What qualities (and design) do you most value in a harp amp?

[d. spree]

yes, I know this is a very subjective question, but I am not looking to find consensus or a definitive "answer" to teh question. I am most interested in hearing about the variety and range of opinions forum members have.

[Mick Bailey]

I've been working interactively with a harp player on customising a VHT 12/20 guitar head for harp use. It took quite a few trials but he's been using the amp regularly since the last update.

Here's what was needed for his Chicago style;

1. The treble needed reducing considerably, with the emphasis on bass and lower mids. I had three goes at this and each time the amp came back with the owner saying he needed less treble. It's pretty useless for guitar now, though. The tone stack was replaced with a modified 'Moonlight' stack and the static preset FMV stack bypassed completely. This also gives better drive to the following stage.

2. The input stage was reconfigured to give much earlier break up with a harp mic. This meant lowering the B+, increasing the anode load resistor and re-biasing, more like a Harmony amp configuration. Some experimentation was done to reduce feedback at higher volume, and quite a few NOS preamp tubes were auditioned. There's now very little clean headroom.

3. The standard unbranded Chinese 6V6 output pair were changed for JJ6V6s and this gave a slightly less-harsh sound when the amp was cranked.

This is the non-reverb version of the amp, which is easier to work on.

[Mrsices]

It really depends what you want to use it for... I have an original 80s Paul Rivera Super Champ, which I used to use to record harp and occasionally play harp with a duo. It was fine in those settings, but used to struggle in a band context.

[soundguruman]

yes, I know this is a very subjective question, but I am not looking to find consensus or a definitive "answer" to teh question. I am most interested in hearing about the variety and range of opinions forum members have.

Not really subjective. There are 2 basic things.
1. You must have EQ to notch the feedback out, graphic EQ, parametric EQ.
Once you notch the feedback out, you increase the gain quite a lot.
2. Plenty of gain to get overdrive in the preamp. But this is impossible without a really good EQ.
So it all revolves around EQ ability. The EQ has to be really selective and has to cut -20 db to -40 db per frequency.
This is why parametric is very useful for removing feedback, in say, 3 frequencies.

All harp amps have that very same problem.
Otherwise you will never get enough volume without squealing feedback.

And without that volume, you can't get overdrive to work...it will just squeal instead.

ALL professional PA systems are built around that EQ principle.
Without the good EQ, the PA will never get loud enough.

You need to apply that same principle, as a professional PA...with professional EQ.

WMD Effects Utility Parametric EQ

Here is a parametric. You select 3 frequencies and cut all 3, and the band is variable from narrow to wide in each frequency.
By cutting 3 frequencies, you remove the squealing feedback.
And as a result, you are now able to increase the volume.
As you increase the volume, you get more saturation and overdrive, without squealing.

[km6xz]

Compression, a fast attack, 150ms release and 2:1 ratio is a good starting point. A high Q notch filter will work much better for FB control than EQ unless you want a wide range sucked out of where it is needed most. One key to getting a richer should is consider the mic impedance. Most use old pawn shop crystal or ceramic mics which are very high Z and match a direct grid connection. A dynamic ca sound smoother and less edge but does not match direct grid connection. Dynamics usually have a 130-300 ohm Z so if loaded by an unterminated load, will ring and sound harsh or a bit brittle. So use a good mic to line transformer before the amp input so both the amp and mic are seeing the Z they want. That harsh edgy sound of unterminated dynamics is usually the cause for the knock on small balanced line input mic preamps in mixers because few people understand the importance of matching the load and source Z when dealing with low Z, power circuits. The goal is maximum power transfer, as opposed to the voltage transfer in a bridging application(very low source Z feeding one or more high Z loads). Dynamics sound much better when matched source to load Z

[Chuck H]

What Stan said. I'm guessing this has worked for him in a recording atmosphere, but it's all relative, right? Here's what worked for me.

I had a little amp I built with the guts from a VOM record player. Tiny OT and the PT only put 300V on a pair of cathode biased 6V6's through a 5y3. I used a BF "normal" channel preamp into a LTP, both typical Fender values but the TS was hardwired to a chosen voicing. The amp only had a power switch and a volume control in a 13X13X9 pine box with a single 10 and covered in purple vinyl. A harp playing friend asked me if I had a little amp he could use. So we re-voiced it for his mic. This amounted to changing the TS hardwired values to something like bass-10 mid-7 treble-0. That was it. The slight mid scoop probably helped with acoustic feedback control and was compensated for by the low HV and small boxy combo sound. A tad bright, but very smooth and not peaky at all. Probably about ten or eleven watts. I looked into "mods for harp amps" but my friend asked me not to change a thing. When he needed more power (not often) he mic'd the amp into the PA. Said all the harp guys were gaga for his tone. He was a pretty good player too so that doesn't hurt.

I agree that getting feedback under control when pushing a clipped signal via a bright mic is probably the trickiest problem. And I'll side with SGM and Stan with a narrow notch filter. I just got lucky in that the above amp was well behaved with my friends two mic's.

[km6xz]

For recording I would be working in a different environment, recording, even live is not the same performance...playing or production techniques. I had a number of harp players want sounds on stage that we got in the studio. It is a different task, much easier in the studio where conditions were more under control. But a challenge I took up a number of times just because I like the player and his work. After these tweaks a friend, Norton Buffalo, said he finally got what he had been looking for years when on stage. In most cases harp players are live players and not often in the studio because there are not many who can get the budgets for that type of production. So my work with folksingers, harp players, bluegrass, delta acoustic blues, chants, bagpipe bands was always free, outside the studio just because I liked those styles of music personally and in addition to classical and jazz, are what I go see live. Rock concerts bore me, it is getting old and tied sounding with very little innovation. I love rock so that is why hearing bands live in concerts is sad, almost all is impersonations of creative original work done far better in the past.
Also, some of those acoustic instruments used in those genres are technical challenges, which I enjoy. Scottish Bagpipes are hard to record so they are realistic because they only play best when moving, marching. I recorded a record that is well known in the bagpipe world of the Blackwatch while marching along with them with a fishpole and microphone on each side, and a Nagra recorder hanging on my side. I tried it in the studio but it just did not work as well for the players as open field marching. Irish bagpipes on the other hand are easy to record, but one of the hardest instruments to play well. In fact, all Irish acoustic folk music works well in small venues for playing or recording based on the tone range and DR of the instruments. Stringed harp is thought of as an open piano but it is not anything like for micing, much easier, with lower DR.
Anyway, harp is similar to vocals in spectrum and DR(but narrower) and challenges to a PA system, excess gain is needed for high average peak to peak levels or else it sounds thin to the audience. The compression, done either with a compression circuit that it controlled or by lowering the B+ as Chuck H did, it still favorably alters that ratio and sound fuller and richer, the technical term is "more stuff";>). The harp is, due to its relatively narrower DR than vocals, means the adjustment range of dynamics alteration is not so critical as with vocals. Setting it once will usually be fine for a wide range of venues.
Small venues for harp blues is closer to a recording environment than a rock or pop concert. The main difference is projection. A small venue has the audience in a close in radius of the sound sources, middle rows would likely be within 15-20 feet. The total sound need to project a blend optimized for within 20 feet or so, like a small jazz club. So micing in a studio or live recording is closer to the natural blend the placement and playing style of the individual instruments would be. A rock venue that distance where acoustic blend is aimed might be 100-300 feet so what the monitors tell the musician and what the audience hears is radically different. I like small venues partly for this reason. They just sound more like the musicians and arranger intended, and their acoustic feedback is close to what the audience is hearing. Small venues also allow monitor volume on stage to be much lower since it does not have to overcome the relatively loud late reflections in a large venue. Low stage SPL improves every aspect of a performance, but mostly vocals. It is not accident that some of the best performances, even of big venue rock stars, is in intimate unplugged settings for this reason. Harp almost always sounds best in small intimate venues, with controlled reverberation(like audience close in, wood surfaces, lower ceilings over the audience), with low monitor levels, the player has a lot more flexibility for dynamics.
One thing I differ on, rolling off the upper mids and highs so severely might be a mistake, a lively articulate sound benefits good players, and such deep cuts are not needed when compression is early in the signal chain, don't wait until the output section for power tube compression, besides the tendency to suppress 2nd harmonic distortion in a PP output, while compressing, is where the harsh sound reputation comes from, in part.