DIY Simple Active Preamp

[ghazzer]

Nice work Scott!
.

 

[sfox52]

Thanks, Steve. Do any of the popular op amps have more gain than another type? I may try changing it out tonight.

 

[HypnoToad]

You can lower the value of the 8.2k resistors to increase the gain.

OPA2134's have slightly more gain than AD823's.

 

[sfox52]

That's what I'll try. I like the way things sound but the volume peaks about 2/3 up the travel of the pot. It reminds me of the way a basic Haller passive attenuator behaves.

 

[murali_n]

Hi all,

Here is my build;


N.Murali

 

[Kappaholic]

Any more updates with SSP BOM?

The latest recommendations for SSP I can make out are:

1) replace 10 uF with 100 uF Caps
2) replace 100K with 200K resistors

Should 2.2uF caps be removed? (I want to be able to connect CNC & HTMCPS plus one AUX input) with LSA

Would I have enough volume gain with 100K pot with LSA? Should I need to get different value resisters than 8.2K?

Would this source selector work for my application?

Thanks in advance

 

[HypnoToad]

1) replace 10 uF with 100 uF Caps
2) replace 100K with 200K resistors

Should 2.2uF caps be removed? (I want to be able to connect CNC & HTMCPS plus one AUX input) with LSA

1) You can use 100uf or 47uf caps.

2) You can replace the 100k with 200k resistors it will slightly lower the corner frequency. ie: slightly more bass extension, but probably not that noticeable.

With the 2.2uf caps in the SSP, they are for DC blocking, if you end up with DC offset these will stop it from reaching your amp.

You can safely remove the 1uf cap from the CNC and the 1.5uf or 2.2uf caps (depending on what you went with) from the HTMCPS IF you are running it through the SSP though. You can try shorting them out first with a jumper (don't put the jumper in place with it switched on) and see if there is any noticeable difference.

 

[ghazzer]

Scott: You can check out other listener's imperssions of various opamps in the CNC here. A few of the variables that will affect you impressions of each opamp & combinations are:

Your ears
Your listening area
Component selection
Your gear & the way you set controls
Humidity
Day of the week . . .
# of beers . . .
.

 

[Renron]

Murali,
Congratulations on finishing your build. I can only imagine how good it (doesn't) sound! Hoorah.

Kappa,
The 100K pot you asked about is the variable resistor for the LDRs, the 100k pot itself does not attenuate the volume. (signal doesn't go thru the pot)
Looking at the relay board you posted, I downloaded the spec sheet for the relays themselves, they look pretty good.
Bifurcated (Gold overlay silver-palladium), 5V coils, high sensitivity, non latching, 1A at our input voltage. Can't speak of the board itself, any documentation by the seller? It's got pretty black and gold caps thou.
Price is right? Go for it and let us know what you think.
Ron

 

[omishra]

This is how LSA need to connect SSP, Where SSP input is fed by CNC phono or any other source.

 

[Kappaholic]

1) You can use 100uf or 47uf caps.

2) You can replace the 100k with 200k resistors it will slightly lower the corner frequency. ie: slightly more bass extension, but probably not that noticeable.

With the 2.2uf caps in the SSP, they are for DC blocking, if you end up with DC offset these will stop it from reaching your amp.

You can safely remove the 1uf cap from the CNC and the 1.5uf or 2.2uf caps (depending on what you went with) from the HTMCPS IF you are running it through the SSP though. You can try shorting them out first with a jumper (don't put the jumper in place with it switched on) and see if there is any noticeable difference.

Thanks for the recommendations. I will implement the changes to the build.
In regards to the 47uf caps, is this the cap for the opamp? I am curious in the changes made from the CNC, which the 10uf was used, and the HTMCPS & SSP now being recommend for 100uf & 47uf. Would these cap values may be related in some way to do with compatibilities of the opamps? As you have also noticed that some opamps seems to be more difficult to drive, i.e. LME49990 compared to other opamps for the input socket for HTMCPS. Would using 47uf in HTMCPS also help or would 100uf in SSP poses similar symptoms as HTMCPS for opamp compatibility?

Thanks again for all your help. I am sure this will turn out to be another awesome build for me.

 

[Kappaholic]

Kappa,
The 100K pot you asked about is the variable resistor for the LDRs, the 100k pot itself does not attenuate the volume. (signal doesn't go thru the pot)
Looking at the relay board you posted, I downloaded the spec sheet for the relays themselves, they look pretty good.
Bifurcated (Gold overlay silver-palladium), 5V coils, high sensitivity, non latching, 1A at our input voltage. Can't speak of the board itself, any documentation by the seller? It's got pretty black and gold caps thou.
Price is right? Go for it and let us know what you think.
Ron

Thanks for looking it up. I wouldn't know much about the parts being used, but they do sound like quality parts. I will start placing orders for the build soon. I am very likely to order the input selector in the pic. I hope they play along nice with other parts.

 

[Kappaholic]

This is how LSA need to connect SSP, Where SSP input is fed by CNC phono or any other source.

This is awesome! Thanks for the wiring diagram.

 

[Renron]

About the "Pot". I know you can use either type, logarithmic or linear. Here's what Udaily , who makes a tweaked version of the lightspeed had to say about which pot he prefers.
"Log pot will help the volume come up slower than a linear pot. You can order log or audio taper. I like the Alpha pots a lot. "
So there ya go. I'm ordering an Alpha 100K log pot cause I like the way the Alpha's feel.
Ron

 

[Renron]

Here's another post, from the Man himself who invented the Lightspeed LDR.
"A log pot 100k will give better low level sweep than a lin.
With match quad set of ldrs you will get more low level control in the first half of rotation. With matched pairs anything can happen depends which is in series and which is in shunt.
Cheers George "

 

[HypnoToad]

Thanks for the recommendations. I will implement the changes to the build.
In regards to the 47uf caps, is this the cap for the opamp? I am curious in the changes made from the CNC, which the 10uf was used, and the HTMCPS & SSP now being recommend for 100uf & 47uf. Would these cap values may be related in some way to do with compatibilities of the opamps? As you have also noticed that some opamps seems to be more difficult to drive, i.e. LME49990 compared to other opamps for the input socket for HTMCPS. Would using 47uf in HTMCPS also help or would 100uf in SSP poses similar symptoms as HTMCPS for opamp compatibility?

Some opamps don't behave well in the input section of the HTMCPS, but since there are plenty of op amps that do it's not a problem.

The capacitors reduce noise and the 0.1uf ceramics reduce the possibility of oscillation. It's not that important if you use either 10uf / 47uf / 100uf especially if using batteries. But any of these sizes will help a lot if using a PSU, I prefer either 47uf or 100uf though.

 

[Kappaholic]

Some opamps don't behave well in the input section of the HTMCPS, but since there are plenty of op amps that do it's not a problem.

The capacitors reduce noise and the 0.1uf ceramics reduce the possibility of oscillation. It's not that important if you use either 10uf / 47uf / 100uf especially if using batteries. But any of these sizes will help a lot if using a PSU, I prefer either 47uf or 100uf though.

Thanks again for your patience and information. I will order bunch of the 47uf caps and give it a whirl also on CNC & HTMCPS as well.

 

[Kappaholic]

LSA board BOM question

I am trying to place my order for the build and got stuck at 7805 -3 pin regular. Can someone please direct me the correct 7805 regulator for the LSA? It would be greatly appreciated if someone can share the links for the components. Better yet, Let me provide the links for what I have so far.

Here's a LSA BOM I have reserved so far from Mouser:

100 Ohm resistor - http://www.mouser.com/Search/Produc...B14virtualkey61300000virtualkey71-RN60D-F-100

1K Trimmer - http://www.mouser.com/Search/Produc...virtualkey65210000virtualkey652-3296W-1-102LF

1uF Cap - http://www.mouser.com/Search/Produc...Uvirtualkey66720000virtualkey667-ECE-A1HN010U

10uF Cap - http://www.mouser.com/Search/Produc...Uvirtualkey66720000virtualkey667-ECE-A1VN100U

7805 V-Regulator - ?

100K V. Pot - ?

Is 2mm the right lead spacing for the caps?
Thanks in advance.

 

[Renron]

Looking at Mouser's page of 5V regulators, the very first one accepts up to 35DCV and up to 1.5A. It has a Ripple Rejection of 62dB. If you need to you can hang a heat sink on it too. (depends on the input voltage) .69 cents.
511-L7805CV-DG

For a Pot, this one looks decent, and it's cheaper than the Alps I was looking at too!
$2.16
652-PTD902-2015KA104

I don't have that board yet so I can't measure the cap lead spacing.
Ron

 

[omishra]

LSA parts list

Cap lead spacing is 2.5mm.

No affiliation from below locations.

1 X LM7805CT-ND (5V linear regulator) http://www.digikey.com/product-detail/en/LM7805CT/LM7805CT-ND/458698

1 X P10389TB-ND (1uF/50V) http://search.digikey.com/us/en/products/ECA-1HM010B/P10389TB-ND/268474

1 X P10393TB-ND (10uF/50V) http://search.digikey.com/us/en/products/ECA-1HM100B/P10393TB-ND/268478

2 X 3296W-102LF-ND (trimmer 1K) http://search.digikey.com/us/en/products/3296W-1-102LF/3296W-102LF-ND/1088044

4 X 100XTR-ND (100 ohm, 1% 1/4W MFR) http://search.digikey.com/us/en/products/MFR-25FRF-100R/100XTR-ND/14795

1 X (Dual ganged pot 100K) http://www.ebay.com/itm/2pcs-Dual-S...634?pt=LH_DefaultDomain_0&hash=item5642be1baa

5 X A98442-ND (2-pin terminal blocks) http://search.digikey.com/us/en/products/796689-2/A98442-ND/1153986

4 X NSL-32SR2 (Matched LDRs) from http://www.buildanamp.com/2-Light-Dependent-Resistors-LDRs_c2.htm
or http://www.alliedelec.com/search/productdetail.aspx?SKU=70136788
Buy matched from first location or umatched 10 from any of them and match them for min current nearest resistance values.