the power supply before starting with the board operation (and disgrace it heheh).

Taking in care the OPA's are the only active component mounted on the board , every OPA2134PA have max current requirement of 5 mA x 2 , not ? , must assume the max consumption of the board gonna be 30 mA ? thats right ?

at the power supply a transformer with something like 0,97 A (3,5 VA) can be enought ? its a problem have oversized transformer ?

Thanks

[markrob]

Aha , MarK considerations about adapting with the Grampian gonna taked in care for me , maybe a document about use the board with the Grampian can be do it , not ?

For me its a very long term project but someone with better skills (and more instant results wanted ) can be useful.

Seeinng the old "Jamaika Style" sheet I must assume the new board follows that idea ? (not ?)

I'm totally new to electronics , and is more for plasure than per function , try to do the power supply before starting with the board operation (and disgrace it heheh).

Taking in care the OPA's are the only active component mounted on the board , every OPA2134PA have max current requirement of 5 mA x 2 , not ? , must assume the max consumption of the board gonna be 30 mA ? thats right ?

at the power supply a transformer with something like 0,97 A (3,5 VA) can be enought ? its a problem have oversized transformer ?

Thanks

The Jamaika has the same issue, no dominant pole in the forward loop. You will run into the same stability issues with any large amount of feedback applied. The fix is similar to Flo's.

Mark

[maniman]

Aha , I understand most changes you are talking about here (thats a theorical way to fix the issue , not ?) , but when say "Remove R606 (sets SSM2019 gain to unity)" , i dont understand that part , SSM2019 is another operational than the used here , not ?

Thanks.

[flozki]

for the grampian you can leave out the SSM2019 totally. if you watch the pictures on vinylike.com you can see that i just inserted a wire bridge between pin 3 and pin6 also the 10 ohm resistors R601,R602 you can replace by wires... but it doesnt change big things..jsut save parts if you dont have them and if you are never intend to run it with a moving coil feedback head later.

for the power supply bigger is always better. but somethink like 100-200mA each side is great.
i use standard 7815/7915 designs normally and use 5-15W transformer.2x15V secondary.

but you find tons of schematics and links how to build the power supply together.

[maniman]

Ohhhh , yes yes , the IC601 part , really i wasnt see that , ok ok , now totally clear , I think have all the parts to start with this.

Thanks Mark and Flo for the fast responses and take the time for that newbie dumb questions.

Best Regards

[flozki]

just checked power consumption:

preamp board version1.0
all TL082 opamps (fet and low power)and IC601 not used. this is the version you have:
11mA at +15V
11mA at -15V

preamp board v1.1
all NE5532 (bipolar and not low power) opamps and SSM2017 for IC601
33mA at +15V
33mA at -15V

preamp board v1.1
all NE5532 (bipolar and not low power) opamps and INA 126P for IC601
23mA at +15V
23mA at -15V

so if you have +/- 50mA thats quite ok

[maniman]

Thanks for that data , today i finalized the power supply , monday at work ask to the guys to see what that does under the oscilloscope and check for the N+R achieved , some suggestion about isolate the power supply possible noises ? , actually

Transformer (2.4 VAC) -> rectifier -> 2200 uF -> 22 uF -> Regulators -> 100 uF

its a generic design , seems quite right ? quite wrong ? maybe can i expect feed 2 boards in the future with that PS ? (aprox 90 mA)

super cool project , i am really enloying , thanks.

[flozki]

just a standard power supply:

http://www.eleccircuit.com/power-supply-regulator-15v-15v-1a-by-ic-7815-7915/"


for example when you want make it even better use LM117 (317) instead of 7815/7915



very easy you find tons of links. should be no problem.
7815/7915 is totally fine.
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[maniman]

I'm ready to test it.

test the board without the opamps first.

check with a multimeter if you have connection between pin1 &2,Pin2&3 and Pin1&3. if you have connection between those pis. something is bad.

Thats mean between the opamps 1,2&3 pins ? or the J100 power pins ?


And about the power , what is the pinout of J100 ? the common is the center one ? or its the right one with square form connection ?


Mani

[flozki]

hello mani.
yes of cours the j100 power supply connector.
if you have no short between ground and +15V and -15V then you can plug in the chips. shoudl work.
but this quick test is worth to do. needs 30 seconds...

[maniman]

Yes , sorry i saw all in the schema later , now the board is complete , i attached the ps and try somethings , but no sound at the output , maybe is something related with the 2 resistors bug ? more tests these days.