What is on your workbench right now?

[Rick Sykora]

since my Sure-based bench amp came up shy, decided to upgrade it to a Hypex NC250MP. Have a Ghent case that will work, but is stereo one and thinking will use the less expensive case I used for the Sure...

This is the first Hypex amp I obtained that supposedly improves power down behavior. So looking forward to testing it!

 

[dfuller]

Got two guitar amps in right now.

1. A Fender Twin Reverb reissue that was no-loaded by a faulty speaker cable and nuked some socket mounted resistors bad enough that I'm just replacing the sockets rather than trying to clean the carbon off.


2. A Bogner Uberschall Twin Jet with what I'm almost entirely certain is a bad plate resistor on the input stage.

Update on the Bogner: Was not a bad plate resistor, rather a plate-to-grid local NFB cap went leaky (silver mica, it happens) and pulled the B+ rail down to 15V on that stage. Replacing it with a C0G MLCC as they're less prone to go leaky.

Oh, and the Twin Reverb: the nuked half of the power amp is rebuilt. Those big heater wires are a pain in the ass to fit through the solder lugs - at least, on the one where there are no less than 3 connections.

 

[Rick Sykora]

Before the NC250, had to finish adding clip indicators to my NC502MP....

the little board in the upper right (with light blue resistors) is an LED board salvaged from my first hifi cassette deck. Still debating whether to add standby switch.

In the meanwhile, my brother asked for a memory upgrade for his new Mac mini...

 

[JP]

Victor TT-101. I despise working on TT-101s.

 

[Rick Sykora]

Added the standby switch to NC502MP and buttoned it up...

Planning to start on NC250MP after Thanksgiving. After learning the Hypex amps need RF filtering, am researching how best to add. Seems to be a lot of filters for non-audio applications, but no canned solutions. Any suggestions?

 

[dfuller]

Another day, another guitar amp. This time, some ancient and extremely obscure 1960s era Japanese 5 watter - "Tempo" brand, apparently a sub-brand of Univox. 1 12AX7, 1 6AV6 (half a 12AX7, plus 2 small signal diodes), 1 6AQ5 (more or less a 6V6 stuffed inside a B7G tube). I'm thinking a recap is in order because so far as I can tell, this multisection can cap is the original.

 

[boXem]

Added the standby switch to NC502MP and buttoned it up...

Planning to start on NC250MP after Thanksgiving. After learning the Hypex amps need RF filtering, am researching how best to add. Seems to be a lot of filters for non-audio applications, but no canned solutions. Any suggestions?

The NCxxxMP modules have an RF filter embedded. Unless you specifically have an issue, do not loose your time.

 

[Rick Sykora]

The NCxxxMP modules have an RF filter embedded. Unless you specifically have an issue, do not loose your time.

Thanks! Good to know. No time wasted as still need something for my NC500 monoblocks. But will save some cash not having to add to my MP family amps.

 

[MarsianC#]

Cambridge Audio AR30. Both power supply fuses burned, main fuse is ok. No obvious faults to be seen.
I will investigate further

 

[Rick Sykora]

After some distractions, worked out the NC250MP layout and did the fabrication today.

Due to smaller case needed to downsize the speaker jacks...

 

[Rick Sykora]

Round 2. Wired up and passed initial checks with flying colors...

Now to add standby power switch and maybe a clipping LED.

 

[boXem]

Round 2. Wired up and passed initial checks with flying colors...

View attachment 98411

Now to add standby power switch and maybe a clipping LED.

May I suggest to find a way to keep the input wiring away from speakers outputs (already the case) and from the AC (at the left of the picture)?

 

[dfuller]

Another day, another guitar amp. This time, some ancient and extremely obscure 1960s era Japanese 5 watter - "Tempo" brand, apparently a sub-brand of Univox. 1 12AX7, 1 6AV6 (half a 12AX7, plus 2 small signal diodes), 1 6AQ5 (more or less a 6V6 stuffed inside a B7G tube). I'm thinking a recap is in order because so far as I can tell, this multisection can cap is the original.

Update on this: Recapped (thanks to CE Distribution having 500V 20uF 105C caps for uber-cheap), but another issue has presented itself: The controls that are supposed to be grounded kinda... aren't. I imagine there's some oxidation between the chassis and the pot shafts. I could clean them, or I could do the other simple solution which is just attach them to the main ground buss and proceed to not worry about it again.

 

[drfous]

A pair of Sansui Q-16s. If anyone has information on these I would appreciate any input. Not much coming through the google machine.

 

[Rick Sykora]

May I suggest to find a way to keep the input wiring away from speakers outputs (already the case) and from the AC (at the left of the picture)?

Thanks, the pictured wiring layout is not complete as I still have more to do. Am very aware of the need to keep signal wiring away from higher level ones to avoid induced noise. I used to work in industrial electronics. It may be a bit tricky with the limited space, but will reevaluate when I put the case halves together. I have a audio analyzer, so can see when different wiring routing choices affects noise levels.

Am still working on how to nicely secure the ribbon cable connectors. Likely they will get some RTV when am closing up.
The ribbon connectors are my least favorite part of the Hypex design, but see they have retention on the some of the other modules where space was less of a concern.

 

[Rick Sykora]

Final wiring is done. Kept the AC wiring away from the signal by running it across the case top whereas the signal cable runs along the bottom. Here is a pic with the standby power switch...

Here is my test measurement on my QA401...

A quick listen test correlates with the clean measurement and the output power is spot on Hypex spec. The little jag at around 300 mW is due to dual stage attenuation in the QA401. Am still hearing some power transients when using unbalanced inputs but balanced is fine.

 

[tomchr]

Currently my bench contains three projects:
- TCA HPA-10.
- A headphone load box that I'm building. It will allow for remote control of the load resistance and capacitance so an APx500 audio analyzer can switch the load automatically.
- A Threshold SL-10 that needs recapping.

Tom

 

[Rick Sykora]

Some paying work for a member that wants his Pioneer crossover to be modded with Dennis’s upgrades...

 

[pma]

Tube preamp - preparing a listening test that is posted at

https://www.audiosciencereview.com/...-world-tube-preamplifier-about-2-7-thd.18392/

 

[Rick Sykora]

Some paying work for a member that wants his Pioneer crossover to be modded with Dennis’s upgrades...

View attachment 99053

Now with the mods. Lots more parts! Main pcb has 5 and added daughtercard has 4...