First Pass Build. F5. General Help Needed.

[madisonroberts]

Hello,
I have been collecting parts for this build for 6 months or so and finally started to put it all together. I am using a 400V, dual 18V Antek AS-4218. I had been planning on going full dual mono but i cannot seem to get my hands on another Antek transformer because their factory burned down or something. There are 4 68A 600V IXYS rectifier bridges. I know these are overkill, but it is all they had in stock when i ordered them. I have two power supply boards with 88,000 in capacitance on each side (total of 176,000).

I am having trouble figuring out how to go about wiring for this configuration... I attached a drawing of how i believe it can be done below. This is my first solid state build and i am just a little bit confused. Any help with wiring this pseudo dual-mono F5 would be much appreciated. I only need help with wiring from transformer secondary and forward.

This has been an extremely fun project and i have learned A TON! I can't wait to get this thing fired up.

Thanks in advance,
Madison

 

[Zen Mod]

give us little bigger sketch

this one is thumbnailish in size

 

[madisonroberts]

Oops. hopefully this works. I think you can enlarge it a little bit now.

 

[Zen Mod]

it will work - just go for it

don't forget to enjoy ........

 

[madisonroberts]

Ok great. I will complete all the wiring when i get off work. Hope to hear some music tonight. Thanks

 

[AudioSan]

just take your time with adjusting, warm up and final(ish) adjustment

 

[madisonroberts]

When grounding the power supply boards, do i need to use two thermistors at separate grounding points? Or two thermistors on (one on each side) that meet at Earth ground? I believe this is my last dilemma.. Any help would be great. Thanks

 

[Zen Mod]

one ground - one ntc to chassis

you have two grounds , for my understanding

 

[madisonroberts]

Ok, so just to be clear. Both power supply boards ground to meet on one end of a thermistor? Also, should I leave the power transformer shield floating, or connect to it ground? I have seen both been done..

 

[Zen Mod]

connect both shields directly to chassis in one point

connects both main audio grounds , each through own separate NTC , to one (common) point on chassis

 

[madisonroberts]

I finished my F5. It biased nicely and all measurements seem to be within spec. I am having a problem though. When both RCA cables are connected, I am getting some low level hum. It is not volume dependent. Music is playing but there is hum in the background. But when only one is connected, that channel is crisp and clear with no audible hum whatsoever. Here is the source:

Squeezebox Touch=>
Cambridge Audio DacMagic Plus=>
Grounded Grid Preamplifier (Tube)=>
F5

This configuration works like a charm when powered by my 125W KT120 Tube Monoblocks. Is this some sort of grounding issue. Impedance problem? Any direction would be great because I am at the end of the road with this build and i am extremely excited to listen to some tunes.

I am in the process of ordering parts for a DCB1 build to match the F5.

Thanks in advance..

 

[Zen Mod]

give me pics and few words about concept - stereo amp with one PSU, monoblocks in one case , ........ yukyuk ?

 

[madisonroberts]

400V Antek AS-4218 - Dual 18V Secondary

(4X22K Capacitors) X 2 = 166K Total Capacitance

(4) 68A 600V IXYS Bridge Rectifiers

I believe this hum to be some sort of grounding issue. Right now i have each PSU grounded through its own NTC (1 per side) and then connected to a common ground point. Earth ground also meets in this point. Along with the purple "Shield" wire from the transformer. PSU and amp boards are connected through V+, V-, and ground.

I tried connecting a wire between the RCA input ground on both sides. I did this on the actual RCA jack side of the wire, not PCB side. This cut the hum in half. This is not shown in the photos by the way.

Any ideas on what else this could be. I have the hum down from where i started and it is quite faint. It can only be heard when music is at low volume or off. The hum does not increase with volume.

As i said earlier, while only one RCA cable is connected, that channel has absolutely zero hum.

Any suggestions on some grounding schemes would be great.

I am a beginner (maybe an intermediate) and this is my first build that wasn't purchased as a kit.

I must say that when music began to play (even know there is this slight hum), i felt a profound sense of accomplishment. This is a great hobby and i have learned very much from this forum (mostly reading though).

Thanks in advance

 

[madisonroberts]

Oh yeah, and the LEDs on the AMP boards are not lighting up.. I am almost 100% positive i put them in the correct way. Maybe i will remove them and insert new ones. I checked everything like three times before soldering though.

 

[madisonroberts]

Biased at .59V with almost zero DC offset. Power supply rails are +25V/-25V

 

[Zen Mod]

trick No.1 - put 10-15R resistor in series with one black wire on one RCA

trick No.2 - solder fat (shortest you can manage ) wire bridge between two central gnd points - those gnd points on pcb(s) , left up of P1

No.1 or/and No.2 will solve ground loop problem

 

[madisonroberts]

Ok great thanks for the advice. I chose option two and connected a 14 gauge wire from ground to ground on the amp pcb's. This solved my problem. The amp is almost totally silent now. I have extremely high efficiency horn speakers and the amp is still quite silent.

I have ooooone more question and ill leave you alone (for now). I have been regularly checking voltages to make sure everything remains constant. The bias is not fluctuating at all and has remained pretty much constant at .59VDC. Anyway, i have noticed that the power supply voltage has lowered evenly from the previous +/-25VDC to around +/-22.9VDC. The AC voltage from the wall has remained the same at 119VAC and i have checked the secondaries to be constant at 18/18V. Was this caused by the ground connection i made? This is the only change i have made.

Just want to be sure these voltages are OK and wondering was may have caused it..

Thanks in advance

-Madison

 

[Zen Mod]

just chill

22V9dc is what you can and must expect from 18Vac , when loaded with standard FW Iq (between 1A5 and 2A)