Need a pair of eyes on a spectra sonics 101 vero layout

[digitana]

I think its an error on the schematic. If you look at the component layer  on your 110A photo.. you can make out the  3 diodes and their colour coding reads yellow blue brown brown. On 4 band diodes this translates as 1N461A ..the last band denotes suffix type and brown = 'A' .

 

[Whoops]

I think its an error on the schematic. If you look at the component layer  on your 110A photo.. you can make out the  3 diodes and their colour coding reads yellow blue brown brown. On 4 band diodes this translates as 1N461A ..the last band denotes suffix type and brown = 'A' .

Thanks, I thought the same just wanted to confirm

 

[orangechili]

I've been using the 101 and 110 I've built quite a bit and love the sound of these!

The more I think about it, setting the fixed resistor might help the heat stability of these amps as well, make them run more stable as mentioned. When i get a chance, i'm gonna implement the input pad idea. Thanks for that Whoops! On the 101/110 wiring diagram you posted I notice 3 capacitors to chassis ground, 2 of which coming off xlr pin 1's. Do you happen to know the value on those?

 

[digitana]

Hi orangechilli..can I ask if you used 1n461A or 1n461 diodes ? Also did you play around  using higher quality input/output caps  (eg film type) than the  generic electrolytics  seen on  the 101/110 boards ?

 

[orangechili]

I'm not sure if they were 1n461a's or not. I got them at a local surplus place a few months back. They look like a spot on match with the ones i've seen on SS boards though. I'll look better next time i'm there. The forward voltage on the ones i had measured were in the 820-880 range if i recall. On a slightly related note i've built ampeg scrambler fuzz pedal clones which used the 1n461 diodes and replaced them with modern 1n4148 diodes and had great results. Obviously there's more at play here in the SS circuits but figured i'd mention that as well.

I actually used 220uf cheap electrolytics(instead of 250uf) for the caps on the 110 board. Sounds great and quiet. Even with the gain maxed out at 50-55db range.

The next boards I do i'm gonna be a lot more strict with component selection. I just wanted to test the layouts basically for functionality. Another option, maybe not ideal, if the Q4 and Q5 transistors run a little too hot is to heatsink them. No one's gonna say the pre's sound good except for the heatsinks

 

[digitana]

ok thanks..well I'll try 1n461.. just worried their current rating is a little low .  The specs of 1n461 and 1n461A are identical except for the forward current rating.  Having said that the spec of the 110A claims only 20ma  used !

 

[digitana]

also to be honest  I am not  that convinced 1n461A is needed. The  lowly 1n4148 can handle 300ma and  also has a forward voltage drop close to 1V when  current  around 20-30ma is flowing through it ..so I might also try those..

 

[mutterd]

Wow - good work!

I have been out of town for a while - just getting back home and was pleased to see this…

so - a couple things:

Get rid of that pot in the feedback loop - if you think the amp is quiet now - what till you put a good low noise 10.7k resistor in there. You'll get 40db of dead silent gain, stability, and the instant overload recovery that is magic in these things. Putting a pot, or switching feedback resistors is just a kick in the knee…

In my designs with Spectra stuff I have been using a Grayhill 71 series shorting 2 pole 6 position switch (Jeff at CAPI sells them) for a 30dB input pad in 6dB increments - it works great… One thing to remember for working out the math for the pad is the input resistor (604 in a 101, 2k4 in a 110) is in parallel with the shunt resistors of the input pad…

As for the heat - these things do get hot - I have a 8 channel mixer with 16 101  cards and i do sessions on it regularly - it gets warm after being on for a few days - but not hot in a way that would make me feel like a heat sink is necessary - if you feel that way with just bench use, something is wrong.

one of the most important things to remember with this amp - balance is paramount - like whoops said - these pairs have to be precisely matched - the stability of the circuit, the noise, the overload recovery - and the thermal stability - are all dependant on the matching and biasing of the transistor pairs. I'm not sure how many 3566/4248's you have - but I would build a jig and go thru them and really see what you are dealing with…

The diodes are in fact 1n461A's - I have heard that they were chosen for their particular thermal characteristics…

Also - dont worry about the 220uf/250uf caps - just use some good quality 220uf's for both inout and output. The big things are keeping the transistors balanced and the precision low noise resistors help - all the resistors are RN60D's except the 3 10R carbon comp's..

Finally - a good quiet power supply and a proper DC and HF grounding scheme is very important - there are few tricks to racking them up - when you are ready we can get into it...

If any one is interested I have some PCB's  I made that are the perfect front end to a 101/110 circuit - its the variable 6dB input pad, phase reverse, phantom power and the mic/line switch - I'll take some photos when I'm at the lab tomorrow...

Also - I'm glad people are slowly starting to hear about the site Richard and I are working on - we are compiling all the Spectra info we've gathered into one place - hopefully it will help people to realize what a powerful tool it truly is.

hope this helps.
Timothy

 

[mutterd]

I've been using the 101 and 110 I've built quite a bit and love the sound of these!

The more I think about it, setting the fixed resistor might help the heat stability of these amps as well, make them run more stable as mentioned. When i get a chance, i'm gonna implement the input pad idea. Thanks for that Whoops! On the 101/110 wiring diagram you posted I notice 3 capacitors to chassis ground, 2 of which coming off xlr pin 1's. Do you happen to know the value on those?

the fixed resistor will help with stability for sure. If the pot is causing HF oscillations then maybe it will help with the heat, but i have a feeling the heat is due to things being out of balance...

those 3 caps are .47uf 10V ceramics - they provide high frequency grounding.

 

[digitana]

Hi Timothy.. thanks so much for the invaluable info. I am just about to build a 110 on  some decent quality perf board..having gathered pretty much most of the parts..including the RN60D resistors and parts for a quality +/-24v psu. I'll need to  test the transistors I have  to see if I can get close matches and if need be  buy more. As you say this must be an important key to the  reduction in thermal noise.  I am still amazed at the simplicity of this design  vs the performance ! I am eager to start building soon...

ps: I  would be very interested in purchasing the pcb's you mention ..please send pm ..

 

[mutterd]

I'll take some photos when i get to the lab later, but yeah - its built around this:

http://classicapi.com/catalog/product_info.php?cPath=51_133&products_id=323

and has the circuity for:
6 step input pad
Phantom Power (power supply not included and requires an input transformer)
Phase Reverse  (also requires the use of an input transformer)
High Pass
Low Pass

you can set it up for any HP/LP points you want as well as any steps on the input pad...

I also have mounting boards for a67's and HS56/ HS66's if you are interested…

one thing tho - I wouldn't discount the 101 just because of the experiment in this thread - I have a feeling that any diffence orangechilli found were anomalies to the breadboarding/pots in the circuit/component selection rather than being indicative of the actual differences between the 101 and 110.

The 101 is NOT an inferior amp,  just a different one. In fact - if you look at the spec sheets you'll see that the noise figure is the same - the one thing that is different is the +24dBM output and that's actually an input transfer function thing. Sonically speaking, they do sound slightly different - but the my ears, the 101 with a 500eq driving into a 600 mixing fader is gold.

I have been doing all my designs with 101's because:
a. it requires only a single ended power supply - so you only have to spend the money to get 1 clean power bar
b. in the Spectra lexicon we are not talking about +24dbM or +18dBM peak - we are talking about average - that's an important difference - and +18 dBM has been plenty in my experiences…

I'm not trying to push in one direction or the other - just saying there are benefits to both designs and the 101 is no slouch!

Another thing to mention about the heat/heatsinks - and i am pretty sure i have mentioned this in another thread here - but Flickinger built a lot of his original designs using Spectra cards, at some point he decided it would be cheaper to just copy them and he built lots of pirate Spectra stuff (i actually have a few Flickinger copy 500 eq's)- legend has it that they he couldnt figure out how to get them thermally stable and they used to actually catch fire!!! Bill Cheney said when he took over the company he had a box of burnt out Flickinger copies!

if you take a look at the Flickinger 290 - it looks an awful lot like another amplifier were talking about here!!!

In all seriousness the thermal stability of the 101/110's is a lesser talked about benefit, but it was something that Dilley was very proud of - the amps had the same specs from 40 degrees to 140 degrees - and as you are seeing - thats no small feat…

ok.
Timothy

 

[digitana]

thanks for the 101 vs 110A information .. . I was planning on building both just to compare for myself and well also just out of plain curisoity  :0)

I would also be interested in the traffo pcb's :0) 

I really wish I could get hold of an EQ 500 schemo.. and try to build one.  I know these are being offered along with very nice 1010/110 cards. kits etc on Ebay ..but as I already mentioned..those of us in the EU get clobbered with high levels of VAT + Import duty which makes  all these  nice things a bit out of reach if you just want something to experiment with...

The people in Customs here  in the UK seem to ignore everything coming from China (secret trade agreement ??)  but  look at even the smallest/low value  package from the  USA/CA like hawks...

 

[orangechili]

Wow. Great info indeed. Thank you so much! Another thing to consider is i used Edcor wsm transformers instead of the shielded Triads, probably a considerable difference to these preamps performance. The transistor pairs in mine were matched within 2mv but I still need to get some RN60D resistors on the boards and go the fixed gain resistor route mentioned above.  Two circuits thrown together on veroboard is definitely way too small of a sample size to judge any of these pres. They both sound great!

Also, if you build from scratch definitely bend the legs on those older 1n461a diodes with pliers instead of by hand, they break really easy. I learned the hard way, that's the whole reason this thread was started

 

[digitana]

just wondering where you sourced the 1n461A's ?
[Edit] ok found some on Ebay :0)

 

[digitana]

I decided not to use vero board for the 110 but rather use some nice quality 2mm FR4 pad board I got from China (130mmx56mm)  I  managed to layout the components  almost the same as on original SS 110 boards. The  wiring up  on the rear is  essentially point to point.. but  keeping with the original  layout its  not too messy...though haven't quite finished yet.  Can't wait to finish the  psu I'm building to test this out ..

 

[Whoops]

I decided not to use vero board for the 110 but rather use some nice quality 2mm FR4 pad board I got from China (130mmx56mm)  I  managed to layout the components  almost the same as on original SS 110 boards. The  wiring up  on the rear is  essentially point to point.. but  keeping with the original  layout its  not too messy...though haven't quite finished yet.  Can't wait to finish the  psu I'm building to test this out ..

Looks Cool

 

[marconemusic]

Hey guys.

Im new here. was searching for spectra info out of curiosity.

Just letting yall know. I have a SS110 built with the A67j transformer and the 66 output transformer. My build includes a Selectable input gain and a trim for the output, -20db pad, led meters on the front for signal, as well as a selectable Di input on the front for bass guitar or what not. Line out, xlr in and out on the rear.

This beast was built in 2008 and is stable, has been 'on' pretty much non stop since then and still is one of my fav. The selectable gain is possible and stable.

Being almost ten years ago, i dont remember exactly what components and specs but im about to make a side car with 10 more.

FWIW the card i got for my this one was original and has the 2n transistors that look modern, not like the fairchild ones. also the diodes are 1n461a black that look like little caps. not the clear color banded ones. It seems maybe they made different versions along the way with slightly different components? Anyways, i got myself pretty much enough components to build 30 more cards. Might just do it one day if i can find any more transformers only have enough for 6 full pres.

Ramble over.

Moral of the story, selectable gain is possible and stable. Proven now for almost ten years in my build.

 

[pH]

Hey guys, wondering if you could help me troubleshoot a problem here.
I've racked up a pair of 101 cards and one of them isn't working, no voltages going through any of the transistors nor DC output, only B+  at the dropping resistors and through the three 461A diodes. I swap the cards in the EDAC connectors and the problem follows the card. Resistances and connections checked against the good card, nothing obvious wrong.
Would one bad transistor take down the whole circuit like this? Any suggestions where to look?

Thanks,
Paul

 

[mutterd]

selectable Di input on the front for bass guitar or what not.

Id be curious to hear more about this - does it have its own transformer?

also - I'm curious how you did the "input gain" adjustments.

thanks,
T

 

[Whoops]

Hey guys, wondering if you could help me troubleshoot a problem here.
I've racked up a pair of 101 cards and one of them isn't working, no voltages going through any of the transistors nor DC output, only B+  at the dropping resistors and through the three 461A diodes. I swap the cards in the EDAC connectors and the problem follows the card. Resistances and connections checked against the good card, nothing obvious wrong.
Would one bad transistor take down the whole circuit like this? Any suggestions where to look?

Thanks,
Paul

I would check all the Resistors after B+, do they all have the right value? is any if them open?
Also Check the Cap
Then also the Diodes, are they good? is the orientation correct?

transistors one by one will follow, also check the PCB traces for a possible short

Not a lot of components on the board so it should be easy to troubleshoot

let us know how it goes